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 (⟨AL⟩), heavy mass (⟨AH⟩) 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 ⟨AL⟩ and ⟨AH⟩ values with the increase of excitation energy are entirely different in between the two reactions.