Abstract: To improve the measurement efficiency of low-level radioactivity and to ensure the accuracy and reliability of monitoring data, the authors participated in the proficiency test organized by China Institute for Radiation Protection in 2021. Thick source method with ²⁴¹Am powder and ⁹⁰Sr/⁹⁰Y powder as standard sources was used for determination of gross α and gross β radioactivity in water and aerosol samples. Relative comparison method with ²⁴¹Am solution and ⁹⁰Sr/⁹⁰Y solution as standard sources was used for the determination of gross α and gross β radioactivity in water samples. Results showed that the relative deviation and Z-score of thick source method were 4.2%-18.8% and -0.42 to 0.95, respectively; while the values of relative comparison method were 3.7%-14.4% and -0.13 to 0.72, respectively. The evaluation result was “satisfactory” for both methods. The quality assurance and quality control of low-level α/β radioactivity measurement system in our laboratory are satisfactory and effective. The radioactivity measurement methods and data processing methods are reliable.

Key words: Proficiency test, Gross α and β radioactivity, Thick source, Relative comparison