Abstract: 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.

Key words: environmental background radiation, high-purity germanium detector, sequential decay law