In-situ measurement of surface radioactivity in nuclear emergency response

The in-situ measurement method of ground surface radioactivity based on HPGe γ spectrometer in nuclear emergency response is studied. The key to measuring the surface activity of the ground is the calibrating of detection efficiency, which is obtained by the numerical integration method in this paper. The HPGe γ-spectrometer is set up at the height of 1 m from the ground, with the detector direction vertically downward. First, the experimental method obtains the point source detection efficiency of the spectrometer for different energies of γ-rays at different horizontal distances. Then, 95% of the maximum contribution of the count rate is defined as the effective contribution region. Finally, with the effective contribution region as the integration limit, the point source detection efficiency as the integrand, the detection efficiency of the spectrometer for surface radioactive sources is obtained by numerical integration. The surface activity is calculated based on the detection efficiency. The method is experimentally validated by stitching hexagonal radioactive surface sources with a side length of 1m. The relative deviation of the surface activity results obtained by the numerical integration method from the experimental standard value is 5.48%, which verifies the validity of the method. • HPGe γ spectrometer used for surface radioactivity measurement in nuclear emergency. • The efficiency calibration method based on numerical integration is simple and practical. • Experimental verification uses the spliced hexagonal radioactive surface source.