Abstract: To address the problems in efficiencycalibration of in-situ radioactivity measuring equipment, an approach to efficiency calibration was presented using point source in lieu of liquid volume source. Through Monte Carlo calculation, photoelectric count efficiency of lanthanumbromide detector to point and volume sources are obtained respectively and the relationship of calibration efficiency were established between point and volumesources for simplified use of efficiency calibration in practice.

Key words: Radioactivity in water, Lanthanum bromide detector, Efficiency calibration