Pair breaking and Coulomb effects in cold fission from thermal neutron induced fission of U 233, U 235 and Pu 239

TL;DR

This study analyzes the mass and energy distribution in cold fission of U-233, U-235, and Pu-239, highlighting Coulomb effects and nucleon pair-breaking phenomena near the maximum reaction energy.

Contribution

It provides new insights into Coulomb and pairing effects in cold fission, especially regarding minimal excitation energy and charge asymmetry.

Findings

Cold fission shows no high odd-even effect in mass distribution.

Higher odd-even effects are observed in proton or neutron number distributions.

Coulomb effects increase with charge asymmetry in fragmentations.

Abstract

In this paper, the distribution of mass and kinetic energy in the cold region of the thermal neutron induced fission of U 233, U 235 and Pu 239, respectively, is interpreted in terms of nucleon pair-breaking and the Coulomb interaction energy between complementary fragments (Coulomb effect). In order to avoid the erosive consequences of neutron emission, one studies the cold fission regions, corresponding to total kinetic energy (TE) close to the maximum available energy of the reaction (Q). Contrary to expected, in cold fission is not observed high odd-even effect in mass number distribution. Nevertheless, the measured values are compatible with higher odd-even effects on proton or neutron number distribution, respectively. In addition, in cold fission, the minimal total excitation energy (X) is correlated with the Coulomb energy excess, which is defined as the difference between C (the electrostatic interaction energy between complementary fragments taken as spherical in scission configuration) and Q. These Coulomb effects increase with the asymmetry of the charge fragmentations. In sum, the experimental data on cold fission suggest that scission configurations explore all the possibilities permitted by the available energy for fission.