JP2004108999A

JP2004108999A - Irradiation material for radiation measuring, and instrument and method for measuring radiation

Info

Publication number: JP2004108999A
Application number: JP2002273372A
Authority: JP
Inventors: Akihiro Oshima; 大島　明博; Masaichi Washio; 鷲尾　方一
Original assignee: Waseda University
Current assignee: Waseda University
Priority date: 2002-09-19
Filing date: 2002-09-19
Publication date: 2004-04-08
Anticipated expiration: 2022-09-19
Also published as: JP4162079B2

Abstract

<P>PROBLEM TO BE SOLVED: To easily measure the absorbed dose of radiation and a sample temperature or their distributions over a wide range by utilizing the characteristics of an ethylene-tetrafluoroethylene copolymer. <P>SOLUTION: A radiation measuring instrument 10 measures the absorbed dose of radiation and sample temperature by using irradiation films F composed of an ethylene-tetrafluoroethylene copolymer (ETFE). Namely, the instrument 10 measures the absorbance variation of an irradiation film F1 by projecting ultraviolet rays having a prescribed wavelength upon the irradiation film F1 irradiated with the radiation to be measured and another irradiation film F2 unirradiated with the radiation and finds the absorbed dose of radiation and sample temperature based on the absorbance variation and the wavelength of the ultraviolet rays by utilizing the characteristics of the FTFE. When this instrument 10 is used, the absorbed dose can be measured over a wider range than the conventional example and, in addition, it is not required to strictly manage the environmental conditions for measuring the radiation and, in addition, can simultaneously find the sample temperature. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、放射線測定用の照射材及び放射線測定装置並びに放射線測定方法に係り、更に詳しくは、放射線の吸収線量及び試料温度やそれらの分布を簡単且つ広範囲で測定することのできる放射線測定用の照射材及び放射線測定装置並びに放射線測定方法に関する。
【０００２】
【従来の技術】
粒子加速器やラジオアイソトープ等の放射線源から放射線を照射した際に、その吸収線量を測定する方法として、三酢酸セルロース（ＣＴＡ）フィルムを用いた方法やアラニンを用いた方法等が知られている（非特許文献１参照）。ＣＴＡフィルムを用いた方法では、当該フィルムに測定対象の放射線を照射し、当該照射によって生じるフィルムの化学的変化に関連した量を測定することで吸収線量が求められる。すなわち、このＣＴＡフィルムを用いた方法は、波長２８０ｎｍ付近における放射線照射前後の吸光度変化が、吸収線量に対して比例することを利用したものであり、波長２８０ｎｍ付近の吸光度変化を測定し、これによって、吸収線量が求められる。
一方、アラニンを用いた方法では、アラニンを含むペレット体に放射線が照射されると、当該放射線の照射によってアラニンが分解してラジカルが生じることを利用したものであり、当該ラジカルを電子スピン共鳴装置（ＥＳＲ）で測定することで、吸収線量が求められる。
【０００３】
また、放射線照射時における試料温度の測定の際には、当該試料に取り付けられる熱電対が用いられる。
【０００４】
【非特許文献１】
森内和之、他６名著「工業照射用の電子線量計測」、第１版、株式会社地人書館、平成２年３月２５日、ｐ．２７−３０、ｐ１７２−１８０
【０００５】
【発明が解決しようとする課題】
しかしながら、ＣＴＡフィルムを用いた前述の方法にあっては、測定環境を厳格に保持しながら行う必要があり、吸収線量の測定に手間がかかるという不都合がある。すなわち、この方法では、放射線照射後のフィルムに当てる光の波長が２８０ｎｍ付近に限定されるばかりか、放射線を照射する雰囲気の温度及び湿度を所定の値に保たなければならず、しかも、放射線を照射した後のフィルムの特性が経過時間に応じて変わるため、当該経過時間を一定にしなければならない。また、放射線をフィルムに照射しているときに、当該フィルムの試料温度がビーム加熱によって上昇する場合もあり、この場合には、吸収線量の値を正確に求めることができないという不都合もある。
一方、アラニンを用いた方法にあっては、ＣＴＡフィルムを用いた場合と同様に温度管理を厳格にする必要がある他、測定に際しては、高価な電子スピン共鳴装置（ＥＳＲ）が必要になり、当該装置をあらゆる測定施設に導入することができず、放射線を照射した後のペレット体を所定の施設に搬送する手間がかかるという不都合がある。
また、これらＣＴＡフィルムやアラニンを用いた方法では、例えば、数秒間に１００ｋＧｙ以上の線量等、短時間に多量の線量が試料に与えられる場合には、実際の吸収線量に対する誤差が大きくなって用いることができない他、吸収線量を測定できる範囲がせいぜい２００ｋＧｙ程度とされ、それ以上の吸収線量が短時間で付与される場合には、使用できないという不都合もある。
【０００６】
また、熱電対を用いて放射線照射時の試料温度を測定する方法にあっては、温度測定装置等を放射線環境下で使用することから、温度測定装置の遮蔽などの放射線防護措置を行う必要があり、温度測定作業に手間がかかるという不都合がある。また、高線量率での放射線照射の場合、熱電対そのものが放射線によって直接加熱されてしまい、放射線の照射による実際の試料温度を正確に測定することができないという不都合もある。
【０００７】
ところで、本発明者らは、このような不都合に鑑み、放射線照射時の吸収線量及び試料温度を測定する際の照射材に用いられる各種高分子材料について、種々の実験及び研究を行った。その結果、フッ素系高分子であるエチレン−テトラフルオロエチレン共重合体（ＥＴＦＥ）に放射線を照射すると、当該ＥＴＦＥに着色現象が生じ、特に、放射線の吸収線量及び試料温度が増大すると、次第に色彩が濃くなることを知見した。すなわち、ＥＴＦＥをフィルム状として放射線を照射した後、当該フィルムに所定の光を透過させたときに、従来よりも広範囲となる光の波長で、フィルムの吸光度変化と、前記吸収線量及び試料温度との間に一定の関係が存在することを見出した。
【０００８】
すなわち、光の波長が約２００ｎｍ〜約９００ｎｍの範囲、吸収線量が約１ｋＧｙ〜約５０ＭＧｙの範囲、及び試料温度が約４Ｋ〜約５５３Ｋの範囲内では、図１及び図２に示されるように、吸光度変化ＯＤと吸収線量Ｄとが、正比例関係にあるとともに、図３及び図４に示されるように、吸光度変化ＯＤと試料温度Ｔとが、当該試料温度Ｔの一定範囲毎でそれぞれ正比例関係にあることが判明した。このことは、吸収線量Ｄや試料温度Ｔに比例して、分子の共役二重結合の量が増大することに起因すると考えられる。
【０００９】
具体的に、図１及び図２に示されるように、吸光度変化ＯＤは、吸収線量Ｄに対して、所定の比例定数（以下、「線量係数」と称する）を乗じた関係となる。この線量係数は、波長λ及び試料温度Ｔ毎に異なり、これら波長λ及び試料温度Ｔに対して一義的に定まる。また、前記線量係数は、波長λが増大するに従い減少し、試料温度Ｔが増大するに従い増大する。
【００１０】
また、図３及び図４に示されるように、吸光度変化ＯＤは、試料温度Ｔに対して、所定の比例定数（以下、「温度係数」と称する）を乗じた関係となる。この温度係数は、波長λ及び吸収線量Ｄ毎に異なり、更には、一波長λ、一吸収線量Ｄにつき、三つの値が存在する。この三つの値は、各波長λ及び吸収線量Ｄで共通した二箇所の転移温度ｔ１，ｔ２を境に変化するようになっている。この転移温度ｔ１，ｔ２は、高分子鎖の分子運動における運動モードが変化する温度であり、２１０Ｋ付近、４００Ｋ付近にそれぞれ存在する。従って、線量係数は、波長λ、吸収線量Ｄ及び試料温度Ｔ毎に異なり、これら波長λ、吸収線量Ｄ及び試料温度Ｔに対して一義的に定まる。また、前記温度係数は、ｔ１未満の温度領域、ｔ１以上ｔ２未満の温度領域、ｔ３以上の温度領域の順に増大し、しかも、波長λが増大するに従い減少し、吸収線量Ｄが増大するに従い増大する。
【００１１】
【発明の目的】
本発明は、このような発明者の知見に基づいて案出されたものであり、その目的は、放射線の吸収線量及び試料温度やそれらの分布を簡単且つ広範囲で測定することができる放射線測定用の照射材及び放射線測定装置並びに放射線測定方法を提供することにある。
【００１２】
【課題を解決するための手段】
前記目的を達成するため、本発明に係る照射材は、測定対象となる放射線が照射されたときの吸光度変化を測定することで、前記放射線の吸収線量及び試料温度が測定可能となる放射線測定用の照射材であって、
前記放射線が照射される部分をエチレン−テトラフルオロエチレン共重合体により形成する、という構成を採っている。このような構成によれば、放射線の照射部分がエチレン−テトラフルオロエチレン共重合体（ＥＴＦＥ）で形成されているため、前述したＥＴＦＥの性質上、測定対象の放射線が照射された照射材に対し、少なくとも二種類の波長における各吸光度変化を測定することで、前記放射線の吸収線量及び試料温度を同時に求めることができる。また、吸収線量及び試料温度の測定に際しては、様々な光の波長や温度等で行うことが可能であり、測定環境を厳格に管理しなくてもよく、放射線の吸収線量及び試料温度を簡単に求めることができる。更に、約１ｋＧｙ〜約５０ＭＧｙの広範囲で吸収線量を測定することができ、従来の線量計で測定可能となる吸収線量の範囲に加え、当該範囲よりも高線量域での測定も可能となり、吸収線量の測定に対する高い汎用性を付与することができる。また、温度測定装置を用いなくても試料温度の測定が可能となるため、従来において問題とされた温度測定装置の遮蔽等が不要となり、試料温度の測定を簡単に行うことができる。しかも、従来の方法では試料温度を正確に測定できない高線量率での放射線照射の場合についても、試料温度を正確に測定することができる。
【００１３】
また、本発明に係る放射線測定装置は、前記照射材を用いて放射線の吸収線量及び試料温度を求める放射線測定装置において、
所定の波長の光を前記照射材に透過させることにより当該波長の光に対する吸光度変化を求める吸光度変化算出手段と、前記照射材の特性に基づく所定のデータを記憶する記憶手段と、前記吸光度変化から前記記憶手段内のデータに基づき前記吸収線量及び試料温度を決定する線量・温度決定手段とを備え、
前記線量・温度決定手段は、測定対象の放射線が照射された照射材に対し、少なくとも二種類の波長の光を透過させたときの各吸光度変化から、吸収線量及び試料温度を決定する、という構成を採っている。このような構成によれば、前述したように、放射線の吸収線量及び試料温度を簡単且つ広範囲で測定することができる。
【００１４】
更に、本発明に係る放射線測定方法は、前記照射材を用いた放射線測定方法であって、
前記照射材に測定対象の放射線を照射した後、当該照射材に少なくとも二種類の波長の光を透過させることで、各波長に対する照射材の吸光度変化を測定し、当該各波長及び各吸光度変化から、前記照射材の特性に基づくデータを用いて前記放射線の吸収線量及び試料温度を決定する、という手法を採っており、このような手法によっても、前述した目的を達成することができる。
【００１５】
ここにおいて、放射線の測定が可能となる光の波長範囲及び吸収線量範囲が存在し、
予想される吸収線量が、前記吸収線量範囲内の上限側に位置する場合には、前記波長範囲の上限側の波長を選択する一方、予想される吸収線量が、前記吸収線量範囲内の下限側に位置する場合には、前記波長範囲の下限側の波長を選択する、という手法を採ることができる。このようにすることで、照射材に照射された放射線の吸収線量をより正確に求めることができる他、当該吸収線量を適切なオーダーで測定することが可能となる。
【００１６】
また、本発明に係る放射線測定方法は、前記照射材を用いた放射線測定方法であって、
前記照射材に測定対象の放射線を照射したときに、当該照射材の色彩と、前記吸収線量及び／又は試料温度毎に塗り分けられた着色表の色彩とを対比することにより、前記放射線の吸収線量及び／又は試料温度を求める、という手法を採っている。このような手法によれば、放射線測定装置を使わなくても、放射線の吸収線量や試料温度を簡単に測定することができ、照射材を放射線測定装置にセットする手間が省け、且つ、従来よりも広範囲となる吸収線量を測定することが可能になる。
【００１７】
更に、本発明に係る放射線測定方法は、前記照射材を用いた放射線測定方法であって、
前記照射材に測定対象の放射線を照射したときに、当該照射材に施された色彩の濃淡で、前記放射線の吸収線量及び／又は試料温度の分布を求める、という手法を採っており、この手法によれば、従来測定が困難であった放射線の吸収線量及び／又は試料温度の分布を簡単且つ広範囲で測定することができる。これによって、例えば、放射線を照射する際に照射材を載せる載置台からの熱伝導等の影響を調べることが可能となる。すなわち、この場合は、照射材を部分的に載置台から浮かせ、当該浮いた部分の試料温度とそれ以外の部分の試料温度とを比較することによって、載置台からの熱伝導による照射材の加熱等の影響を、具体的に数値化して把握することができる。
【００１８】
なお、本明細書における「放射線」とは、電子線、Ｘ線、γ線、中性子線、高エネルギーイオン、放射光等の電離性放射線を意味し、単独或いはそれらの混合放射線をも含む概念として用いる。
【００１９】
また、「吸光度変化」とは、照射材に対する放射線の照射前後の吸光度の変化量を意味する。
【００２０】
更に、「試料温度」とは、測定対象となる放射線が照射材に照射されたときの当該照射部位の温度を意味し、「照射温度」とは、前記放射線が照射される雰囲気の温度を意味する。
【００２１】
また、「エチレン−テトラフルオロエチレン共重合体」は、その不純物をも含む概念として用いる。ここで不純物として含有される物質は、ヘキサフルオロプロピレン−テトラフルオロエチレン共重合体（ＦＥＰ）、パープルオロアルキルビニルエーテル共重合体（ＰＦＡ）、ポリプロピレン（ＰＰ）、ポリエチレン（ＰＥ）等のポリオレフィン系材料、そのオリゴマー等を例示できる。
【００２２】
【発明の実施の形態】
以下、本発明の実施の形態について図面を参照しながら説明する。
【００２３】
［第１実施例］
図５には、第１実施例に係る放射線測定装置の概略システム構成図が示されている。この図において、放射線測定装置１０は、テトラフルオロエチレン共重合体（ＥＴＦＥ）からなる照射材としての照射フィルムＦを用いて放射線の吸収線量及び試料温度を測定する装置である。すなわち、放射線測定装置１０は、測定対象の放射線が照射された照射フィルムＦ１、及び放射線が未照射の照射フィルムＦ２にそれぞれ所定の波長のＵＶ光を当てることで、照射フィルムＦ１の吸光度変化を測定し、当該吸光度変化と前記ＵＶ光の波長に基づいて放射線の吸収線量及び試料温度を求めるようになっている。
なお、特に限定されるものではないが、本実施例において、照射フィルムＦは、略全域が放射線の照射部分となるように形成されており、その厚みが２００μｍ以下に設定されている。
【００２４】
具体的に、前記放射線測定装置１０は、ＵＶ光を照射可能なキセノンランプ等のＵＶ光源１２と、このＵＶ光源１２から照射されたＵＶ光が通過するレンズ１３と、このレンズ１３を通過したＵＶ光のうち、測定者によって任意に選択した所定波長のみに分光する分光器１４と、当該分光器１４で分光された波長のＵＶ光を二方向に分岐させるハーフミラー１６及び全反射ミラー１７と、測定対象の放射線が照射された照射フィルムＦ１及び未照射の照射フィルムＦ２をそれぞれ保持するとともに、当該各照射フィルムＦ１，Ｆ２にミラー１６，１７によって二方向に分岐されたＵＶ光をそれぞれ当てる照射部１９と、当該照射部１９における照射フィルムＦ１，Ｆ２を透過したＵＶ光の強度をそれぞれ検出するフォトダイオード２０，２１と、このフォトダイオード２０，２１で検出されたＵＶ光の強度に基づいて、照射フィルムＦ１に照射された放射線の吸収線量及び試料温度を検出する線量・温度検出部２３とを備えて構成されている。なお、ここでは、フォトダイオード２０，２１を用いているが、代わりに、フォトマルチプライヤーを用いることもできる。
【００２５】
前記照射部１９は、測定対象の放射線が照射された照射フィルムＦ１を着脱自在に保持する第１の保持部２５と、放射線が照射されていないリファレンス材としての照射フィルムＦ２を着脱自在に保持する第２の保持部２６とを備えている。
【００２６】
前記線量・温度検出部２３は、フォトダイオード２０，２１からの信号がそれぞれ入力されるＡ／Ｄコンバーター２８，２９と、このＡ／Ｄコンバーター２８，２９からの信号に基づいて、照射フィルムＦ１の吸光度変化を求める吸光度変化算出手段３１と、照射フィルムＦの特性に基づく所定のデータを記憶する記憶手段３２と、吸光度変化算出手段３１で求めた吸光度変化から、当該記憶手段３２内のデータを用いて照射フィルムＦ１に照射された放射線の吸収線量及び試料温度を決定する線量・温度決定手段３３とを備えて構成されている。
【００２７】
前記吸光度変化算出手段３１は、各照射フィルムＦ１，Ｆ２に対し、フォトダイオード２０，２１によって検出された透過ＵＶ光の強度から、公知の計算式を用いて各フィルムＦ１，Ｆ２の吸光度を算出し、放射線が照射された照射フィルムＦ１の吸光度から、未照射の照射フィルムＦ２の吸光度を減算することにより、照射フィルムＦ１の吸光度変化が求められるようになっている。
【００２８】
前記記憶手段３２は、前述したＥＴＦＥの特性により、ＵＶ光の波長毎に、一吸光度変化、一吸収線量に対し、試料温度の値が一つ記憶されている。これらデータは、予め行った幾つかの実験データに基づき、吸収線量及び試料温度と吸光度変化との比例式から、多数のデータを算出した状態で記憶されている。なお、前記実験は、予め吸収線量が判っている照射フィルムＦの吸光度変化を複数種の波長について測定するとともに、そのときの試料温度が熱電対で測定される。このときの放射線は、照射フィルムＦに対するビーム加熱の影響の少ない電子線やコバルト線が用いられる。
【００２９】
前記線量・温度決定手段３３は、照射フィルムＦ１，Ｆ２のそれぞれに対し、異なる二種類の波長のＵＶ光を照射したときに求められる二種類の吸光度変化により、後述するように、記憶手段３２のデータを用いて吸収線量及び試料温度を決定する。
【００３０】
なお、前述した以外の構成及び構造については、公知の構造が採用されており、ここでは詳細な説明を省略する。
【００３１】
次に、前記放射線測定装置１０を用いた放射線の測定手順につき、以下に説明する。
【００３２】
まず、所定の放射線源から照射される放射線に対し、所定の照射温度となる所望の場所に照射フィルムＦ１を所定時間置くことで、当該照射フィルムＦ１に放射線を当てる。そして、そこから照射フィルムＦ１を回収し、放射線未照射の照射フィルムＦ２とともに、前記第１及び第２の保持部２５，２６に保持させる。このとき、照射フィルムＦ２は、略無色透明状となっているのに対し、放射線が照射された照射フィルムＦ１は、茶褐色若しくは黄色状となる有色透明状に変色した状態となっている。
【００３３】
そして、ＵＶ光源１２からＵＶ光を各照射フィルムＦ１，Ｆ２に向かって照射する。このとき、測定者の操作により、分光器１４でＵＶ光の波長が所望の波長に限定され、吸光度変化算出手段３１により、限定された波長に対する吸光度変化が算出される。そして、ＵＶ光の波長を異なる別の波長に限定し、この場合における吸光度変化も吸光度変化算出手段３１で算出される。
【００３４】
このように、異なる二種類の波長に対する各吸光度変化が求まれば、前述したＥＴＦＥの特性から、照射フィルムＦ１に照射された放射線の吸収線量及び試料温度が一義的に決まることになる。
【００３５】
すなわち、吸光度変化ＯＤと吸収線量Ｄとの間には比例関係が生じ、ここでの比例定数（線量係数）は、波長λ及び試料温度Ｔに応じて定まる。また、吸光度変化ＯＤと試料温度Ｔとの間にも比例関係が生じ、ここでの比例定数（温度係数）は、波長λ、吸収線量Ｄ及び試料温度Ｔに応じて定まる。従って、ＥＴＦＥの特性から、四変数（波長λ、吸光度変化ＯＤ、吸収線量Ｄ、試料温度Ｔ）からなる二つの比例式が存在し、少なくとも二点の波長λ１，λ２と、当該各波長λ１，λ２に対する各吸光度変化ＯＤ１，ＯＤ２が判れば、前記二つの比例式を二変数（吸収線量Ｄ、試料温度Ｔ）からなる二式とすることができ、この二元連立方程式を解くことで、吸収線量Ｄ及び試料温度Ｔをそれぞれ一つの値に特定できることは自明である。
【００３６】
以上のような吸収線量Ｄ及び試料温度Ｔの特定は、線量・温度決定手段３３によって行われるが、ここでは、図１及び図２を用い、一例を挙げて説明する。
【００３７】
吸光度変化算出手段３１で、波長λ１（ｎｍ）のときの吸光度変化ＯＤがＯＤ１と算出され、波長λ２（ｎｍ）のときの吸光度変化ＯＤがＯＤ２と算出されたとする。これによって、予め記憶された記憶手段３２のデータを用いることで、吸収線量Ｄ及び試料温度Ｔが特定されることになる。すなわち、図１に示されるように、波長λ１（ｎｍ）の場合に、吸光度変化ＯＤがＯＤ１と算出されたことにより、試料温度ＴがＴ１（Ｋ），Ｔ２（Ｋ），Ｔ３（Ｋ）のときにおける吸収線量Ｄが、Ｄ３（ＭＧｙ），Ｄ２（ＭＧｙ），Ｄ１（ＭＧｙ）にそれぞれ特定される。同様に、図２に示されるように、波長λ２（ｎｍ）の場合に、吸光度変化ＯＤがＯＤ２と算出されたことにより、試料温度ＴがＴ１（Ｋ），Ｔ２（Ｋ），Ｔ３（Ｋ）のときにおける吸収線量Ｄが、Ｄ４（ＭＧｙ），Ｄ２（ＭＧｙ），Ｄ０（ＭＧｙ）にそれぞれ特定される。ここで、波長λ１（ｎｍ），λ２（ｎｍ）の双方の場合で、同一の試料（照射フィルムＦ１）が用いられているため、何れの場合でも、吸収線量Ｄ及び試料温度Ｔは同じ値になる。そこで、この場合は、双方の場合で同じ値となる放射線の吸収線量Ｄは、Ｄ２（ＭＧｙ）であり、これによって、試料温度Ｔは、Ｔ２（Ｋ）であると決定される。
【００３８】
なお、図３及び図４に示されるグラフからも、同様に、放射線の吸収線量Ｄ及び試料温度Ｔをそれぞれ一つの値に決定できることが理解できるであろう。
すなわち、図３に示されるように、波長λ１（ｎｍ）の場合に、吸光度変化ＯＤがＯＤ１と算出されると、吸収線量ＤがＤ１（ＭＧｙ）、Ｄ２（ＭＧｙ）、Ｄ３（ＭＧｙ）のときにおける試料温度Ｔが、それぞれＴ３（Ｋ）、Ｔ２（Ｋ）、Ｔ０（Ｋ）にそれぞれ特定される。同様に、図４に示されるように、波長λ２（ｎｍ）の場合に、吸光度変化ＯＤがＯＤ２と算出されると、吸収線量ＤがＤ１（ＭＧｙ）、Ｄ２（ＭＧｙ）、Ｄ３（ＭＧｙ）のときにおける試料温度Ｔが、それぞれＴ４（Ｋ）、Ｔ２（Ｋ）、Ｔ１（Ｋ）にそれぞれ特定される。従って、このように図４の関係を用いても、図３の関係を用いた場合と同様に、放射線の吸収線量ＤがＤ２（ＭＧｙ）と決定でき、且つ、試料温度Ｔは、Ｔ２（Ｋ）と決定できる。
【００３９】
なお、本実施例においては、記憶手段３２で記憶された各数値データに基づいて、放射線の吸収線量Ｄと試料温度Ｔを求めたが、本発明はこれに限らず、前述したＥＴＦＥの特性による二種類の比例式等を記憶手段３２に記憶し、波長λ及び吸光度変化ＯＤを前述と同様に二組求め、線量・温度決定手段３３で、この二組の数値を二種類の比例式に代入し、これらの連立方程式を解いて、吸収線量Ｄと試料温度Ｔを求めることもできる。
【００４０】
また、図６に示されるように、照射されるＵＶ光の波長が約２００ｎｍから約９００ｎｍの範囲内、すなわち、ＥＴＦＥの特性上測定可能となる波長範囲内においては、波長が長くなる程、測定可能な最大吸収線量（最大測定可能線量）が次第に大きくなる。従って、予想される吸収線量Ｄが最大測定可能線量の範囲（吸収線量範囲）の上限側にある場合には、前記波長範囲の上限側の波長を選択する一方、予想される吸収線量Ｄが前記吸収線量範囲の下限側にある場合には、前記波長領域の下限側の波長を選択するとよい。このようにすると、照射フィルムＦ１に照射された放射線の吸収線量Ｄをより正確に求めることができる他、当該吸収線量Ｄを適切なオーダーで測定することが可能となる。
【００４１】
更に、照射フィルムＦを複数用意し、各照射フィルムＦに対し、各放射線の照射時間や放射線源からの距離を変えて放射線を照射する等、異なる照射条件で放射線を照射し、それぞれについて、照射線量Ｄや照射温度Ｔを求めると、求めようとする照射線量Ｄや照射温度Ｔの精度をより高めることができる。
【００４２】
従って、このような第１実施例によれば、照射フィルムＦがＥＴＦＥによって形成されているため、当該ＥＴＦＥの特性により、放射線を照射フィルムＦ１に照射する際の温度や湿度、放置時間等の環境条件を厳格に管理しなくても、放射線の吸収線量Ｄを正確に測定することができる他、同時に試料温度Ｔの測定もでき、別手段で試料温度Ｔを測定する手間を省くことができるという効果を得る。
【００４３】
なお、図７に示されるように、図５の構成に対して第２の保持部２６を省略し、放射線未照射の照射フィルムＦ２の吸光度を吸光度変化算出手段３１に予め記憶しておき、この記憶値を照射フィルムＦ１の吸光度から減算することで、吸光度変化を求めてもよい。但し、前記実施例の方が、照射フィルムＦの製造上のバラツキ等を考慮することができ、吸光度変化の誤差を少なくして、当該吸光度変化をより正確に求めることができる。
【００４４】
次に、本発明の第２実施例について説明する。なお、以下の説明において、前記第１実施例と同一若しくは同等の構成部分については同一符号を用いるものとし、説明を省略若しくは簡略にする。
【００４５】
［第２実施例］
この第２実施例は、放射線の照射による照射フィルムＦの着色現象を利用して、放射線照射後の照射フィルムＦ１の色彩と、吸収線量及び照射温度毎に塗り分けられた図８の着色表３６の色彩とを対比し、照射フィルムＦ１に照射された放射線の吸収線量及び試料温度を求めるようにしたところに特徴を有する。
【００４６】
照射フィルムＦは、放射線が照射されていない初期状態で略無色透明状をなし、放射線が照射されると、次第に茶褐色若しくは黄色状の有色透明状に変色し、照射した放射線の吸収線量や試料温度の上昇に伴って色彩の濃度が増大する特質を有する。
【００４７】
前記着色表３６は、所定の照射温度毎に、吸収線量に対する照射フィルムＦの色彩が塗り分けられた線量決定用の着色表３６Ａと、所定の吸収線量毎に、試料温度に対する照射フィルムＦの色彩が塗り分けられた温度決定用の着色表３６Ｂとからなる。
【００４８】
前記着色表３６を用い、次のようにして吸収線量又は試料温度が求められる。
【００４９】
先ず、照射温度が判明しているときには、着色表３６Ａを用い、当該照射温度における着色表３６Ａの色彩群と照射フィルムＦ１の色彩とを目視等により対比し、照射フィルムＦの色彩に合致する着色表３６Ａの色彩を見つけ、当該色彩に対応する吸収線量が求める値となる。
一方、照射した放射線の吸収線量の値がある程度目安が付く場合には、着色表３６Ｂを用い、着色表３６Ａと同様に、着色表３６Ｂの色彩群と照射フィルムＦの色彩とを目視等により対比することで試料温度を求める。
また、照射温度や吸収線量が全く特定できない場合には、放射線が照射された照射フィルムＦの色彩と、着色表３６Ａ、着色表３６Ｂの全ての色彩群とを対比し、略同一となる色彩が施された着色表３６Ａ，３６Ｂの部分における吸収線量及び試料温度を選び出すことで、吸収線量及び試料温度を求めることができる。
【００５０】
従って、このような第２実施例によれば、特別な放射線測定装置等を用いなくても、放射線の吸収線量及び試料温度を簡単且つ広範囲で測定できるという効果を得る。
【００５１】
また、当該照射フィルムＦに放射線を照射したときに、放射線の吸収線量及び／又は試料温度が部分的に異なる場合には、前述したＥＴＦＥの着色現象から、照射フィルムＦに施された色彩に濃淡が生じ、これを目視等することで、前記吸収線量及び／又は試料温度の分布を容易に確認することができる。このときに、前記着色表３６を用いると、当該分布毎における吸収線量及び／又は試料温度の値を求めることも可能となる。
【００５２】
【発明の効果】
以上説明したように、本発明によれば、エチレン−テトラフルオロエチレン共重合体の特性を利用することにより、放射線の吸収線量及び試料温度やそれらの分布を簡単且つ広範囲で測定することができる。
【図面の簡単な説明】
【図１】エチレン−テトラフルオロエチレン共重合体における吸収線量と吸光度変化との関係を示すグラフ。
【図２】図１に対して、吸光度変化を測定する際の光の波長を変えた場合における図１と同様のグラフ。
【図３】エチレン−テトラフルオロエチレン共重合体における試料温度と吸光度変化との関係を示すグラフ。
【図４】図３に対して、吸光度変化を測定する際の光の波長を変えた場合における図３と同様のグラフ。
【図５】第１実施例に係る放射線測定装置のシステム構成図。
【図６】前記放射線測定装置における最大測定可能線量を前記波長毎及び試料温度毎に示した図表。
【図７】第１実施例の変形例に係る放射線測定装置のシステム構成図。
【図８】第２実施例に係る着色表を説明するための概念図。
【符号の説明】
１０　放射線測定装置
３１　吸光度変化算出手段
３２　記憶手段
３３　線量・温度決定手段
３６　着色表
３６Ａ　着色表
３６Ｂ　着色表
Ｆ　照射フィルム（照射材）
Ｆ１　照射フィルム（照射材）
Ｆ２　照射フィルム（照射材）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an irradiation material for radiation measurement, a radiation measurement device, and a radiation measurement method, and more particularly, to a radiation measurement device capable of easily and widely measuring the absorbed dose of radiation and the sample temperature and their distribution. The present invention relates to an irradiation material, a radiation measurement device, and a radiation measurement method.
[0002]
[Prior art]
As a method for measuring the absorbed dose when radiation is irradiated from a radiation source such as a particle accelerator or a radioisotope, a method using a cellulose triacetate (CTA) film, a method using alanine, and the like are known ( Non-Patent Document 1). In a method using a CTA film, the absorbed dose is determined by irradiating the film with radiation to be measured and measuring an amount related to a chemical change of the film caused by the irradiation. That is, the method using the CTA film utilizes the fact that the change in absorbance before and after irradiation at a wavelength of about 280 nm is proportional to the absorbed dose, and measures the change in absorbance near the wavelength of 280 nm. , The absorbed dose is determined.
On the other hand, the method using alanine is based on the fact that when a pellet body containing alanine is irradiated with radiation, alanine is decomposed by irradiation of the radiation to generate radicals. By measuring with (ESR), the absorbed dose is obtained.
[0003]
When measuring the sample temperature during irradiation, a thermocouple attached to the sample is used.
[0004]
[Non-patent document 1]
Kazuyuki Moriuchi and six others, "Electron Dosimetry for Industrial Irradiation," 1st Edition, Jinjinshokan Co., Ltd., March 25, 1990, p. 27-30, p172-180
[0005]
[Problems to be solved by the invention]
However, in the above-described method using a CTA film, it is necessary to perform the measurement while maintaining the measurement environment strictly, and there is a disadvantage that the measurement of the absorbed dose requires time and effort. That is, in this method, not only the wavelength of light applied to the film after irradiation is limited to around 280 nm, but also the temperature and humidity of the atmosphere to be irradiated must be kept at predetermined values. Since the characteristics of the film after the irradiation change with the elapsed time, the elapsed time must be kept constant. In addition, when irradiating the film with the radiation, the sample temperature of the film may increase due to the beam heating. In this case, there is a disadvantage that the value of the absorbed dose cannot be accurately obtained.
On the other hand, in the method using alanine, temperature control must be strict as in the case of using a CTA film, and an expensive electron spin resonance apparatus (ESR) is required for measurement. The apparatus cannot be introduced into any measurement facility, and there is a disadvantage that it takes time and effort to transport the irradiated pellet to a predetermined facility.
Further, in the method using these CTA films or alanine, when a large amount of dose is given to a sample in a short time, for example, a dose of 100 kGy or more in several seconds, the error with respect to the actual absorbed dose is increased. In addition to this, the range in which the absorbed dose can be measured is at most about 200 kGy, and when the absorbed dose larger than that is given in a short time, there is a disadvantage that it cannot be used.
[0006]
In addition, when using a thermocouple to measure the sample temperature during irradiation, it is necessary to take protective measures such as shielding the temperature measurement device because the temperature measurement device is used in a radiation environment. In addition, there is an inconvenience that it takes time to perform the temperature measurement work. Further, in the case of radiation irradiation at a high dose rate, the thermocouple itself is directly heated by the radiation, and there is also a disadvantage that the actual sample temperature due to the radiation irradiation cannot be accurately measured.
[0007]
By the way, in view of such inconvenience, the present inventors have conducted various experiments and studies on various polymer materials used as irradiation materials when measuring the absorbed dose during irradiation and the sample temperature. As a result, when the ethylene-tetrafluoroethylene copolymer (ETFE), which is a fluorine-based polymer, is irradiated with radiation, a coloring phenomenon occurs in the ETFE. In particular, as the absorbed dose of radiation and the sample temperature increase, the color gradually increases. I found that it became darker. That is, after irradiating ETFE in the form of a film and then irradiating the film with a predetermined light, the light absorbance change of the film, the absorbed dose and the sample temperature at a wavelength of light that is wider than before, and Found that there is a certain relationship between them.
[0008]
That is, as shown in FIGS. 1 and 2, when the wavelength of light is in the range of about 200 nm to about 900 nm, the absorbed dose is in the range of about 1 kGy to about 50 MGy, and the sample temperature is in the range of about 4 K to about 553 K, The absorbance change OD and the absorbed dose D are in a direct proportional relationship, and as shown in FIGS. 3 and 4, the absorbance change OD and the sample temperature T are in a direct proportional relationship for each predetermined range of the sample temperature T. It turned out to be. This is considered to be due to an increase in the amount of conjugated double bonds in the molecule in proportion to the absorbed dose D and the sample temperature T.
[0009]
Specifically, as shown in FIGS. 1 and 2, the absorbance change OD has a relationship obtained by multiplying the absorbed dose D by a predetermined proportional constant (hereinafter, referred to as “dose coefficient”). This dose coefficient differs for each wavelength λ and sample temperature T, and is uniquely determined for these wavelength λ and sample temperature T. Further, the dose coefficient decreases as the wavelength λ increases, and increases as the sample temperature T increases.
[0010]
As shown in FIGS. 3 and 4, the absorbance change OD has a relationship obtained by multiplying the sample temperature T by a predetermined proportional constant (hereinafter, referred to as a “temperature coefficient”). This temperature coefficient differs for each wavelength λ and absorbed dose D, and there are three values for one wavelength λ and one absorbed dose D. These three values change at two transition temperatures t1 and t2 which are common to each wavelength λ and absorbed dose D. The transition temperatures t1 and t2 are temperatures at which the motion mode in the molecular motion of the polymer chain changes, and exist around 210K and 400K, respectively. Therefore, the dose coefficient differs for each of the wavelength λ, the absorbed dose D, and the sample temperature T, and is uniquely determined for the wavelength λ, the absorbed dose D, and the sample temperature T. In addition, the temperature coefficient increases in the order of a temperature region of less than t1, a temperature region of t1 or more and less than t2, and a temperature region of t3 or more, and decreases as the wavelength λ increases, and increases as the absorbed dose D increases. I do.
[0011]
[Object of the invention]
The present invention has been devised based on the knowledge of the inventor, and has as its object the purpose of radiation measurement that can easily and broadly measure the absorbed dose of radiation and the sample temperature and their distribution. And a radiation measuring device and a radiation measuring method.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the irradiation material according to the present invention is used for radiation measurement in which the absorption dose of the radiation and the sample temperature can be measured by measuring a change in absorbance when the radiation to be measured is irradiated. Irradiation material,
The radiation-irradiated portion is formed of an ethylene-tetrafluoroethylene copolymer. According to such a configuration, the radiation-irradiated portion is formed of the ethylene-tetrafluoroethylene copolymer (ETFE). Therefore, due to the above-described properties of the ETFE, the irradiation material irradiated with the radiation to be measured is irradiated. By measuring each change in absorbance at at least two wavelengths, the absorbed dose of the radiation and the sample temperature can be determined simultaneously. In addition, when measuring the absorbed dose and the sample temperature, it is possible to perform measurement at various wavelengths and temperatures of light, and it is not necessary to control the measurement environment strictly. You can ask. Furthermore, the absorbed dose can be measured in a wide range of about 1 kGy to about 50 MGy, and in addition to the range of the absorbed dose that can be measured by a conventional dosimeter, measurement in a higher dose range than the range is also possible. High versatility for dose measurement can be provided. In addition, since the sample temperature can be measured without using a temperature measuring device, it is not necessary to shield the temperature measuring device, which has been a problem in the related art, and the sample temperature can be easily measured. In addition, the sample temperature can be measured accurately even in the case of irradiation at a high dose rate where the sample temperature cannot be measured accurately by the conventional method.
[0013]
Further, the radiation measuring apparatus according to the present invention, in the radiation measuring apparatus for determining the absorbed dose of radiation and the sample temperature using the irradiation material,
Absorbance change calculation means for determining a change in absorbance for light of the wavelength by transmitting light of a predetermined wavelength to the irradiation material, storage means for storing predetermined data based on characteristics of the irradiation material, and from the change in absorbance A dose / temperature determining means for determining the absorbed dose and the sample temperature based on the data in the storage means,
The dose / temperature determining means determines an absorbed dose and a sample temperature from changes in absorbance when light of at least two wavelengths is transmitted to an irradiation material irradiated with radiation to be measured. Has been adopted. According to such a configuration, as described above, the absorbed dose of radiation and the sample temperature can be measured simply and over a wide range.
[0014]
Furthermore, the radiation measurement method according to the present invention is a radiation measurement method using the irradiation material,
After irradiating the irradiation material with the radiation to be measured, by transmitting light of at least two types of wavelengths to the irradiation material, the absorbance change of the irradiation material is measured for each wavelength, and from each of the wavelengths and each absorbance change. The method employs a method of determining the absorbed dose of the radiation and the sample temperature using data based on the characteristics of the irradiation material, and the above-described object can be achieved also by such a method.
[0015]
Here, there is a wavelength range of light and an absorbed dose range where radiation can be measured,
When the expected absorbed dose is located on the upper side of the absorbed dose range, the wavelength on the upper side of the wavelength range is selected, while the expected absorbed dose is on the lower side of the absorbed dose range. , A method of selecting a wavelength on the lower limit side of the wavelength range can be adopted. In this way, the absorbed dose of the radiation applied to the irradiation material can be obtained more accurately, and the absorbed dose can be measured in an appropriate order.
[0016]
Further, the radiation measurement method according to the present invention is a radiation measurement method using the irradiation material,
When the irradiation material is irradiated with the radiation to be measured, the color of the irradiation material is compared with the color of the coloring table which is separately applied for each of the absorbed dose and / or the sample temperature, thereby absorbing the radiation. The method of obtaining the dose and / or the sample temperature is adopted. According to such a method, it is possible to easily measure the absorbed dose of radiation and the sample temperature without using a radiation measuring device, to save the trouble of setting an irradiation material in the radiation measuring device, and to reduce It is also possible to measure the absorbed dose over a wide range.
[0017]
Furthermore, the radiation measurement method according to the present invention is a radiation measurement method using the irradiation material,
When irradiating the irradiation material with the radiation to be measured, a method of obtaining the absorbed dose of the radiation and / or the distribution of the sample temperature based on the density of the color applied to the irradiation material is adopted. According to the method described above, it is possible to measure the distribution of the absorbed dose of radiation and / or the temperature of the sample, which has been conventionally difficult to measure, in a simple and wide range. Thus, for example, when irradiating radiation, it is possible to investigate the influence of heat conduction from the mounting table on which the irradiation material is mounted. That is, in this case, the irradiation material is partially floated from the mounting table, and the sample temperature of the floating portion is compared with the sample temperature of the other portion, thereby heating the irradiation material by heat conduction from the mounting table. And the like can be specifically digitized and grasped.
[0018]
In this specification, "radiation" means ionizing radiation such as electron beam, X-ray, γ-ray, neutron beam, high-energy ion, and radiation, and is a concept including single or mixed radiation thereof. Used.
[0019]
Further, “absorbance change” means the amount of change in absorbance before and after irradiation of the irradiation material with radiation.
[0020]
Furthermore, the “sample temperature” means the temperature of the irradiated part when the radiation to be measured is irradiated on the irradiation material, and the “irradiation temperature” means the temperature of the atmosphere to which the radiation is irradiated. I do.
[0021]
The term "ethylene-tetrafluoroethylene copolymer" is used as a concept including its impurities. Here, substances contained as impurities include polyolefin-based materials such as hexafluoropropylene-tetrafluoroethylene copolymer (FEP), purple fluoroalkyl vinyl ether copolymer (PFA), polypropylene (PP), and polyethylene (PE); The oligomer etc. can be illustrated.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0023]
[First embodiment]
FIG. 5 is a schematic system configuration diagram of the radiation measuring apparatus according to the first embodiment. In this figure, a radiation measuring apparatus 10 is an apparatus that measures an absorbed dose of radiation and a sample temperature using an irradiation film F as an irradiation material made of a tetrafluoroethylene copolymer (ETFE). That is, the radiation measurement device 10 measures the absorbance change of the irradiation film F1 by irradiating the irradiation film F1 irradiated with the radiation to be measured and the irradiation film F2 not irradiated with the irradiation with UV light having a predetermined wavelength. Then, the absorbed dose of radiation and the sample temperature are determined based on the change in absorbance and the wavelength of the UV light.
Although not particularly limited, in the present embodiment, the irradiation film F is formed so that substantially the entire area is a portion irradiated with radiation, and the thickness is set to 200 μm or less.
[0024]
Specifically, the radiation measuring apparatus 10 includes a UV light source 12 such as a xenon lamp capable of irradiating UV light, a lens 13 through which the UV light emitted from the UV light source 12 passes, and a UV light passing through the lens 13. Of the light, a spectroscope 14 for splitting only into a predetermined wavelength arbitrarily selected by the measurer, a half mirror 16 and a total reflection mirror 17 for splitting the UV light of the wavelength split by the spectroscope 14 into two directions, An irradiation unit that holds the irradiated film F1 and the unirradiated irradiated film F2 irradiated with the radiation to be measured, and irradiates the irradiated films F1 and F2 with UV light branched in two directions by mirrors 16 and 17, respectively. And photodiodes 20 and 21 for detecting the intensity of UV light transmitted through the irradiation films F1 and F2 in the irradiation unit 19, respectively. And a dose / temperature detecting unit 23 for detecting the absorbed dose of the radiation applied to the irradiation film F1 and the sample temperature based on the intensity of the UV light detected by the photodiodes 20 and 21. . Although the photodiodes 20 and 21 are used here, a photomultiplier may be used instead.
[0025]
The irradiation unit 19 detachably holds a first holding unit 25 that detachably holds an irradiation film F1 irradiated with radiation to be measured and an irradiation film F2 as a reference material that is not irradiated with radiation. And a second holding unit 26.
[0026]
The dose / temperature detection unit 23 detects the A / D converters 28 and 29 to which signals from the photodiodes 20 and 21 are input, respectively, and detects the irradiation film F1 based on the signals from the A / D converters 28 and 29. From the absorbance change calculation means 31 for calculating the absorbance change, the storage means 32 for storing predetermined data based on the characteristics of the irradiation film F, and the data in the storage means 32 from the absorbance change calculated by the absorbance change calculation means 31, And a dose / temperature determining means 33 for determining the absorbed dose of the radiation applied to the irradiation film F1 and the sample temperature.
[0027]
The absorbance change calculating means 31 calculates the absorbance of each of the irradiated films F1 and F2 from the intensity of the transmitted UV light detected by the photodiodes 20 and 21 using a known calculation formula. By subtracting the absorbance of the unirradiated irradiated film F2 from the absorbance of the irradiated film F1 irradiated with the radiation, the change in the absorbance of the irradiated film F1 can be obtained.
[0028]
The storage unit 32 stores one sample temperature value for one change in absorbance and one absorbed dose for each wavelength of UV light, based on the above-described ETFE characteristics. These data are stored in a state in which a large number of data are calculated from a proportional expression between the absorbed dose and the sample temperature and the change in absorbance based on some experimental data performed in advance. In the experiment, the change in absorbance of the irradiation film F whose absorption dose is known in advance is measured for a plurality of wavelengths, and the sample temperature at that time is measured by a thermocouple. As the radiation at this time, an electron beam or a cobalt beam, which is less affected by beam heating on the irradiation film F, is used.
[0029]
The dose / temperature determining unit 33 uses the two types of absorbance changes obtained when each of the irradiation films F1 and F2 is irradiated with UV light having two different wavelengths, as described later, to store the data in the storage unit 32. Use the data to determine absorbed dose and sample temperature.
[0030]
In addition, as for the configuration and structure other than those described above, a known structure is adopted, and the detailed description is omitted here.
[0031]
Next, a procedure for measuring radiation using the radiation measuring apparatus 10 will be described below.
[0032]
First, the irradiation film F1 is irradiated with radiation from a predetermined radiation source by placing the irradiation film F1 at a desired location having a predetermined irradiation temperature for a predetermined time. Then, the irradiated film F1 is collected therefrom and held in the first and second holding units 25 and 26 together with the irradiated film F2 not irradiated with radiation. At this time, the irradiation film F2 is in a substantially colorless and transparent state, whereas the irradiation film F1 irradiated with the radiation is in a state of being changed to a brown or yellow colored and transparent state.
[0033]
Then, UV light is irradiated from the UV light source 12 toward each of the irradiation films F1 and F2. At this time, the wavelength of the UV light is limited to a desired wavelength by the spectroscope 14 by the operation of the measurer, and the absorbance change for the limited wavelength is calculated by the absorbance change calculator 31. Then, the wavelength of the UV light is limited to another different wavelength, and the absorbance change in this case is also calculated by the absorbance change calculator 31.
[0034]
As described above, if the absorbance changes for the two different wavelengths are obtained, the absorbed dose of the radiation applied to the irradiation film F1 and the sample temperature are uniquely determined from the ETFE characteristics described above.
[0035]
That is, there is a proportional relationship between the absorbance change OD and the absorbed dose D, and the proportionality constant (dose coefficient) here is determined according to the wavelength λ and the sample temperature T. In addition, a proportional relationship occurs between the absorbance change OD and the sample temperature T, and the proportionality constant (temperature coefficient) here is determined according to the wavelength λ, the absorbed dose D, and the sample temperature T. Therefore, from the characteristics of ETFE, there are two proportional expressions consisting of four variables (wavelength λ, absorbance change OD, absorbed dose D, and sample temperature T). At least two wavelengths λ1, λ2 and the respective wavelengths λ1, If the respective absorbance changes OD1 and OD2 with respect to λ2 are known, the two proportional equations can be made into two equations composed of two variables (absorbed dose D and sample temperature T). It is obvious that the dose D and the sample temperature T can each be specified to one value.
[0036]
The above-described specification of the absorbed dose D and the sample temperature T is performed by the dose / temperature determining unit 33. Here, an example will be described with reference to FIGS. 1 and 2.
[0037]
It is assumed that the absorbance change calculator 31 calculates the absorbance change OD at the wavelength λ1 (nm) as OD1 and the absorbance change OD at the wavelength λ2 (nm) as OD2. As a result, the absorbed dose D and the sample temperature T are specified by using the data of the storage means 32 stored in advance. That is, as shown in FIG. 1, when the wavelength λ1 (nm), the absorbance change OD was calculated as OD1, and thus the sample temperature T was changed to T1 (K), T2 (K), and T3 (K). The absorbed dose D at that time is specified as D3 (MGy), D2 (MGy), and D1 (MGy). Similarly, as shown in FIG. 2, when the absorbance change OD is calculated as OD2 at the wavelength λ2 (nm), the sample temperature T becomes T1 (K), T2 (K), T3 (K). Absorbed dose D at the time is specified as D4 (MGy), D2 (MGy), and D0 (MGy). Here, in both cases of the wavelengths λ1 (nm) and λ2 (nm), since the same sample (irradiation film F1) is used, in each case, the absorbed dose D and the sample temperature T have the same value. Become. Therefore, in this case, the absorbed dose D of the radiation having the same value in both cases is D2 (MGy), whereby the sample temperature T is determined to be T2 (K).
[0038]
It can be understood from the graphs shown in FIGS. 3 and 4 that the absorbed dose D of the radiation and the sample temperature T can be similarly determined to one value.
That is, as shown in FIG. 3, when the absorbance change OD is calculated as OD1 in the case of the wavelength λ1 (nm), when the absorbed dose D is D1 (MGy), D2 (MGy), and D3 (MGy). Are specified as T3 (K), T2 (K), and T0 (K), respectively. Similarly, as shown in FIG. 4, when the absorbance change OD is calculated as OD2 in the case of the wavelength λ2 (nm), the absorbed dose D is D1 (MGy), D2 (MGy), and D3 (MGy). The sample temperature T at that time is specified as T4 (K), T2 (K), and T1 (K), respectively. Therefore, even if the relationship of FIG. 4 is used, the absorbed dose D of radiation can be determined to be D2 (MGy), and the sample temperature T is T2 (Ky), as in the case of using the relationship of FIG. ).
[0039]
In the present embodiment, the absorbed dose D of the radiation and the sample temperature T are obtained based on the respective numerical data stored in the storage means 32. However, the present invention is not limited to this, and is based on the above-described ETFE characteristics. The two kinds of proportional expressions and the like are stored in the storage means 32, two sets of the wavelength λ and the absorbance change OD are obtained in the same manner as described above, and the dose / temperature determining means 33 substitutes these two sets of numerical values into the two kinds of proportional expressions. Then, by solving these simultaneous equations, the absorbed dose D and the sample temperature T can be obtained.
[0040]
As shown in FIG. 6, when the wavelength of the irradiated UV light is in a range of about 200 nm to about 900 nm, that is, in a wavelength range in which measurement is possible due to the characteristics of ETFE, the longer the wavelength, the longer the measurement. The maximum possible absorbed dose (maximum measurable dose) gradually increases. Therefore, if the expected absorbed dose D is on the upper limit of the maximum measurable dose range (absorbed dose range), the wavelength on the upper limit of the wavelength range is selected, while the expected absorbed dose D is When it is on the lower limit side of the absorbed dose range, it is preferable to select the wavelength on the lower limit side of the wavelength region. In this way, the absorbed dose D of the radiation applied to the irradiation film F1 can be obtained more accurately, and the absorbed dose D can be measured in an appropriate order.
[0041]
Further, a plurality of irradiation films F are prepared, and each irradiation film F is irradiated with radiation under different irradiation conditions such as changing the irradiation time of each radiation or the distance from the radiation source, and irradiating each of the irradiation films F. When the dose D and the irradiation temperature T are obtained, the accuracy of the irradiation dose D and the irradiation temperature T to be obtained can be further improved.
[0042]
Therefore, according to the first embodiment, since the irradiation film F is formed by ETFE, due to the characteristics of the ETFE, environmental factors such as temperature, humidity, and standing time when irradiating the irradiation film F1 with the radiation. Even if the conditions are not strictly controlled, it is possible to accurately measure the absorbed dose D of the radiation, and at the same time, it is possible to measure the sample temperature T, so that it is not necessary to measure the sample temperature T by another means. Get the effect.
[0043]
As shown in FIG. 7, the second holding unit 26 is omitted from the configuration of FIG. 5, and the absorbance of the irradiated film F2 that has not been irradiated is stored in the absorbance change calculating unit 31 in advance. The absorbance change may be obtained by subtracting the stored value from the absorbance of the irradiation film F1. However, in the above-described embodiment, it is possible to consider variations in the manufacture of the irradiation film F and the like, and it is possible to reduce the error of the absorbance change and more accurately calculate the absorbance change.
[0044]
Next, a second embodiment of the present invention will be described. In the following description, the same reference numerals are used for the same or equivalent components as in the first embodiment, and the description is omitted or simplified.
[0045]
[Second embodiment]
This second embodiment uses the coloring phenomenon of the irradiated film F by irradiation of radiation, and uses the coloring table 36 of FIG. 8 in which the color of the irradiated film F1 after irradiation and the absorbed dose and the irradiation temperature are separately applied. This is characterized in that the absorbed dose of the radiation applied to the irradiation film F1 and the sample temperature are obtained by comparing the color of the irradiation film F1.
[0046]
The irradiated film F has a substantially colorless and transparent state in an initial state where the radiation is not irradiated, and when irradiated with the radiation, the color gradually changes to a brown or yellow colored transparent state, and the absorbed dose of the irradiated radiation and the sample temperature. Has the characteristic that the color density increases with the rise of the color.
[0047]
The coloring table 36 includes a coloring table 36A for dose determination in which the color of the irradiation film F with respect to the absorbed dose is separately applied for each predetermined irradiation temperature, and the color of the irradiation film F with respect to the sample temperature for each predetermined absorption dose. And a coloring table 36 </ b> B for temperature determination, which is colored separately.
[0048]
Using the coloring table 36, the absorbed dose or the sample temperature is determined as follows.
[0049]
First, when the irradiation temperature is known, the coloring table 36A is used, and the color group of the coloring table 36A at the irradiation temperature is compared with the color of the irradiation film F1 by visual observation or the like, and the color matching the color of the irradiation film F is obtained. The color shown in Table 36A is found, and the absorbed dose corresponding to the color becomes a value to be obtained.
On the other hand, in the case where the value of the absorbed dose of the irradiated radiation gives some indication, the coloring table 36B is used, and similarly to the coloring table 36A, the color group of the coloring table 36B and the color of the irradiation film F are visually compared. To determine the sample temperature.
When the irradiation temperature or the absorbed dose cannot be specified at all, the color of the irradiated film F irradiated with the radiation is compared with all the color groups of the coloring table 36A and the coloring table 36B. The absorbed dose and the sample temperature can be obtained by selecting the absorbed dose and the sample temperature at the portions of the applied coloring tables 36A and 36B.
[0050]
Therefore, according to the second embodiment, there is an effect that the absorbed dose of radiation and the sample temperature can be measured easily and in a wide range without using a special radiation measuring device or the like.
[0051]
Further, when the irradiated film F is irradiated with the radiation, if the absorbed dose of the radiation and / or the sample temperature is partially different, the color applied to the irradiated film F is shaded from the ETFE coloring phenomenon described above. The distribution of the absorbed dose and / or the temperature of the sample can be easily confirmed by visually observing this. At this time, if the coloring table 36 is used, it is also possible to obtain the value of the absorbed dose and / or the sample temperature for each distribution.
[0052]
【The invention's effect】
As described above, according to the present invention, by utilizing the characteristics of the ethylene-tetrafluoroethylene copolymer, the absorbed dose of radiation, the sample temperature, and the distribution thereof can be easily and widely measured.
[Brief description of the drawings]
FIG. 1 is a graph showing a relationship between an absorbed dose and a change in absorbance of an ethylene-tetrafluoroethylene copolymer.
FIG. 2 is a graph similar to FIG. 1 in a case where the wavelength of light used to measure a change in absorbance is changed.
FIG. 3 is a graph showing a relationship between a sample temperature and a change in absorbance of an ethylene-tetrafluoroethylene copolymer.
FIG. 4 is a graph similar to FIG. 3 in a case where the wavelength of light used to measure a change in absorbance is changed.
FIG. 5 is a system configuration diagram of the radiation measuring apparatus according to the first embodiment.
FIG. 6 is a table showing the maximum measurable dose in the radiation measuring device for each wavelength and each sample temperature.
FIG. 7 is a system configuration diagram of a radiation measuring apparatus according to a modification of the first embodiment.
FIG. 8 is a conceptual diagram illustrating a coloring table according to a second embodiment.
[Explanation of symbols]
10 Radiation measuring device
31 Absorbance change calculation means
32 storage means
33 Dose / temperature determination means
36 Coloring Table
36A coloring table
36B coloring table
F Irradiated film (irradiated material)
F1 Irradiated film (irradiated material)
F2 Irradiated film (irradiated material)

Claims

By measuring the change in absorbance when the radiation to be measured is irradiated, the radiation dose for radiation measurement becomes possible to measure the absorbed dose of the radiation and the sample temperature,
An irradiation material for radiation measurement, wherein a portion to be irradiated with the radiation is formed of an ethylene-tetrafluoroethylene copolymer.

A radiation measuring apparatus for determining an absorbed dose of radiation and a sample temperature using the irradiation material according to claim 1,
Absorbance change calculation means for determining a change in absorbance for light of the wavelength by transmitting light of a predetermined wavelength to the irradiation material, storage means for storing predetermined data based on characteristics of the irradiation material, and from the change in absorbance A dose / temperature determining means for determining the absorbed dose and the sample temperature based on the data in the storage means,
The dose / temperature determining means determines an absorbed dose and a sample temperature from changes in absorbance when light of at least two wavelengths is transmitted to an irradiation material irradiated with radiation to be measured. Radiation measurement device.

A radiation measurement method using the irradiation material according to claim 1,
After irradiating the irradiation material with the radiation to be measured, by transmitting light of at least two types of wavelengths to the irradiation material, the absorbance change of the irradiation material is measured for each wavelength, and from each of the wavelengths and each absorbance change. And determining the absorbed dose of the radiation and the sample temperature using data based on the characteristics of the irradiation material.

There is a wavelength range of light and an absorbed dose range where radiation can be measured,
When the expected absorbed dose is located on the upper side of the absorbed dose range, the wavelength on the upper side of the wavelength range is selected, while the expected absorbed dose is on the lower side of the absorbed dose range. 4. The radiation measuring method according to claim 3, wherein when the position is located at the lower limit, a wavelength on the lower limit side of the wavelength range is selected.

A radiation measurement method using the irradiation material according to claim 1,
When the irradiation material is irradiated with the radiation to be measured, the color of the irradiation material is compared with the color of the coloring table which is separately applied for each of the absorbed dose and / or the sample temperature, thereby absorbing the radiation. A radiation measurement method characterized by determining a dose and / or a sample temperature.

A radiation measurement method using the irradiation material according to claim 1,
A radiation measurement method, wherein when the irradiation material is irradiated with radiation to be measured, a distribution of an absorbed dose of the radiation and / or a distribution of a sample temperature is obtained based on a density of a color applied to the irradiation material.