COMPARISON OF NAA METHODS TO DETERMINE MEDIUM-LIVED RADIONUCLIDES IN NIST SOIL STANDARD REFERENCE MATERIALS

In order to determine the elemental concentrations of three new soil s tandard reference materials SRMs 2709, 2710 and 2711 from the National Institute of Standards and Technology (NIST), a comparative study of different medium-lived neutron activation analysis methods was careful ly performed. Three irradiation conditions (1-hour thermal, 1-hour epi thermal and 5-minute epithermal) and two counting modes (normal and Co mpton suppression) have been evaluated for following ten elements: As, Au, Cd, Ga, K, La Mo, Sb, Sm, and W. The results show that the method of 5-minute epithermal and a 1-day decay is the optimum way to analyz e Ga, while the addition of the Compton suppression is very beneficial for the determination of K. Using the Compton suppression system in c onjunction with the 1-hour epithermal and a 1-week decay, is ideal to determine Au, Cd, Mo and W, while routine 1-hour thermal and a 1-week decay, is adequate to determine As, Sb, Sm and La in concentrations fo und in soil.