Scaling Laws, Transient Times and Shell Effects in Helium Induced Nuclear Fission

Abstract

Fission excitation functions have been studied over the last decades and they have shown a dramatical variation from nucleus to nucleus over the periodic table^[1,2,3]. Some of these differences can be understood in terms of a changing liquid-drop fission barrier, others are due to strong shell effects which occur e.g. in the neighborhood of the double magic numbers Z=82 and N=126. Further effects may be associated with pairing and the angular momentum dependence of the fission barrier^[4,5,6]. With the availability of newer accelerators, several studies have investigated heavy ion and high energy light particle induced fission ^[5]. These reactions show a large deposit of energy, mass and most important angular momentum. The strong dependence of the fission probability on the latter quantity makes comparisons to liquid drop model calculations difficult. The problem of extensive angular momentum, energy and mass transfer can be minimized by the use of light ion induced fission at moderate bombarding energies. In contrast to heavy ion reactions, it has been shown that the fission barriers extracted from low energy light ion induced fission reactions differ only slightly from liquid drop predictions^[7,8].