Estimating neutron dose equivalent rates from heavy ion reactions around 10 MeV amu using the PHITS code

Iwamoto, Yosuke   ; Ronningen, R. M.*; Niita, Koji*

The influence of the "switching time" in PHITS calculations of low-energy heavy ion reactions, defined as the time when the JAERI Quantum Molecular Dynamics model calculation stops and the Generalized Evaporation Model calculation begins, was studied using neutron energy spectra from around 10 MeV/u heavy ion incident on a copper target. Using a value of 100 fm/c for the switching time, calculated neutron energy spectra obtained agree well with the experimental data. PHITS was then used with the switching time of 100 fm/c to simulate an experimental study by calculating neutron dose equivalent rates produced by 3 MeV/u to 16 MeV/u heavy ion beams incident on iron, nickel and copper targets. The calculated neutron dose equivalent rates agree very well with the data and follow a general pattern which appears to be insensitive to the heavy ion species but is sensitive to the target material.