Abstract: The detection efficiency of ²⁴¹Am and natural alpha radionuclide with different mass thickness was analyzed through experiments and Monte Carlo simulation. The relationship between mass thickness and detection efficiency, count rate, detection efficiency correction factor, as well as reciprocal detection efficiency were analyzed. And the relationship between detection efficiency, effective saturation thickness and energy were also analyzed. The results show that the detection efficiency of alpha radionuclide in water needs to be corrected by the detection efficiency correction factor, branch ratio and component ratio. When the mass thickness is 7 mg/cm², the equilibrium uranium detection efficiency correction factor is 0.96; With a mass thickness of 2 mg/cm², the equilibrium thorium detection efficiency correction factor is 1.01, and the equilibrium ²²⁶Ra-²²²Rn detection efficiency correction factor is 1.05. When the mass thickness is greater than 4 mg/cm², the detection efficiency correction factors of natural uranium, 4% enriched uranium and 97% enriched uranium are basically constant, which are 0.39, 039 and 0.47, respectively. When the mass thickness is less than 0.510 mg/cm², the detection efficiency correction factor of single alpha radionuclide radiation source is greater than 0.70. When the mass thickness is greater than the effective saturation thickness, the reciprocal of the detection efficiency is linear with the mass thickness. The effective saturation thickness is linearly related to the alpha ray energy.

Key words: natural alpha radionuclides, mass thickness, detection efficiency, correction factor, effective saturation thickness