Mass yield distributions of fission products from photo-fission of 238U induced by 11.5–17.3 MeV bremsstrahlung

Abstract

The yields of various fission products in the 11.5, 13.4, 15.0 and 17.3 MeV bremsstrahlung-induced fission of 238U have been determined by recoil catcher and an off-line γ-ray spectrometric technique using the electron linac, SAPHIR at CEA, Saclay, France. The mass yield distributions were obtained from the fission product yields using charge-distribution corrections. The peak-to-valley (P/V ratio, average light mass (〈A L〉) and heavy mass (〈A H〉) and average number of neutrons (〈v〉) in the bremsstrahlung-induced fission of 238U at different excitation energies were obtained from the mass yield data. From the present and literature data in the 238U (γ, f ) and 238U (n, f ) reactions at various energies, the following observations were obtained: i) The mass yield distributions in the 238U (γ, f ) reaction at various energies of the present work are double-humped, similar to those of the 238U (n, f ) reaction of comparable excitation energy. ii) The yields of fission products for A = 133–134, A = 138–140, and A = 143–144 and their complementary products in the 238U (γ, f) reaction are higher than other fission products due to the nuclear structure effect. iii) The yields of fission products for A = 133–134 and their complementary products are slightly higher in the 238U (γ, f ) than in the 238U (n, f ) , whereas for A = 138–140 and 143–144 and their complementary products are comparable. iv) With excitation energy, the increase of yields of symmetric products and the decrease of the peak-to-valley (P/V ratio in the 238U (γ, f) reaction is similar to the 238U (n, f) reaction. v) The increase of 〈v〉 with excitation energy is also similar between the 238U (γ, f ) and 238U (n, f) reactions. However, it is surprising to see that the 〈A L〉 and 〈A H〉 values with excitation energy behave entirely differently from the 238U (γ, f ) and 238U (n, f ) reactions.