Measurement of proton induced fission cross-section of 235U at sub-coulomb barrier energies

Abstract

Abstract It has been observed that in heavy ion induced fission the sub-coulomb cross section does not decrease with energy as rapidly as expected. In order to study the situation prevailing in proton induced fission, measurements of fission cross-sections for protons on 235 U were carried out using plastic track detectors in a close geometry for Ep= 2 to 4 MeV. Care was taken to measure the background tracks due to neutron induced fission at each energy. The results show a much lower fall off of cross-section with energy than is indicated by an optical model prediction. At 2.5 MeV the fission cross-section is several orders of magnitude higher than the predicted reaction cross-section. An interpretation of the results as fission following coulomb excitation is suggested which requires the existence of a third well in the potential energy surface for 235 U.