Yields of Short-Lived Fission Products of Thermal-Neutron Fission of Thorium-229

The absolute yields of 39 fission products representing 30 different mass chains produced by thermal neutron fission of ²²⁹Th and having half-lives between 15 and 4600 s have been determined using Ge(Li) spectroscopy methods. Spectra of gamma rays emitted in the decay of the fission products between 25 and 2400 s after a 15-s irradiation were obtained. Gamma rays were assigned to the responsible fission products by matching gamma-ray energies and half-lives. Fission product yields were then obtained from the data by first determining the appropriate gamma-ray activity as of the end of the irradiation, correcting for detector efficiency and gamma-ray branching ratio, and, finally, dividing by the number of fissions created in the sample. The resulting fission product yields are compared with previous measurements and with recommended yields given in the recent ENDF/B evaluation. Relative uncertainties assigned to the present results range between 6 and 65%, with an absolute normalization uncertainty of 13%. The present uncertainties are smaller than or comparable to uncertainties assigned to previous experimental or evaluated yields for 16 mass chains.