Mass yield distribution in the 3 GeV bremsstrahlung induced fission of 232Th

Abstract The cumulative yields of various fission products within the mass region of 77–153 in the 3-GeV bremsstrahlung induced fission of 232Th have been measured by using the method of recoil catcher and an off-line γ–ray spectrometry at the Pohang accelerator laboratory, Korea. The mass yields were obtained from the cumulative yields of fission products after charge-distribution corrections in the high energy fission. We obtained the mass distribution parameters such as peak-to-valley (P/V) ratio, average light mass ( A L ), and heavy mass ( A H ), as well as the average post-fission number of neutrons ( v exp t ) in the 232Th(γ,f) reactions. We compared the fission yield data in the 232Th(γ,f) and 238U(γ,f) reactions at various bremsstrahlung energies and the following facts were observed. (i) At the bremsstrahlung end-point energy of 2.0–3.5 GeV, the mass yield distribution in the 232Th(γ,f) reaction is triple humps, whereas in the238U(γ,f) reaction, it is double humps. This is due to the different type of potential energy surface between the two fissioning systems. (ii) In both the 232Th(γ,f) and 238U(γ,f) reactions, the yields of asymmetric products decrease marginally, whereas for those of symmetric products increase significantly with bremsstrahlung energy and thus the value of P/V ratio decrease accordingly. (iii) At all the bremsstrahlung energy, the P/V ratio of the 232Th(γ,f) reaction is lower than that of the 238U(γ,f) reaction due to the presence of the third peak in the mass yield distribution of former.