A new treatment of radiation behaviour beyond one-body observables

Abstract

We propose a new treatment of radiation behaviour in transport calculations by introducing an event generator model in which we combine the nuclear data and the reaction models so as to trace all correlations of ejectiles keeping the energy and momentum conservation in a collision. By this new model, we can estimate the fluctuations around the mean values of one-body observables, for example, the deposit energy distribution in a cell, which cannot be obtained by the transport calculations based on the Boltzmann equation with the nuclear data. Nuclear data are extensively used in Monte Carlo transport calculations to analyze the radiation behaviour in various fields such as accelerator facilities, space radiation, and ra- diotherapy. Most of the Monte Carlo transport calculations are based on Boltzmann equation for one-body phase space distribution of the transport particles. In such transport cal- culations, one can obtain only the mean value of the one- body observables in the phase space, e.g., heat, flux, and dose, but not the fluctuations around the mean value, since the Boltzmann equation, nor the nuclear data has information on the two-body and higher order correlations which determine the fluctuation around the mean value. Recently, however, the higher order quantities, i.e., the fluctuations around the mean values of the one-body ob- servables are often required. A typical example for such a correlated quantity is the deposit energy distribution in a cell, which is necessary to estimate the response function of detectors, the single event upset probability of semiconductor memory cells and the radiation effects in a micro-dosimetric treatment. The solution of the Boltzmann equation cannot describe the distribution but only the mean value. Furthermore, Monte Carlo calculations using the nuclear data cannot deal with these quantities, since the nuclear data includes only the inclusive one-body cross sections but no information of the correlations. We have therefore developed a new treatment of radiation behaviour in the transport calculations by introducing an event generator model, in which we have combined the nuclear data and the reaction models so as to trace all higher correlations of ejectiles keeping the energy and momentum conservation in a collision.