环境中天然伽马射线主要来源于⁴⁰ K 以及钍系、铀系和锕系. 通过探测伽马射线来识别放射性核素并得到它们的相对含量，是核科学与核技术中的一个重要方法. 利用高分辨的高纯锗探测器，北航以及国内部分高校已开设了鉴别环境中放射性核素的实验. 在此基础上，本文进一步利用特征 γ 射线与递次衰变规律，对北航沙河校区土壤中的⁴⁰ K、²³⁸ U 和²³² Th 的相对含量进行了测量，结果与普查数据一致.

The natural gamma rays in environment mainly come from ⁴⁰K and the thorium

series，uranium series and actinium series. It is an important method to identify the relevant

radioactive nuclides and determine the relative abundances in nuclear science and

technology. At Beihang and some domestic universities， a lab experiment is developed

to identify the radioactive nuclides in environment via characteristic gamma rays by

using the high-resolution high-purity germanium detectors. In this paper，a new lab

experiment to deduce the relative abundances of ⁴⁰K，238 U，and ²³²Th in the soil at Beihang

Shahe Campus is reported，which is done by using their characteristic gamma rays and successive

decays. The results are consistent with the previous data measured

in 1985.