Mass distribution in the 50-, 60-, and 70-MeV bremsstrahlung-induced fission of232Th

Abstract

The postneutron yields of various fission products in the mass regions of 77-153 have been determined in the 50-, 60-, and 70-MeV bremsstrahlung-induced fission of 232 Th by using a recoil catcher and an off-line γ -ray spectrometric technique in the electron linac at the Pohang Accelerator Laboratory, Korea. The mass-yield distributions were obtained from the fission-product yield data using charge-distribution corrections. The fission yields of the present paper and the existing data from the 232 Th(γ ,f ) reaction at various energies are compared with those from the 232 Th(n,f ), the 238 U(n,f ), and the 238 U(γ ,f ) reactions. We observe that the yields of fission products for A = 133-134, A = 138-139, A = 143-144, and their complementary products in the above fissioning systems are higher than those of other fission products, which is explained based on the nuclear-structure effect. However, we observed that the yields of fission products for A = 133-134 were lower than those for A = 143-144 in the 232 Th(γ ,f ) reaction compared to those of the 232 Th(n,f ), 238 U(n,f ), and 238 U(γ ,f ) reactions. The yields of fission products for A = 133-134 increase, but those for A = 143-144 decrease with an increase in the excitation energy in the 232 Th(γ ,f ) and 232 Th(n,f ) reactions; however, those trends are reversed in the 238 U(γ ,f ) and 238 U(n,f ) reactions. The increasing or decreasing trends for the yields of fission products for A = 133-134 and A = 143-144 with the excitation energy in the 232 Th(γ ,f ), 232 Th(n,f ), 238 U(n,f ), and 238 U(γ ,f ) reactions are explained from the shell effect of the complementary products based on the static scission-point model and the standard I and II channels of bimodal fission. The peak-to-valley (P/V) ratio for the above fissioning systems also was obtained from the mass-yield distribution. The P/V ratio for the 232 Th(γ ,f ) and 238 U(γ ,f ) reactions at different energies from the present data and the existing literature data are interpreted to examine the role of excitation energy.

Review on the progress in nuclear fission

“…In this domain, the coupled-channels model, the dispersive optical potential, and an heuristic model for resonant transmission are of eminent importance. On the experimental side there have been several publications on refinements of existing [109,110,111,112,113,114] or the development of novel techniques [115,116] as well as on new experimental findings [117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,…”