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

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 (left angle AL right angle) and heavy mass (left angle AH right angle) and average number of neutrons (left angle v right angle) 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 left angle v right angle with excitation energy is also similar between the 238U (γ, f) and 238U (n, f) reactions. However, it is surprising to see that the left angle AL right angle and left angle AH right angle values with excitation energy behave entirely differently from the 238U (γ, f) and 238U (n, f) reactions. (orig.)