Preparation of Low-level Environmental Radionuclide Calibration Samples for Proficiency Tests

Loess samples collected at mountain ridge sites on loess plateau terrain were selected as matrices for soil reference materials. Low-level environmental radionuclide calibration samples were made through a non-blending environmental radionuclides method. Homogeneity and reference samples values were determined using two distinct gamma spectrometry systems. The measurement results indicated that the activity of ¹³⁷Cs was 4.2 Bq/kg with an uncertainty of 0.3 Bq/kg(1s), the activity of ²¹⁰Pb was 80.4 Bq/kg with an uncertainty of 8.4 Bq/kg (1s). The reference samples did not contain any other artificial radionuclides, so the content was both appropriate and uniform. The results of a homogeneity test using oneway ANOVA analysis indicated that the standard deviation of ¹³⁷Cs and ²¹⁰Pb activity were 0.22 Bq/kg, 2.10 Bq/kg, respectively, and the activity of ¹³⁷Cs and ²¹⁰Pb between the 3 proficiency test (PT) sample groups exhibited no significant differences at the 0.05 level, indicating relatively good uniformity. The PT samples have been distributed to six laboratories of IAEA cooperation projects in the Asia-Pacific region for proficiency test in ¹³⁷Cs and ²¹⁰Pb environmental radionuclides activity measurement, and the results showed good uniformity and stability in the PT samples.