Post-Neutron Mass Yield Distribution in the Thermal Neutron Induced-Fission of 239Pu

초록

Mass chain yield distribution has been done in the thermal neutron-induced fission of Pu-239 by measuring the cumulative yields of various fission products within the mass range of 78 to 159 and the independent yields of a few products. An off-line gamma-ray spectrometric technique was used to measure the gamma-ray activities of the fission products. From the measured values of the cumulative yields, the post-neutron mass chain yield distribution was obtained after applying the charge distribution correction. Data from the present and earlier work of our laboratory in the Pu-239(n(th),f) reaction were compared with similar data of Pu-238,Pu-241(n(th),f) and Pu-240(n,f) reactions, and it was found that the fine structures of the mass yield distributions are similar. The mass yield distribution in the Pu-239(n(th),f) reaction was also compared with those of Th-229(n(th),f) and Cf-252(SF) reactions to examine the effect of charge and mass difference of the fissioning systems on the mass yield distribution. It was found that the asymmetric standard I mode of fission is favorable in the Pu-238,Pu-239,Pu-241(n(th),f) and Pu-240(n,f) reactions whereas the standard II mode is favorable in the Th-229(n(th),f) and Cf-252(SF) reactions.

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