Detection of abnormal radioactivity by gamma spectrum block counting method in environmental monitoring

The block counting method is employed to explore whether a sodium iodide (NAI) detector can detect abnormal radioactivity is environmental monitoring, and to determine the specific value of early warning value. Four kinds of radioactive sources, ⁴⁰K, ¹³³Ba, ²⁴¹Am and ⁶⁰Co, were used for the experiment. The results show that it is feasible to use the method to detect abnormal radioactivity. The early warning value should be set to be greater than the mean value of background count plus 1-1.5 times the standard deviation of background count. (authors)