Electromagnetic Dissociation Cross Sections Using Weisskopf-Ewing Theory

Abstract

It is important that accurate estimates of crew exposure to radiation are obtained for future long-term space missions. Presently, several space radiation transport codes, all of which take as input particle interaction cross sections that describe the nuclear interactions between the particles and the shielding material, exist to predict the radiation environment. The space radiation transport code HZETRN uses the nuclear fragmentation model NUCFRG2 to calculate electromagnetic dissociation (EMD) cross sections. Currently, NUCFRG2 employs energy-independent branching ratios to calculate these cross sections. Using Weisskopf-Ewing (WE) theory to calculate branching ratios for compound nucleus reactions, however, is more advantageous than the method currently employed in NUCFRG2. The WE theory can calculate not only neutron and proton emission, as in the energy-independent branching ratio formalism used in NUCFRG2, but also deuteron, triton, helion, and alpha-particle emission. These particles can contribute significantly to total exposure estimates. In this work, photonuclear cross sections are calculated using WE theory and the energy-independent branching ratios used in NUCFRG2 and then compared to experimental data. It is found that the WE theory gives comparable but mainly better agreement with data than the energy-independent branching ratio. Furthermore, EMD cross sections for single neutron removal are calculated using WE theory and an energy-independent branching ratio used in NUCFRG2 and compared to experimental data.