WO2015146424A1 - Radiation-detecting material - Google Patents

Radiation-detecting material Download PDF

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Publication number
WO2015146424A1
WO2015146424A1 PCT/JP2015/055153 JP2015055153W WO2015146424A1 WO 2015146424 A1 WO2015146424 A1 WO 2015146424A1 JP 2015055153 W JP2015055153 W JP 2015055153W WO 2015146424 A1 WO2015146424 A1 WO 2015146424A1
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Prior art keywords
single crystal
radiation
specific resistance
gamma rays
detection material
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PCT/JP2015/055153
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French (fr)
Japanese (ja)
Inventor
太郎 野島
高史 久保田
広己 高橋
優 百武
松澤　雅人
高橋　司
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三井金属鉱業株式会社
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Priority to JP2015515068A priority Critical patent/JPWO2015146424A1/en
Publication of WO2015146424A1 publication Critical patent/WO2015146424A1/en

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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/46—Sulfur-, selenium- or tellurium-containing compounds
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B13/00—Single-crystal growth by zone-melting; Refining by zone-melting
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/032—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
    • H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by at least one potential-jump barrier or surface barrier, e.g. phototransistors
    • H01L31/115—Devices sensitive to very short wavelength, e.g. X-rays, gamma-rays or corpuscular radiation

Definitions

  • the present invention relates to a radiation detection material capable of detecting radiation such as alpha rays, beta rays, and gamma rays.
  • the present invention relates to a direct conversion type radiation detection material that can absorb radiation, particularly gamma rays, and convert it directly into an electrical signal.
  • a direct conversion system that converts radiation directly into electric charge and stores the charge
  • indirect conversion that converts the radiation into light once with a phosphor, and converts the light into electric charge and stores it with a photoconductive layer.
  • Non-Patent Document 1 Non-Patent Document 1
  • the material that can be represented by Tl 4 + 2x S x I 4 has a higher density than CdTe and CdZnTe, so it can not only increase the detection sensitivity of radiation, but also has a large band cap and high specific resistance. Since the energy resolution can be increased and a high-resolution image can be obtained, it is one of the remarkable radiation detection materials.
  • Tl 4 + 2x S x I 4 that has been disclosed in the past is not limited to the numerical value of specific resistance, but PET (positron emission tomography) or SPECT (single photon emission computed tomography) It was not practical for use in radiation detectors such as radiation tomography)).
  • the present invention relates to a radiation detecting material containing a single crystal body which can be represented by Tl 4 + 2x S x I 4 , it can be sufficiently used in a practical radiation detector, such as a PET, a new radiation It is intended to propose a detection material.
  • a radiation detection material having a specific resistance of 1 ⁇ 10 11 ⁇ ⁇ cm or more is proposed.
  • the radiation detection material proposed by the present invention not only absorbs radiation, particularly gamma rays, and can be directly converted into an electric signal, but also has a sufficiently high specific resistance, so that it can be used sufficiently for practical radiation detectors such as PET. Can do.
  • FIG. 3 is an X-ray diffraction profile of a single crystal produced in Example 3.
  • FIG. 4 is a transmission image (photograph) of a detection element produced using the single crystal produced in Example 3.
  • FIG. It is a wave height distribution spectrum before and after irradiating the single crystal produced in Example 3 with gamma rays from a 137 Cs ray source. Similarly, it is a wave height distribution spectrum when the single crystal body of Example 3 is irradiated with gamma rays from a 109 Cd ray source. Similarly, it is a wave height distribution spectrum when the gamma ray from a 241 Am ray source is irradiated to the single crystal body of Example 3.
  • FIG. 6 is a graph plotting the relationship between the x value of the formula: Tl 4 + 2x S x I 4 and the specific resistance of the single crystals produced in Examples 1 to 4 and Comparative Examples 1 to 3.
  • a radiation detection material containing a single crystal (referred to as “the present single crystal”).
  • the density of a single crystal that can be represented by Tl 4 + 2x S x I 4 (where x 0.77 to 1.10) is 7.25 g / cm 3 , and CdTe (6.2 g / cm 3 ) And CdZnTe (6.0 g / cm 3 ), the radiation detection sensitivity can be increased.
  • composition of this single crystal In the composition formula Tl 4 + 2x S x I 4 of this single crystal, it is important that x is 0.77 to 1.10, and among these, 0.83 or more or 1.07 or less is preferable.
  • TlI thallium iodide
  • TlI thallium iodide
  • the ampoule is made an inert gas atmosphere and the heating temperature is made as low as possible, specifically 440 to 450 ° C., while suppressing the evaporation of TlI (thallium iodide)
  • TlI thallium iodide
  • the radiation detection material of the present invention preferably has a specific resistance of 1 ⁇ 10 11 ⁇ ⁇ cm or more, more preferably 1 ⁇ 10 12 ⁇ ⁇ cm or more, and more preferably 1 ⁇ 10 13 ⁇ ⁇ cm or more. Preferably there is. Since the specific resistance of Tl 6 SI 4 that has been disclosed in the past was about 5.7 ⁇ 10 9 ⁇ ⁇ cm to 2.6 ⁇ 10 10 ⁇ ⁇ cm, the specific resistance of the radiation detection material of the present invention is higher than this. Remarkably high.
  • the single crystal body preferably has a purity of 4N or higher, more preferably 6N or higher, and particularly preferably 8N or higher.
  • the ampoule is made an inert gas atmosphere and the heating temperature is set as low as possible. Specifically, by adjusting the temperature to 440 to 450 ° C., the evaporation number of thallium iodide is suppressed and the number of purifications is performed at least 50 times or more. Then, only the high-purity tip is taken out and placed in another ampoule. It is preferable to carry out purification 50 times or more. However, it is not limited to this method.
  • the radiation detection material of the present invention is a direct conversion type radiation detection material capable of absorbing radiation, particularly gamma rays, and converting it directly into an electrical signal.
  • radiation include electromagnetic radiation such as gamma rays and X-rays, and particle radiation such as alpha rays, beta rays, electron beams, proton beams, neutron beams, and heavy particle beams.
  • the radiation detection material of the present invention can be effectively used as a radiation detection material for a radiation medical apparatus such as PET or SPECT.
  • a predetermined amount of TlI (thallium iodide) powder and a predetermined amount of Tl 2 S powder are mixed, and the mixture is sealed in a glass tube and heated to Tl.
  • a method of synthesizing a —SI compound, subjecting the resultant compound to a predetermined purification, and thereafter crystal growth to obtain a single crystal, and polishing as necessary to obtain the present single crystal can be mentioned.
  • single-phase TlI (thallium iodide) and single-phase Tl 2 S are preferably manufactured or purchased and prepared, and these are preferably used as raw materials. At this time, if either TlI (thallium iodide) or Tl 2 S has a heterogeneous phase, there is a high possibility that the produced single crystal will also have a heterogeneous phase. Like a material, it is difficult to make the specific resistance 1 ⁇ 10 11 ⁇ ⁇ cm or more.
  • the atmosphere in the sealed tube when synthesizing the Tl-SI compound is preferably an inert gas atmosphere such as argon, and the heating temperature is preferably 500 to 700 ° C, and more preferably 550 ° C or higher or 650 ° C or lower. More preferably.
  • the heating time is preferably several minutes or longer, preferably 6 hours or longer, and appropriately adjusted depending on the heating temperature.
  • the purification method is extremely important in producing this single crystal.
  • the Tl-SI compound synthesized as described above is put into an ampule, sealed as an inert atmosphere such as argon, and the ampule is heated from the surroundings with a moving heater (zone melt purification). Is preferably performed repeatedly. At this time, after performing the purification at least 50 times while suppressing the evaporation of TlI (thallium iodide) by setting the temperature during the zone purification as low as possible, specifically 440 to 450 ° C., It is preferable to take out only the high-purity tip and place it again in another ampoule, and further purify it 50 times or more.
  • TlI thallium iodide
  • evaporation of TlI thallium iodide
  • evaporation of TlI thallium iodide
  • a high-resistance single crystal can be obtained.
  • the crystal growth method is arbitrary as long as it is a method capable of growing a single crystal.
  • CZ method Czochralski method
  • HB method horizontal Bridgman method
  • VB method vertical Bridgman method
  • TH method traveling heater method
  • the polishing method is also arbitrary. For example, polishing with abrasive paper or wet polishing may be employed as appropriate.
  • the purified product thus obtained was crystal-grown by a traveling heater method (TH method) at a heating temperature of 440 ° C. and a growth rate of 5 mm / hour to obtain a single crystal, which was obtained using a 0.3 ⁇ m alumina abrasive. A single crystal was obtained by buffing.
  • TH method traveling heater method
  • FIG. 2 shows a transmission image (photograph) of the detection element produced using the single crystal produced in Example 3.
  • ⁇ Radiation evaluation: gamma-ray response measurement> The detection element was placed in an Al guard box, and the gold electrode and the external circuit were connected by a spring contact. The output of the detection element was connected to a charge sensitive preamplifier 581K type (manufactured by Clear Pulse Co., Ltd.), and the bias voltage was applied by a bias power source 6661P type (manufactured by Clear Pulse Co., Ltd.).
  • the output from the preamplifier is amplified by a spectroscopic amplifier 4417 type (manufactured by Clear Pulse Co., Ltd.), and the current peak (signal) generated by the interaction with gamma rays using a digital phosphor oscilloscope TDS5052B (manufactured by Tektronix) is used. Observed.
  • the output of the spectroscopic amplifier was processed by an analog / digital converter 1125 type (manufactured by Clear Pulse Co., Ltd.), and a signal for 600 seconds was recorded by a PC.
  • the gamma ray source 1 MBq of 137 Cs, 109 Cd, and 241 Am was used, and the gamma ray source was installed at a distance of 5 mm from the detection element.
  • the gamma-ray response was evaluated according to the following criteria, and the evaluation results are shown in Table 1.
  • ⁇ (good) A signal could be detected with gamma rays from a 137 Cs radiation source, and photoelectric peaks of gamma rays from a 109 Cd radiation source and 241 Am radiation source could be confirmed.
  • ⁇ (fair) Signals could be detected with gamma rays from a 137 Cs source, but no photopeaks of gamma rays from a 109 Cd source and 241 Am source could be confirmed.
  • X (poor) No signal was detected with gamma rays from a 137 Cs source.
  • the specific resistance of the detection element using the example 3 is as high as 1.1 ⁇ 10 13 ⁇ ⁇ cm, so the noise (dark current) at the time of gamma ray detection is low. I was able to suppress it. Similarly, in other examples, noise (dark current) at the time of gamma ray detection could be suppressed to a low level. On the other hand, since the resistance of the detection element using Comparative Example 3 is as low as 7.7 ⁇ 10 5 ⁇ ⁇ cm, noise (dark current) at the time of gamma ray detection has increased. Similarly, the noise (dark current) at the time of gamma ray detection was large for the other comparative examples.
  • FIG. 137 Cs gamma rays could be detected because the wave height distribution spectrum clearly differed with and without gamma ray irradiation.
  • FIG. 4 and FIG. 5 show the wave height distribution spectra of Example 3 when gamma rays from a 109 Cd, 241 Am radiation source are irradiated under the same conditions.
  • Example 3 has an ability to measure gamma dose by discriminating gamma ray energy.
  • Examples 2 and 4 having a large specific resistance 137 Cs gamma rays could be detected, and photoelectric peaks of 109 Cd and 241 Am ray sources were observed.
  • Example 1 gamma rays of 137 Cs could be detected, but no photoelectric peak of gamma rays from 109 Cd, 241 Am source was observed.
  • Comparative Examples 1 to 3 have low specific resistance, 137 Cs gamma rays could not be detected.
  • FIG. 8 plots the relationship between the x value of the formula: Tl 4 + 2x S x I 4 and the specific resistance for Examples 1 to 4 and Comparative Examples 1 to 3. From this figure, in order to detect gamma rays, it is necessary that the specific resistance of the radiation detection material is 10 11 ⁇ ⁇ cm or more, and x expressed in the Tl 4 + 2x S x I 4 equation at that time. Was found to be in the range of 0.77 to 1.10. Desirably, the specific resistance of the single crystal is 10 12 ⁇ ⁇ cm or more, and the range of x at that time is considered to be 0.83 or more or 1.07 or less.
  • the radiation detection material contained, in particular, the radiation detection material having a specific resistance of the single crystal of 1 ⁇ 10 11 ⁇ ⁇ cm or more can confirm ON / OFF of the 37 Cs source with respect to gamma rays.
  • the response signal of 109 Cd, 241 Am radiation source to gamma rays could be confirmed, and the photopeak could be measured. Therefore, it turned out that it can fully be used for practical radiation detectors, such as PET.

Abstract

The present invention relates to a radiation-detecting material comprising a single crystal body that can be represented by Tl4+2xSxI4, and proposes a radiation-detecting material that can be used in a practical radiation detector such as PET. Proposed is a radiation-detecting material comprising a single crystal body that can be represented by the formula Tl4+2xSxI4 (wherein x = 0.77 to 1.10), and particularly, a radiation-detecting material in which the specific resistance of the single crystal body is 1×1011 Ω·cm or greater.

Description

放射線検出材料Radiation detection material
　本発明は、アルファ線、ベータ線、ガンマ線などの放射線を検出できる放射線検出材料に関する。中でも、放射線、特にガンマ線を吸収して直接電気信号に変換できる直接変換型放射線検出材料に関する。 The present invention relates to a radiation detection material capable of detecting radiation such as alpha rays, beta rays, and gamma rays. In particular, the present invention relates to a direct conversion type radiation detection material that can absorb radiation, particularly gamma rays, and convert it directly into an electrical signal.
　放射線検出器としては、放射線を直接電荷に変換して電荷を蓄積する直接変換方式と、放射線を一度、蛍光体で光に変換し、その光を光導電層で電荷に変換し蓄積する間接変換方式がある。
　間接変換方式による放射線検出装置は、小型化するのが困難であるなどの課題を抱えていたため、近年、直接変換方式による放射線検出装置が注目を集めている。 As a radiation detector, a direct conversion system that converts radiation directly into electric charge and stores the charge, and indirect conversion that converts the radiation into light once with a phosphor, and converts the light into electric charge and stores it with a photoconductive layer. There is a method.
Since the indirect conversion type radiation detection apparatus has problems such as difficulty in miniaturization, in recent years, the direct conversion type radiation detection apparatus has attracted attention.
　放射線を吸収して直接電気信号に変換できる材料として、例えばＣｄＴｅやＣｄＺｎＴｅなどが知られている。また、ガンマ線検出材料としてＴｌＢｒが研究されている。
　さらに最近、Ｔｌ6ＳｅＩ4がＸ線を直接電気信号に変換できることが開示され（特許文献１、特許文献２）、Ｔｌ6ＳＩ4についてもＸ線を直接電気信号に変換できることが報告されている（非特許文献１）。 For example, CdTe and CdZnTe are known as materials that can absorb radiation and convert it directly into an electrical signal. Further, TlBr has been studied as a gamma ray detection material.
More recently, it has been disclosed that Tl 6 SeI 4 can directly convert X-rays into electrical signals (Patent Documents 1 and 2), and Tl 6 SI 4 has also been reported to be able to directly convert X-rays into electrical signals. (Non-Patent Document 1).
ＵＳ８５１９３４７Ｂ２US8519347B2 ＷＯ２０１２０２１５１９WO20112021519
　Ｔｌ4+2xＳxＩ4で表すことができる材料は、ＣｄＴｅやＣｄＺｎＴｅに比べて密度が高いため、放射線の検出感度を高くすることができるばかりか、バンドキャップが大きく、比抵抗が高いため、エネルギー分解能を高くすることができ、高解像度の画像を得ることもできるため、注目に値する放射線検出材料の一つである。 The material that can be represented by Tl 4 + 2x S x I 4 has a higher density than CdTe and CdZnTe, so it can not only increase the detection sensitivity of radiation, but also has a large band cap and high specific resistance. Since the energy resolution can be increased and a high-resolution image can be obtained, it is one of the remarkable radiation detection materials.
　ところが、従来開示されていたＴｌ4+2xＳxＩ4は、比抵抗の数値などをみても、ＰＥＴ（positron emission tomography (陽電子放出断層撮影)）やＳＰＥＣＴ（single photon emission computed tomography（単一光子放射断層撮影））などの放射線検出器に使用するには実用性に乏しいものであった。 However, Tl 4 + 2x S x I 4 that has been disclosed in the past is not limited to the numerical value of specific resistance, but PET (positron emission tomography) or SPECT (single photon emission computed tomography) It was not practical for use in radiation detectors such as radiation tomography)).
　そこで本発明は、Ｔｌ4+2xＳxＩ4で表すことができる単結晶体を含有する放射線検出材料に関し、ＰＥＴなどの実用的な放射線検出器に十分に使用することができる、新たな放射線検出材料を提案せんとするものである。 The present invention relates to a radiation detecting material containing a single crystal body which can be represented by Tl 4 + 2x S x I 4 , it can be sufficiently used in a practical radiation detector, such as a PET, a new radiation It is intended to propose a detection material.
　本発明は、式：Ｔｌ4+2xＳxＩ4（式中、ｘ＝０．７７～１．１０）で表すことができる単結晶体を含有する放射線検出材料、中でも、前記単結晶体の比抵抗が１×１０11Ω・ｃｍ以上であることを特徴とする放射線検出材料を提案する。 The present invention relates to a radiation detection material containing a single crystal that can be represented by the formula: Tl 4 + 2x S x I 4 (where x = 0.77 to 1.10). A radiation detection material having a specific resistance of 1 × 10 11 Ω · cm or more is proposed.
　本発明が提案する放射線検出材料は、放射線、特にガンマ線を吸収して直接電気信号に変換できるばかりか、比抵抗が十分に高いため、ＰＥＴなどの実用的な放射線検出器に十分に使用することができる。 The radiation detection material proposed by the present invention not only absorbs radiation, particularly gamma rays, and can be directly converted into an electric signal, but also has a sufficiently high specific resistance, so that it can be used sufficiently for practical radiation detectors such as PET. Can do.
実施例３で作製した単結晶体のＸ線回折プロファイルである。3 is an X-ray diffraction profile of a single crystal produced in Example 3. FIG. 実施例３で作製した単結晶体を使用して作製した検出素子の透過像（写真）である。4 is a transmission image (photograph) of a detection element produced using the single crystal produced in Example 3. FIG. 実施例３で作製した単結晶体に対して137Ｃｓ線源からのガンマ線を照射した前後での波高分布スペクトルである。It is a wave height distribution spectrum before and after irradiating the single crystal produced in Example 3 with gamma rays from a 137 Cs ray source. 同じく実施例３の単結晶体に対して109Ｃｄ線源からのガンマ線を照射したときの波高分布スペクトルである。Similarly, it is a wave height distribution spectrum when the single crystal body of Example 3 is irradiated with gamma rays from a 109 Cd ray source. 同じく実施例３の単結晶体に対して241Ａｍ線源からのガンマ線を照射したときの波高分布スペクトルである。Similarly, it is a wave height distribution spectrum when the gamma ray from a 241 Am ray source is irradiated to the single crystal body of Example 3. FIG. 同じく実施例３の単結晶体のＩ－Ｖカーブである。Similarly, it is an IV curve of the single crystal of Example 3. 比較例３で作製した単結晶体のＩ－Ｖカーブである。4 is an IV curve of a single crystal produced in Comparative Example 3. 実施例１～４及び比較例１～３で作製した単結晶体について、式：Ｔｌ4+2xＳxＩ4のｘ値と、比抵抗との関係をプロットした図である。FIG. 6 is a graph plotting the relationship between the x value of the formula: Tl 4 + 2x S x I 4 and the specific resistance of the single crystals produced in Examples 1 to 4 and Comparative Examples 1 to 3.
　次に、実施の形態例に基づいて本発明を説明する。但し、本発明が次に説明する実施形態に限定されるものではない。 Next, the present invention will be described based on an embodiment. However, the present invention is not limited to the embodiment described below.
＜本発明放射線検出材料＞
　本発明に係る放射線検出材料（以下「本発明放射線検出材料」と称する）は、式：Ｔｌ4+2xＳxＩ4（式中、ｘ＝０．７７～１．１０）で表すことができる単結晶体（「本単結晶体」と称する）を含有する放射線検出材料である。 <Radiation detection material of the present invention>
The radiation detection material according to the present invention (hereinafter referred to as “the radiation detection material of the present invention”) can be represented by the formula: Tl 4 + 2x S x I 4 (where x = 0.77 to 1.10). A radiation detection material containing a single crystal (referred to as “the present single crystal”).
　Ｔｌ4+2xＳxＩ4（式中、ｘ＝０．７７～１．１０）で表すことができる単結晶体の密度は７．２５ｇ／ｃｍ３であり、ＣｄＴｅ（６．２ｇ／ｃｍ３）やＣｄＺｎＴｅ（６．０ｇ／ｃｍ３）に比べて密度が高いため、放射線の検出感度を高くすることができる。また、ガンマγ線の検知に重要な光電効果を起こす確率は、物質の原子番号Ｚの５乗に比例するため、Ｚの大きいＴｌ（Ｚ＝８１）を含むＴｌ4+2xＳxＩ4（式中、ｘ＝０．７７～１．１０）で表すことができる単結晶体は、Ｃｄ（Ｚ＝４８）及びＴｅ（Ｚ＝５２）を含むＣｄＴｅやＣｄＺｎＴｅに比べ、放射線の検出感度を高くすることができる。
　さらに、バンドキャップが大きく、比抵抗が高いため、エネルギー分解能を高くすることができ、高解像度の画像を得ることができる。
　また、Ｔｌ4+2xＳxＩ4（式中、ｘ＝０．７７～１．１０）で表すことができる単結晶体は、素子化において適度な硬度を有しており、潮解性もないため、加工性の問題もない点でも優れている。
　さらに、Ｔｌ4+2xＳxＩ4（式中、ｘ＝０．７７～１．１０）で表すことができる単結晶体の融点は、最高でも４４０℃と低く、ＣｄＴｅ（融点８１９℃）やＣｄＺｎＴｅ（融点１０９２～１２９５℃）といった高融点の物質と比べて結晶製造時の電力コストが低いという点でも生産性にも優れている。 The density of a single crystal that can be represented by Tl 4 + 2x S x I 4 (where x = 0.77 to 1.10) is 7.25 g / cm 3 , and CdTe (6.2 g / cm 3 ) And CdZnTe (6.0 g / cm 3 ), the radiation detection sensitivity can be increased. In addition, since the probability of causing a photoelectric effect important for detection of gamma γ rays is proportional to the fifth power of the atomic number Z of the substance, Tl 4 + 2x Sx I 4 (including Tl with a large Z (Z = 81)) In the formula, a single crystal that can be represented by x = 0.77 to 1.10) has higher radiation detection sensitivity than CdTe and CdZnTe containing Cd (Z = 48) and Te (Z = 52). can do.
Furthermore, since the band cap is large and the specific resistance is high, the energy resolution can be increased and a high-resolution image can be obtained.
In addition, a single crystal that can be represented by Tl 4 + 2x S x I 4 (wherein x = 0.77 to 1.10) has an appropriate hardness in device formation and does not have deliquescence. Therefore, it is excellent in that there is no problem of workability.
Further, the melting point of the single crystal that can be represented by Tl 4 + 2x S x I 4 (wherein x = 0.77 to 1.10) is as low as 440 ° C. at the maximum, and CdTe (melting point 819 ° C.) Compared with a high melting point material such as CdZnTe (melting point: 1092 to 1295 ° C.), it is excellent in productivity in that the power cost at the time of crystal production is low.
（本単結晶体の組成）
　本単結晶体の組成式Ｔｌ4+2xＳxＩ4において、ｘは０．７７～１．１０であることが重要であり、中でも０．８３以上或いは１．０７以下であるのが好ましい。 (Composition of this single crystal)
In the composition formula Tl 4 + 2x S x I 4 of this single crystal, it is important that x is 0.77 to 1.10, and among these, 0.83 or more or 1.07 or less is preferable.
　本単結晶体の組成は、比抵抗を高める観点から、化学量論組成（stoichiometry）であるｘ＝１．０から所定の範囲内、すなわちｘ＝０．７７～１．１０であることが重要である。但し、ｘ＝０．７７～１．１０に制御することは簡単なことではない。後述するように、ゾーンメルト精製（帯域精製）では、ＴｌＩ（ヨウ化タリウム）が蒸発して再混入することによってＴｌＩ（ヨウ化タリウム）リッチになり易いため、後述するような特別な工夫が必要である。例えば、帯溶融精製において、アンプル内を不活性ガス雰囲気とすると共に、加熱温度をできるだけ低温、具体的には４４０～４５０℃にすることで、ＴｌＩ（ヨウ化タリウム）の蒸発を抑制しつつ、精製回数を少なくとも５０回以上行った後、純度の高い先端部のみ取り出し、再度別のアンプルに入れて、さらに５０回以上の精製を行うようにするなどの工夫が必要である。 From the viewpoint of increasing the specific resistance, it is important that the composition of this single crystal is within a predetermined range from x = 1.0 which is a stoichiometric composition, that is, x = 0.77 to 1.10. It is. However, it is not easy to control x = 0.77 to 1.10. As will be described later, in zone melt refining (zone refining), TlI (thallium iodide) tends to become rich by TlI (thallium iodide) evaporation and remixed, so special measures as described later are required. It is. For example, in zone melting and refining, the ampoule is made an inert gas atmosphere and the heating temperature is made as low as possible, specifically 440 to 450 ° C., while suppressing the evaporation of TlI (thallium iodide) After performing the purification at least 50 times or more, it is necessary to devise such that only the high-purity tip is taken out and placed in another ampoule and further purified 50 times or more.
（比抵抗）
　本発明放射線検出材料は、比抵抗が１×１０11Ω・ｃｍ以上であることが好ましく、中でも１×１０12Ω・ｃｍ以上であるのが好ましく、その中でも１×１０13Ω・ｃｍ以上であるのが好ましい。
　従来開示されていたＴｌ6ＳＩ4の比抵抗は５．７×１０9Ω・ｃｍ～２．６×１０10Ω・ｃｍ程度であったため、これに比べて本発明放射線検出材料の比抵抗は顕著に高いことが認められる。このように本発明放射線検出材料の比抵抗が高い原因としては、単結晶体の組成が所定範囲内すなわちｘ＝０．７７～１．１０に制御されており、且つ、不純物が極めて少ないためであると推察することができる。 (Resistivity)
The radiation detection material of the present invention preferably has a specific resistance of 1 × 10 11 Ω · cm or more, more preferably 1 × 10 12 Ω · cm or more, and more preferably 1 × 10 13 Ω · cm or more. Preferably there is.
Since the specific resistance of Tl 6 SI 4 that has been disclosed in the past was about 5.7 × 10 9 Ω · cm to 2.6 × 10 10 Ω · cm, the specific resistance of the radiation detection material of the present invention is higher than this. Remarkably high. As described above, the reason why the specific resistance of the radiation detection material of the present invention is high is that the composition of the single crystal is controlled within a predetermined range, that is, x = 0.77 to 1.10, and the impurities are extremely small. It can be inferred that there is.
（純度）
　本単結晶体は、その純度が４Ｎ以上であるのが好ましく、中でも６Ｎ以上、その中でも８Ｎ以上であるのが特に好ましい。
　上述したように、本単結晶体の組成が所定範囲内すなわちｘ＝０．７７～１．１０に制御されており、且つ、不純物が極めて少ないことに起因して、本発明放射線検出材料の比抵抗を顕著に高くすることができる。 (purity)
The single crystal body preferably has a purity of 4N or higher, more preferably 6N or higher, and particularly preferably 8N or higher.
As described above, the composition of the present single crystal body is controlled within a predetermined range, that is, x = 0.77 to 1.10, and the ratio of the radiation detection material of the present invention is reduced due to extremely few impurities. The resistance can be significantly increased.
　本単結晶体の純度を上記の如く高めて不純物濃度を下げるためには、例えば、後述するように、帯溶融精製において、アンプル内を不活性ガス雰囲気とすると共に、加熱温度をできるだけ低温、具体的には４４０～４５０℃にすることで、ヨウ化タリウムの蒸発を抑制しつつ、精製回数を少なくとも５０回以上行った後、純度の高い先端部のみ取り出し、再度別のアンプルに入れて、さらに５０回以上の精製を行うようにするのが好ましい。但し、この方法に限定するものではない。 In order to increase the purity of the single crystal as described above and reduce the impurity concentration, for example, as described later, in the zone melt purification, the ampoule is made an inert gas atmosphere and the heating temperature is set as low as possible. Specifically, by adjusting the temperature to 440 to 450 ° C., the evaporation number of thallium iodide is suppressed and the number of purifications is performed at least 50 times or more. Then, only the high-purity tip is taken out and placed in another ampoule. It is preferable to carry out purification 50 times or more. However, it is not limited to this method.
＜本発明放射線検出材料の特性＞
　本発明放射線検出材料は、放射線、特にガンマ線を吸収して直接電気信号に変換することができる直接変換型放射線検出材料である。
　放射線としては、ガンマ線やＸ線などの電磁放射線と、アルファ線、ベータ線、電子線、陽子線、中性子線、重粒子線などの粒子放射線とを挙げることができる。 <Characteristics of the radiation detection material of the present invention>
The radiation detection material of the present invention is a direct conversion type radiation detection material capable of absorbing radiation, particularly gamma rays, and converting it directly into an electrical signal.
Examples of radiation include electromagnetic radiation such as gamma rays and X-rays, and particle radiation such as alpha rays, beta rays, electron beams, proton beams, neutron beams, and heavy particle beams.
　本単結晶体、すなわちＴｌ4+2xＳxＩ4（式中、ｘ＝０．７７～１．１０）で表すことができる単結晶体は、密度が高く、放射線、特にガンマ線の検出材料として検出感度を高くすることができる。 This single crystal, that is, a single crystal that can be represented by Tl 4 + 2x S x I 4 (where x = 0.77 to 1.10) has a high density and is used as a material for detecting radiation, particularly gamma rays. Detection sensitivity can be increased.
　本単結晶体を用いて作製した検出素子にバイアス電圧を印加すると、137Ｃｓ線源からのガンマ線が検出素子に入射したときに発生する相互作用により電荷が発生し、電流ピークとしてガンマ線の応答を確認することができる。
　また、本単結晶体を用いて作製した検出素子にバイアス電圧を印加すると、109Ｃｄ線源および241Ａｍ線源のガンマ線に対するシグナルを確認することができ、光電ピークを測定することができる。
　よって、本発明放射線検出材料は、例えばＰＥＴやＳＰＥＣＴなどの放射線医療装置の放射線検出材料として有効に用いることができる。 When a bias voltage is applied to a detection element fabricated using this single crystal, charge is generated by the interaction that occurs when gamma rays from a 137 Cs radiation source enter the detection element, and the response of gamma rays as a current peak is generated. Can be confirmed.
In addition, when a bias voltage is applied to a detection element manufactured using this single crystal body, signals with respect to gamma rays of 109 Cd ray source and 241 Am ray source can be confirmed, and a photoelectric peak can be measured.
Therefore, the radiation detection material of the present invention can be effectively used as a radiation detection material for a radiation medical apparatus such as PET or SPECT.
＜製造方法＞
　本単結晶体の製造方法の一例としては、例えば、所定量のＴｌＩ（ヨウ化タリウム）粉末と、所定量のＴｌ2Ｓ粉末とを混合し、混合物をガラス管内に封入し、加熱してＴｌ－Ｓ－Ｉ化合物を合成し、得られた合成物に対して所定の精製を行い、その後、結晶育成を行って単結晶体を得、必要に応じて研磨して本単結晶体を得る方法を挙げることができる。 <Manufacturing method>
As an example of the method for producing the single crystal, for example, a predetermined amount of TlI (thallium iodide) powder and a predetermined amount of Tl 2 S powder are mixed, and the mixture is sealed in a glass tube and heated to Tl. A method of synthesizing a —SI compound, subjecting the resultant compound to a predetermined purification, and thereafter crystal growth to obtain a single crystal, and polishing as necessary to obtain the present single crystal Can be mentioned.
　原料としては、単相のＴｌＩ（ヨウ化タリウム）及び単相のＴｌ2Ｓを、それぞれ製造するか或いは購入して用意し、これらを原料として用いて製造するのが好ましい。
　この際、ＴｌＩ（ヨウ化タリウム）及びＴｌ2Ｓのいずれかが異相を有するものであると、製造される単結晶体も異相を有するものとなる可能性が高くなり、例えば、本発明放射線検出材料のように、比抵抗を１×１０11Ω・ｃｍ以上とすることが困難となる。 As raw materials, single-phase TlI (thallium iodide) and single-phase Tl 2 S are preferably manufactured or purchased and prepared, and these are preferably used as raw materials.
At this time, if either TlI (thallium iodide) or Tl 2 S has a heterogeneous phase, there is a high possibility that the produced single crystal will also have a heterogeneous phase. Like a material, it is difficult to make the specific resistance 1 × 10 11 Ω · cm or more.
　Ｔｌ－Ｓ－Ｉ化合物を合成する際の密閉管内の雰囲気としては、アルゴンなどの不活性ガス雰囲気が好ましく、その際の加熱温度としては５００～７００℃が好ましく、中でも５５０℃以上或いは６５０℃以下であるのがさらに好ましい。加熱時間は、数分以上、好ましくは６時間以上で加熱温度により適宜調整するのが好ましい。 The atmosphere in the sealed tube when synthesizing the Tl-SI compound is preferably an inert gas atmosphere such as argon, and the heating temperature is preferably 500 to 700 ° C, and more preferably 550 ° C or higher or 650 ° C or lower. More preferably. The heating time is preferably several minutes or longer, preferably 6 hours or longer, and appropriately adjusted depending on the heating temperature.
　精製方法は、本単結晶体を製造する上で極めて重要である。
　例えば、上述のようにして合成したＴｌ－Ｓ－Ｉ化合物をアンプルに入れて、アルゴンなどの不活性雰囲気として密封し、このアンプルを、移動型ヒーターで周囲から加熱する帯域精製（ゾーンメルト精製）を繰り返し行うのが好ましい。
　この際、帯域精製の際の温度をできるだけ低温、具体的には４４０～４５０℃にすることで、ＴｌＩ（ヨウ化タリウム）の蒸発を抑制しながら、精製回数を少なくとも５０回以上行った後、純度の高い先端部のみ取り出し、再度別のアンプルに入れて、さらに５０回以上の精製を行うのが好ましい。
　これにより、ＴｌＩ（ヨウ化タリウム）の蒸発を抑制することができ、しかも、蒸発したＴｌＩ（ヨウ化タリウム）が再混入することを抑制することができるため、１×１０11Ω・ｃｍ以上という高抵抗の単結晶を得ることができる。 The purification method is extremely important in producing this single crystal.
For example, the Tl-SI compound synthesized as described above is put into an ampule, sealed as an inert atmosphere such as argon, and the ampule is heated from the surroundings with a moving heater (zone melt purification). Is preferably performed repeatedly.
At this time, after performing the purification at least 50 times while suppressing the evaporation of TlI (thallium iodide) by setting the temperature during the zone purification as low as possible, specifically 440 to 450 ° C., It is preferable to take out only the high-purity tip and place it again in another ampoule, and further purify it 50 times or more.
Thereby, evaporation of TlI (thallium iodide) can be suppressed, and furthermore, evaporation of TlI (thallium iodide) can be suppressed from being mixed again, so that it is 1 × 10 11 Ω · cm or more. A high-resistance single crystal can be obtained.
　結晶育成方法は、単結晶を育成できる方法であれば任意である。例えば、チョクラルスキー法（ＣＺ法）、徐冷法、水平ブリッジマン法（ＨＢ法）、垂直ブリッジマン法（ＶＢ法）、トラベリングヒーター法（ＴＨ法）などを挙げることができる。 The crystal growth method is arbitrary as long as it is a method capable of growing a single crystal. For example, the Czochralski method (CZ method), the slow cooling method, the horizontal Bridgman method (HB method), the vertical Bridgman method (VB method), the traveling heater method (TH method) and the like can be mentioned.
　研磨法も任意であり、例えば研磨紙による研磨や、湿式研磨を適宜採用すればよい。 The polishing method is also arbitrary. For example, polishing with abrasive paper or wet polishing may be employed as appropriate.
＜語句の説明＞ 
　本明細書において「Ｘ～Ｙ」（Ｘ，Ｙは任意の数字）と表現する場合、特にことわらない限り「Ｘ以上Ｙ以下」の意と共に、「好ましくはＸより大きい」或いは「好ましくはＹより小さい」の意も包含する。
　また、「Ｘ以上」（Ｘは任意の数字）或いは「Ｙ以下」（Ｙは任意の数字）と表現した場合、「Ｘより大きいことが好ましい」或いは「Ｙ未満であることが好ましい」旨の意図も包含する。 <Explanation of words>
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” or “preferably Y”, with the meaning of “X to Y” unless otherwise specified. It also includes the meaning of “smaller”.
In addition, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is “preferably greater than X” or “preferably less than Y”. Includes intentions.
　以下、本発明を下記実施例及び比較例に基づいてさらに詳述する。 Hereinafter, the present invention will be described in further detail based on the following examples and comparative examples.
＜単結晶体の作製＞
　単相のＴｌＩ（ヨウ化タリウム）（４Ｎ）と単相のＴｌ2Ｓ（４Ｎ）の量を、実施例・比較例毎に変えて混合し、混合物をガラス管内に封入し（アルゴン０．５ａｔｍ）、６００℃で６時間加熱してＴｌ－Ｓ－Ｉ化合物を合成した。得られた合成物を、４４０℃で帯域精製を繰り返し５０回行った後、純度の高い先端部のみ取り出してガラス製アンプル内に封入し（アルゴン０．５ａｔｍ）、再び４４０℃で帯域精製を繰り返し５０回行い、精製品を得た。
　こうして得られた精製品を、トラベリングヒーター法（ＴＨ法）により、加熱温度４４０℃、育成速度５ｍｍ／時間で結晶育成して単結晶体を得、これを０．３μｍのアルミナ研磨剤を用いてバフ研磨して単結晶体を得た。 <Production of single crystal>
The amounts of single-phase TlI (thallium iodide) (4N) and single-phase Tl 2 S (4N) were mixed for each of the Examples and Comparative Examples, and the mixture was sealed in a glass tube (Argon 0.5 atm). ) And heated at 600 ° C. for 6 hours to synthesize a Tl-SI compound. The obtained compound was subjected to repeated zone purification at 440 ° C. 50 times, then only the high-purity tip was taken out and sealed in a glass ampoule (Argon 0.5 atm), and the zone purification was repeated again at 440 ° C. The purified product was obtained 50 times.
The purified product thus obtained was crystal-grown by a traveling heater method (TH method) at a heating temperature of 440 ° C. and a growth rate of 5 mm / hour to obtain a single crystal, which was obtained using a 0.3 μm alumina abrasive. A single crystal was obtained by buffing.
＜組成測定＞
　前記のようにして単結晶体を秤量して塩酸と硝酸の混合物中で溶解し、適宜希釈した後ＩＣＰ発光分析装置により液中のＴｌ、Ｓ、Ｉの定量を行った。単結晶体の重量と希釈率により、単結晶体のＴｌ、Ｓ、Ｉ組成（重量％）を算出した。各Ｔｌ、Ｓ、Ｉ組成値から、式：Ｔｌ4+2xＳxＩ4におけるｘを算出し表１に示した。 <Composition measurement>
The single crystal was weighed as described above, dissolved in a mixture of hydrochloric acid and nitric acid, diluted as appropriate, and then Tl, S, and I in the liquid were quantified using an ICP emission spectrometer. The Tl, S, and I composition (% by weight) of the single crystal was calculated from the weight and dilution rate of the single crystal. From the respective Tl, S, and I composition values, x in the formula: Tl 4 + 2x S x I 4 was calculated and shown in Table 1.
＜ＸＲＤ測定＞
　前記のようにして得られた単結晶体をメノウ乳鉢で粉砕し、粉末Ｘ線回折測定（ＸＲＤ測定）を行った。測定装置は、試料水平型強力Ｘ線回折装置 RINT-TTR III（株式会社リガク製）を用いた。測定にはＣｕＫα線を用い、加速電圧は５０ｋＶ、印加電流は３００ｍＡとした。実施例３で作製した単結晶体のＸ線プロファイルを図１に示す。
　ＸＲＤ測定した結果、実施例１～４及び比較例１～３で作製した単結晶体はいずれも、単相のＴｌ６ＳＩ４からなる単結晶体であることが分かった。 <XRD measurement>
The single crystal obtained as described above was pulverized in an agate mortar, and powder X-ray diffraction measurement (XRD measurement) was performed. As a measuring apparatus, a sample horizontal strong X-ray diffractometer RINT-TTR III (manufactured by Rigaku Corporation) was used. CuKα rays were used for the measurement, the acceleration voltage was 50 kV, and the applied current was 300 mA. An X-ray profile of the single crystal produced in Example 3 is shown in FIG.
As a result of XRD measurement, it was found that all the single crystals produced in Examples 1 to 4 and Comparative Examples 1 to 3 were single crystals composed of single-phase Tl 6 SI 4 .
＜検出素子の作製＞
　前記のようにして単結晶体を、０．３μｍのアルミナ研磨剤を用いてバフ研磨して、０．３～１．５ｍｍの厚みの平板状の単結晶体を得た。これをアセトン中で超音波洗浄した後、室温で乾燥させ、真空蒸着機ＳＶＣ－７００（サンユー電子株式会社製）にセットした。金ワイヤーをタングステン製電極にセットして、５×１０－３Ｐａに真空引きをした後、電流約３５ｍＡで加熱し、単結晶体へ金を蒸着させ、厚さ約１００ｎｍ、直径３ｍｍの電極を形成し、検出素子を得た。
　実施例３で作製した単結晶体を使用して作製した検出素子の透過像（写真）を図２に示す。 <Preparation of detection element>
The single crystal was buffed using 0.3 μm alumina abrasive as described above to obtain a flat single crystal having a thickness of 0.3 to 1.5 mm. This was ultrasonically washed in acetone, then dried at room temperature, and set in a vacuum deposition machine SVC-700 (manufactured by Sanyu Electronics Co., Ltd.). A gold wire is set on a tungsten electrode, vacuumed to 5 × 10 −3 Pa, heated at a current of about 35 mA to deposit gold on the single crystal, and an electrode having a thickness of about 100 nm and a diameter of 3 mm is formed. The detection element was obtained.
FIG. 2 shows a transmission image (photograph) of the detection element produced using the single crystal produced in Example 3.
＜放射線評価：ガンマ線応答測定＞
　検出素子をＡｌ製のガードボックス内に納め、金電極と外部回路との接続はバネ接点によって行った。検出素子の出力を電荷敏感型プリアンプ５８１Ｋ型（クリアパルス株式会社製）に接続し、バイアス電圧の印加はバイアス電源６６６１Ｐ型（クリアパルス株式会社製）により行った。プリアンプからの出力は、スペクトロスコピー・アンプ４４１７型（クリアパルス株式会社製）で増幅し、デジタル・フォスファ・オシロスコープＴＤＳ５０５２Ｂ（テクトロニクス社製）を用いてガンマ線との相互作用で生じる電流ピーク（シグナル）を観察した。波高分布スペクトルの計測は、スペクトロスコピー・アンプの出力をアナログ／デジタル変換機１１２５型（クリアパルス株式会社製）で処理し、６００秒間の信号をＰＣで記録した。ガンマ線源としては、１ＭＢｑの137Ｃｓ、109Ｃｄ、241Ａｍを用い、ガンマ線測定時は検出素子から５ｍｍの距離に設置した。 <Radiation evaluation: gamma-ray response measurement>
The detection element was placed in an Al guard box, and the gold electrode and the external circuit were connected by a spring contact. The output of the detection element was connected to a charge sensitive preamplifier 581K type (manufactured by Clear Pulse Co., Ltd.), and the bias voltage was applied by a bias power source 6661P type (manufactured by Clear Pulse Co., Ltd.). The output from the preamplifier is amplified by a spectroscopic amplifier 4417 type (manufactured by Clear Pulse Co., Ltd.), and the current peak (signal) generated by the interaction with gamma rays using a digital phosphor oscilloscope TDS5052B (manufactured by Tektronix) is used. Observed. For measurement of the pulse height distribution spectrum, the output of the spectroscopic amplifier was processed by an analog / digital converter 1125 type (manufactured by Clear Pulse Co., Ltd.), and a signal for 600 seconds was recorded by a PC. As the gamma ray source, 1 MBq of 137 Cs, 109 Cd, and 241 Am was used, and the gamma ray source was installed at a distance of 5 mm from the detection element.
　ガンマ線応答性を次の基準で評価し、評価結果を表１に示した。
　○（good）: 137Ｃｓ線源のガンマ線でシグナルが検出でき、且つ、109Ｃｄ線源のガンマ線及び241Ａｍ線源のガンマ線の光電ピークが確認できた。
　△（fair）: 137Ｃｓ線源のガンマ線でシグナルが検出できたが、109Ｃｄ線源のガンマ線及び241Ａｍ線源のガンマ線の光電ピークが確認できなかった。
　×（poor）: 137Ｃｓ線源のガンマ線でシグナルが検出できなかった。 The gamma-ray response was evaluated according to the following criteria, and the evaluation results are shown in Table 1.
○ (good): A signal could be detected with gamma rays from a 137 Cs radiation source, and photoelectric peaks of gamma rays from a 109 Cd radiation source and 241 Am radiation source could be confirmed.
Δ (fair): Signals could be detected with gamma rays from a 137 Cs source, but no photopeaks of gamma rays from a 109 Cd source and 241 Am source could be confirmed.
X (poor): No signal was detected with gamma rays from a 137 Cs source.
＜比抵抗測定＞
　検出素子をＡｌ製のガードボックス内に納め、金電極と外部回路との接続はバネ接点によって行った。検出素子の出力をＢＮＣの同軸ケーブルにてデジタルエレクトロメーターＲ８２５２（株式会社エーディーシー製）に接続し、Ｉ－Ｖ測定を実施した。Ｉ－Ｖ測定の傾きから、検出素子の抵抗Ｒ（Ω）を求めた。また、単結晶体の比抵抗ρ（Ω・ｃｍ）は、以下の式から算出した。ただし、Ｓは電極の面積（ｃｍ２）、ｄは検出素子の厚み（ｃｍ）である。
　ρ＝Ｒ・Ｓ／ｄ
　図６に実施例３、図７に比較例３のＩ－Ｖカーブを示した。
　実施例１～４及び比較例１～３について、ｘと、比抵抗と、ガンマ線測定の結果を表１に示す。 <Specific resistance measurement>
The detection element was placed in an Al guard box, and the gold electrode and the external circuit were connected by a spring contact. The output of the detection element was connected to a digital electrometer R8252 (manufactured by ADC Corporation) with a BNC coaxial cable, and IV measurement was performed. From the slope of the IV measurement, the resistance R (Ω) of the detection element was obtained. The specific resistance ρ (Ω · cm) of the single crystal was calculated from the following equation. However, S is an area (cm < 2 >) of an electrode, d is the thickness (cm) of a detection element.
ρ = R · S / d
FIG. 6 shows the IV curve of Example 3 and FIG. 7 shows the comparative example 3.
Table 1 shows the results of x, specific resistance, and gamma ray measurement for Examples 1 to 4 and Comparative Examples 1 to 3.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
（考察）
　実施例・比較例の比抵抗についてみると、実施例３を用いた検出素子の比抵抗は１．１×１０１３Ω・ｃｍと非常に高いため、ガンマ線検出時のノイズ（暗電流）を低く抑えることができた。他の実施例についても、同様にガンマ線検出時のノイズ（暗電流）を低く抑えることができた。
　他方、比較例３を用いた検出素子の抵抗は７．７×１０５Ω・ｃｍと低いため、ガンマ線検出時のノイズ（暗電流）が大きくなってしまった。他の比較例についても、同様にガンマ線検出時のノイズ（暗電流）は大きいものであった。 (Discussion)
As for the specific resistance of the example and comparative example, the specific resistance of the detection element using the example 3 is as high as 1.1 × 10 13 Ω · cm, so the noise (dark current) at the time of gamma ray detection is low. I was able to suppress it. Similarly, in other examples, noise (dark current) at the time of gamma ray detection could be suppressed to a low level.
On the other hand, since the resistance of the detection element using Comparative Example 3 is as low as 7.7 × 10 5 Ω · cm, noise (dark current) at the time of gamma ray detection has increased. Similarly, the noise (dark current) at the time of gamma ray detection was large for the other comparative examples.
　実施例３の検出素子に８００Ｖのバイアス電圧を印加して137Ｃｓ線源を近づけると、シグナルが確認できた。ガンマ線照射前後での実施例３の波高分布スペクトルを図３に示す。ガンマ線照射の有無で明確に波高分布スペクトルが異なるため、137Ｃｓのガンマ線を検知できた。また、同条件で109Ｃｄ、241Ａｍ線源からのガンマ線を照射したときの実施例３の波高分布スペクトルを図４、図５に示す。
　109Ｃｄの２２ｋｅＶ、８８ｋｅＶ、241Ａｍの５９．５ｋｅＶのエネルギーのガンマ線による光電ピークが明確に判別できる。このことから、実施例３はガンマ線のエネルギーを弁別してガンマ線量を計測できる能力を有すると考えられる。 When a bias voltage of 800 V was applied to the detection element of Example 3 and a 137 Cs radiation source was brought closer, a signal could be confirmed. The wave height distribution spectrum of Example 3 before and after gamma ray irradiation is shown in FIG. 137 Cs gamma rays could be detected because the wave height distribution spectrum clearly differed with and without gamma ray irradiation. In addition, FIG. 4 and FIG. 5 show the wave height distribution spectra of Example 3 when gamma rays from a 109 Cd, 241 Am radiation source are irradiated under the same conditions.
The photoelectric peaks due to gamma rays with 109 Cd of 22 keV, 88 keV, and 241 Am of 59.5 keV can be clearly distinguished. From this, it is considered that Example 3 has an ability to measure gamma dose by discriminating gamma ray energy.
　実施例１の検出素子に１００Ｖのバイアス電圧を印加して137Ｃｓ線源を近づけると、シグナルが確認できたため、ガンマ線への応答が可能なことを確認した。しかし、109Ｃｄ、241Ａｍ線源からのガンマ線を照射したときの波高分布スペクトルでは、光電ピークが確認できないため、ガンマ線検出素子としての能力は実施例３に比べると劣るものであった。これは、組成分析結果で得られたｘが小さく、比抵抗が低いためであると考えられる。
　他方、比較例１～３のように比抵抗が低い単結晶体を用いた検出素子の場合、検出素子に137Ｃｓ線源を近づけてもシグナルが確認できなかった。これは、ガンマ線との相互作用による電流が流れないか、もしくは信号が弱くノイズに埋もれてしまうためと考えられる。 When a bias voltage of 100 V was applied to the detection element of Example 1 and a 137 Cs radiation source was brought closer, a signal was confirmed, and it was confirmed that a response to gamma rays was possible. However, in the wave height distribution spectrum when gamma rays from a 109 Cd, 241 Am radiation source were irradiated, the photoelectric peak could not be confirmed, so the ability as a gamma ray detection element was inferior to that of Example 3. This is considered to be because x obtained from the composition analysis result is small and the specific resistance is low.
On the other hand, in the case of the detection element using a single crystal having a low specific resistance as in Comparative Examples 1 to 3, no signal was confirmed even when a 137 Cs radiation source was brought close to the detection element. This is presumably because current due to interaction with gamma rays does not flow or the signal is weak and buried in noise.
　比抵抗の大きい実施例２、３、４については、137Ｃｓのガンマ線を検知でき、109Ｃｄ、241Ａｍ線源のガンマ線の光電ピークを観測できた。実施例１は137Ｃｓのガンマ線を検知できたが、109Ｃｄ、241Ａｍ線源のガンマ線の光電ピークは観測されなかった。
　一方で、比較例１～３は比抵抗が低いため、137Ｃｓのガンマ線を検知できなかった。 In Examples 2, 3, and 4 having a large specific resistance, 137 Cs gamma rays could be detected, and photoelectric peaks of 109 Cd and 241 Am ray sources were observed. In Example 1, gamma rays of 137 Cs could be detected, but no photoelectric peak of gamma rays from 109 Cd, 241 Am source was observed.
On the other hand, since Comparative Examples 1 to 3 have low specific resistance, 137 Cs gamma rays could not be detected.
　図８に、実施例１～４及び比較例１～３について、式：Ｔｌ4+2xＳxＩ4のｘ値と比抵抗との関係をプロットした。
　この図から、ガンマ線を検出するためには、放射線検出材料の比抵抗が１０１１Ω・ｃｍ以上あることが必要であり、そのときのＴｌ4+2xＳxＩ4式中で表されるｘの範囲は０．７７～１．１０であることを見出した。望ましくは、単結晶体の比抵抗が１０１２Ω・ｃｍ以上であり、そのときのｘの範囲は０．８３以上或いは１．０７以下であると考えられる。 FIG. 8 plots the relationship between the x value of the formula: Tl 4 + 2x S x I 4 and the specific resistance for Examples 1 to 4 and Comparative Examples 1 to 3.
From this figure, in order to detect gamma rays, it is necessary that the specific resistance of the radiation detection material is 10 11 Ω · cm or more, and x expressed in the Tl 4 + 2x S x I 4 equation at that time. Was found to be in the range of 0.77 to 1.10. Desirably, the specific resistance of the single crystal is 10 12 Ω · cm or more, and the range of x at that time is considered to be 0.83 or more or 1.07 or less.
　上記実施例及びこれまで発明者が行ってきた試験結果などから、式：Ｔｌ4+2xＳxＩ4（式中、ｘ＝０．７７～１．１０）で表すことができる単結晶体を含有する放射線検出材料、中でも、前記単結晶体の比抵抗が１×１０11Ω・ｃｍ以上である放射線検出材料であれば、37Ｃｓ線源のガンマ線に対するＯＮ／ＯＦＦを確認することができるばかりか、109Ｃｄ、241Ａｍ線源のガンマ線に対する応答シグナルを確認することができ、光電ピークを測定することができた。よって、ＰＥＴなどの実用的な放射線検出器に十分に使用することができることが分かった。 From the above examples and the results of tests conducted by the inventors so far, a single crystal that can be represented by the formula: Tl 4 + 2x S x I 4 (where x = 0.77 to 1.10) is obtained. The radiation detection material contained, in particular, the radiation detection material having a specific resistance of the single crystal of 1 × 10 11 Ω · cm or more can confirm ON / OFF of the 37 Cs source with respect to gamma rays. In addition, the response signal of 109 Cd, 241 Am radiation source to gamma rays could be confirmed, and the photopeak could be measured. Therefore, it turned out that it can fully be used for practical radiation detectors, such as PET.

Claims (4)

  1. 　式：Ｔｌ4+2xＳxＩ4（式中、ｘ＝０．７７～１．１０）で表すことができる単結晶体を含有する放射線検出材料。 A radiation detection material containing a single crystal that can be represented by the formula: Tl 4 + 2x S x I 4 (where x = 0.77 to 1.10).
  2. 　前記単結晶体の比抵抗が１×１０11Ω・ｃｍ以上であることを特徴とする請求項1に記載の放射線検出材料。 2. The radiation detection material according to claim 1, wherein the specific resistance of the single crystal body is 1 × 10 11 Ω · cm or more.
  3. 　前記単結晶体は、単相のＴｌＩ（ヨウ化タリウム）及び単相のＴｌ2Ｓを原料として製造された単結晶体であることを特徴とする請求項１又は２に記載の放射線検出材料。 The radiation detection material according to claim 1, wherein the single crystal is a single crystal manufactured using single-phase TlI (thallium iodide) and single-phase Tl 2 S as raw materials.
  4. 　ガンマ線検出材料であることを特徴とする請求項１～３の何れかに記載の放射線検出材料。 The radiation detection material according to any one of claims 1 to 3, which is a gamma ray detection material.
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WO2004077098A1 (en) * 2003-02-27 2004-09-10 Kabushiki Kaisha Toshiba X-ray detector and x-ray examination device using it
US20120153178A1 (en) * 2010-08-10 2012-06-21 Northwestern University Methods and compositions for the detection of x-ray and gamma-ray radiation
JP2013241289A (en) * 2012-05-18 2013-12-05 Jx Nippon Mining & Metals Corp Compound semiconductor crystal for radiation detection element, radiation detection element, radiation detector, and method for producing compound semiconductor crystal for radiation detection element

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Publication number Priority date Publication date Assignee Title
WO2004077098A1 (en) * 2003-02-27 2004-09-10 Kabushiki Kaisha Toshiba X-ray detector and x-ray examination device using it
US20120153178A1 (en) * 2010-08-10 2012-06-21 Northwestern University Methods and compositions for the detection of x-ray and gamma-ray radiation
JP2013241289A (en) * 2012-05-18 2013-12-05 Jx Nippon Mining & Metals Corp Compound semiconductor crystal for radiation detection element, radiation detection element, radiation detector, and method for producing compound semiconductor crystal for radiation detection element

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