Analysis of the transverse shielding problem at proton accelerators using a hadronic cascade code with low energy particle modules
Radiation protection quantities of interest (dose equivalent and absorbed dose in tissue, particle currents emerging from a shield, mean quality factors) have been obtained behind ordinary and heavy concrete of various thicknesses, at transverse directions relative to a high energy (25-800 GeV) proton beam hitting a thick iron target. The calculations were performed by using the FLUNEV program, linking the Monte Carlo hadronic cascade code FLUKA87, the EVAP-5/HETC-KFA module describing nuclear evaporation, and a low energy neutron transport module based on the MORSE code and the HILO multigroup cross section library (from 50 MeV down to thermal neutron energy). The total dose equivalents estimated by using two nearly independent methods (by multiplication of particle currents entering the tissue boundary by fluence-to-dose conversion factors, and by multiplication of absorbed doses in the tissue volume by quality factors) are in a good agreement. The neutron current and dose spectra are presented, indicating the dominance of neutrons in the 0.5-20 MeV energy range due to the evaporation process; the contributions from neutrons above 20 MeV for ordinary concrete and from neutrons below 0.5 MeV for heavy concrete are also remarkable. The dose equivalents are fitted to the simple attenuation formula suggested previously. The dose attenuation lengths are 107 g cm -2 for ordinary concrete and 116 g cm -2 for heavy concrete.