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 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 Th(γ,) reaction at various energies are compared with those from the Th(,), the U(,), and the U(γ,) reactions. We observe that the yields of fission products for = 133-134, = 138-139, = 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 = 133-134 were lower than those for = 143-144 in the Th(γ,) reaction compared to those of the Th(,), U(,), and U(γ,) reactions. The yields of fission products for = 133-134 increase, but those for = 143-144 decrease with an increase in the excitation energy in the Th(γ,) and Th(,) reactions; however, those trends are reversed in the U(γ,) and U(,) reactions. The increasing or decreasing trends for the yields of fission products for = 133-134 and = 143-144 with the excitation energy in the Th(γ,), Th(,), U(,), and U(γ,) 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 Th(γ,) and U(γ,) reactions at different energies from the present data and the existing literature data are interpreted to examine the role of excitation energy.
4 More- Received 27 December 2011
DOI:https://doi.org/10.1103/PhysRevC.85.024623
©2012 American Physical Society