On the determination of the isotopic composition of potassium by neutron activation

The isotopic ratio of ⁴¹K/³⁹K was determined by neutron activation analysis. About 100 mg of potassium nitrate sample was treated in fused state with zirconyl phosphate as ion exchanger to separate the isotope, and irradiated for 10 min in JRR-1. Potassium nitrate was taken as standard reference sample possessing the natural isotopic ratio and irradiated in the same manner. After irradiation, the activity of ⁴²K produced by the ⁴¹K (n, γ) ⁴²K reaction was measured with a 256 channel pulse height analyzer. The isotopic ratio of unknown samples were calculated from the specific activities of the unknown and standard samples. The separation ratio E is defined as follows: E = [⁴¹K/³⁹K]_unknown/[⁴¹K/³⁹K]_std. = S_b/S_a, where S_a and S_b are specific activities of the unknown and the standard samples, respectively. The result of neutron activation was slightly affected by the irradiation geometry of the samples, but the ununiformity of neutron flux could be calibrated by parallel tests using standard samples. While the results obtained, were not quite as accurate as mass-spectrometrical data, they were fairly correct, and the proposed method could be used in many ways as a convenient technique where a number of samples must be analyzed at the same time. (author)