Gamma-Ray Emission Probabilities in the Decay of Barium-140 and Lanthanum-140

Gamma rays from the fission product nuclides ¹⁴⁰Ba and ¹⁴⁰La are frequently used for monitoring fission rates in neutron activation detectors consisting of fissionable materials. Systematic errors that can occur when the 1596-keV line of ¹⁴⁰La is taken as the monitor line can be avoided by using the 537-keV line of ¹⁴⁰Ba. The gamma-ray emission probabilities per decay of ¹⁴⁰Ba and ¹⁴⁰La were redetermined for the more abundant lines with a relative uncertainty of about ±1% at the 68% confidence level.