The yield of 139Ba in the fission of natural uranium by fast and slow neutrons

ABSTRACT The yields of 139Ba per fission in natural uranium by unslowed neutrons from a mixed radium-beryllium source and by C-group neutrons were compared. In each case the fission rates measured with an ionization chamber were correlated with the β-ray activity of 139Ba, chemically extracted from a mass of uranium oxide exposed to an identical neutron spectrum. The ratio of the two fission yields is found to be 0·84 ± 0·03. The possibility of using 139Ba as a local or integrating indicator of fission in extended uraniferous media, and of distinguishing between the contributions by fast neutrons and by slow neutrons is discussed.