Uranium Photofission Yields

Abstract

The photofission yield-mass curve of natural uranium for 48-Mev x-rays was determined radiochemically. Isolation of selected peak and trough fission products at various maximum x-ray energies, 7 Mev, 10 Mev, 16 Mev, 21 Mev, 48 Mev, 100 Mev, and 300 Mev showed that the peak-to-trough ratio decreased from 300 to 4 as the maximum x-ray energy increased from 7 Mev to 300 Mev. The observed photofission yield curves may be quantitatively interpreted as the superposition of two components, a low-energy asymmetric (doublehumped) curve and a high-energy single-humped curve. The average cross section for symmetric fission for photons in the energy range 16 Mev to 300 Mev is about 7 millibarns. I. INTRODUCTIONM ANY investigations of high-energy fission, induced by particles and x-rays, have been reported. 1-12 One striking feature of these studies is the decrease in the peak-to-trough yield ratio of the yieldmass curve as the energy of the bombarding particle increases, resulting in the one hump yield-mass curve as the energy of the particle enters the hundred-Mev range. A systematic investigation of the photofission of a heavy nuclide at various energies has not been reported.The purpose of this work was essentially threefold; (1) to determine the yield-mass curve of natural uranium for 48-Mev maximum x-rays by the comparison method; 4,13,14 (2) to study the changes in the photoyield curve of uranium as a function of increasing maximum x-ray energy from 7 Mev to 300 Mev; and (3) to study the change in the neutron-to-proton ratio of primary fission fragments with increasing x-ray energy. On the assumption that the observed fission-yield curves are composites of two idealized curves, 14 one *

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

“…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.…”

Photofission of235U and238U at intermediate energies: absolute cross sections and fragment mass distributions

“…At intermediate energies the first pioneering analysis of photofission experiments on 238U with fragment mass determinations were performed in 1955 by L.Katz et al [24]. They analyzed their own data and results from Schmitt and Sugarman [25]. In these first experiments bremsstrahlung beams up to 300 MeV were used.…”

Fission Mass Yield Studies

“…Superscripts (1), (2), and (3) refer to first-, second-, and third-chance fission of U236, U235, and U234, respectively. The absence of a superscript denotes a cambination of available stages.…”

“…,0) but the corresponding population vectors q:(2) for U235, 1(3) for U 34, and 4 ) for #133 are to be calculated. The probability of a nucleus being in state j after the first neutron emission is q (2) (2->3) j and the conditioned probability pjk is the probability of such a (3) nucleus in state j contributing to the probability Sk of state k by means of neutron emission (or fission, or neither). The conditional probabilities are matrix elements of transition matrices P(1->2), , p(2->3) etc.…”