B. Grynyov, N. Gurdzhian, O. Zelenskaya, V. Lyubynskiy, N. Molchanova, L. Mitcay, V. Tarasov
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Influence of PS sizes, energy radiation detected and distance from PS to the source of ionizing radiation (SIR) on the value of MDA precision measurement was studied. Precision coefficients of radionuclides MDA measurement evaluated when changing PS sizes from 500×300×50 mm (7500 cm3) up to 500×500×50 mm (12500 cm3), changing the energy radiation detected from 662 keV (137Cs) until 1332 keV (60Co), changing the distance from the PS to SIR from 10 to 50 cm. The results are presented in Fig. 6—9 and Table. Found, that the greatest contribution to the increase in MDA precision coefficient measurements makes a change in the irradiation geometry. It is shown that when distance from PS to SIR increases from 10 to 50 cm, precision values increase: when registering 137Cs, from 3,9 to 7,0 % (V = 7500 cm3) and from 3,6 to 6,3 % (V = 12500 cm3); when registering 60Co, from 3,1 to 4,3 % (V = 7500 cm3) and from 3,2 to 3,8 % (V = 12500 cm3). \nIt is established, that the obtained results are due to the change in the contribution of background count rate to PS count rate under different measurements conditions. 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引用次数: 0
摘要
本文研究了利用塑料闪烁体(PS)测量γ辐射放射性核素137Cs和60Co的最小可探测活性(MDA)的精度评价。闪烁体是探测器的一部分,是辐射门户监视器(PM)的敏感元件。PS是在乌克兰国家科学院闪烁材料研究所(ISMA NAS of Ukraine)生产的。根据乌克兰国家标准ISO 5725-2:2005[1]对实验材料进行统计处理,得出评价结果。这使得在没有模型方程的情况下考虑决定结果散射的因素成为可能。研究了PS尺寸、检测能量辐射以及PS到电离辐射源(SIR)的距离对MDA精密度测量值的影响。将PS尺寸从500×300×50 mm (7500 cm3)改变到500×500×50 mm (12500 cm3),将检测到的能量辐射从662 keV (137Cs)改变到1332 keV (60Co),将PS到SIR的距离从10改变到50 cm时,评估了放射性核素MDA测量的精度系数。结果如图6-9和表所示。发现,对MDA精度系数测量值的增加贡献最大的是辐照几何形状的变化。结果表明,当从PS到SIR的距离从10 cm增加到50 cm时,精度值增加:当记录137Cs时,从3,9 %增加到7,0 % (V = 7500 cm3),从3,6 %增加到6,3 % (V = 12500 cm3);当注册60Co时,从3,1到4,3 % (V = 7500 cm3)和从3,2到3,8 % (V = 12500 cm3)。结果表明,在不同的测量条件下,背景计数率对PS计数率的贡献发生了变化。这种贡献影响灵敏度系数的值,从而影响MDA和精度系数的值。
Precision Measurements of the Minimum Detectable Activity of Radionuclides by Plastic Scintillators for Radiation Monitoring
This work is devoted to the precision evaluation of the minimum detectable activity (MDA) measurement of gamma radiation radionuclides 137Cs and 60Co using plastic scintillators (PS). Scintillators are part of the detectors, which are sensitive elements of radiation portal monitors (PM). PS were produced at the Institute for scintillation materials of the National Academy of Sciences of Ukraine (ISMA NAS of Ukraine).
The evaluation was generate in accordance with State standard of Ukraine ISO 5725-2:2005 [1] through statistical processing of experimental material. This made it possible to take into account the factors that determine the scattering of results without a model equation. Influence of PS sizes, energy radiation detected and distance from PS to the source of ionizing radiation (SIR) on the value of MDA precision measurement was studied. Precision coefficients of radionuclides MDA measurement evaluated when changing PS sizes from 500×300×50 mm (7500 cm3) up to 500×500×50 mm (12500 cm3), changing the energy radiation detected from 662 keV (137Cs) until 1332 keV (60Co), changing the distance from the PS to SIR from 10 to 50 cm. The results are presented in Fig. 6—9 and Table. Found, that the greatest contribution to the increase in MDA precision coefficient measurements makes a change in the irradiation geometry. It is shown that when distance from PS to SIR increases from 10 to 50 cm, precision values increase: when registering 137Cs, from 3,9 to 7,0 % (V = 7500 cm3) and from 3,6 to 6,3 % (V = 12500 cm3); when registering 60Co, from 3,1 to 4,3 % (V = 7500 cm3) and from 3,2 to 3,8 % (V = 12500 cm3).
It is established, that the obtained results are due to the change in the contribution of background count rate to PS count rate under different measurements conditions. This contribution affects on the value of sensitivity coefficient and consequently on the value of MDA and precision coefficient.