Development of high energy transport code HETC-3STEP applicable to the nuclear reaction with incident energies above 20 MeV

Spallation reaction calculation based on the intranuclear-cascade-evaporation model is modified to take into account the pre-equilibrium process by using a closed form exciton model. For the double differential (p.xn) reaction cross section, the calculation of the exciton model is devised to produce smooth connection of that the cascade process. The result of the exciton model calculation is compared with the neutron energy spectra decomposed from the experimental data by the moving source model analysis. Two parameters for the transition probability of the excitons and the termination conditions of the pre-equilibrium process are adjusted to reproduce the experimental data. The addition of pre-equilibrium process into the intranuclear-cascade- evaporation model improves the accuracy of the calculation code. The improvement is significant in the backward emission at incident energy between 20 and 100 MeV for target nuclei more massive than aluminum.