Photofission Experiments Research Articles

Formalism and applications of electrofission and photofission fragment angular distributions

A formalism for the joint analysis of angular distributions of electro- and photofission fragments is presented, utilizing the vitual-photon spectrum technique in DWBA. This formalism is applied to the study of angular distributions for the electrofission of 238U, measured near the fission barrier, to obtain information about the low-lying levels ( J π , K) of the transition nucleus. The (2 +, 0), (1 −, 0), and (1 −, 1) levels, previously detected in photofission experiments, were confirmed. Evidences of a significant contributions of (1 +, 1), (2 +, 1)and (2 +, 2) levels are also presented.

The mass and kinetic energy distributions in the fission of 237Np, 232Th, 238U, 235U and 209Bi induced by 110 MeV electrons

Fission of 232Th, 237Np, 209Bi, 235U and 238U induced by 110 MeV electrons has been studied by means of surface barrier detectors. The resulting mass and kinetic energy distributions are presented. Comparison with the liquid drop model predictions shows reasonable agreement in the case of 209Bi. The data are analysed in terms of a two component model of fission and the mean total kinetic energies of the components are shown to depend linearly on Z1Z2(A113 + A213). Interesting differences are found when the present results are compared with the recent photofission experiments of Areskoug et al. and features in both sets of data correlate with changes of fragment deformation implied by the calculations of Wilkins et al.

Applicability of a simple parallel plate avalanche detector to photofission experiments

A simple parallel plate avalanche detector (PPAD) has been tested for its applicability to photofission experiments at intense bremsstrahlung beams. Performance tests with a 252Cf spontaneous fission source showed a good time resolution (≈ 500 ps) and discrimination between α-particles and fission fragments. An investigation of the 236U fission isomer via the 238U(γ, 2n) reaction at the bremsstrahlung beam of the 65 MeV Giessen linac demonstrates the advantages of the PPAD. The results [T 1 2 = 118 ± 7 ns] excellently agree with previous data obtained with semiconductor detectord. The time of data collection can be reduced by one order of magnitude.

Photofission cross sections of 232Th and 236U from threshold to 8 MeV

Measurements of the photofission cross sections of 232Th and 236U for an energy range of 5.0 to 8.0 MeV are reported. The Compton scattering facility at the Ames Laboratory Research Reactor was used for these measurements. Resonance structure at γ-ray energies of 6.3 and 7.6 MeV is observed in 232Th and at 5.3, 6.0, 6.5, and 7.5 MeV in 236U. The present results are compared with other photofission experiments and particle-induced fission studies. Suggestions for the interpretation of the resonances are given on the basis of Bohr's fission-channel theory and the existence of a double-humped fission barrier.