PDF《2017》

2017 IMP & HIRFL Annual Report ・

185 ・ Fig.

1 The schematic drawing of perfusion and exhaust for the CsI(Tl) crystal array. Fig.

2 The pictures of the CsI(Tl) crystal array. Reference [1] E. Seeram, Canadian Journal of Medical Radiation Technology, 36(4)(2006)15. [2] Bo Kyung Cha, Jeong-Hyun Shin, Jun Hyung Bae,et al., Nucl. Instr. Meth. A, 604(1-2)(2009)224.

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8 Study of Testing and Comparison of CsI(Tl) Crystals Coupled with PD under Di?erent Conditions Shi Guozhu, Chen Ruofu, Shen Aihua and Li Hengyuan CsI(Tl) is a kind of the colorless transparent cubic crystal with the advantages of high average atomic number, high density, no cleavage plane, easy processing, radiation resistance, good optical performance, etc. It has high e?ciency used as the x/γ-rays detector[1] . Coupled with silicon photodiode, it is one of the largest scintillation light output in all known scintillation materials with small size, low electric, magnetic ?eld interference, and so on. CsI(Tl) detector can be used for discrimination of ray pulse shape. CsI(Tl) is widely used as excellent performance in high-energy nuclear physics[2,3] , nuclear medicine (such as XCT, PET), geophysics, radiation chemistry, security check, and many other ?elds. To study the optimal energy resolution of CsI(Tl)(size:

50 mm*50 mm) crystals grown by the crystal detector research group, a scintillator detector was developed based on the CsI(Tl) crystal grown at Institute of Modern Physics. The CsI(Tl) crystal was coupled with a high sensitive Hamamastu S3204-08 silicon photodiode(PD), pre- ampli?er(Mesytec), and VME data acquisition system during the measurement, the measurement results under di?erent conditions are shown in the Figs.

1 and 2. Fig.

1 (color online) The test of energy resolution under di?erent conditions. (a) Energy resolution:η=10.34%, (b) Energy resolution: η=8.03%. Condition one: The α source is attached to the CsI(Tl) crystal detector wrapped by several layers of Te?on, there is a Φ5 mm hole between the α source and CsI(Tl) crystal detector, the

70 V voltage is applied to PD by CAMAC voltage plug-in, meanwhile, the CsI(Tl) crystal detector is exposed in the air. From the test results Fig. 1(a), it can be found that the counting rate is too high, the energy trailing phenomenon is very serious, and the energy resolution is also very bad. At last, the energy resolution is 10.34%. Condition two: The only one di?erence relative to the condition one is that a Φ2 mm hole takes place of the Φ5 mm hole. We found that energy resolution was signi?cantly improved and energy resolution of 8.03% was obtained, the test results are shown in the Fig. 1(b). ・

186 ・ IMP & HIRFL Annual Report

2017 Condition three: The only one di?erence relative to the condition two is that the whole CsI(Tl) crystal detector is placed in a vacuum target chamber pumped by molecular pump. We found the energy resolution of CsI(Tl) crystal detector is further improved, the results are shown in Fig. 2(a). Condition four: The only one di?erence relative to the condition three is that the α source is separated from the CsI(Tl) crystal by pegboard with a lot of holes. The best energy resolution of 6.38% was obtained. Fig.

2 (color online) The test of energy resolution under di?erent conditions. (a) Energy resolution:η=7.65%,(b) Energy resolution:η=7.53%. In a word, The most in?uence factor to the energy resolution of CsI(Tl) crystals coupled with PD in process testing is interference of noise from environmental background. If the noise can be reduced, the better energy resolution of the detector will be obtained. References [1] E. Seeram, Canadian Journal of Medical Radiation Technology, 36(4)(2006)15. [2] K. Yue,H. S. XU,Z. Y. SUN,et al., Chin. Phys. C, 35(1)(2011)67. [3] V. D. Ryzhikov, A. D. Opolonin,P. V. Pashko,et al., Nucl. Instr. Meth. A, 537(1-2)(2005)424.