4πγ井型NaI(Tl)晶体探测器性能研究和初步实验结果

Study and Preliminary Results of the 4πy Well-type Nal （TI） Crystal Detector

介绍了中国计量科学研究院用于测量放射性核素活度的4πy井型NaI（T1）晶体装置。通过分析测量得到的印co放射源发射的y射线能谱发现，采用4πy井型NaI（T1）晶体对衰变纲图较为复杂的核素进行测量时存在相加峰效应。当放射源从井型NaI（TI）晶体井口附近逐渐移至井底的过程中，相加峰的计数率逐渐增加，从而使得对60co特征y射线全能峰探测效率逐渐降低；此外，由于在井口附近探测器对放射源所张立体角相对较小，对1射线的探测效率也较低；放射源在井型晶体内的位置发生变化也会对探测器的能量刻度带来影响。

4πy well-type NaI （T1） crystal counting device for gamma-ray detection at NIM is introduced. By analyzing the detected gamma spectrum of 60Co, it is found that the sum-peak counting effect is inevitable for nuclei with complex decay scheme using 4πy well-type NaI （T1） crystal. Further, a series of test experiments are carried out to investigate the performance of detector by changing the depth of 60Co source in the well. The results reveal that the sum- peak counting rate increases as the source moved to the bottom of the well, and the efficiency for full-energy peak has a slight reduction for the increasing sum-peak effect. Besides, the efficiency is reasonable lower at the mouth of the well-type NaI（T1） crystal for the smaller solid angle coverage. Moreover, the energy calibration is also effected by the variation of source position.