Improved dose and fluence calculations by using tabulated cross sections in PHITS

In this paper we present a new method to increase the accuracy of the calculated fragmentation yields for light fragments when using the particle and heavy ion Monte Carlo transport code PHITS. The method consists in biasing the event generator without giving up fundamental conservation laws within each event; in particular, the possibility for the user to specify tables of projectile-fragmentation cross sections for heavy ions is introduced. The cross-section tables are used to determine a priori what reaction channel should be chosen. With this method PHITS can combine its event generators for nuclear reactions with external models or measured values to correct the cross sections which are not calculated with the required accuracy by default. The method is based on the possibility to identify the projectile-like “leading” fragment, i.e. the one with the highest charge. If the fragment can be produced with multiplicity higher than one, our procedure cannot reproduce the user-supplied fragmentation cross section.