Photofission ofU238Induced by 17.5-MeV Monoenergetic Gamma Rays

Abstract

у RAYS FROM DECAY OF 35-DAY Nb 95 691been estimated to be about 1.5% that of the strong line. This intensity is consistent with about a 3% impurity of Zr 95 in the sample. Another well-known gamma ray 6 from the decay of Zr 95 has an energy of 760 keV and its intensity is about 80% of that of the 726-keV gamma ray. Its presence is suggested by a slight hump on the low-energy side of the line from the decay of Nb 95 . It is clear from the figures that no gamma ray of any ap preciable intensity is present in the spectrum near 753 keV. It has been estimated that such a gamma ray would have been detected if its intensity were ^ \°/ 0 of that of the strong line at 765.8 keV.The spectrometer was calibrated by observing the gamma ray 7 at 661.S95zbO.076 keV from Cs 137 (Fig. 2)

Mass distribution in the bremsstrahlung-induced fission of 232Th, 238U and 240Pu

“…This observation can be confirmed by comparing the data on mono-energetic photon-and bremsstrahlung-induced fission of the same actinides. However, fission yield data in the mono-energetic photon-induced fission of actinides are available only for 238 U [64], where the P /V ratio is not given. In addition to this, there are no data on fission yields for the mono-energetic photon-induced fission of other actinides.…”

“…In order to examine this aspect, the yield of fission products in the peak position, in the symmetric region and their ratio (i.e. peak-to-valley (P /V ) ratio) in the bremsstrahlung-induced fission of 232 Th [55][56][57][58][59][60]89] and 238 U [61][62][63][64][65][66][67][68][69][70][71][72][73][74]90] are given in Tables 4 and 5, respectively. Similarly the yield of fission products in the peak position, the symmetric region and their ratio (i.e., peak-to-valley (P /V ) ratio) in the mono-energetic neutron-induced fission of 232 Th [38][39][40][41][42] and 238 U [45][46][47][48] are given in Tables 6 and 7, respectively.…”

“…However, the yield of fission products around mass numbers 133-135 is more pronounced compared to mass numbers 143-145, in both neutron- [28][29][30][31][32][33] and bremsstrahlung-induced [61][62][63][64][65][66][67][68][69][70][71][72][73][74] fission of uranium isotopes and heavier actinides. In the electromagnetic fission of lighter actinides [52][53][54], higher yields of fission products around mass numbers 133-135 corresponding to a most probable charge of 52 have been observed.…”

“…Similarly yields of fission fragments in the excitation energy range of the GDR region due to electromagnetic fission in inverse kinematics [52][53][54] are available for neutron-deficient lighter actinides such as 214-223 Ac, 220-229 Th, 224-232 Pa and 231-234 U. On the other hand, yields of fission products in the bremsstrahlung-induced fission of actinides are available in a broad energy range for a limited number of actinides including 232 Th [55][56][57][58][59][60], 235,238 U [61][62][63][64][65][66][67][68][69][70][71][72][73][74] and 240,242,244 Pu [75][76][77][78]. Most of the yield data on fission products available in the 9 MeV to several GeV bremsstrahlung-induced fission of 232 Th [55][56][57][58][59] and 235,238 U [61][62][63][64][65][66][67] are based on radiochemical separation and beta counting or γ -ray spectrometric techniques.…”

Cumulative yields in the photofission of 232Th and 238U in the symmetric region

“…Richter and Coryell (2), Katz et al (3). and others (4)(5)(6)(7)(8) reported the yields for selected fission products in 2 3 8~ and 23ZTh at various energies. The results of these studies indicate that the shapes of mass-yield curves are generally similar to those obtained in other fissioning systen~s, except that the yields for mass numbers ranging from 77 to 84 are substantially h~gher compared to those obtained In thermal neutron fission, and the yields in the symmetric reglon are also h~gher.…”