JP3840424B2 - Stimulable phosphor, radiation imaging method and radiation imaging material - Google Patents

Description

【００５１】
（放射線吸収蛍光体）
本発明の放射線画像形成材料の放射線吸収性蛍光体層および蛍光スクリーンで用いられる放射線吸収蛍光体は、本発明の方法による画像形成に用いられる、Ｘ線、γ線、β線、α線、紫外線、中性子線等の放射線を吸収して、通常は瞬時に紫外乃至可視領域に発光を示す蛍光体である。本発明で用いる放射線吸収蛍光体は、母体の主成分として、原子番号が３７以上の元素を含む蛍光体であることが好ましく、特に好ましいのは、原子番号が５５乃至８３の元素を含む蛍光体である。その例としては、ＬｎＴａＯ₄：（Ｎｂ，Ｇｄ，Ｔｍ）系、Ｌｎ₂ＳｉＯ₅：Ｃｅ系、ＬｎＯＸ：Ｔｍ系（Ｌｎは希土類元素）、ＣｓＸ系（Ｘはハロゲン）、Ｇｄ₂Ｏ₂Ｓ：Ｔｂ、Ｇｄ₂Ｏ₂Ｓ：Ｐｒ，Ｃｅ、ＺｎＷＯ₄、ＬｕＡｌＯ₃：Ｃｅ、Ｇｄ₃Ｇａ₅Ｏ₁₂：Ｃｒ，Ｃｅ、ＨｆＯ₂等を挙げることができる。
下記の表２に、代表的な放射線吸収蛍光体の密度と発光波長を示す。
【００５２】
【表２】

【００５３】
これらのうちでも前記輝尽性蛍光体と組み合わせるのが好ましい放射線吸収蛍光体としては、ＹＴａＯ₄：ＮｂおよびＣｓＩ：Ｎａを挙げることができる。
ただし、本発明に用いられる放射線吸収蛍光体は、表１に示した蛍光体に限定されるものではない。放射線吸収蛍光体は、上記輝尽性蛍光体の一次励起特性とのマッチングを考慮して選択される。放射線吸収蛍光体は一般に粒子状で用いられ、その粒子径は約１乃至２０μｍの範囲にあることが望ましい。
【００５４】
マッチングの点から、放射線吸収蛍光体の発光波長領域と輝尽性蛍光体の一次励起波長領域とは７０％以上重なっていることが好ましい。この規定において、各波長領域は、発光スペクトルまたは励起スペクトルのピーク値の１０％以上の値を有する波長範囲を意味する。
【００５５】
放射線吸収蛍光体は、フロント側の放射線吸収性の蛍光体層に含有されるものと、バック側の放射線吸収性の蛍光体層に含有されるものとで、母体の主成分として互いに異なる（原子番号が３７以上の）元素を含んでいることが好ましい。より好ましくは、バック側の放射線吸収蛍光体が原子番号が相対的に大きな元素を含んでいることである。このように蛍光体の元素の種類を変えて、放射線に対する吸収特性をずらすことにより、放射線を両蛍光体層に効率良く吸収させることができる。なお、一つの蛍光体層中に二種類以上の放射線吸収蛍光体を含有させてもよい。
【００５６】
［放射線画像形成材料の製造法］
（放射線像変換パネル）
次に、本発明の放射線画像形成材料の製造方法を、図１に示した放射線画像形成材料の放射線像変換パネル１０ａを例にとって、蓄積性蛍光体層および放射線吸収性蛍光体層がそれぞれ、蛍光体粒子とこれを分散状態で含有支持する結合剤とからなる場合について説明する。各蛍光体層は、たとえば次のような公知の方法により支持体上に順に形成することができる。
【００５７】
（支持体）
支持体は通常、柔軟な樹脂材料からなる厚みが５０μｍ乃至１ｍｍのシートあるいはフィルムである。支持体は透明であってもよく、あるいは支持体に、励起光（一次、二次）もしくは輝尽発光光を反射させるための光反射性材料（例、アルミナ粒子、二酸化チタン粒子、硫酸バリウム粒子）を充填してもよく、あるいは空隙を設けてもよい。または、支持体に励起光もしくは輝尽発光光を吸収させるため光吸収性材料（例、カーボンブラック）を充填してもよい。支持体の形成に用いることのできる樹脂材料の例としては、ポリエチレンテレフタレート、ポリエチレンナフタレート、アラミド樹脂、ポリイミド樹脂などの各種樹脂材料を挙げることができる。必要に応じて、支持体は金属シート、セラミックシート、ガラスシート、石英シートなどであってもよい。
【００５８】
（放射線吸収性蛍光体層）
まず、上記の放射線吸収蛍光体粒子と結合剤とを溶剤に加え、これを十分に混合して、結合剤溶液中に放射線吸収蛍光体粒子が均一に分散した塗布液を調製する。蛍光体粒子を分散支持する結合剤については様々な種類の樹脂材料が知られており、本発明の放射線像変換パネルの製造においても、それらの公知の結合剤樹脂を中心とした任意の樹脂材料から適宜選択して用いることができる。塗布液における結合剤と蛍光体との混合比は、目的とする放射線像変換パネルの特性、蛍光体の種類などによって異なるが、一般には結合剤と蛍光体との混合比率（結合体／蛍光体）は、１乃至０．０１（重量比）の範囲から選ばれる。なお、塗布液にはさらに、塗布液中における蛍光体の分散性を向上させるための分散剤、形成後の蛍光体層中における結合剤と蛍光体との間の結合力を向上させるための可塑剤、蛍光体層の変色を防止するための黄変防止剤、硬化剤、架橋剤など各種の添加剤が混合されていてもよい。
【００５９】
このようにして調製された塗布液を次に、支持体の表面に均一に塗布することにより塗膜を形成する。塗布操作は、通常の塗布手段、たとえばドクターブレード、ロールコータ、ナイフコータなどを用いる方法により行うことができる。この塗膜を乾燥して、支持体上への放射線吸収性蛍光体層の形成を完了する。なお、蛍光体層は、必ずしも上記のように支持体上に塗布液を直接塗布して形成する必要はなく、例えば、別にガラス板、金属板、プラスチックシートなどの仮支持体上に塗布液を塗布し乾燥することにより蛍光体層を形成した後、これを支持体上に押圧するか、あるいは接着剤を用いるなどして支持体上に蛍光体層を接合する方法を利用してもよい。あるいは、特願２０００−１５８２１３号明細書に記載されているような、針状蛍光体を配向させて異方化した蛍光体層も用いることができる。
【００６０】
本発明に係る放射線吸収性蛍光体層は、放射線吸収蛍光体とこれを分散状態で含有支持する結合剤とからなるのものばかりでなく、結合剤を含まないで放射線吸収蛍光体の凝集体のみから構成されるもの、蒸着膜、あるいは放射線吸収蛍光体の凝集体の間隙に高分子物質が含浸されている蛍光体層などでもよい。
【００６１】
（隔壁）
また、放射線吸収性蛍光体層には、発光光の散乱を防止して得られる画像の画質を高める目的で、蛍光体層を平面方向に沿って細分区画する隔壁が設けられていてもよい。放射線吸収性蛍光体層は層厚が比較的厚いので、隔壁を設けることにより発光光の拡散を有効に防止することができる。隔壁は縞状、格子状など任意の形状で設けることができ、あるいは円形、六角形など任意の形状の放射線吸収蛍光体が充填された領域を隔壁が囲むように形成されてもよい。また、隔壁の頂部と底部はともに蛍光体層の両表面に露出していてもよいし、あるいは頂部と底部の両方あるいはいずれか一方が蛍光体層に埋没していてもよい。
【００６２】
隔壁は、例えばアルミニウム、チタン、ステンレスなど金属製の板、酸化アルミニウム、ケイ酸アルミニウムなどセラミックス製の板、あるいは感光性樹脂など有機高分子物質からなるシートに好適なエッチング処理をすることにより、多数の凹部（穴）もしくは透孔が形成されたハニカム状のシートを用意し、このハニカム状シートの上に上記の蛍光体層を載せたのち加熱圧縮することにより、ハニカム状シートを蛍光体層の中に押し込んで形成することができる。あるいは、蛍光粒子を分散含有する結合剤からなる多数の薄膜状の蛍光体シートと高分子物質からなる多数の薄膜状の隔壁用シートをそれぞれ形成し、蛍光体シートと隔壁用シートを交互に多数枚積層した後、積層方向に垂直に裁断することからなる積層スライス法によっても形成することができる。あるいはまた、上記のように蛍光体層が蒸着膜などのように放射線吸収蛍光体の凝集体からなる場合には、クラックを形成させることにより隔壁とすることができる。そのような蛍光体層の例としては、ＣｓＩ：Ｎａ、ＣｓＩ：Ｔｌ、ＣｓＢｒ：Ｔｌなどの針状結晶膜を挙げることができる。隔壁には、酸化アルミニウム、二酸化チタン等の低光吸収性微粒子が分散含有されていてもよいし、あるいは放射線吸収蛍光体からの発光光を選択的に吸収するような着色剤で着色されていてもよい。
【００６３】
あるいは、隔壁を蛍光体層材料（ただし、結合剤：蛍光体の比率および／または粒子サイズは、蛍光体層を形成する場合とは変える）から形成してもよい。一般に放射線吸収蛍光体は高屈折率であるので、平面方向の散乱をより効果的に防止することができる。また、高い放射線吸収を維持しながら、高鮮鋭度の画像を得ることができる。
【００６４】
あるいは、放射線吸収性蛍光体層を、図７に示すように、ファイバプレートと放射線吸収蛍光体の針状結晶膜とから構成してもよい。図７において、放射線吸収性蛍光体層１２ｂ’は支持体１１ｂ側の蛍光体の針状結晶膜１２ｂ₁と、その上に設けられたファイバプレート１２ｂ₂とからなる。蛍光体の針状結晶膜１２ｂ₁は、上記のように隔壁としてクラックを有するものである。一方、ファイバプレート１２ｂ₂は、直径数μｍのファイバを深さ方向に数百万本束にした光学シートであり、蛍光体の針状結晶膜１２ｂ₁でＸ線等の放射線から紫外乃至可視領域の光に変換された光は、ファイバプレート１２ｂ₂を通して平面方向に散乱することなく、かつ光の損失が少なくて蓄積性蛍光体層１３に到達することができる。
【００６５】
なお、図７では、放射線画像形成材料１０’のフロント側の放射線像変換パネル１０ａではなく、バック側の蛍光スクリーン１０ｂ’の放射線吸収性蛍光体層１２ｂ’を、蛍光体の針状結晶膜１２ｂ₁とファイバプレート１２ｂ₂とから構成した場合を示したが、鮮鋭度向上の点からは、この構成を含めて隔壁は蓄積性蛍光体層よりも層厚の厚い放射線吸収性蛍光体層に設けることが好ましく、より好ましくはバック側の放射線吸収性蛍光体層に設けることであり、特に好ましくは図７に示したようにバック側に配置される蛍光スクリーンの蛍光体層に設けることである。これにより、隔壁を有するバック側スクリーンによる高画質化と、フレキシブルなフロント側パネルの読取装置内での良好な搬送性とを両立させることができる。
【００６６】
（蓄積性蛍光体層）
この放射線吸収性蛍光体層の上に、上記と同様にして、輝尽性蛍光体を分散状態で含有支持する結合剤からなる蓄積性蛍光体層を形成する。この蓄積性蛍光体層も、輝尽性蛍光体の凝集体のみから構成されるもの、あるいは輝尽性蛍光体の凝集体の間隙に高分子物質が含浸されているものであってもよいし、あるいは隔壁が設けられていてもよい。
【００６７】
放射線吸収性蛍光体層および蓄積性蛍光体層がそれぞれ、上記のように蛍光体粒子と結合剤とから構成される場合に、放射線画像を、より高画質とするためには、放射線吸収性蛍光体層における結合剤と蛍光体の重量比（結合剤Ｂ₁／蛍光体Ｐ₁）は、蓄積性蛍光体層における結合剤と蛍光体の重量比（結合剤Ｂ₂／蛍光体Ｐ₂）と同等もしくはそれより小さく、かついずれも１以下であることが望ましい（１≧Ｂ₂／Ｐ₂≧Ｂ₁／Ｐ₁）。すなわち、放射線吸収性蛍光体層中の蛍光体の比率が蓄積性蛍光体層中の蛍光体の比率と同等かそれよりも高いことが望ましい。
【００６８】
放射線吸収性蛍光体層のＢ₁／Ｐ₁比（重量比）は、１／８乃至１／５０の範囲にあることが好ましく、より好ましくは１／１５乃至１／４０の範囲にある。蓄積性蛍光体層のＢ₂／Ｐ₂比（重量比）は、１／１乃至１／４０の範囲にあることが好ましく、より好ましくは１／２乃至１／２０の範囲にある。
なお、この結合剤と蛍光体についての関係は、放射線像変換パネルの蓄積性蛍光体層と蛍光スクリーンの放射線吸収性蛍光体層との間においても同様に成り立つことが望ましい。
【００６９】
（蛍光体の粒子径）
各蛍光体層に含有される放射線吸収蛍光体及び輝尽性蛍光体の平均粒子径は、
（輝尽性蛍光体の平均粒子径）≦（放射線吸収蛍光体の平均粒子径）
なる関係を満たすことが望ましい。特に好ましくは、
（輝尽性蛍光体の平均粒子径）≦（放射線吸収蛍光体の平均粒子径）×０．５なる関係を満たすことである。この結果、放射線吸収蛍光体の相対的に大きな粒子径によって放射線に対する発光効率を上げて感度を高めることができるとともに、輝尽性蛍光体の相対的に小さな粒子径により画像の鮮鋭度を高めることができる。
【００７０】
放射線吸収蛍光体の平均粒子径は、一般には１μｍ以上、２０μｍ以下であって、好ましくは２μｍ以上、１０μｍ以下である。一方、輝尽性蛍光体の平均粒子径は、一般には０．２μｍ以上、２０μｍ以下であり、好ましくは０．５μｍ以上、５μｍ以下である。ただし、特願２０００−２１９８７７号明細書に記載されているように、輝尽性の量子ドット蛍光体のような、より小さな粒子でも、その効率が高ければ、その使用に問題はない。
【００７１】
上記放射線吸収蛍光体粒子および輝尽性蛍光体粒子はそれぞれ、例えば特開２０００−２８４０９７号公報、同２０００−１９２０３０号公報又は特開昭５８−１８２６００号公報に記載されているような粒径分布を有していてもよい。
【００７２】
（蛍光体の吸収係数）
放射線画像の画質向上の点から、放射線吸収性蛍光体層の放射線吸収係数と、蓄積性蛍光体層の放射線吸収蛍光体からの発光光（一次励起光）に対する吸収係数とは、以下の関係を満たすことが望ましい。
（蓄積性蛍光体層の一次励起光の吸収係数） ＞
（放射線吸収性蛍光体層の放射線吸収係数）×２
特に好ましくは、
（蓄積性蛍光体層の一次励起光の吸収係数） ＞
（放射線吸収性蛍光体層の放射線吸収係数）×５
なる関係を満たすことである。
【００７３】
ここで、一次励起光の吸収係数は、本出願人による特願平１１−３４９６３３号明細書に記載されているように、見かけの吸収係数であり、以下のようにして規定される値である。蛍光体層を厚さｄの均一層とみなし、蛍光体層を空間に孤立して置いた場合のその光反射率をｒ、光透過率をｔとする。光反射率ｒは、標準白色板との相対比較により求める。蛍光体層の裏側に白色板（反射率ｒ_w）を置いた場合と黒色板（反射率ｒ_b）を置いた場合の、系全体の反射率をそれぞれＲ_wおよびＲ_bとする。系全体の反射は、蛍光体層による反射と、白色板または黒色板による反射との合計となるので、次式で表される。
Ｒ_w＝ｒ＋ｒ_w×ｔ²
Ｒ_b＝ｒ＋ｒ_b×ｔ²
【００７４】
蛍光体層の見かけの吸収係数Ｋは、吸収が蛍光体層の厚さｄに関して指数関数的に減衰すると仮定すると、エネルギー保存則により反射と吸収と透過との合計は１であることから、次式により求められる。

【００７５】
一方、放射線吸収係数は、質量エネルギー吸収係数μ_en／ρに蛍光体層の密度を掛けた値として求めることができる。各物質のＸ線領域における質量エネルギー吸収係数μ_en／ρは、各物質の成分元素の質量吸収係数と質量比を用いて求めることができる。各元素の質量エネルギー吸収係数のデータは、http://physics.nist.gov/PhysRefData/XrayMassCoef/cover.html等から入手できる。蛍光体層の密度ρは、蛍光体自体の密度に層中の蛍光体充填率を掛けた値として求められ、通常は３〜５程度の値である。
【００７６】
放射線吸収性蛍光体層は、放射線吸収係数を高めて高画質の放射線画像を得るためには、含有される放射線吸収蛍光体の密度が６．０ｇ／ｃｍ³以上であるか、あるいは蛍光体層の平均密度が４．０ｇ／ｃｍ³以上であることが好ましい。
【００７７】
（同時重層塗布）
輝尽性蛍光体の粒子が形成しようとする蛍光体層の層厚に対して充分に小さくない場合、すなわち輝尽性蛍光体の平均粒子径をａμｍ、蛍光体層の層厚をｄμｍで表したとき、両者が、
ｄ／１０＜ａ＜ｄ
なる関係を満たす場合には、蓄積性蛍光体層とその下の大きな層厚の放射線吸収性蛍光体層とを同時重層塗布により形成することが好ましい。これにより、５〜２０μｍという薄い層厚の蛍光体層を均一に形成することができる。
【００７８】
同時重層塗布は、別々に調製した塗布液を一緒に二連式ホッパー型塗布装置などを用いて支持体表面に均一に、一度に同時に重層塗布することにより、あるいは放射線吸収性蛍光体層用塗布液を支持体表面に塗布した後直ちに、溶剤が蒸発しないようにして、蓄積性蛍光体層用塗布液を重層塗布することにより行うことができる。その場合に、各塗布液に使用する結合剤は互いに相溶性があることが好ましく、特に同一であることが好ましい。また、溶剤は、重層した塗膜の乾燥速度を一致させる必要から互いに相溶性があることが望ましい。このようにして形成された二層の蛍光体層は、両者の結合剤が互いに相溶性がある場合には、電子顕微鏡等で観察してもその境界面を明確に区別することができない。
【００７９】
（保護層）
蓄積性蛍光体層の表面には、蛍光体層を物理的および化学的に保護するために透明な保護層を設けてもよい。保護層は、励起光の入射や輝尽発光光の出射に殆ど影響を与えないように、光吸収を実質的に示さないことが望ましく、また外部から与えられる物理的衝撃や化学的影響から放射線像変換パネルを充分に保護することができるように、化学的に安定でかつ高い物理的強度を持つことが望ましい。保護層としては、セルロース誘導体、ポリメチルメタクリレート、有機溶媒可溶性フッ素系樹脂などのような透明な有機高分子物質を適当な溶媒に溶解させて調製した溶液を蛍光体層の上に塗布することで形成されたもの、あるいはポリエチレンテレフタレートなどの有機高分子フィルムや透明なガラス板などの保護層形成用シートを別に形成して蛍光体層の表面に適当な接着剤を用いて設けたもの、あるいは無機化合物を蒸着などによって蛍光体層上に成膜したものなどが用いられる。また、保護層中にはパーフルオロオレフィン樹脂粉末、シリコーン樹脂粉末等の滑り剤、およびポリイソシアネート等の架橋剤など各種の添加剤が分散含有されていてもよい。
【００８０】
形成される放射線画像の鮮鋭度を高めるためには、保護層を一定範囲で光散乱性とすることが望ましい。一般に保護層の光散乱長は、輝尽性蛍光体からの発光光の主発光波長において５乃至８０μｍの範囲にあり、好ましくは１０乃至７０μｍの範囲にある。光散乱性の保護層は、上記保護層用材料中に光散乱性微粒子を分散、含有させることによって形成することができる。光散乱性微粒子としては、光屈折率が１．６以上であり、粒子径が０．１乃至１．０μｍの範囲にあるのが好ましい。特に好ましくは光屈折率は１．９以上であり、粒子径は０．１乃至０．５μｍの範囲である。好適な光散乱性微粒子の例としては、ベンゾグアナミン樹脂粒子、メラミンホルムアルデヒド縮合樹脂粒子、酸化亜鉛、硫化亜鉛、酸化チタンおよび炭酸鉛の微粒子を挙げることができる。
【００８１】
保護層の表面にはさらに、保護層の耐汚染性を高めるためにフッ素樹脂塗布層を設けてもよい。フッ素樹脂塗布層は、フッ素樹脂を有機溶媒に溶解（または分散）させて調製したフッ素樹脂溶液を保護層の表面に塗布し、乾燥することにより形成することができる。フッ素樹脂は単独で使用してもよいが、通常はフッ素樹脂と膜形成性の高い樹脂との混合物として使用する。また、ポリシロキサン骨格を持つオリゴマーあるいはパーフルオロアルキル基を持つオリゴマーを併用することもできる。フッ素樹脂塗布層には、干渉むらを低減させて更に放射線画像の画質を向上させるために、微粒子フィラーを充填することもできる。フッ素樹脂塗布層の層厚は通常は０．５μｍ乃至２０μｍの範囲にある。フッ素樹脂塗布層の形成に際しては、架橋剤、硬膜剤、黄変防止剤などのような添加成分を用いることができる。特に架橋剤の添加は、フッ素樹脂塗布層の耐久性の向上に有利である。
【００８２】
放射線像変換パネルと蛍光スクリーンの密着性や引き離し易さなど取り扱い性を高めるために、保護層またはフッ素樹脂塗布層はその最大摩擦係数が０．１８以下であることが好ましく、特に好ましくは０．１２以下である。また、表面の平均粗さが０．０５乃至０．５μｍの範囲にあることが好ましく、特に好ましくは０．１乃至０．３μｍの範囲である。例えば、保護層またはフッ素樹脂塗布層の表面に、エンボス処理を行うことなどにより微小な凹凸を設けてもよい。
【００８３】
放射線像変換パネルの帯電、特に蛍光スクリーンからパネルを引き離すときに生じがちな剥離帯電を有効に防止するためには、密着状態で重ね合わされるパネルとスクリーンの対向する両保護層の帯電列が揃っていることが望ましい。両保護層の帯電列は、例えば同一の材料を用いて両保護層を形成することにより揃えることができる。また、放射線撮影に際してはカセッテに両者を挿入する前に除電することが好ましい。
【００８４】
あるいは、放射線像変換パネルを構成する層のうちのいずれかの層に、ポリピロールなどの透明導電性ポリマーおよび／または輝尽性蛍光体の発光波長よりも小さい粒子径を持つ導電性微粉末（酸化すず微粉末など）を含有させることが好ましい。粒子径を輝尽性蛍光体の発光波長よりも小さくすることにより、薄層で導電率の高い膜構成が可能となり、発光光の吸収による集光効率の損失を回避することができる。
【００８５】
（選択的反射層）
さらに、放射線吸収性蛍光体層と蓄積性蛍光体層との間には、図８に示すように、放射線吸収蛍光体からの発光光を透過し、励起光および輝尽性蛍光体からの発光光を反射するような選択的反射層を設けることが好ましい。これにより、放射線画像情報の読み取り時における集光効率を高めることができると同時に、その結果蓄積性蛍光体層の層厚をより薄くできるので、画像の鮮鋭度を向上させることができる。
【００８６】
図８において、放射線像変換パネル１０ａ’は順に、支持体１１ａ、放射線吸収性蛍光体層１２ａ、選択的反射層１５、蓄積性蛍光体層１３、および保護層１４ａから構成されている。
【００８７】
選択的反射層は例えば、放射線吸収蛍光体の発光波長を含む短波長領域の光を透過し、それよりも長波長領域の光を反射するような特性を有すればよい。選択的反射層は、薄膜フィルムとその上に形成されたこのような特性を有する多層膜とから構成することができる。多層膜は、屈折率の異なる二種類以上の物質が光の波長の１／４程度の厚さ（約５０〜２００ｎｍ）で逐次積層されたものであっって、具体的には、ＳｉＯ₂、ＭｇＦ₂などの低屈折率物質とＴｉＯ₂、ＺｒＯ₂、Ｔａ₂Ｏ₅、ＺｎＳなどの高屈折率物質とが交互に数層乃至数十層積層された総厚約０．１乃至１０μｍの多層干渉フィルタである。
【００８８】
一例として、ＳｉＯ₂とＴｉＯ₂とが交互に合計１７層積層されてなる多層膜について述べる。この多層膜は、図９に概略的に示すように、ＴｉＯ₂の高屈折率層１５ａとＳｉＯ₂の低屈折率層１５ｂとからなり、表３に示すような構成を有する。
【００８９】
【表３】

【００９０】
図１０は、上記表３に示した構成を有する多層膜の光透過特性を示すグラフである。この多層膜の透過率（光の入射角０゜）は波長６３３ｎｍで約９７％である。
なお、この多層膜は光の入射角に対しても選択性を有する。図１１は、この多層膜の、波長４００ｎｍおよび６３３ｎｍにおける光の入射角と透過率との関係を示すグラフである。多層膜は、波長６３３ｎｍの光については入射角０゜〜２５゜で５０％以上の透過率を示し、２５゜より大きい入射角では透過率は約５％に減少する。一方、波長４００ｎｍの光については入射角０゜〜約７０゜にわたって９０％以上の透過率を示す。
多層膜の材料や構成を変えることにより、所望の光透過特性を有する多層膜を形成することが可能である。
【００９１】
選択的反射層は、高分子物質などからなる薄膜フィルム（厚さ：４乃至２０μｍ）上に、上記多層膜材料を蒸着、スパッタリング、イオンプレーティングなどの方法により逐次積層することにより形成することができる。次いで、この多層膜を有する薄膜フィルムを、前記放射線吸収性蛍光体層上にカレンダー処理などにより貼り合わせた後、この上に蓄積性蛍光体層を塗布などにより形成するか、あるいは別途形成した蛍光体層を貼り合わせることにより行う。あるいは、先に多層膜を有する薄膜フィルム上に蓄積性蛍光体層を塗布などにより形成した後、得られた薄膜フィルムを放射線吸収性蛍光体層上に貼り合わせてもよい。なお、上記の多層膜形成時および／または蓄積性蛍光体層形成時に、薄膜フィルムの下には剥離可能な仮支持体を接合させておいてもよい。あるいは、選択的反射層として、前述した支持体材料の中から適宜選択した材料を用いて薄層を形成してもよい。
【００９２】
（拡散反射層）
また、この放射線像変換パネルがフロント側となる場合には、支持体と放射線吸収性蛍光体層との間に、図１２に示すように、拡散反射層を設けることが好ましい。本発明の画像形成材料に用いることのできる拡散反射層は、放射線吸収蛍光体からの発光光を反射する機能を有する層である。この拡散反射層の設置によって、蓄積性蛍光体層に入射する放射線吸収蛍光体からの発光光（一次励起光）の光量を増加させて、高感度の放射線像変換パネルとすることができる。
図１２において、放射線像変換パネル１０ａ”は順に、支持体１１ａ、拡散反射層１６、放射線吸収性蛍光体層１２ａ、蓄積性蛍光体層１３、および保護層１４ａから構成されている。
【００９３】
拡散反射層は、二酸化チタン、酸化イットリウム、酸化ジルコニウム、酸化アルミニウム（アルミナ）などの光反射性物質を含有する層である。光反射性物質は、拡散反射層がフロント側のパネルまたはスクリーンに設けられることを考慮して、Ｘ線等の放射線の吸収が小さい必要があるとともに、反射の鮮鋭度の点からは、屈折率が高いことが望ましい。よって、光反射性物質として好ましいのは二酸化チタンであり、特により屈折率の高いルチル型が好ましい。ただし、二酸化チタンは約４３０ｎｍよりも長波長の領域で高い反射率を示すので、放射線吸収蛍光体がＧｄ₂Ｏ₂Ｓ：Ｔｂなどである場合に適している。放射線吸収蛍光体の発光波長が約４３０ｎｍよりも短波長である場合には、酸化アルミニウム、酸化イットリウム、酸化ジルコニウムなどその発光波長領域に吸収のない物質を選択する必要がある。
【００９４】
拡散反射層は、感度および鮮鋭度の点から、できるだけ薄い層厚で高い光反射率を達成することが望ましい。拡散反射層が単独で存在する場合に、その層厚と拡散反射率との関係は、図１３において斜線で示す領域にあることが好ましい。ここで、拡散反射率は、特開平９−２１８９９号公報に詳細に記載されているように、ＢａＳＯ₄粉末が全面に一様に塗布してある積分球を用いて標準白板に対して求めた反射率である。そのためには光反射性物質の平均粒子径は、一般には０．１乃至０．５μｍの範囲にあり、好ましくは０．１乃至０．４μｍの範囲にある。光反射性物質の拡散反射層における体積充填率は、一般には２５乃至７５％の範囲にあり、好ましくは４０％以上である。拡散反射層の層厚は一般に１５乃至１００μｍの範囲にある。
【００９５】
拡散反射層は、上記微粒子状の光反射性物質および結合剤を溶剤中に混合分散して塗布液を調製した後、これを支持体上に塗布乾燥することにより形成することができる。結合剤および溶剤は、前記蛍光体層に使用することが可能なものの中から適宜選択して用いることができる。
【００９６】
支持体上に拡散反射層を設ける代わりに、支持体自体に上記のような光反射性物質を分散含有させて、拡散反射機能を有する支持体としてもよい。また、後述するように、拡散反射層および／または支持体を着色してもよい。
なお、蛍光スクリーンをフロント側に用いる場合にも、拡散反射層または拡散反射機能を有する支持体を設けることが望ましい。また、バック側に用いられるパネルまたはスクリーンに使用すれば、感度的に優れたものが設計しやすい。
【００９７】
さらに目的に応じて、蛍光体層と支持体との間に光吸収層、接着層、導電層などの補助機能層を設けてもよく、また支持体表面には多数の凹部を形成してもよい。支持体の蛍光体層を設けない側の表面には、搬送性を向上させたり、耐傷性を向上させたりするために、摩擦低減層や耐傷層を設けることもできる。
【００９８】
上述のような材料と製法を利用して本発明に係る放射線像変換パネルが得られるが、本発明のパネルの構成は、公知の各種のバリエーションを含むものであってもよい。また、上記においては、支持体および保護層を有するパネルについて説明したが、蛍光体層が自己支持性である場合には、本発明に係るパネルは必ずしも支持体や保護層を備えている必要はない。
【００９９】
（着色）
放射線画像の鮮鋭度を高める目的で、上記放射線像変換パネルの少なくともいずれかの層を、放射線吸収蛍光体からの発光光および／または輝尽性蛍光体の二次励起光（潜像（蓄積放射線画像）の読み取り時に用いる）を吸収する着色剤、あるいは場合により、輝尽性蛍光体から放出される発光光の一部を吸収する着色剤によって着色してもよい。具体的には、放射線吸収性蛍光体層、保護層、更に下塗層などの中間層を、放射線吸収蛍光体からの発光光および／または輝尽性蛍光体の二次励起光を吸収する着色剤で着色することが望ましい。着色は、上記の層のいずれか一つだけであってもよいし、あるいは部分的であってもよく、また任意に組み合わせてもよい。着色剤は、後述の光電子倍増管を用いた点検出系では、輝尽性蛍光体からの発光光を吸収しないものであることが望ましい。
【０１００】
着色剤としては、例えば放射線吸収蛍光体からの発光光が緑色発光光であり、輝尽性蛍光体が緑色光を吸収し、近赤外光で二次励起されて、赤色の発光光を放出する場合には、緑色領域および近赤外領域の光を吸収し、赤色領域の光を吸収しない着色剤が好ましい（点検出系で用いられる場合）。二種類以上の着色剤を組み合わせて使用してもよい。
【０１０１】
上記の目的に適した赤色着色剤の例としては、カドミウムレッド、べんがら、モリブデンレッドなどの無機顔料を挙げることができる。ただし、これらの赤色着色剤は近赤外領域の光を殆ど吸収しないので、特開平１１−１０９１２６号公報に記載されているシアニン色素、インドアニリン色素、スクアリリウム色素などの近赤外吸収材料を併用することが望ましい。
【０１０２】
また例えば、放射線吸収蛍光体からの発光光が近紫外発光光であり、輝尽性蛍光体が近紫外光を吸収し、赤色光で励起されて、青乃至緑色の発光光を放出する場合には、近紫外領域および赤色領域の光を吸収し、青乃至緑色領域の光を吸収しない着色剤が好ましい（点検出系で用いられる場合）。
【０１０３】
適した青乃至緑色の有機系着色剤の例としては、ザボンファーストブルー３Ｇ（ヘキスト社製）、エストロールブリルブルーＮ−３ＲＬ（住友化学(株)製）、スミアクリルブルーＦ−ＧＳＬ（住友化学(株)製）、Ｄ＆ＣブルーＮｏ１（ナショナル・アニリン社製）、スピリットブルー（保土谷化学(株)製）、オイルブルーＮｏ６０３（オリエント(株)製）、キトンブルーＡ（チバ・ガイギー社製）、アイゼンカチロンブルーＧＬＨ（保土谷化学(株)製）、レイクブルーＡ、Ｆ、Ｈ（協和産業(株)製）、ローダリンブルー６ＧＸ（協和産業(株)製）、ブリモシアニンブルー６ＧＸ（稲畑産業(株)製）、ブリルアシッドグリーン６ＢＨ（保土谷化学(株)製）、シアニンブルーＢＮＲＳ（東洋インキ(株)製）、ライオノルブルーＳＬ（東洋インキ(株)製）を挙げることができる。また、無機系着色剤の例としては、群青、コバルトブルー、セルリアンブルー、酸化クロム、ＴｉＯ₂−ＺｎＯ−ＣｏＯ−ＮｉＯ系顔料を挙げることができる。
【０１０４】
あるいは、後述するように放射線画像情報の読み取りを光電子増倍管等を用いる点検出の代わりに、ラインセンサ等を用いるライン検出により行う場合には、放射線吸収性蛍光体層、さらに下塗層などの中間層は、放射線吸収蛍光体からの発光光、輝尽性蛍光体の二次励起光、および／または輝尽性蛍光体からの発光光を吸収する着色剤で着色することが望ましい。輝尽性蛍光体からの発光光のうち励起部分よりも広がった分が画像のボケを招くからである。
【０１０５】
着色剤としては、放射線吸収蛍光体からの発光が緑色発光、輝尽性蛍光体の二次励起光が近赤外光、そして輝尽性蛍光体からの発光が赤色発光である場合には、緑色、赤色および／または近赤外領域の光を吸収する着色剤が好ましい。すなわち、赤色、青乃至緑色または灰色の着色剤であって近赤外吸収を有する着色剤が好ましい。適した赤色着色剤としては、上記の着色剤を用いることができる。青乃至緑色の着色剤であって近赤外吸収を有する着色剤の例としては、チタニルフタロシアニンＴｉＯ−Ｐｃ（山陽色素(株)製）を挙げることができる。上記の青乃至緑色着色剤と近赤外吸収材料とを組み合わせてもよい。灰色着色剤の例としては、カーボンブラック、Ｃｕ−Ｆｅ−Ｍｎ酸化物を挙げることができる。
【０１０６】
また、放射線吸収蛍光体からの発光が近紫外発光、輝尽性蛍光体の二次励起光が赤色光、そして輝尽性蛍光体からの発光が青乃至緑色発光である場合には、近紫外、青乃至緑色および／または赤色領域の光を吸収する着色剤が好ましい。すなわち、黄色、赤色、青乃至緑色または灰色の着色剤が好ましい。上記の赤色、青乃至緑色および灰色の着色剤を用いることができる。黄色着色剤の例としては、黄色酸化鉄、チタンイエロー、カドミウムイエローを挙げることができる。
【０１０７】
なお、着色による放射線像変換パネルの感度の低下は、放射線吸収性蛍光体層の層厚を厚くしたり、あるいは読み取り時の励起光のエネルギーを強くすることにより調整することができ、感度と鮮鋭度との関係でそれらの最適化を図ることができる。
【０１０８】
（蛍光スクリーン）
バック側の蛍光スクリーン１０ｂ、および他の構成の放射線像変換パネルも、上記と同様の材料を用いて同様の方法により製造することができる。なお、蛍光体層に隔壁を設ける場合には、バック側の蛍光スクリーンの放射線吸収性蛍光体層のみに隔壁を形成し、フロント側の放射線像変換パネルはフレキシブルとすることが好ましく、これにより画像形成システム（例えば、放射線画像情報読取装置）をよりコンパクトにでき、かつ高画質の放射線画像を得ることができる。
【０１０９】
放射線画像の鮮鋭度を高めるためには、蛍光スクリーンの保護層もまた一定範囲で光散乱性とすることが望ましい。一般に保護層の光散乱長は、放射線吸収蛍光体からの発光光の主発光波長において５乃至８０μｍの範囲にあり、好ましくは１０乃至７０μｍの範囲にある。このスクリーンの光散乱性保護層も、前記パネルの光散乱性保護層と同様の材料を用いて同様の方法により形成することができる。
【０１１０】
同じく放射線画像の鮮鋭度を高める目的で、蛍光スクリーンの放射線吸収性蛍光体層および／または保護層を、放射線吸収蛍光体からの発光光を吸収するような上記着色剤で着色してもよい。
【０１１１】
［放射線画像形成方法］
次に、上記の放射線画像形成材料を用いた本発明の放射線画像形成方法について、図１に示した構成の放射線画像形成材料（輝尽性蛍光体として輝尽性蛍光体を含有）を例にとって、添付図面の図６を参照しながら説明する。図６は、点検出系を利用する片面集光方式の放射線画像情報読取装置の構成の例を示す概略断面図である。
【０１１２】
まず、放射線画像情報（放射線の空間的エネルギー分布情報）を、放射線像変換パネルと蛍光スクリーンの組体からなる放射線画像形成材料に記録する。画像情報の記録（撮影）に際しては、図１に示した放射線画像形成材料１０のフロント側放射線像変換パネル１０ａとバック側蛍光スクリーン１０ｂを、各々の保護層１４ａ、１４ｂが接するように密着した状態で重ね合わせる。この際に、カセッテを用いて密着状態にある組体を固定することが望ましく、またバック側スクリーン１０ｂは通常はカセッテ内に固定して使用するのが望ましい。また、放射線撮影の撮影台の内部において同様な構成とすることもできる。
【０１１３】
放射線撮影装置（図示なし）などを用いて、Ｘ線発生装置等の放射線源と放射線画像形成材料との間に被検体を配置した後、放射線源から発生した放射線を被検体に照射する。放射線としては、Ｘ線、γ線、α線、β線、電子線、紫外線などの電離放射線、および中性子線を利用することができる。中性子線を用いる場合には、蛍光体として、Ｇｄや¹⁰Ｂ、⁶Ｌｉなどを含む母体のものか、あるいはこれらの元素を含む化合物を蛍光体に混合して用いることが好ましい。
【０１１４】
放射線は、放射線および被検体の種類に応じて被検体を透過したり、あるいは被検体により回折または散乱されて、被検体に関する空間的エネルギー分布情報を有する放射線としてフロント側パネル１０ａに入射する。入射した放射線の一部は、放射線吸収性蛍光体層１２ａの放射線吸収蛍光体に吸収されて、紫外乃至可視領域の波長の光（瞬時発光光）に変換される。この発光光は、隣接する蓄積性蛍光体層１３に入射し、蛍光体層中の輝尽性蛍光体に吸収されてそのエネルギーが蓄積され、蓄積性蛍光体層１３には被検体の空間的エネルギー分布情報が潜像として記録される。
【０１１５】
フロント側パネル１０ａを透過した放射線は、バック側スクリーン１０ｂに入射し、放射線吸収性蛍光体層１２ｂの放射線吸収蛍光体に吸収されて、紫外乃至可視領域の発光光に変換される。この発光光の多くは、再びフロント側パネル１０ａに入射し、蓄積性蛍光体層１３の輝尽性蛍光体に吸収されてエネルギーとして蓄積され、これも潜像形成に寄与する。すなわち、蓄積性蛍光体層１３はその両面から、放射線吸収蛍光体の発光光により露光されることになる。
【０１１６】
なお、放射線の照射は、フロント側パネル１０ａとバック側スクリーン１０ｂの位置を逆にすることにより、バック側スクリーン１０ｂの側から行われてもよい。また、オートラジオグラフィーのように被検体自体がβ線等の放射線を放出する場合には、被検体自体が放射線源となるため、別に放射線源を設けることを必要としない。
【０１１７】
次に、図６の放射線画像情報読取装置を用いて、フロント側パネル１０ａに記録された被検体の空間的エネルギー分布情報を読み取る。まず、密着状態にあるフロント側パネル１０ａとバック側スクリーン１０ｂを引き離し、フロント側パネル１０ａのみを読取装置に装填する。
【０１１８】
図６において、放射線像変換パネル６０は、二組のニップローラからなる移送手段６１、６２により矢印の方向に移送される。一方、レーザビーム等の励起光６３は、パネル６０の保護層側表面（蓄積性蛍光体層側表面）より照射される。励起光６３の照射を受けたパネル６０の蓄積性蛍光体層内の箇所からは、蓄積されたエネルギーレベルに応じた（すなわち、潜像として記録蓄積された放射線のエネルギー分布情報を担持した）放射線画像に対応する輝尽発光光６４が発せられる。輝尽発光光６４は、直接あるいはミラー６９で反射されて、上方に設けられた集光ガイド６５により集光され、その集光ガイド６５の基部に備えられた光電変換装置（フォトマルチプライヤ）６６にて電気信号に変換され、増幅器６７で増幅され信号処理装置６８に送られる。
【０１１９】
信号処理装置６８では、増幅器６７から送られてきた電気信号について、目的とする放射線画像の種類や放射線像変換パネルの特性に基づいて予め決められている加算、減算などの適当な演算処理を行い、処理後の信号を画像信号として送り出す。
【０１２０】
送り出された画像信号は画像再生装置（図示なし）にて可視画像として再生され、これにより被検体に関する放射線の空間的エネルギー分布に対応した画像が再構成される。再生装置は、ＣＲＴ等のディスプレイ手段であってもよいし、感光フィルムに光走査記録あるいは感熱記録フィルムによる熱記録を行なう記録装置であってもよいし、あるいはまた、そのために画像信号を一旦光ディスク、磁気ディスク等の画像ファイルに記憶させる装置に置き換えられてもよい。
【０１２１】
一方、放射線像変換パネル６０は、ニップローラ６１、６２により矢印の方向に順次移動していき、読取工程に供された領域は次いで、ナトリウムランプ、蛍光灯、赤外線ランプ等の消去光源（図示なし）を利用する消去工程に供される。これにより、読取工程の後なおパネルに残存している蓄積エネルギーが放出除去され、次回の放射線画像の記録（撮影）工程において、残存エネルギーによる潜像が悪影響を及ぼすことがないようにされる。
【０１２２】
なお、放射線像変換パネルが図２、３および４に示したような構成である（すなわち、放射線吸収性蛍光体層を有しない）場合には、支持体および保護層を透明とすることにより、パネルの両面から輝尽発光光を読み取ることができる。例えば、図６において、集光ガイド６５および光電変換装置６６を放射線像変換パネル６０の下方にも配置することにより、輝尽発光光６４の読み取りを励起光６３の照射とは反対の側からも、すなわち両側から行うことができる。
【０１２３】
あるいは、放射線の空間的エネルギー分布情報が潜像として蓄積記録された放射線像変換パネルをその平面方向に移送しながら、または励起光照射装置をパネルの平面方向に移動させながら、パネルに対して励起光を、ＬＤアレイ、ＬＥＤアレイ、蛍光導光シート等を用いて、移送方向とほぼ直交する方向に線状に照射し、パネルの励起光照射部分の潜像から放出される輝尽発光光を多数の固体光電変換素子を線状に配置してなるラインセンサ等を用いて逐次一次元的に光電検出して、その放射線エネルギー分布情報を電気的画像信号として得る放射線画像情報読取方法を利用することもできる。
【０１２４】
【実施例】
［実施例１］ ＳｒＯ・1.75Ａｌ₂Ｏ₃：0.01Ｅｕ，0.001Ｓｍ蛍光体
炭酸ストロンチウム（ＳｒＣＯ₃）２．２５ｇ、酸化アルミニウム（Ａｌ₂Ｏ₃）２．７２ｇ、酸化ユーロピウム（Ｅｕ₂Ｏ₃）０．０２７ｇ、酸化サマリウム（Ｓｍ₂Ｏ₃）０．００３ｇ、およびホウ酸（Ｈ₂ＢＯ₃）０．０５ｇをそれぞれ秤量し、乳鉢にて混合した。この混合物をアルミナるつぼ（小）に入れて蓋をした。別のアルミナるつぼ（大）に粉末カーボン１０ｇを入れ、その上に混合物の入ったるつぼ（小）を置き、更にアルミナるつぼ（中）を逆さまにしてるつぼ（小）の上に被せた後、るつぼ（大）に蓋をした。次に、このるつぼ（大）を電気炉に入れて、１３００℃の温度で弱還元性雰囲気で４時間焼成した。焼成後、炉内温度を１時間かけて８００℃まで冷却した後、室温まで急冷した。焼成物を取り出して、標記の組成式で表されるユーロピウム・サマリウム付活酸化ストロンチウムアルミニウム輝尽性蛍光体を得た。
【０１２５】
［実施例２］ ＳｒＯ・1.75Ａｌ₂Ｏ₃：0.01Ｅｕ，0.001Ｔｍ蛍光体
実施例１において、Ｓｍ₂Ｏ₃の代わりに酸化ツリウム（Ｔｍ₂Ｏ₃）０．００３ｇを用いたこと以外は実施例１と同様にして、標題の組成式で表されるユーロピウム・ツリウム付活酸化ストロンチウムアルミニウム輝尽性蛍光体を得た。
【０１２６】
［実施例３］ ＳｒＯ・1.75Ａｌ₂Ｏ₃：0.01Ｅｕ，0.001Ｓｍ蛍光体
実施例１において、ＳｒＣＯ₃を２．６６ｇ、Ａｌ₂Ｏ₃を２．３０ｇ、およびＥｕ₂Ｏ₃を０．０３２ｇに変更したこと以外は実施例１と同様にして、標題の組成式で表されるユーロピウム・サマリウム付活酸化ストロンチウムアルミニウム輝尽性蛍光体を得た。このとき、結晶系はＳｒＡｌ₂Ｏ₄であることを、Ｘ線回折パターンで確認した。
【０１２７】
［比較例１］ ＳｒＯ・1.75Ａｌ₂Ｏ₃：0.01Ｅｕ蛍光体
実施例１において、Ｓｍ₂Ｏ₃を用いなかったこと以外は実施例１と同様にして、標題の組成式で表されるユーロピウム付活酸化ストロンチウムアルミニウム輝尽性蛍光体を得た。
【０１２８】
［輝尽性蛍光体の評価］
上記の各輝尽性蛍光体の輝尽発光特性について評価した。
輝尽性蛍光体に、蛍光分光光度計（F4500、日立製作所(株)製）を用いて波長４１５ｎｍの光を１２０秒間照射して一次励起した。２分後に、この蛍光体に波長６５０ｎｍの光を１００秒間照射して二次励起し、波長５００ｎｍにおける輝尽発光を測定した。励起後１００秒間に渡る輝尽発光光を積算して、輝尽発光強度（相対値）を求めた。
得られた結果をまとめて表４に示す。
【０１２９】
【表４】

【０１３０】
表４から明らかなように、本発明の希土類で共付活された酸化ストロンチウムアルミニウム輝尽性蛍光体（実施例１〜３）はいずれも、比較のためのユーロピウム付活酸化ストロンチウムアルミニウム輝尽性蛍光体（比較例１）に比べて、著しく高い輝尽発光強度を示した。
【０１３１】
【発明の効果】
本発明の希土類付活アルカリ土類三価金属酸化物系輝尽性蛍光体は、紫外乃至可視領域の光を吸収したのち可視乃至赤外領域の光で励起されると可視領域に輝尽発光を示す蓄積性蛍光体であり、従来よりも顕著に高い輝尽発光強度を示す。この蛍光体は、上述した放射線画像形成方法のみならず、情報の記録や読み出しが可能な光メモリーや、高密度化および高速度化された光素子に利用することも可能である。
【０１３２】
また、この輝尽性蛍光体を用いる本発明の方法によれば、放射線画像形成に関わる蛍光体の放射線吸収機能とエネルギー蓄積機能を分離して、二種類の蛍光体に各機能を分担させ、放射線吸収機能を担う蛍光体には放射線吸収率の高い蛍光体を用いることにより、エネルギー蓄積機能を担う蛍光体には輝尽発光強度の高い輝尽性蛍光体を用いることにより、また蓄積性蛍光体層を両面から露光することによって、検出量子効率の高い画像形成を実現することができる。また、この輝尽性蛍光体を放射線像変換パネルに用いることにより、化学的な安定性が向上した放射線像変換パネルを提供できる。さらに、エネルギー蓄積機能を担う蛍光体として応答性の優れた蛍光体を用いることにより、より一層検出量子効率の高い画像形成を達成することができる。その結果、被検体（被写体）に対して被曝線量を低減することが可能となり、あるいはオートラジオグラフィーのような被検体自体が放射線を放射する場合には、より微量の放射線の解析が可能となる。また、本発明の放射線画像形成方法によれば、Ｘ線解析やオートラジオグラフィーなどにおいても、放射線の二次元情報を得ることができる。
【図面の簡単な説明】
【図１】本発明の放射線画像形成材料の構成の代表的な例を示す概略断面図である。
【図２】本発明の放射線画像形成材料の構成の別の例を示す概略断面図である。
【図３】本発明の放射線画像形成材料の構成の別の例を示す概略断面図である。
【図４】本発明の放射線画像形成材料の構成の別の例を示す概略断面図である。
【図５】本発明の放射線画像形成材料の構成の別の例を示す概略断面図である。
【図６】本発明の放射線画像形成方法に用いられる読取装置の構成の例を示す概略側面図である。
【図７】本発明の放射線画像形成材料の構成の別の例を示す概略断面図である。
【図８】本発明に係る放射線像変換パネルの構成の別の例を示す概略断面図である。
【図９】本発明に係る多層膜の構成の例を示す概略断面図である。
【図１０】多層膜の光透過特性を示すグラフである。
【図１１】多層膜の特定波長における光の入射角と透過率との関係を示すグラフである。
【図１２】本発明に係る放射線像変換パネルの構成の別の例を示す概略断面図である。
【図１３】本発明に係る拡散反射層の層厚と拡散反射率との関係において好ましい領域を示すグラフである。
【図１４】本発明の輝尽性蛍光体について、２ｂ／ａと輝尽発光強度との関係を示すグラフである。
【図１５】本発明の輝尽性蛍光体について、ｘと輝尽発光強度との関係を示すグラフである。
【図１６】本発明の輝尽性蛍光体について、ｙと輝尽発光強度との関係を示すグラフである。
【図１７】本発明の輝尽性蛍光体について、ｙと輝尽発光強度との関係を示すグラフである。
【符号の説明】
１０、１０’、２０、３０、４０、５０ 放射線画像形成材料
１０ａ、１０ａ’、１０ａ”、２０ａ、３０ａ、４０ａ、６０
放射線像変換パネル
１０ｂ、１０ｂ’、２０ｂ、２０ｃ、３０ｂ、３０ｃ、４０ｂ
蛍光スクリーン
１２ａ、１２ｂ、１２ｂ’、２２ｂ、２２ｃ、３２ｂ、３２ｃ、４２、５２
放射線吸収性蛍光体層
１３、２３、３３、３３’、４３、５３ 蓄積性蛍光体層
１５ 選択的反射層（多層膜）
１６ 拡散反射層
６３ 励起光
６４ 輝尽発光光
６５ 集光ガイド
６６ 光電変換装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photostimulable phosphor, a radiographic image forming method using the photostimulable phosphor, and a radiographic image forming material advantageously used in the method.
[0002]
[Prior art]
A radiation image conversion method (radiation image forming method) using a stimulable phosphor is known as an alternative to the conventional radiography method. This method uses a radiation image conversion panel (accumulative phosphor sheet) containing a stimulable phosphor. The panel transmits the radiation transmitted through the subject or emitted from the subject. The radiation energy stored in the stimulable phosphor is absorbed by the phosphor, and then the stimulable phosphor is excited in time series by electromagnetic waves (excitation light) such as visible light and infrared light. It emits as fluorescence (stimulated luminescence light), photoelectrically reads this fluorescence, obtains an electrical signal, and reproduces the subject or a radiographic image of the subject as a visible image based on the obtained electrical signal. is there. The panel which has been read is prepared for the next photographing after the remaining image is erased. That is, the radiation image conversion panel is used repeatedly.
[0003]
This radiographic image conversion method has an advantage that a digital radiographic image rich in information can be obtained as compared with a conventional radiographic method using a combination of a radiographic film and an intensifying screen. Furthermore, while the conventional radiographic method consumes a radiographic film for each radiographing, the radiographic image forming method repeatedly uses a radiographic image conversion panel. It is advantageous.
[0004]
The radiation image conversion panel used in the radiation image conversion method includes, as a basic structure, a support and a phosphor layer (stimulable phosphor layer) provided thereon. However, a support is not necessarily required when the phosphor layer is self-supporting. In addition, a protective layer is usually provided on the upper surface of the phosphor layer (the surface not facing the support) to protect the phosphor layer from chemical alteration or physical impact.
[0005]
The phosphor layer is usually composed of a stimulable phosphor and a binder containing and supporting the phosphor in a dispersed state. However, it is also known that the phosphor layer is composed only of a photostimulable phosphor aggregate without containing a binder formed by vapor deposition or sintering. There is also known a radiation image conversion panel having a phosphor layer in which a polymer substance is impregnated in a gap between aggregates of stimulable phosphors. In any of these phosphor layers, the photostimulable phosphor has the property of exhibiting photostimulated luminescence when irradiated with excitation light after absorbing radiation such as X-rays. The radiation emitted from the subject is absorbed by the phosphor layer of the radiation image conversion panel in proportion to the radiation dose, and a radiation image of the subject or the subject is formed on the panel as an accumulated image of radiation energy. This accumulated image can be emitted as stimulated emission light by irradiating with the excitation light, and by reading this stimulated emission light photoelectrically and converting it into an electrical signal, the accumulated image of radiation energy is imaged. Can be realized.
[0006]
Although the radiation image conversion method has many excellent advantages as described above, the radiation image conversion panel used in this method is as sensitive as possible and has high image quality (sharpness, graininess). Etc.) is desired.
[0007]
Numerous photostimulable phosphors have been proposed and put to practical use in the above radiation image conversion method, but any of the photostimulable phosphors directly absorbs radiation and accumulates its energy. . In other words, since a phosphor that absorbs radiation also serves as a phosphor that accumulates energy, when selecting a phosphor, it is possible to select an optimum phosphor by sufficiently considering the high level of radiation absorption. could not. Therefore, stimulable phosphors that have been proposed or put to practical use have not always been phosphors that are sufficiently satisfactory in their radiation absorption.
[0008]
In addition, rare earth activated alkaline earth metal fluoride halide phosphors are well known as stimulable phosphors for radiation image conversion methods, and these phosphors are excited by excitation light to emit stimulated emission. The response at the time of showing is not necessarily fast enough for all applications, and a stimulable phosphor having better response is desired. However, if a method of reading a plurality of pixels at the same time, such as line sensor reading, is used, there may be no practical problem even if the response is insufficient.
[0009]
As a stimulable phosphor used in the radiation image conversion method, that is, a stimulable phosphor that absorbs radiation and accumulates its energy, JP-A-55-12142 discloses a ZnS-based phosphor. Kaihei 2-692 discloses alkaline earth metal sulfide phosphors such as CaS and SrS. However, these photostimulable phosphors have a very low radiation absorption rate and are not practical as long as they absorb radiation directly. In addition, these sulfide-based phosphors have a chemically unstable surface, and it is necessary to consider this point in practical use.
[0010]
Japanese Patent Laid-Open No. 2001-255610 discloses a radiation image conversion containing at least a stimulable phosphor (energy storage phosphor) by separating the radiation absorbing function and the energy storage function of a conventional stimulable phosphor. A radiation image forming method and a radiation image forming material using a combination of a panel and a phosphor screen containing a phosphor (radiation absorbing phosphor) that absorbs radiation and emits light in the ultraviolet to visible region have been proposed. In this method, radiation transmitted through a subject is first converted into light in the ultraviolet or visible region by the radiation absorbing phosphor of the screen or panel, and then the light is imaged by the energy storage phosphor of the panel. Accumulate and record as information. Next, the panel is scanned with excitation light to emit stimulated emission light, and this stimulated emission light is photoelectrically read to obtain an image signal.
[0011]
Japanese Patent Application Laid-Open No. 2001-123162 discloses mMO · nAl.₂O_Three(Wherein M is at least one metal element selected from the group consisting of Mg, Ca, Sr and Ba), and a compound in which the ratio of m to n is 0.5 ≦ m / n ≦ 1 As materials and activators, transition metal elements of Ti, Zr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, W, Bi, and Eu, La, Ce, 0.0001 mol% of at least one of the rare earth elements Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu with respect to the metal element represented by M There has been disclosed a phosphor for optical memory which is added in an amount of 20 mol% or less and enables recording and reading by exciting the electrons of the activator with visible light.
[0012]
[Problems to be solved by the invention]
The present inventor has studied a photostimulable phosphor that exhibits photostimulated luminescence when it is excited by light in the visible to infrared region after absorbing light in the ultraviolet to visible region. It was found that the active alkaline earth trivalent metal oxide-based photostimulable phosphor exhibits high photostimulated luminescence intensity. Further, this stimulable phosphor has been found to be preferable as the above-described radiation image forming method and energy storage phosphor of the radiation image forming material, and the present invention has been achieved.
[0013]
Accordingly, it is an object of the present invention to provide a photostimulable phosphor having a high photostimulated emission intensity. Another object of the present invention is to provide a radiation image forming method with high detection quantum efficiency. In particular, the present invention provides a radiographic image forming method capable of providing a radiographic image with high image quality and reducing the exposure dose. Furthermore, the present invention also provides a radiation image forming material comprising a radiation image conversion panel and a fluorescent screen having high sensitivity and high chemical stability.
[0014]
[Means for Solving the Problems]
The present invention resides in a rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor having the following chemical composition formula (I).
[0015]
      M^IIO ・ aM^III ₂O_Three: XEu, yLn (I)
[However, M^IIRepresents at least one alkaline earth metal selected from the group consisting of Mg, Ca, Sr and Ba;^IIIRepresents at least one trivalent metal selected from the group consisting of B, Al and Ga;Sm and / or TmAnd a, x and y are 0.5 ≦ a ≦ 5.5 and 1 × 10 respectively.^-6≦ x ≦ 0.2, 1 × 10^-6Represents a numerical value in the range of ≦ y ≦ 0.2],
  Or
[However, M ^II Represents at least one alkaline earth metal selected from the group consisting of Mg, Ca, Sr and Ba; ^III Represents at least one trivalent metal selected from the group consisting of B, Al and Ga; Ln represents La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. And at least one rare earth element selected from the group consisting of: and a, x and y are 1.1 ≦ a ≦ 3.0 and 1 × 10 respectively. ^-6 ≦ x ≦ 0.2, 1 × 10 ^-6 Represents a numerical value in the range of ≦ y ≦ 0.2].
[0016]
The present invention also includes a radiation-absorbing phosphor layer containing a phosphor that absorbs image-forming radiation and emits emitted light in the ultraviolet to visible region, and absorbs the emitted light to accumulate its energy, A radiation image conversion panel having a stimulable phosphor layer containing the photostimulable phosphor that emits the energy as emitted light when excited by light in the visible to infrared region, and absorbs radiation for image formation A fluorescent screen having a radiation-absorbing phosphor layer containing a phosphor that emits emission light in the ultraviolet to visible region is arranged so that the screen is in close contact with the surface of the panel on the side of the stimulable phosphor layer. Or, from the side of the screen, irradiate the radiation transmitted through the subject, diffracted or scattered by the subject, or emitted from the subject, and the spatial energy distribution information of the radiation is displayed on the panel. After recording as an image, the panel is detached from the screen, the surface of the panel is irradiated with excitation light, and the emitted light emitted from the latent image of the panel is photoelectrically read into an image signal. The radiation image forming method includes converting and forming an image corresponding to the spatial energy distribution of the radiation from the image signal.
[0017]
The present invention also provides the emission light between two fluorescent screens each having a radiation absorbing phosphor layer containing a phosphor that absorbs image forming radiation and emits emission light in the ultraviolet to visible region. A radiation image having a stimulable phosphor layer containing the stimulable phosphor that absorbs and accumulates its energy and emits the accumulated energy as emitted light when excited by light in the visible to infrared region. The conversion panels are arranged in close contact with each other and irradiated with radiation transmitted through the subject, diffracted or scattered by the subject, or emitted from the subject, from either one of the screen sides. After recording the spatial energy distribution information of the radiation as a latent image, the panel is separated from both screens, and then the surface of the panel is irradiated with excitation light to emit light emitted from the latent image. Was converted into an image signal read photoelectrically from one side or both sides of the panel, and also in the radiation image-forming method which comprises forming an image corresponding to the spatial energy distribution of the radiation from said image signal.
[0018]
The present invention further provides a phosphor screen having a radiation-absorbing phosphor layer containing a phosphor that absorbs image-forming radiation and emits emitted light in the ultraviolet to visible region. A state of adhesion to the surface of a radiation image conversion panel having a stimulable phosphor layer containing the stimulable phosphor that accumulates and is excited by light in the visible to infrared region and emits the accumulated energy as emitted light. The spatial energy distribution information of the radiation is placed on the panel by irradiating the panel or panel from the side of the screen or panel with the radiation transmitted through the subject, diffracted or scattered by the subject, or emitted from the subject. Is recorded as a latent image, and then the panel is pulled away from the screen, the surface of the panel is irradiated with excitation light, and the emitted light emitted from the latent image is emitted from one or both sides of the panel. It is converted into an image signal, and also the radiation image-forming method which comprises forming an image corresponding to the spatial energy distribution of the radiation from said image signals read in electrostatically.
[0019]
The present invention also provides a radiation-absorbing phosphor layer containing a phosphor that absorbs image-forming radiation and emits emitted light in the ultraviolet to visible region, and absorbs the emitted light to accumulate its energy, thereby visible. A stimulable phosphor layer containing the stimulable phosphor that is excited by light in the infrared region and emits the accumulated energy as emitted light, and the layer thickness of the stimulable phosphor layer is A radiation image conversion panel smaller than the thickness of the radiation-absorbing phosphor layer is irradiated with radiation that has passed through the subject, is diffracted or scattered by the subject, or is emitted from the subject, and the panel is irradiated with the radiation image conversion panel. After recording the spatial energy distribution information of the radiation as a latent image, the surface of the panel is irradiated with excitation light, and the emitted light emitted from the latent image is photoelectrically read from the panel. Converted into an image signal and the image There is also a radiographic image forming method comprising forming an image corresponding to the spatial energy distribution of the radiation from the item.
[0020]
The present invention also resides in a radiation image forming material comprising a radiation image conversion panel and a fluorescent screen used in each of the above-described radiation image forming methods.
[0021]
In the present invention, radiation means ionizing radiation such as X-rays, γ-rays, β-rays, α-rays, ultraviolet rays, and neutron rays. In general, the ultraviolet to visible region means a wavelength range of 200 nm to 600 nm, and the visible to infrared region means a wavelength range of 400 nm to 1600 nm.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
In the stimulable phosphor of the present invention having the chemical composition formula (I), M^IIPreferably contains Sr in an amount of 50% (molar ratio) or more, particularly preferably Sr. M^IIIPreferably contains 50% (molar ratio) or more of Al, particularly preferably made of Al. M^IIIPreferably contains B. Ln is preferably Sm and / or Tm. Further, a is preferably a numerical value within a range of 1.1 ≦ a ≦ 3.0, and x is 1 × 10.^-3≦ x ≦ 5 × 10^-2Is preferably in the range of y and y is 1 × 10^-FourIt is preferable that the numerical value is within a range of ≦ y ≦ 0.1.
[0023]
Moreover, the preferable aspect of the radiographic image forming material used for the radiographic image forming method of this invention is given.
(1) A radiation image forming material using an oxide-based phosphor as a stimulable phosphor contained in a stimulable phosphor layer of a radiation image conversion panel.
(2) A radiation image forming material in which the layer thickness of the stimulable phosphor layer of the radiation image conversion panel is smaller than the layer thickness of the radiation absorbing phosphor layer of the radiation image conversion panel or the phosphor screen.
(3) Radiation in which the layer thickness of the stimulable phosphor layer of the radiation image conversion panel is in the range of 0.2 to 20% of the layer thickness of the total radiation absorbing phosphor layer of the radiation image conversion panel and / or phosphor screen. Imaging material.
(4) A radiation image forming material in which a barrier rib for subdividing the phosphor layer along the plane direction is provided on the radiation absorbing phosphor layer.
[0024]
(5) A radiation image-forming material in which the phosphor of the radiation-absorbing phosphor layer is a needle-like phosphor crystal and arranged so as to exhibit anisotropy.
(6) At least one layer of the radiation image conversion panel is colored by a colorant that absorbs excitation light and / or light emitted from the stimulable phosphor and / or light emitted from the radiation-absorbing phosphor. Radiation imaging material. That is, in a system in which a radiation image is detected and read from a radiation image conversion panel using a line sensor described later, it is better to absorb a part of the emitted light from the stimulable phosphor layer to improve the sharpness of the image. In some cases, this is advantageous.
[0025]
[Stimulable phosphor]
The alkaline earth trivalent metal oxide photostimulable phosphor co-activated with a rare earth having the following chemical composition formula (I) of the present invention absorbs light in the ultraviolet to visible region and accumulates its energy. When excited by light in the visible to infrared region, the energy is emitted into the visible region as emitted light. By co-activating with the rare earth, a carrier trap in which energy is stored can be positively introduced into the phosphor, so that the stimulated emission intensity can be improved.
[0026]
  Chemical composition formula (I):
      M^IIO ・ aM^III ₂O_Three: XEu, yLn (I)
[However, M^IIRepresents at least one alkaline earth metal selected from the group consisting of Mg, Ca, Sr and Ba;^IIIRepresents at least one trivalent metal selected from the group consisting of B, Al and Ga;Sm and / or TmAnd a, x and y are 0.5 ≦ a ≦ 5.5 and 1 × 10 respectively.^-6≦ x ≦ 0.2, 1 × 10^-6Represents a numerical value in the range of ≦ y ≦ 0.2],
  Or
[However, M ^II Represents at least one alkaline earth metal selected from the group consisting of Mg, Ca, Sr and Ba; ^III Represents at least one trivalent metal selected from the group consisting of B, Al and Ga; Ln represents La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. And at least one rare earth element selected from the group consisting of: and a, x and y are 1.1 ≦ a ≦ 3.0 and 1 × 10 respectively. ^-6 ≦ x ≦ 0.2, 1 × 10 ^-6 Represents a numerical value in the range of ≦ y ≦ 0.2].
[0027]
Taking the europium samarium (thulium) activated strontium aluminum oxide (strontium aluminate) phosphor having the following composition formulas (II) to (V) as one of the photostimulable phosphors as an example, The relationship with the stimulated emission intensity will be described.
[0028]
FIG. 14 is a graph showing Al for a phosphor having the following composition formula (II).₂O_ThreeIt is a graph which shows the relationship between the quantity a and stimulated luminescence intensity (integrated value).
SrO · aAl₂O_Three: 0.01Eu, 0.001Sm (II)
From FIG. 14, it can be seen that stimulated luminescence is exhibited when a is in the range of about 0.5 to 5.5, and particularly high stimulated luminescence intensity is exhibited when in the range of 1.1 to 3.0. .
[0029]
FIG. 15 is a graph showing the relationship between the Eu amount x and the stimulated emission intensity (integrated value) with respect to the Sr molar ratio for a phosphor having the following composition formula (III).
SrO ・ 1.75Al₂O_Three: XEu, 0.001Sm (III)
From FIG. 15, when x is about 0.2 or less, sufficient stimulated emission intensity is shown, and in particular, 1 × 10^-3~ 5x10^-2It can be seen that high stimulated emission intensity is exhibited when it is in the range of.
[0030]
FIG. 16 is a graph showing the relationship between the Sm amount y with respect to the Sr molar ratio and the stimulated emission intensity (integrated value) for a phosphor having the following composition formula (IV).
SrO ・ 1.75Al₂O_Three: 0.01 Eu, ySm (IV)
From FIG. 16, y is approximately 1 × 10.^-6It exhibits sufficient stimulated emission intensity when it is in the range of ~ 0.2, particularly 1 × 10^-FourIt can be seen that a high stimulated emission intensity is exhibited when it is in the range of ˜0.1.
[0031]
FIG. 17 is a graph showing the relationship between the amount y of Tm with respect to the Sr molar ratio and the stimulated emission intensity (integrated value) for a phosphor having the following composition formula (V).
SrO ・ 1.75Al₂O_Three: 0.01 Eu, yTm (V)
From FIG. 17, y is approximately 1 × 10.^-6It exhibits sufficient stimulated emission intensity when it is in the range of ~ 0.2, particularly 1 × 10^-FourIt can be seen that a high stimulated emission intensity is exhibited when it is in the range of ˜0.1.
[0032]
The rare earth activated alkaline earth trivalent metal oxide based photostimulable phosphor can be produced, for example, as follows.
[0033]
As a phosphor raw material, alkaline earth metal carbonate, trivalent metal oxide, europium oxide, and rare earth oxides other than europium are prepared. These phosphor materials and boric acid are mixed using a mortar or the like. Furthermore, if desired, for the purpose of improving the photostimulable luminescence properties, a compound such as an alkali metal halide is added to an alkaline earth metal (M^II) May be added and mixed in an amount of 0.2 mol or less.
[0034]
This phosphor raw material mixture is filled in a heat-resistant container such as an alumina crucible, platinum crucible, or quartz boat, and then placed in the core of an electric furnace for firing. The firing temperature is suitably in the range of 800 to 1700 ° C, particularly preferably around 1300 ° C. The firing atmosphere is preferably a weakly reducing atmosphere such as firing in the presence of carbon. The firing time varies depending on the filling amount of the mixture, the firing temperature, the temperature of taking out from the furnace, and the like, but generally 2 to 6 hours is appropriate, and preferably 3 to 5 hours.
[0035]
The phosphor thus obtained may be subjected to various general operations in the production of the phosphor, such as pulverization and sieving, as necessary. Thereby, the rare earth activated alkaline earth trivalent metal oxide-based stimulable phosphor represented by the above-mentioned chemical composition formula (I) is obtained.
[0036]
[Configuration of radiation image forming material]
Next, the radiation image forming material used in the radiation image forming method of the present invention will be described in detail.
The radiation image forming material of the present invention is an assembly comprising at least a radiation image conversion panel having a stimulable phosphor layer and a phosphor screen having a radiation absorbing phosphor layer. The radiation-absorbing phosphor layer is a layer containing a phosphor that absorbs radiation and emits light in the ultraviolet to visible region (hereinafter referred to as a radiation-absorbing phosphor). The stimulable phosphor layer absorbs the emitted light from the radiation-absorbing phosphor and accumulates the energy. When excited by light in the visible or infrared region, the stimulable phosphor layer emits the accumulated energy as emitted light. It is a layer containing a phosphor. Since the stimulable phosphor layer does not absorb radiation at all, the energy of the radiation directly absorbed by the stimulable phosphor layer is also used in conjunction with the formation of the radiation image.
[0037]
An example of the configuration of the radiation imaging material of the present invention will be described with reference to the accompanying drawings.
1 to 5 are schematic cross-sectional views showing typical examples of the configuration of the radiation image forming material of the present invention. The arrow indicates the irradiation direction of radiation such as X-rays.
[0038]
In FIG. 1, a radiation image forming material 10 is composed of a front side radiation image conversion panel 10a and a back side fluorescent screen 10b. The radiation image conversion panel 10a on the front side includes a support 11a, a radiation absorbing phosphor layer 12a, a storage phosphor layer 13 and a protective layer 14a in this order. The back fluorescent screen 10b is composed of a support 11b, a radiation absorbing phosphor layer 12b, and a protective layer 14b in this order. It is also possible to arrange a fluorescent screen on the front side and a radiation image conversion panel on the back side.
[0039]
The layer thickness of the radiation absorbing phosphor layer 12a on the front side is generally in the range of 50 to 200 μm, preferably in the range of 100 to 150 μm. The layer thickness of the back-side radiation-absorbing phosphor layer 12b is preferably equal to or greater than the layer thickness of the front-side radiation-absorbing phosphor layer 12a, and is generally in the range of 50 to 300 μm. , Preferably in the range of 100 to 250 μm. However, when the radiation-absorbing phosphor layer has anisotropy, the phosphor layer has a thickness of about 600 μm (preferably 500 μm or less) in both the front side and the back side. May be.
[0040]
On the other hand, the energy of the stimulable phosphor layer 13 is accumulated by absorption of light in the ultraviolet to visible region, so that the layer thickness can be reduced and is generally in the range of 1 to 50 μm, preferably 5 Or in the range of 20 μm. Preferably, the stimulable phosphor layer 13 is thinner than the radiation absorbing phosphor layer 12a, and more preferably, the thickness of the stimulable phosphor layer 13 is the total thickness of the radiation absorbing phosphor layers 12a and 12b. It is in the range of 0.2 to 20%.
[0041]
The thickness of the supports 11a and 11b is generally in the range of 50 to 1000 μm, preferably in the range of 120 to 350 μm. The support may be attached to a substrate such as a carbon fiber sheet or an aluminum sheet. The layer thickness of the protective layers 14a and 14b is generally in the range of about 1 μm to 20 μm, and preferably in the range of 3 to 15 μm.
[0042]
In FIG. 2, the radiation image forming material 20 includes a front side fluorescent screen 20b, a back side fluorescent screen 20c, and a center radiation image conversion panel 20a therebetween. The front screen 20b is composed of a support 21b, a radiation absorbing phosphor layer 22b, and a protective layer 24b in this order. The back-side screen 20c is composed of a support 21c, a radiation-absorbing phosphor layer 22c, and a protective layer 24c in this order. The center panel 20a includes a protective layer 24a, a stimulable phosphor layer 23, and a protective layer 24'a in this order.
[0043]
In FIG. 3, the radiation image forming material 30 includes a front side fluorescent screen 30b, a back side fluorescent screen 30c, and a center radiation image conversion panel 30a therebetween. The front screen 30b is composed of a support 31b, a radiation absorbing phosphor layer 32b, and a protective layer 34b in this order. The back side screen 30c is composed of a support 31c, a radiation absorbing phosphor layer 32c, and a protective layer 34c in this order. The center panel 30a includes a protective layer 34a, a stimulable phosphor layer 33, a support 31a, a stimulable phosphor layer 33 ', and a protective layer 34'a in this order.
[0044]
In FIG. 4, the radiation image forming material 40 includes a radiation image conversion panel 40a on the front side and a fluorescent screen 40b on the back side. The front panel 40a is composed of a support 41a, a stimulable phosphor layer 43, and a protective layer 44a in this order. The back-side screen 40b is composed of a support 41b, a radiation-absorbing phosphor layer 42, and a protective layer 44b in this order.
[0045]
In FIG. 5, a radiation image forming material 50 is a special embodiment in which a radiation image conversion panel and a phosphor screen are integrated, and in order, a support 51, a radiation absorbing phosphor layer 52, and a storage phosphor layer. 53 and a protective layer 54.
[0046]
The layer thickness of the stimulable phosphor layer 53 is usually smaller than the layer thickness of the radiation-absorbing phosphor layer 52, and preferably in the range of 0.2 to 20% of the layer thickness of the radiation-absorbing phosphor layer 52. . The layer thickness of the stimulable phosphor layer 53 is generally in the range of 1 to 50 μm, and preferably in the range of 5 to 20 μm. The layer thickness of the radiation absorbing phosphor layer 52 is generally in the range of 50 to 300 μm, preferably in the range of 100 to 250 μm. However, when the radiation-absorbing phosphor layer has anisotropy, the phosphor layer has a thickness of about 600 μm (preferably 500 μm or less) in both the front side and the back side. May be. The thickness of the support 51 is generally in the range of 50 to 1000 μm, preferably in the range of 120 to 350 μm. The support may be attached to a substrate such as a carbonaceous sheet or an aluminum sheet. The layer thickness of the protective layer 54 is generally in the range of about 1 μm to 20 μm, preferably in the range of 3 to 15 μm.
[0047]
In addition, although the irradiation direction of the radiation is shown by arrows in FIGS. 1 to 5, for any of the above-described radiation image forming materials, the back side screen of the assembly or the support of the radiation image conversion panel is turned upside down. It is possible to irradiate the body side with radiation. However, even in that case, it is preferable that the front-side and back-side radiation-absorbing phosphor layers have a small thickness on the front side.
[0048]
(Stimulable phosphor)
The stimulable phosphor used in the image forming method of the present invention is a rare earth-activated alkaline earth trivalent metal oxide-based stimulable phosphor having the chemical composition formula (I) described above. This phosphor absorbs light emitted from the radiation-absorbing phosphor described later (light in the ultraviolet to visible region) and accumulates its energy. When excited by light in the visible to infrared region, this phosphor emits that energy as emitted light. Can be released as The phosphor is generally used in the form of particles, and the particle diameter is preferably about 5 μm or less, particularly preferably 2 μm or less.
[0049]
Table 1 below shows the peak wavelength of the excitation spectrum and the peak wavelength of the emission spectrum for typical examples of the photostimulable phosphor. In Table 1, the primary excitation wavelength corresponds to an absorption wavelength for storing energy in the stimulable phosphor, and the secondary excitation wavelength is used when reproducing a radiation image using the energy accumulated in the stimulable phosphor. This corresponds to the excitation wavelength for emitting the light.
[0050]
[Table 1]

[0051]
(Radiation absorbing phosphor)
The radiation-absorbing phosphor used in the radiation-absorbing phosphor layer and the phosphor screen of the radiation image-forming material of the present invention is used for image formation by the method of the present invention. X-ray, γ-ray, β-ray, α-ray, ultraviolet ray It is a phosphor that absorbs radiation such as neutron rays and usually emits light in the ultraviolet to visible region instantaneously. The radiation-absorbing phosphor used in the present invention is preferably a phosphor containing an element having an atomic number of 37 or more as a main component of the matrix, and particularly preferably a phosphor containing an element having an atomic number of 55 to 83. It is. For example, LnTaO_Four: (Nb, Gd, Tm) system, Ln₂SiO_Five: Ce, LnOX: Tm (Ln is a rare earth element), CsX (X is halogen), Gd₂O₂S: Tb, Gd₂O₂S: Pr, Ce, ZnWO_Four, LuAlO_Three: Ce, Gd_ThreeGa_FiveO₁₂: Cr, Ce, HfO₂Etc.
Table 2 below shows the density and emission wavelength of typical radiation-absorbing phosphors.
[0052]
[Table 2]

[0053]
Among these, the radiation-absorbing phosphor preferably combined with the photostimulable phosphor is YTaO._Four: Nb and CsI: Na.
However, the radiation absorbing phosphor used in the present invention is not limited to the phosphors shown in Table 1. The radiation absorbing phosphor is selected in consideration of matching with the primary excitation characteristic of the photostimulable phosphor. The radiation-absorbing phosphor is generally used in the form of particles, and the particle diameter is desirably in the range of about 1 to 20 μm.
[0054]
From the point of matching, it is preferable that the emission wavelength region of the radiation-absorbing phosphor and the primary excitation wavelength region of the stimulable phosphor overlap by 70% or more. In this definition, each wavelength region means a wavelength range having a value of 10% or more of the peak value of the emission spectrum or excitation spectrum.
[0055]
The radiation-absorbing phosphors are different from those contained in the front-side radiation-absorbing phosphor layer and those contained in the back-side radiation-absorbing phosphor layer as the main component of the matrix (atom It preferably contains an element having a number of 37 or more. More preferably, the radiation absorbing phosphor on the back side contains an element having a relatively large atomic number. Thus, by changing the type of phosphor element and shifting the absorption characteristics for radiation, the radiation can be efficiently absorbed by both phosphor layers. In addition, you may contain two or more types of radiation absorption fluorescent substance in one fluorescent substance layer.
[0056]
[Production method of radiation imaging material]
(Radiation image conversion panel)
Next, the radiation image forming material manufacturing method of the present invention will be described with reference to the radiation image conversion panel 10a of the radiation image forming material shown in FIG. The case where it consists of a body particle and the binder which contains and supports this in a dispersed state is demonstrated. Each phosphor layer can be sequentially formed on the support by, for example, the following known method.
[0057]
(Support)
The support is usually a sheet or film made of a flexible resin material and having a thickness of 50 μm to 1 mm. The support may be transparent, or a light reflective material (eg, alumina particles, titanium dioxide particles, barium sulfate particles) for reflecting excitation light (primary or secondary) or stimulated emission light to the support. ) Or a void may be provided. Alternatively, the support may be filled with a light-absorbing material (eg, carbon black) in order to absorb excitation light or stimulated emission light. Examples of resin materials that can be used to form the support include various resin materials such as polyethylene terephthalate, polyethylene naphthalate, aramid resin, and polyimide resin. If necessary, the support may be a metal sheet, a ceramic sheet, a glass sheet, a quartz sheet, or the like.
[0058]
(Radiation absorbing phosphor layer)
First, the radiation-absorbing phosphor particles and the binder are added to a solvent and mixed well to prepare a coating solution in which the radiation-absorbing phosphor particles are uniformly dispersed in the binder solution. Various types of resin materials are known for binders that support and disperse phosphor particles, and in the production of the radiation image conversion panel of the present invention, any resin material centered on those known binder resins. Can be appropriately selected and used. The mixing ratio of the binder and the phosphor in the coating liquid varies depending on the characteristics of the intended radiation image conversion panel, the type of the phosphor, and the like, but generally the mixing ratio of the binder and the phosphor (conjugate / phosphor). ) Is selected from the range of 1 to 0.01 (weight ratio). The coating solution further includes a dispersant for improving the dispersibility of the phosphor in the coating solution, and a plastic for improving the binding force between the binder and the phosphor in the formed phosphor layer. Various additives such as an agent, a yellowing prevention agent for preventing discoloration of the phosphor layer, a curing agent, and a crosslinking agent may be mixed.
[0059]
The coating solution thus prepared is then uniformly applied to the surface of the support to form a coating film. Application | coating operation can be performed by the method of using a normal application means, for example, a doctor blade, a roll coater, a knife coater etc. This coating film is dried to complete the formation of the radiation-absorbing phosphor layer on the support. The phosphor layer is not necessarily formed by directly applying the coating solution on the support as described above. For example, the phosphor layer is separately applied on a temporary support such as a glass plate, a metal plate, or a plastic sheet. After forming the phosphor layer by coating and drying, a method of bonding the phosphor layer on the support by pressing it on the support or using an adhesive may be used. Or the fluorescent substance layer which orientated the needle-like fluorescent substance as described in Japanese Patent Application No. 2000-158213 specification can also be used.
[0060]
The radiation-absorbing phosphor layer according to the present invention includes not only a radiation-absorbing phosphor and a binder that contains and supports the radiation-absorbing phosphor in a dispersed state, but also includes only an aggregate of the radiation-absorbing phosphor without including the binder. Or a phosphor layer in which a polymer substance is impregnated in a gap between aggregates of radiation-absorbing phosphors.
[0061]
(Partition wall)
In addition, the radiation-absorbing phosphor layer may be provided with partition walls that subdivide the phosphor layer along the plane direction for the purpose of improving the image quality of the image obtained by preventing scattering of emitted light. Since the radiation-absorbing phosphor layer has a relatively large layer thickness, diffusion of emitted light can be effectively prevented by providing a partition wall. The partition walls can be provided in any shape such as a stripe shape or a lattice shape, or the partition walls may be formed so as to surround a region filled with a radiation-absorbing phosphor having an arbitrary shape such as a circle or a hexagon. Further, both the top and bottom of the partition wall may be exposed on both surfaces of the phosphor layer, or both or one of the top and bottom may be buried in the phosphor layer.
[0062]
For example, a large number of partition walls can be obtained by performing a suitable etching process on a metal plate such as aluminum, titanium, and stainless steel, a ceramic plate such as aluminum oxide and aluminum silicate, or a sheet made of an organic polymer material such as a photosensitive resin. A honeycomb sheet having recesses (holes) or through holes formed therein is prepared, and the above phosphor layer is placed on the honeycomb sheet and then heated and compressed, whereby the honeycomb sheet is formed into the phosphor layer. It can be formed by being pushed in. Alternatively, a large number of thin-film phosphor sheets made of a binder containing dispersed fluorescent particles and a large number of thin-film barrier rib sheets made of a polymer material are formed, and a large number of phosphor sheets and barrier rib sheets are alternately formed. It can also be formed by a lamination slicing method that consists of laminating one sheet and then cutting perpendicularly to the lamination direction. Alternatively, when the phosphor layer is composed of an aggregate of radiation-absorbing phosphors such as a vapor deposition film as described above, it can be formed as a partition by forming cracks. Examples of such a phosphor layer include needle crystal films such as CsI: Na, CsI: Tl, and CsBr: Tl. The partition walls may contain dispersed low light-absorbing fine particles such as aluminum oxide and titanium dioxide, or may be colored with a colorant that selectively absorbs light emitted from the radiation-absorbing phosphor. Also good.
[0063]
Alternatively, the barrier ribs may be formed from a phosphor layer material (however, the binder: phosphor ratio and / or particle size is different from the case of forming the phosphor layer). In general, since the radiation-absorbing phosphor has a high refractive index, scattering in the plane direction can be more effectively prevented. In addition, a high sharpness image can be obtained while maintaining high radiation absorption.
[0064]
Alternatively, the radiation-absorbing phosphor layer may be composed of a fiber plate and a needle-like crystal film of the radiation-absorbing phosphor as shown in FIG. In FIG. 7, the radiation-absorbing phosphor layer 12b 'is a phosphor acicular crystal film 12b on the support 11b side.₁And a fiber plate 12b provided thereon₂It consists of. Phosphor needle crystal film 12b₁Has cracks as partition walls as described above. Meanwhile, the fiber plate 12b₂Is an optical sheet obtained by bundling millions of fibers having a diameter of several μm in the depth direction, and is a needle-like crystal film 12b of phosphor.₁The light converted from radiation such as X-rays into light in the ultraviolet to visible region is the fiber plate 12b.₂The storage phosphor layer 13 can be reached without being scattered in the plane direction through the light source and with little loss of light.
[0065]
In FIG. 7, the radiation-absorbing phosphor layer 12 b ′ of the phosphor screen 10 b ′ on the back side, not the radiation image conversion panel 10 a on the front side of the radiation image forming material 10 ′, is replaced with a needle-like crystal film 12 b of phosphor.₁And fiber plate 12b₂However, from the viewpoint of improving the sharpness, the partition including this structure is preferably provided in the radiation-absorbing phosphor layer having a thicker layer thickness than the stimulable phosphor layer, and more preferably Is provided on the radiation absorbing phosphor layer on the back side, and particularly preferably on the phosphor layer of the phosphor screen arranged on the back side as shown in FIG. Thereby, it is possible to achieve both high image quality by the back side screen having the partition wall and good transportability in the reading device of the flexible front side panel.
[0066]
(Storage phosphor layer)
On the radiation-absorbing phosphor layer, a stimulable phosphor layer made of a binder that contains and supports the stimulable phosphor in a dispersed state is formed in the same manner as described above. This stimulable phosphor layer may also be composed only of an aggregate of stimulable phosphors, or may be one in which a polymer substance is impregnated between the aggregates of stimulable phosphors. Alternatively, a partition wall may be provided.
[0067]
When the radiation-absorbing phosphor layer and the storage phosphor layer are each composed of the phosphor particles and the binder as described above, in order to improve the radiographic image, the radiation-absorbing fluorescence Weight ratio of binder to phosphor in body layer (Binder B₁/ Phosphor P₁) Is the weight ratio of binder to phosphor in the stimulable phosphor layer (Binder B).₂/ Phosphor P₂) Or less, and it is desirable that both are 1 or less (1 ≧ B₂/ P₂≧ B₁/ P₁). That is, it is desirable that the ratio of the phosphor in the radiation-absorbing phosphor layer is equal to or higher than the ratio of the phosphor in the stimulable phosphor layer.
[0068]
B of radiation absorbing phosphor layer₁/ P₁The ratio (weight ratio) is preferably in the range of 1/8 to 1/50, more preferably in the range of 1/15 to 1/40. B of storage phosphor layer₂/ P₂The ratio (weight ratio) is preferably in the range of 1/1 to 1/40, and more preferably in the range of 1/2 to 1/20.
It should be noted that the relationship between the binder and the phosphor is desirably established similarly between the storage phosphor layer of the radiation image conversion panel and the radiation absorbing phosphor layer of the phosphor screen.
[0069]
(Phosphor particle size)
The average particle size of the radiation-absorbing phosphor and stimulable phosphor contained in each phosphor layer is
(Average particle diameter of photostimulable phosphor) ≦ (Average particle diameter of radiation absorbing phosphor)
It is desirable to satisfy this relationship. Particularly preferably,
(Average particle diameter of stimulable phosphor) ≦ (average particle diameter of radiation-absorbing phosphor) × 0.5. As a result, it is possible to increase the luminous efficiency with respect to radiation by the relatively large particle diameter of the radiation-absorbing phosphor and increase the sensitivity, and to enhance the sharpness of the image by the relatively small particle diameter of the stimulable phosphor. Can do.
[0070]
The average particle diameter of the radiation absorbing phosphor is generally 1 μm or more and 20 μm or less, preferably 2 μm or more and 10 μm or less. On the other hand, the average particle size of the photostimulable phosphor is generally 0.2 μm or more and 20 μm or less, preferably 0.5 μm or more and 5 μm or less. However, as described in Japanese Patent Application No. 2000-219877, there is no problem in the use of even smaller particles such as photostimulable quantum dot phosphors if their efficiency is high.
[0071]
The radiation-absorbing phosphor particles and the stimulable phosphor particles have a particle size distribution as described in, for example, JP-A-2000-284097, JP-A-2000-192030, or JP-A-58-182600. You may have.
[0072]
(Phosphor absorption coefficient)
From the viewpoint of improving the image quality of radiographic images, the radiation absorption coefficient of the radiation-absorbing phosphor layer and the absorption coefficient for the emitted light (primary excitation light) from the radiation-absorbing phosphor of the storage phosphor layer have the following relationship: It is desirable to satisfy.
(Absorption coefficient of primary excitation light of stimulable phosphor layer)>
(Radiation absorption coefficient of radiation absorbing phosphor layer) × 2
Particularly preferably,
(Absorption coefficient of primary excitation light of stimulable phosphor layer)>
(Radiation absorption coefficient of radiation absorbing phosphor layer) × 5
To satisfy the relationship.
[0073]
Here, the absorption coefficient of the primary excitation light is an apparent absorption coefficient as described in Japanese Patent Application No. 11-349633 by the applicant of the present application, and is a value defined as follows. . When the phosphor layer is regarded as a uniform layer having a thickness d, the light reflectance when the phosphor layer is placed in space is r, and the light transmittance is t. The light reflectance r is obtained by relative comparison with a standard white plate. A white plate (reflectance r) on the back side of the phosphor layer_w) And black plate (reflectance r_b), The reflectance of the entire system is R_wAnd R_bAnd Since the reflection of the entire system is the sum of the reflection by the phosphor layer and the reflection by the white plate or the black plate, it is expressed by the following equation.
R_w= R + r_wXt²
R_b= R + r_bXt²
[0074]
The apparent absorption coefficient K of the phosphor layer is as follows, assuming that the absorption exponentially decays with respect to the thickness d of the phosphor layer, because the sum of reflection, absorption, and transmission is 1 according to the energy conservation law. It is calculated by the formula.

[0075]
On the other hand, the radiation absorption coefficient is the mass energy absorption coefficient μ_en/ Ρ can be obtained by multiplying the density of the phosphor layer. Mass energy absorption coefficient μ in the X-ray region of each substance_en/ Ρ can be determined using the mass absorption coefficient and mass ratio of the component elements of each substance. Data on the mass energy absorption coefficient of each element can be obtained from http://physics.nist.gov/PhysRefData/XrayMassCoef/cover.html. The density ρ of the phosphor layer is obtained as a value obtained by multiplying the density of the phosphor itself by the phosphor filling rate in the layer, and is usually a value of about 3 to 5.
[0076]
In order to increase the radiation absorption coefficient and obtain a high-quality radiation image, the radiation absorbing phosphor layer has a density of the radiation absorbing phosphor of 6.0 g / cm.^ThreeOr the average density of the phosphor layer is 4.0 g / cm^ThreeThe above is preferable.
[0077]
(Simultaneous multilayer coating)
When the photostimulable phosphor particles are not sufficiently small with respect to the layer thickness of the phosphor layer to be formed, that is, the average particle diameter of the photostimulable phosphor is represented by a μm, and the layer thickness of the phosphor layer is represented by d μm. When both
d / 10 <a <d
In the case where the above relationship is satisfied, it is preferable to form the stimulable phosphor layer and the radiation absorbing phosphor layer having a large layer thickness thereunder by simultaneous multilayer coating. Thereby, a phosphor layer having a thin layer thickness of 5 to 20 μm can be formed uniformly.
[0078]
Simultaneous multi-layer coating can be performed by coating the separately prepared coating solutions together on the support surface using a double hopper type coating device, etc., simultaneously at the same time, or for radiation absorbing phosphor layers. Immediately after the liquid is applied to the surface of the support, it can be carried out by applying a multi-layer coating of the stimulable phosphor layer coating liquid so that the solvent is not evaporated. In that case, the binder used in each coating solution is preferably compatible with each other, and particularly preferably the same. Moreover, it is desirable that the solvents are compatible with each other because it is necessary to match the drying speeds of the laminated coating films. When the two phosphor layers formed in this way are compatible with each other, their boundary surfaces cannot be clearly distinguished even when observed with an electron microscope or the like.
[0079]
(Protective layer)
A transparent protective layer may be provided on the surface of the stimulable phosphor layer in order to physically and chemically protect the phosphor layer. It is desirable that the protective layer does not substantially exhibit light absorption so as not to substantially affect the incidence of excitation light or emission of stimulated emission light, and radiation from physical impact or chemical influence given from the outside. It is desirable to be chemically stable and have high physical strength so that the image conversion panel can be adequately protected. As the protective layer, a solution prepared by dissolving a transparent organic polymer substance such as cellulose derivative, polymethyl methacrylate, organic solvent-soluble fluororesin in an appropriate solvent is applied on the phosphor layer. Formed, or separately formed a protective layer forming sheet such as an organic polymer film such as polyethylene terephthalate or a transparent glass plate, and provided with an appropriate adhesive on the surface of the phosphor layer, or inorganic A compound formed on the phosphor layer by vapor deposition or the like is used. Further, the protective layer may contain various additives such as a sliding agent such as perfluoroolefin resin powder and silicone resin powder, and a crosslinking agent such as polyisocyanate.
[0080]
In order to increase the sharpness of the formed radiographic image, it is desirable that the protective layer has a light scattering property within a certain range. In general, the light scattering length of the protective layer is in the range of 5 to 80 μm, preferably in the range of 10 to 70 μm, at the main emission wavelength of the emitted light from the stimulable phosphor. The light-scattering protective layer can be formed by dispersing and containing light-scattering fine particles in the protective layer material. The light-scattering fine particles preferably have a light refractive index of 1.6 or more and a particle diameter in the range of 0.1 to 1.0 μm. Particularly preferably, the photorefractive index is 1.9 or more, and the particle diameter is in the range of 0.1 to 0.5 μm. Examples of suitable light scattering fine particles include fine particles of benzoguanamine resin particles, melamine formaldehyde condensation resin particles, zinc oxide, zinc sulfide, titanium oxide and lead carbonate.
[0081]
A fluororesin coating layer may be further provided on the surface of the protective layer in order to increase the stain resistance of the protective layer. The fluororesin coating layer can be formed by coating a fluororesin solution prepared by dissolving (or dispersing) a fluororesin in an organic solvent on the surface of the protective layer and drying. Although the fluororesin may be used alone, it is usually used as a mixture of a fluororesin and a resin having a high film forming property. In addition, an oligomer having a polysiloxane skeleton or an oligomer having a perfluoroalkyl group can be used in combination. The fluororesin coating layer can be filled with a fine particle filler in order to reduce interference unevenness and further improve the image quality of the radiation image. The thickness of the fluororesin coating layer is usually in the range of 0.5 μm to 20 μm. In forming the fluororesin coating layer, additive components such as a cross-linking agent, a hardener, and a yellowing inhibitor can be used. In particular, the addition of a crosslinking agent is advantageous for improving the durability of the fluororesin coating layer.
[0082]
In order to improve handling properties such as adhesion between the radiation image conversion panel and the fluorescent screen and ease of separation, the protective layer or the fluororesin coating layer preferably has a maximum friction coefficient of 0.18 or less, particularly preferably 0.8. 12 or less. The average surface roughness is preferably in the range of 0.05 to 0.5 μm, particularly preferably in the range of 0.1 to 0.3 μm. For example, minute irregularities may be provided on the surface of the protective layer or the fluororesin coating layer by performing an embossing treatment.
[0083]
In order to effectively prevent the charging of the radiation image conversion panel, particularly the peeling charging that tends to occur when the panel is pulled away from the fluorescent screen, the charged columns of the panel that is superimposed in close contact and the protective layers facing the screen are aligned. It is desirable that The charge trains of both protective layers can be made uniform by forming both protective layers using the same material, for example. In addition, in radiography, it is preferable to remove static electricity before inserting both into the cassette.
[0084]
Alternatively, a conductive fine powder (oxidized) having a particle diameter smaller than the emission wavelength of a transparent conductive polymer such as polypyrrole and / or a stimulable phosphor is formed on any of the layers constituting the radiation image conversion panel. It is preferable to contain tin fine powder. By making the particle diameter smaller than the emission wavelength of the photostimulable phosphor, it is possible to form a thin film with high electrical conductivity, and avoid the loss of light collection efficiency due to absorption of the emitted light.
[0085]
(Selective reflective layer)
Furthermore, between the radiation-absorbing phosphor layer and the storage phosphor layer, as shown in FIG. 8, light emitted from the radiation-absorbing phosphor is transmitted and emitted from the excitation light and the stimulable phosphor. It is preferable to provide a selective reflection layer that reflects light. Thereby, it is possible to increase the light collection efficiency at the time of reading radiation image information, and at the same time, as a result, the layer thickness of the stimulable phosphor layer can be made thinner, so that the sharpness of the image can be improved.
[0086]
In FIG. 8, the radiation image conversion panel 10a 'includes a support 11a, a radiation absorbing phosphor layer 12a, a selective reflection layer 15, a storage phosphor layer 13, and a protective layer 14a in this order.
[0087]
For example, the selective reflection layer may have a characteristic of transmitting light in a short wavelength region including the emission wavelength of the radiation-absorbing phosphor and reflecting light in a longer wavelength region. The selective reflection layer can be composed of a thin film and a multilayer film having such characteristics formed thereon. The multilayer film is formed by sequentially laminating two or more kinds of substances having different refractive indexes at a thickness (about 50 to 200 nm) of about ¼ of the wavelength of light.₂, MgF₂Low refractive index materials such as TiO₂, ZrO₂, Ta₂O_FiveAnd a multilayer interference filter having a total thickness of about 0.1 to 10 μm, in which several to tens of layers of high refractive index materials such as ZnS are alternately laminated.
[0088]
As an example, SiO₂And TiO₂A multilayer film in which a total of 17 layers are alternately stacked will be described. This multilayer film is composed of TiO 2 as schematically shown in FIG.₂High refractive index layer 15a and SiO₂The low refractive index layer 15b has a configuration as shown in Table 3.
[0089]
[Table 3]

[0090]
FIG. 10 is a graph showing the light transmission characteristics of the multilayer film having the configuration shown in Table 3 above. The transmittance of this multilayer film (light incident angle 0 °) is about 97% at a wavelength of 633 nm.
This multilayer film also has selectivity with respect to the incident angle of light. FIG. 11 is a graph showing the relationship between the incident angle of light and the transmittance at wavelengths of 400 nm and 633 nm of this multilayer film. The multilayer film exhibits a transmittance of 50% or more at an incident angle of 0 ° to 25 ° with respect to light having a wavelength of 633 nm, and the transmittance decreases to about 5% at an incident angle greater than 25 °. On the other hand, a light with a wavelength of 400 nm shows a transmittance of 90% or more over an incident angle of 0 ° to about 70 °.
By changing the material and configuration of the multilayer film, it is possible to form a multilayer film having desired light transmission characteristics.
[0091]
The selective reflection layer can be formed by sequentially laminating the multilayer film material on a thin film (thickness: 4 to 20 μm) made of a polymer substance by a method such as vapor deposition, sputtering, or ion plating. it can. Next, the thin film having the multilayer film is bonded to the radiation-absorbing phosphor layer by calendaring or the like, and then a stimulable phosphor layer is formed thereon by coating or the like, or separately formed phosphor This is done by laminating body layers. Alternatively, after the stimulable phosphor layer is formed on the thin film having the multilayer film by coating or the like, the obtained thin film may be bonded onto the radiation absorbing phosphor layer. It should be noted that a detachable temporary support may be bonded under the thin film when forming the multilayer film and / or forming the stimulable phosphor layer. Alternatively, as the selective reflection layer, a thin layer may be formed using a material appropriately selected from the above-described support materials.
[0092]
(Diffuse reflection layer)
When this radiation image conversion panel is on the front side, it is preferable to provide a diffuse reflection layer between the support and the radiation absorbing phosphor layer as shown in FIG. The diffuse reflection layer that can be used in the image forming material of the present invention is a layer having a function of reflecting the emitted light from the radiation absorbing phosphor. By installing this diffuse reflection layer, the amount of emitted light (primary excitation light) from the radiation-absorbing phosphor incident on the stimulable phosphor layer can be increased, and a highly sensitive radiation image conversion panel can be obtained.
In FIG. 12, the radiation image conversion panel 10a ″ includes a support 11a, a diffuse reflection layer 16, a radiation absorbing phosphor layer 12a, a storage phosphor layer 13, and a protective layer 14a in this order.
[0093]
The diffuse reflection layer is a layer containing a light reflective material such as titanium dioxide, yttrium oxide, zirconium oxide, aluminum oxide (alumina). In consideration of the fact that the diffuse reflecting layer is provided on the front panel or screen, the light reflecting material needs to absorb little radiation such as X-rays and has a refractive index in terms of the sharpness of reflection. Is desirable. Therefore, titanium dioxide is preferable as the light reflecting material, and a rutile type having a higher refractive index is particularly preferable. However, since titanium dioxide exhibits a high reflectance in a region having a wavelength longer than about 430 nm, the radiation absorbing phosphor is Gd.₂O₂Suitable for S: Tb or the like. When the emission wavelength of the radiation-absorbing phosphor is shorter than about 430 nm, it is necessary to select a substance that does not absorb in the emission wavelength region, such as aluminum oxide, yttrium oxide, and zirconium oxide.
[0094]
In terms of sensitivity and sharpness, the diffuse reflection layer desirably achieves a high light reflectance with a layer thickness as thin as possible. When the diffuse reflection layer is present alone, the relationship between the layer thickness and the diffuse reflectance is preferably in a region indicated by hatching in FIG. Here, as described in detail in Japanese Patent Application Laid-Open No. 9-21899, the diffuse reflectance is calculated using BaSO._FourThis is a reflectance obtained with respect to a standard white plate using an integrating sphere in which powder is uniformly applied to the entire surface. For this purpose, the average particle diameter of the light reflecting substance is generally in the range of 0.1 to 0.5 μm, preferably in the range of 0.1 to 0.4 μm. The volume filling factor in the diffuse reflection layer of the light reflecting material is generally in the range of 25 to 75%, preferably 40% or more. The thickness of the diffuse reflection layer is generally in the range of 15 to 100 μm.
[0095]
The diffuse reflection layer can be formed by preparing a coating solution by mixing and dispersing the above-described particulate light-reflecting substance and binder in a solvent, and then coating and drying it on a support. The binder and the solvent can be appropriately selected from those that can be used for the phosphor layer.
[0096]
Instead of providing the diffuse reflection layer on the support, the support itself may have a diffuse reflection function by dispersing the light reflecting substance as described above. Further, as will be described later, the diffuse reflection layer and / or the support may be colored.
Even when the fluorescent screen is used on the front side, it is desirable to provide a diffuse reflection layer or a support having a diffuse reflection function. Moreover, if it is used for a panel or screen used on the back side, it is easy to design a product having excellent sensitivity.
[0097]
Furthermore, depending on the purpose, auxiliary functional layers such as a light absorption layer, an adhesive layer, and a conductive layer may be provided between the phosphor layer and the support, and a number of recesses may be formed on the support surface. Good. A friction-reducing layer or a scratch-resistant layer can be provided on the surface of the support on the side where the phosphor layer is not provided in order to improve transportability and scratch resistance.
[0098]
Although the radiation image conversion panel according to the present invention is obtained using the above-described materials and manufacturing method, the configuration of the panel of the present invention may include various known variations. In the above description, the panel having the support and the protective layer has been described. However, when the phosphor layer is self-supporting, the panel according to the present invention is not necessarily provided with the support or the protective layer. Absent.
[0099]
(Coloring)
In order to increase the sharpness of the radiographic image, at least one of the layers of the radiographic image conversion panel is provided with light emitted from the radiation-absorbing phosphor and / or secondary excitation light (latent image (accumulated radiation) of the stimulable phosphor. It may be colored with a colorant that absorbs a) used in reading (image), or optionally a colorant that absorbs part of the emitted light emitted from the stimulable phosphor. Specifically, the intermediate layer such as a radiation-absorbing phosphor layer, a protective layer, and further an undercoat layer is colored to absorb emitted light from the radiation-absorbing phosphor and / or secondary excitation light of the stimulable phosphor. It is desirable to color with an agent. The coloring may be only one of the above layers, or may be partial or may be arbitrarily combined. In the point detection system using a photomultiplier tube described later, it is desirable that the colorant does not absorb light emitted from the stimulable phosphor.
[0100]
As the colorant, for example, the emitted light from the radiation-absorbing phosphor is green light, and the stimulable phosphor absorbs green light and is secondarily excited by near-infrared light to emit red light. In this case, a colorant that absorbs light in the green region and near infrared region and does not absorb light in the red region is preferable (when used in a point detection system). Two or more colorants may be used in combination.
[0101]
Examples of a red colorant suitable for the above purpose include inorganic pigments such as cadmium red, red bean, and molybdenum red. However, since these red colorants absorb almost no light in the near infrared region, they are used in combination with near infrared absorbing materials such as cyanine dyes, indoaniline dyes and squarylium dyes described in JP-A-11-109126. It is desirable to do.
[0102]
Also, for example, when the emitted light from the radiation-absorbing phosphor is near-ultraviolet light, and the stimulable phosphor absorbs near-ultraviolet light and is excited by red light to emit blue to green light. Is preferably a colorant that absorbs light in the near ultraviolet region and red region and does not absorb light in the blue to green region (when used in a point detection system).
[0103]
Examples of suitable blue to green organic colorants include Zavon First Blue 3G (Hoechst), Estrol Brill Blue N-3RL (Sumitomo Chemical Co., Ltd.), Sumiacryl Blue F-GSL (Sumitomo Chemical). D & C Blue No1 (made by National Aniline), Spirit Blue (made by Hodogaya Chemical Co., Ltd.), Oil Blue No603 (made by Orient Co., Ltd.), Kitton Blue A (made by Ciba Geigy) , Eisen Cachiron Blue GLH (manufactured by Hodogaya Chemical Co., Ltd.), Lake Blue A, F, H (manufactured by Kyowa Sangyo Co., Ltd.), Rhodaline Blue 6GX (manufactured by Kyowa Sangyo Co., Ltd.), Brimocyanine Blue 6GX Inabata Sangyo Co., Ltd.), Brill Acid Green 6BH (Hodogaya Chemical Co., Ltd.), Cyanine Blue BNRS (Toyo Ink Co., Ltd.), Lionol Blue SL (Toyo Ink Co., Ltd.) Can be mentioned. Examples of inorganic colorants include ultramarine, cobalt blue, cerulean blue, chromium oxide, and TiO.₂-ZnO-CoO-NiO pigments.
[0104]
Alternatively, as will be described later, when the radiation image information is read by line detection using a line sensor or the like instead of point detection using a photomultiplier tube or the like, a radiation absorbing phosphor layer, an undercoat layer, etc. The intermediate layer is preferably colored with a colorant that absorbs light emitted from the radiation-absorbing phosphor, secondary excitation light of the stimulable phosphor, and / or light emitted from the stimulable phosphor. This is because the portion of the light emitted from the photostimulable phosphor that is wider than the excitation portion causes image blur.
[0105]
As the colorant, when the emission from the radiation absorbing phosphor is green emission, the secondary excitation light of the stimulable phosphor is near infrared light, and the emission from the stimulable phosphor is red emission, Colorants that absorb light in the green, red and / or near infrared regions are preferred. That is, a red, blue to green or gray colorant having a near infrared absorption is preferred. As the suitable red colorant, the above colorants can be used. As an example of a blue to green colorant having near infrared absorption, titanyl phthalocyanine TiO—Pc (manufactured by Sanyo Dye Co., Ltd.) can be given. You may combine said blue thru | or green colorant and a near-infrared absorption material. Examples of the gray colorant include carbon black and Cu—Fe—Mn oxide.
[0106]
In addition, when the light emission from the radiation absorbing phosphor is near ultraviolet light emission, the secondary excitation light of the stimulable phosphor is red light, and the light emission from the stimulable phosphor is blue to green light emission, the near ultraviolet light is emitted. Colorants that absorb light in the blue to green and / or red region are preferred. That is, yellow, red, blue to green or gray colorants are preferred. The red, blue to green and gray colorants described above can be used. Examples of yellow colorants include yellow iron oxide, titanium yellow, and cadmium yellow.
[0107]
The reduction in sensitivity of the radiation image conversion panel due to coloring can be adjusted by increasing the thickness of the radiation-absorbing phosphor layer or by increasing the energy of excitation light during reading. They can be optimized in relation to the degree.
[0108]
(Fluorescent screen)
The back side fluorescent screen 10b and the radiation image conversion panels having other configurations can also be manufactured by the same method using the same material as described above. In addition, when providing a partition in a fluorescent substance layer, it is preferable to form a partition only in the radiation absorption fluorescent substance layer of a back side fluorescent screen, and to make the radiation image conversion panel of a front side flexible, thereby image A forming system (for example, a radiographic image information reading device) can be made more compact, and a high-quality radiographic image can be obtained.
[0109]
In order to increase the sharpness of the radiographic image, it is desirable that the protective layer of the fluorescent screen is also light scattering within a certain range. In general, the light scattering length of the protective layer is in the range of 5 to 80 μm, preferably in the range of 10 to 70 μm, at the main emission wavelength of the emitted light from the radiation-absorbing phosphor. The light-scattering protective layer of this screen can also be formed by the same method using the same material as the light-scattering protective layer of the panel.
[0110]
Similarly, for the purpose of increasing the sharpness of the radiation image, the radiation absorbing phosphor layer and / or the protective layer of the phosphor screen may be colored with the above colorant that absorbs the light emitted from the radiation absorbing phosphor.
[0111]
[Radiation image forming method]
Next, regarding the radiation image forming method of the present invention using the above-described radiation image forming material, the radiation image forming material having the structure shown in FIG. 1 (containing a stimulable phosphor as a stimulable phosphor) is taken as an example. This will be described with reference to FIG. 6 of the accompanying drawings. FIG. 6 is a schematic cross-sectional view showing an example of the configuration of a single-sided condensing type radiographic image information reading apparatus using a point detection system.
[0112]
First, radiation image information (spatial energy distribution information of radiation) is recorded on a radiation image forming material composed of an assembly of a radiation image conversion panel and a fluorescent screen. When recording (photographing) image information, the front-side radiation image conversion panel 10a and the back-side fluorescent screen 10b of the radiation image forming material 10 shown in FIG. 1 are in close contact so that the protective layers 14a and 14b are in contact with each other. Overlapping with. At this time, it is desirable to fix the assembly in a close contact state using a cassette, and the back-side screen 10b is normally preferably used while being fixed in the cassette. Further, the same configuration can be adopted in the radiographic imaging table.
[0113]
A subject is placed between a radiation source such as an X-ray generator and a radiation image forming material using a radiation imaging apparatus (not shown), and the subject is irradiated with radiation generated from the radiation source. As radiation, X-rays, γ-rays, α-rays, β-rays, electron beams, ionizing radiation such as ultraviolet rays, and neutron rays can be used. When using a neutron beam, Gd or^TenB,⁶It is preferable to use a phosphor containing a matrix containing Li or the like, or a compound containing these elements.
[0114]
The radiation passes through the subject according to the type of radiation and the subject, or is diffracted or scattered by the subject, and enters the front side panel 10a as radiation having spatial energy distribution information regarding the subject. Part of the incident radiation is absorbed by the radiation-absorbing phosphor of the radiation-absorbing phosphor layer 12a and converted to light having a wavelength in the ultraviolet to visible region (instantaneous light emission). This emitted light enters the adjacent stimulable phosphor layer 13 and is absorbed by the stimulable phosphor in the phosphor layer to accumulate energy, and the stimulable phosphor layer 13 stores the spatial space of the subject. Energy distribution information is recorded as a latent image.
[0115]
The radiation transmitted through the front panel 10a enters the back screen 10b, is absorbed by the radiation absorbing phosphor of the radiation absorbing phosphor layer 12b, and is converted into emitted light in the ultraviolet to visible region. Most of the emitted light is incident again on the front side panel 10a, absorbed by the stimulable phosphor of the stimulable phosphor layer 13, and stored as energy, which also contributes to latent image formation. That is, the stimulable phosphor layer 13 is exposed from the both sides by the emitted light of the radiation absorbing phosphor.
[0116]
The irradiation of radiation may be performed from the back side screen 10b side by reversing the positions of the front side panel 10a and the back side screen 10b. In addition, when the subject itself emits radiation such as β rays as in autoradiography, the subject itself becomes a radiation source, so that it is not necessary to provide a separate radiation source.
[0117]
Next, the spatial energy distribution information of the subject recorded on the front side panel 10a is read using the radiographic image information reading apparatus of FIG. First, the front side panel 10a and the back side screen 10b that are in close contact with each other are pulled apart, and only the front side panel 10a is loaded into the reading device.
[0118]
In FIG. 6, the radiation image conversion panel 60 is transferred in the direction of the arrow by transfer means 61 and 62 comprising two sets of nip rollers. On the other hand, the excitation light 63 such as a laser beam is irradiated from the protective layer side surface of the panel 60 (storable phosphor layer side surface). Radiation corresponding to the accumulated energy level (that is, carrying energy distribution information of radiation recorded and accumulated as a latent image) from a location in the stimulable phosphor layer of panel 60 that has been irradiated with excitation light 63 Stimulated light 64 corresponding to the image is emitted. The photostimulated light 64 is reflected directly or by a mirror 69 and is collected by a light collecting guide 65 provided above, and a photoelectric conversion device (photomultiplier) 66 provided at the base of the light collecting guide 65. Is converted into an electric signal by the amplifier 67, amplified by the amplifier 67 and sent to the signal processing device 68.
[0119]
The signal processing device 68 performs appropriate arithmetic processing such as addition and subtraction determined in advance on the basis of the type of the intended radiographic image and the characteristics of the radiographic image conversion panel, on the electrical signal sent from the amplifier 67. The processed signal is sent out as an image signal.
[0120]
The sent image signal is reproduced as a visible image by an image reproducing device (not shown), thereby reconstructing an image corresponding to the spatial energy distribution of the radiation relating to the subject. The playback device may be a display means such as a CRT, or may be a recording device that performs optical scanning recording on a photosensitive film or thermal recording using a heat-sensitive recording film. Alternatively, it may be replaced with a device for storing in an image file such as a magnetic disk.
[0121]
On the other hand, the radiation image conversion panel 60 is sequentially moved in the direction of the arrow by the nip rollers 61 and 62, and the area subjected to the reading process is then an erasing light source (not shown) such as a sodium lamp, a fluorescent lamp, and an infrared lamp. It is used for the erasing process using As a result, the accumulated energy remaining on the panel after the reading process is released and removed, so that the latent image due to the residual energy is not adversely affected in the next radiographic image recording (imaging) process.
[0122]
When the radiation image conversion panel is configured as shown in FIGS. 2, 3 and 4 (that is, does not have a radiation absorbing phosphor layer), by making the support and the protective layer transparent, The photostimulated luminescence can be read from both sides of the panel. For example, in FIG. 6, the condensing guide 65 and the photoelectric conversion device 66 are also arranged below the radiation image conversion panel 60, so that the reading of the stimulated emission light 64 can be performed from the side opposite to the irradiation of the excitation light 63. I.e. from both sides.
[0123]
Alternatively, the radiation image conversion panel in which the spatial energy distribution information of the radiation is stored and recorded as a latent image is transported in the plane direction, or the excitation light irradiation device is moved in the plane direction of the panel to excite the panel. Using a LD array, LED array, fluorescent light guide sheet, etc., light is emitted linearly in a direction substantially perpendicular to the transfer direction, and the stimulated emission light emitted from the latent image of the excitation light irradiation portion of the panel is emitted. Utilizing a radiation image information reading method that sequentially and one-dimensionally performs photoelectric detection using a line sensor or the like in which a large number of solid state photoelectric conversion elements are linearly arranged, and obtains radiation energy distribution information as an electrical image signal You can also.
[0124]
【Example】
[Example 1] SrO.1.75Al₂O_Three: 0.01Eu, 0.001Sm phosphor
Strontium carbonate (SrCO_Three2.25 g, aluminum oxide (Al₂O_Three2.72 g, europium oxide (Eu)₂O_Three) 0.027g, samarium oxide (Sm₂O_Three) 0.003 g and boric acid (H₂BO_Three) 0.05 g was weighed and mixed in a mortar. This mixture was placed in an alumina crucible (small) and capped. Put 10 g of powdered carbon in another alumina crucible (large), place the crucible (small) containing the mixture on it, and turn the alumina crucible (medium) upside down and put it on the crucible (small). (Large) was covered. Next, this crucible (large) was put into an electric furnace and baked at a temperature of 1300 ° C. in a weakly reducing atmosphere for 4 hours. After firing, the furnace temperature was cooled to 800 ° C. over 1 hour and then rapidly cooled to room temperature. The fired product was taken out to obtain a europium samarium-activated strontium aluminum photostimulable phosphor represented by the composition formula.
[0125]
[Example 2] SrO.1.75Al₂O_Three: 0.01Eu, 0.001Tm phosphor
In Example 1, Sm₂O_ThreeInstead of thulium oxide (Tm₂O_Three) Except for using 0.003 g, a europium / thulium activated strontium oxide stimulable phosphor represented by the title composition was obtained in the same manner as in Example 1.
[0126]
[Example 3] SrO.1.75Al₂O_Three: 0.01Eu, 0.001Sm phosphor
In Example 1, SrCO_Three2.66 g, Al₂O_Three2.30 g, and Eu₂O_ThreeThe europium samarium activated strontium oxide photostimulable phosphor represented by the title compositional formula was obtained in the same manner as in Example 1 except that was changed to 0.032 g. At this time, the crystal system is SrAl₂O_FourIt was confirmed by an X-ray diffraction pattern.
[0127]
[Comparative Example 1] SrO.1.75Al₂O_Three: 0.01 Eu phosphor
In Example 1, Sm₂O_ThreeA europium-activated strontium oxide aluminum stimulable phosphor represented by the title composition was obtained in the same manner as in Example 1 except that was not used.
[0128]
[Evaluation of photostimulable phosphor]
The photostimulable luminescent properties of each of the photostimulable phosphors were evaluated.
The photostimulable phosphor was primarily excited by irradiation with light having a wavelength of 415 nm for 120 seconds using a fluorescence spectrophotometer (F4500, manufactured by Hitachi, Ltd.). Two minutes later, the phosphor was irradiated with light having a wavelength of 650 nm for 100 seconds to undergo secondary excitation, and stimulated emission at a wavelength of 500 nm was measured. The stimulated emission intensity (relative value) was determined by integrating the stimulated emission light over 100 seconds after excitation.
The obtained results are summarized in Table 4.
[0129]
[Table 4]

[0130]
As is clear from Table 4, all of the strontium aluminum photostimulable phosphors co-activated with the rare earth of the present invention (Examples 1 to 3) were europium activated strontium oxide photostimulable for comparison. Compared to the phosphor (Comparative Example 1), the photostimulated emission intensity was extremely high.
[0131]
【The invention's effect】
The rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor of the present invention absorbs light in the ultraviolet to visible region, and then is excited in the visible region when excited by light in the visible to infrared region. This is a stimulable phosphor that exhibits a significantly higher stimulated emission intensity than in the prior art. This phosphor can be used not only for the radiation image forming method described above, but also for an optical memory capable of recording and reading information, and an optical element with high density and high speed.
[0132]
Further, according to the method of the present invention using this photostimulable phosphor, the radiation absorbing function and the energy storage function of the phosphor involved in the radiation image formation are separated, and each function is assigned to two kinds of phosphors, A phosphor with a high radiation absorption rate is used as a phosphor that has a radiation absorption function, and a stimulable phosphor with a high stimulating emission intensity is used as a phosphor with an energy storage function. By exposing the body layer from both sides, image formation with high detection quantum efficiency can be realized. Further, by using this photostimulable phosphor in a radiation image conversion panel, a radiation image conversion panel with improved chemical stability can be provided. Furthermore, by using a phosphor having excellent responsiveness as a phosphor having an energy storage function, it is possible to achieve image formation with higher detection quantum efficiency. As a result, it is possible to reduce the exposure dose to the subject (subject) or to analyze a smaller amount of radiation when the subject itself emits radiation such as autoradiography. . Further, according to the radiation image forming method of the present invention, two-dimensional information of radiation can be obtained also in X-ray analysis, autoradiography, and the like.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a typical example of the configuration of a radiation image forming material of the present invention.
FIG. 2 is a schematic sectional view showing another example of the configuration of the radiation image forming material of the present invention.
FIG. 3 is a schematic sectional view showing another example of the configuration of the radiation image forming material of the present invention.
FIG. 4 is a schematic sectional view showing another example of the configuration of the radiation image forming material of the present invention.
FIG. 5 is a schematic sectional view showing another example of the configuration of the radiation image forming material of the present invention.
FIG. 6 is a schematic side view showing an example of the configuration of a reading apparatus used in the radiation image forming method of the present invention.
FIG. 7 is a schematic sectional view showing another example of the configuration of the radiation image forming material of the present invention.
FIG. 8 is a schematic sectional view showing another example of the configuration of the radiation image conversion panel according to the present invention.
FIG. 9 is a schematic cross-sectional view showing an example of the configuration of a multilayer film according to the present invention.
FIG. 10 is a graph showing light transmission characteristics of a multilayer film.
FIG. 11 is a graph showing the relationship between the incident angle of light and the transmittance at a specific wavelength of a multilayer film.
FIG. 12 is a schematic sectional view showing another example of the configuration of the radiation image conversion panel according to the present invention.
FIG. 13 is a graph showing a preferred region in the relationship between the layer thickness of the diffuse reflection layer and the diffuse reflectance according to the present invention.
FIG. 14 is a graph showing the relationship between 2b / a and the stimulated emission intensity for the photostimulable phosphor of the present invention.
FIG. 15 is a graph showing the relationship between x and stimulated emission intensity for the photostimulable phosphor of the present invention.
FIG. 16 is a graph showing the relationship between y and the stimulated emission intensity for the photostimulable phosphor of the present invention.
FIG. 17 is a graph showing the relationship between y and the stimulated emission intensity for the photostimulable phosphor of the present invention.
[Explanation of symbols]
10, 10 ', 20, 30, 40, 50 Radiation imaging material
10a, 10a ', 10a ", 20a, 30a, 40a, 60
Radiation image conversion panel
10b, 10b ', 20b, 20c, 30b, 30c, 40b
Fluorescent screen
12a, 12b, 12b ', 22b, 22c, 32b, 32c, 42, 52
Radiation absorbing phosphor layer
13, 23, 33, 33 ', 43, 53 Storage phosphor layer
15 Selective reflective layer (multilayer film)
16 Diffuse reflection layer
63 Excitation light
64 photostimulated light
65 Condensing guide
66 Photoelectric conversion device

Claims (22)

Chemical composition formula (I):
M ^II O · aM ^III ₂ O ₃ : xEu, yLn (I)
[Wherein M ^II represents at least one alkaline earth metal selected from the group consisting of Mg, Ca, Sr and Ba; M ^III represents at least one trivalent metal selected from the group consisting of B, Al and Ga; Ln represents Sm and / or Tm ; and a, x, and y are 0.5 ≦ a ≦ 5.5, 1 × 10 ⁻⁶ ≦ x ≦ 0.2, and 1 × 10 ⁻⁶ ≦ y, respectively. Represents a numerical value within the range of ≦ 0.2]
Rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor. Chemical composition formula (I):
M ^II O · aM ^III ₂ O ₃ : xEu, yLn (I)
[Wherein M ^II represents at least one alkaline earth metal selected from the group consisting of Mg, Ca, Sr and Ba; M ^III represents at least one trivalent metal selected from the group consisting of B, Al and Ga; Ln represents at least one rare earth element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; and a, x and y represents a numerical value within the range of 1.1 ≦ a ≦ 3.0 , 1 × 10 ⁻⁶ ≦ x ≦ 0.2, and 1 × 10 ⁻⁶ ≦ y ≦ 0.2, respectively.
Rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor. M ^II is a rare earth activated alkaline earth trivalent metal oxide based stimulable phosphor according to claim 1 or 2 containing Sr 50% or more chemical formula (I). Rare earth activated alkaline earth trivalent metal oxide based stimulable phosphor according to any one of claims of claims 1 to 3 M ^II is Sr chemical composition formula (I). The rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor according to any one of claims 1 to 4, wherein M ^{III of the} chemical composition formula (I) contains 50% or more of Al. Rare earth activated alkaline earth trivalent metal oxide based stimulable phosphor according to claim 5 M ^III is Al chemical composition formula (I). M ^III is claim 1 or rare earth activated alkaline earth trivalent metal oxide based stimulable phosphor according to any one of claims 4 including B in the chemical composition formula (I).   3. The rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor according to claim 2, wherein Ln in the chemical composition formula (I) is Sm and / or Tm.   2. The rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor according to claim 1, wherein a in the chemical composition formula (I) is a numerical value within a range of 1.1 ≦ a ≦ 3.0. The x in the chemical composition formula (I) is a numerical value in the range of 1 × 10 ⁻³ ≦ x ≦ 5 × 10 ^−2. Rare earth activated alkaline earth 3 according to any one of claims 1 to 9 Valuable metal oxide photostimulable phosphor. The rare earth activated alkaline earth trivalent metal according to any one of claims 1 to 10, wherein y in the chemical composition formula (I) is a numerical value within a range of 1 x 10 ^-4 ≤ y ≤ 0.1. Oxide-based stimulable phosphor.   A radiation-absorbing phosphor layer containing a phosphor that absorbs radiation for image formation and emits emitted light in the ultraviolet to visible region, and absorbs the emitted light and accumulates its energy, visible to infrared region 3. A stimulable phosphor layer containing the rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor according to claim 1 or 2, which emits the energy as emitted light when excited by the light of A phosphor screen having a radiation-absorbing phosphor layer containing a radiation image conversion panel and a phosphor that absorbs radiation for image formation and emits light in the ultraviolet to visible region is provided on the storage phosphor layer side of the panel. Place the screen in close contact with the surface and irradiate the panel or screen side with radiation that has passed through the subject, diffracted or scattered by the subject, or emitted from the subject. After the spatial energy distribution information of the radiation is recorded on the panel as a latent image, the panel is pulled away from the screen, and the stimulable phosphor layer side surface of the panel is irradiated with excitation light and emitted from the latent image of the panel. A radiation image forming method comprising: photoelectrically reading emitted light that is converted into an image signal, and forming an image corresponding to the spatial energy distribution of the radiation from the image signal.   A radiation-absorbing phosphor layer containing a phosphor that absorbs radiation and emits emitted light in the ultraviolet to visible region; and absorbs the emitted light and accumulates its energy; The stimulable phosphor layer containing the rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor according to claim 1 or 2, wherein the accumulated energy is released as emitted light when excited. A radiation image forming material comprising: a radiation image conversion panel; and a phosphor screen having a radiation absorbing phosphor layer containing a phosphor that absorbs radiation and emits emitted light in the ultraviolet to visible region.   A radiation-absorbing phosphor layer containing a phosphor that absorbs image-forming radiation and emits emitted light in the ultraviolet to visible region; and absorbs the emitted light and accumulates its energy; 3. A stimulable phosphor containing the rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor according to claim 1 or 2, wherein the accumulated energy is released as emitted light when excited by excitation light. A radiation image conversion panel having a layer, and a phosphor screen having a radiation absorbing phosphor layer containing a phosphor that absorbs image forming radiation and emits emitted light in the ultraviolet to visible region, and the radiation image conversion A radiation image forming material in which the surface of the panel on the side of the stimulable phosphor layer and the phosphor screen are arranged to face each other.   Energy is absorbed between two fluorescent screens each having a radiation-absorbing phosphor layer containing a phosphor that absorbs image-forming radiation and emits light in the ultraviolet to visible region. 3. The rare earth activated alkaline earth trivalent metal oxide photostimulability according to claim 1, wherein, when excited by light in the visible to infrared region, the stored energy is emitted as emitted light. Radiation image conversion panels each having a stimulable phosphor layer containing a phosphor are arranged in close contact with each other, transmitted through the subject from one of the screen sides, diffracted or scattered by the subject, or Irradiates the radiation emitted from the subject, records the spatial energy distribution information of the radiation as a latent image on the panel, pulls the panel away from both screens, and then displays the panel surface. The light emitted from the latent image is photoelectrically read from one or both sides of the panel and converted into an image signal, and the image signal corresponds to the spatial energy distribution of the radiation. A radiographic image forming method comprising forming an image.   Two fluorescent screens each having a radiation-absorbing phosphor layer containing a phosphor that absorbs image-forming radiation and emits light in the ultraviolet to visible region, and absorbs the emitted light to accumulate its energy, 3. The rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor according to claim 1, which emits the stored energy as emitted light when excited by light in the visible to infrared region. A radiation image forming material comprising a radiation image conversion panel having a stimulable phosphor layer.   Energy is absorbed between two fluorescent screens each having a radiation-absorbing phosphor layer containing a phosphor that absorbs image-forming radiation and emits light in the ultraviolet to visible region. 3. The rare earth activated alkaline earth trivalent metal oxide photostimulability according to claim 1, wherein, when excited by light in the visible to infrared region, the stored energy is emitted as emitted light. A radiation image forming material in which a radiation image conversion panel having a stimulable phosphor layer containing a phosphor is disposed.   A fluorescent screen having a radiation-absorbing phosphor layer containing a phosphor that absorbs image-forming radiation and emits emitted light in the ultraviolet to visible region, absorbs the emitted light, accumulates its energy, and is visible or 3. A storage property comprising the rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor according to claim 1 or 2, wherein the stored energy is released as emitted light when excited by light in the infrared region. A radiation image conversion panel having a phosphor layer is disposed in close contact with the surface, and the radiation transmitted through the subject, diffracted or scattered by the subject, or emitted from the subject from the screen or panel side. After irradiation, the spatial energy distribution information of the radiation is recorded on the panel as a latent image, and then the panel is separated from the screen, and the surface of the panel is irradiated with excitation light. Radiographic image forming method which comprises the luminescent light issued into image signals read photoelectrically from one side or both sides of the panel, and forms an image corresponding to the spatial energy distribution of the radiation from said image signal.   A fluorescent screen having a radiation-absorbing phosphor layer containing a phosphor that absorbs image-forming radiation and emits emitted light in the ultraviolet to visible region, and absorbs the emitted light and accumulates its energy, visible to visible The storage containing the rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor according to claim 1 or 2, wherein the stored energy is emitted as emitted light when excited by light in the infrared region. A radiation image forming material comprising a radiation image conversion panel having a fluorescent phosphor layer.   A fluorescent screen having a radiation-absorbing phosphor layer containing a phosphor that absorbs image-forming radiation and emits emitted light in the ultraviolet to visible region; and absorbs the emitted light and accumulates its energy; The storage containing the rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor according to claim 1 or 2, wherein the stored energy is emitted as emitted light when excited by light in the infrared region. A radiation image forming material obtained by laminating a radiation image conversion panel having a fluorescent phosphor layer in a close contact state.   A radiation-absorbing phosphor layer containing a phosphor that absorbs image-forming radiation and emits emitted light in the ultraviolet to visible region; and absorbs the emitted light and accumulates its energy; 3. A stimulable phosphor layer containing the rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor according to claim 1 or 2, wherein the accumulated energy is released as emitted light when excited by light. And a radiation image conversion panel having a thickness of the stimulable phosphor layer smaller than that of the radiation-absorbing phosphor layer is transmitted through the subject, diffracted or scattered by the subject, or After irradiating the radiation emitted from the specimen and recording the spatial energy distribution information of the radiation on the panel as a latent image, the surface of the panel is irradiated with excitation light and the latent image is irradiated with the excitation light. Light emitted from the panel Read into image signals, and a radiation image-forming method which comprises forming an image corresponding to the spatial energy distribution of the radiation from said image signals in manner.   A radiation-absorbing phosphor layer containing a phosphor that absorbs image-forming radiation and emits emitted light in the ultraviolet to visible region; and absorbs the emitted light and accumulates its energy; The stimulable phosphor layer containing the rare earth activated alkaline earth trivalent metal oxide photostimulable phosphor according to claim 1 or 2, which emits the accumulated energy as emitted light when excited by light. A radiation image conversion panel in which the layer thickness of the stimulable phosphor layer is smaller than the layer thickness of the radiation absorbing phosphor layer.

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