Fission product energies and anisotropies following complete fusion of16O+238U

Abstract

Radioactive recoil techniques have been developed for measuring angular distributions and range distributions of individual fission products following heavy ion induced fission. From these measurements, values can be extracted for the recoil velocity of the fissioning nucleus, the velocity imparted by fission, and the fission anisotropy. These techniques were applied to reactions of 101 MeV 160 on 238U, and confirmed that the reaction mechanism is essentially entirely complete fusion-fission. Accepting this, the data determine the kinetic energy release in forming the various products to a precision of 1%; while the overall magnitude of the energy is in good agreement with previous results, the data suggest a systematic correlation between kinetic energy and the position of a product on the nuclear charge dispersion curve, not previously reported, which is similar to but significantly larger in magnitude than the effect expected from simple Coulomb repulsion. Significant variations in anisotropy are also observed between products, which appear to be partially correlated with the variations in kinetic energy.

Fission following complete or incomplete fusion of 135 MeV16O and238U

“…The results are listed in Table 2 and will be discussed later. Analysis of the angular distributions excluded the three central catchers, as suggested above and was performed both including and excluding the two end catchers, as discussed in (1). The two parameters determined in the analysis, the momentum imparted to the fissioning nucleus in the initial interaction, and the inherent anisotropy of the fission process, are quite insensitive to whether these are included.…”

“…For this purpose we have used parameterized forms of the range/energy tabulations of Northcliffe and Schilling [7]. Although the reliability of these relations is in principle open to question, their use in our previous study of complete fusion/fission induced by 101 MeV 160 on 238U [1] led to a deduced average value of v which agreed with the expected recoil velocity of the compound nucleus to within 4%, and an average value of the fission energy which agreed with that measured by Viola et al [4] to within 5%.…”

“…The fitted form of the angular distribution for each product was then used to convert ai~ d into the total cross section, a~, by the formula given in (1). Quoted errors in the total cross sections of Table 1 reflect both the error of column 1 and that introduced by the extraction of k from the analysis of the angular distributions.…”

“…The experimental techniques and analysis procedures were exactly as described in our previous paper [1], and will be briefly summarized here. Three separate irradiations were performed, using a beam of 135 MeV 1605 + from the Harwell Variable Energy Cyclotron, to measure respectively the yields, angular distributions and range distributions of radioactive fission products from reactions on a 238U target, stopped in appropriately designed catchers.…”

“…In a recent paper [1] we described techniques for measuring both the angular distribution and the projected range distribution of radioactive fission products, and applied these to a study of fission induced by 101 MeV 160 on 238U. The kinematics of the fission process are shown in Fig.…”