Fission of238U induced by136Xe for energies close to the Coulomb barrier

Abstract

Excitation functions and angular distributions have been measured for fission of 238U induced by 136Xe ions with bombarding energies between 4.5 and 5.9 MeV/N. Structures expected theoretically as characteristic for Coulomb fission have not been observed. The Q-value of -(7.5+ 1.0)MeV measured for bombarding energies below 4.7MeV/N, however, appears to be compatible with inelastic scattering (e.g. Coulomb excitation) rather than subcoulomb transfer followed by fission. The total kinetic energy of deep inelastic events at 5.9 MeV/N is consistent with the current knowledge about mass diffusion, but also (for the highest excitation energies) with a fast fission process in the presence of the projectile.

Spectroscopy and reaction mechanism of the system90Zr?232Th in the vicinity of the Coulomb barrier

“…Figure 9 shows the measured values as function of the distance of closest approach which are in good agreement with the results of [18,19]. The maximum of the distribution is centered at a distance D~ 14.5 fm, far below the centroids of the neutron transfer channels peaking at around D ~ 15.2 fm.…”

“…In earlier investigations fission of actinide nuclei induced by Kr and Xe projectiles below and at the Coulomb barrier was studied [18,19]. The there observed fission yield was attributed to inelastic scattering rather than transfer reactions.…”

Sub-Coulomb transfer and fission in collisions of129Xe,132Xe and136Xe with238U

“…The authors discussed further that, according to the more negative ground state Q-value Q~g for the stripping reaction as compared to the pick-up reaction, the formation of 135Xe/239U should be of minor importance in the 136Xe+238U collisions. Thus the experimental Qvalue was felt to be more compatible with Coulomb fission than with a transfer process followed by fission [11]. We are now able to compare these conclusions with the experimental data obtained for the 129Xe+ 238U and the 136Xeq-238U system which are shown in Fig.…”

“…Also this is consistent with the opening of many increasingly inelastic transfer channels leading to a dominant contribution of sequential fission processes near the interaction barrier. Habs et [11] observed Q-values of -100 MeV and more at the interaction barrier. For the discussion of the 129Xe+238U and 136Xe +238U results shown in Fig.…”

“…These results were interpreted [10] to be more consistent with sequential fission after quasi-elastic transfer than with pure Coulomb fission. The lowest energy covered in their experiments corresponded to 0.87Ecouv Habs et al [11] extended the study of the 136Xe +238U system to 0.83 Ecou~. Through measurement of the energy of the backscattered projectile they deduced the energy loss (-Q) for the Xe+U interaction which was found to be constant at (7.5 __ 1.0) MeV for bombarding energies below 0.88Ecoul.…”