The half-lives of 90mY and 97Ru

In an attempt to improve the accuracy of neutron activation analysis, gamma-ray spectrometry and least-squares methods developed for other nuclides have been applied to redetermine the decay constants of ^90mY and ⁹⁷Ru. Several irradiated samples of each pure element were counted continually through several half-lives, acquiring up to 100 spectra with good statistics. Photopeaks from each nuclide were evaluated with a region of interest integration routine, and each data point corrected for rate-related losses before fitting to an exponential function by a nonlinear least-squares procedure. The half-lives found are 3.204 ± 0.008 h for ^90mY and 2.836 ± 0.014 days for ⁹⁷Ru, where the uncertainty is an estimate of the 95 % confidence level. Although (by Chi squared criteria) the fits to the decay curves were very good and the uncertainty of the resulting half-lives an order of magnitude smaller than the previously published uncertainty, care is necessary before assigning a best value with a totally defensible uncertainty to the overall data set.