Comparisons of fragmentation spectra using 1 GeV/amu 56Fe data and the PHITS model

Abstract

We present measurements and model calculations of fluence and linear energy transfer in water ( LET ∞ ) obtained using 56Fe beams with 1 GeV/amu kinetic energy incident on aluminum, polyethylene, PMMA, and lead targets. The measured spectra are compared to predictions of the PHITS model. The study is motivated by NASA's need to develop accurate heavy ion transport codes to assess radiation exposures in deep space, where galactic cosmic rays are important. The data were obtained at the Alternating Gradient Synchrotron at the Brookhaven National Laboratory. Distributions of charge and LET depend on the depth and composition of the target. Several of the targets studied are “thick”, defined operationally as a depth that presents at least 50% of an interaction length to the beam ions. In a thick target, the probability of a secondary interaction is significant, tertiary interactions can also be important, and the target-exit fluence and charge distributions depend on unmeasured cross sections that can only be estimated by nuclear interaction models. Comparisons between calculated and measured spectra are therefore of considerable interest. Some targets used in the study are thin, so that secondary and higher interaction probabilities are negligible, allowing more stringent comparisons between the data and the model. We find that PHITS reproduces some aspects of the experimental data well, but fails to accurately reproduce many of the measured fragment fluences.