Thermal neutron capture cross sections of long-lived nuclei measured by activation

Abstract

Thermal neutron capture cross sections have been measured for many radioactive nuclei using the activation technique, in which one compares the activity of the original radioactive nucleus AX with that of the nucleus A+1X which is produced by neutron capture. These measurements have previously been done either by irradiating long-lived sources or by double neutron capture on a stable target (in which case one compares the activity of the final product with that of the intermediate radionuclide). These techniques are made practical if the final product nucleus is much shorter-lived than the original nucleus (or than the intermediate radionuclide in the case of double neutron capture), so that it decays at a greater rate. Both methods require precise knowledge of decay schemes and branching ratios of the observed radiations, as well as detailed information on isomerism in all radionuclides involved in the measurement. Some results of a critical review of previous activation measurements of thermal cross sec...