超铀元素肺部计数器的效率刻度技术

EFFICIENCY CALIBRATION OF TRANSURANIC NUCLIDE IN LUNG COUNTER

本文主要介绍了超铀元素肺部计数器的组成、仿真人体躯干模型的研制、探测效率刻度实验及结果等。超铀元素肺部计数器采用了四个平板型低本底高纯锗探测器,核素识别能力强,探测灵敏度高。研制的仿真人体躯干模型符合中国参考人体型。经过实验选取不同的化学试剂作为基质和添加剂,采用发泡技术和解剖尸体建模等方法,使体模中组织或器官的密度、线衰减系数、几何尺寸等参数能够较精确地等效于对应人体组织或器官。通过覆盖不同厚度的盖板,模拟不同胖瘦的人体,应用该体模,对肺部计数器的探测效率进行了刻度,得出了不同能量下不同肌肉等效胸壁厚度的探测效率曲线。实验得出,每个探测器测量体模和对照人的本底分别小于0.0288cps、0.0372cps(241Am的59.5keV全能峰区内积分计数率)。经效率刻度,测量时间为8000s,一类错误概率α和二类错误概率β均为0.05,肌肉等效胸壁厚度MEQ-CWT(17.6keV)为15.7mm,MEQ-CWT(59.5keV)为16.2mm的状况下,系统对239Pu和241Am的探测下限ADL分别为700Bq和3Bq。若采用241Am示踪,对钚镅活度比小于20∶1的钚,其对239Pu探测下限ADL可降低至60Bq。

The paper introduces composition of transuranic nuclide lung counter, development of anthropomorphic phantom, experiment and result of efficiency calibration. Lung counter uses 4 HPGe detectors, with high nuclide identification ability and detection sensitivity. The anthropomorphic phantom accords with the body of Chinese Reference Man. The basal and additive materials were chosen through experiments. The parameters of tissues and apparatus in the phantom, such as density, linear absorption coefficient and geometry are equivalent to parameters of Chinese Man＇s tissues and apparatus. Using overlay plates with different thickness, the body with different size can be simulated. Efficiency curve with different energy and Muscle Equivalent Chest Wall Thickness is obtained using this anthropomorphic phantom. The background of anthropomorphic phantom and reference man is 0.0288 cps, 0.0372 cps for 59.54 keV peak regions of ^241 Am, respectively. The lower limit of detection is 3 Bq for ^241 Am and 700 Bq for ^239pu when the detection time is 8000 s, α =β =0.05. If the radioactivity ratio of ^241Am/^239pu is less than 20, the lower limit of detection is 60 Bq for ^239 Pu when ^241 Am is regarded as a tracer nuclide.