Measurement of fission product yields in the quasi-mono-energetic neutron-induced fission of 238U

Abstract

The cumulative yield of the fission products within the mass range of 83–117 and 123–153 have been measured in the 6.61and 10.92 MeV quasi-mono-energetic neutron-induced fission of ²³⁸U by using an off-line γ-ray spectrometric technique. The neutron beams were obtained from the ⁷Li(p,n) reactions with the proton energies of 11 and 18.8 MeV. The mass chain yields were obtained from the cumulative yields by using charge distribution correction. The peak-to-valley (P/V) ratio, the average value of light mass (⟨A_L⟩), heavy mass (⟨A_H⟩) and the average number of neutrons (<ν>) were obtained from the mass yield data. The data in the ²³⁸U(n, f) reaction from the present work and literature at various energies were compared with the similar data in the ²³⁸U(γ, f) reaction and following observations were obtained. (i) In both the reactions, the mass yield distributions are double humped. (ii) The yield of fission products for A = 133–134, A = 138–139, and A = 143–144 and their complementary products are higher than those of other fission products due to the nuclear structure effect. (iii) The yield of symmetric product increases and thus the peak-to-valley (P/V) ratio decreases with excitation energy. (iv) With the increase of excitation energy, the <ν> vale increases in a similar way in both the reactions. (v) The changing trend of ⟨A_L⟩ and ⟨A_H⟩ values with the increase of excitation energy are entirely different in between the two reactions.