Secondary particle production in tissue-like and shielding materials for light and heavy ions calculated with the Monte-Carlo code SHIELD-HIT.

Abstract

The Monte Carlo code SHIELD has been modified into a version named SHIELD-HIT which extends the transport of hadron cascades in shielding materials to that of ions in tissue-like materials, and includes ion energy-loss straggling, multiple scattering, track-length calculations and production of secondary particles, which includes all generations, for ion interactions with the media. Calculations using SHIELD-HIT have been performed for 1H, 12C and 26Fe ions with energies up to 1000 MeV/u transported through water, soft tissue and aluminium. These have been validated by comparing Monte Carlo results with experimental data and results from other Monte Carlo codes for ion transport. Good agreement has been found for depth-dose distributions of protons and 12C ions in water up to depths well beyond the Bragg peak, where nuclear fragmentation effects dominate and for the production of secondary particles at different depths. Detailed track-length fluence spectra of secondary particles have been calculated for various combinations of projectiles and targets of interest for space radiation and radiotherapy applications. The secondary particle spectra in water from carbon ions have been used for calculations of stopping-power ratios for ionization chamber dosimetry, confirming the values recommended by the IAEA Code of Practice for radiotherapy dosimetry with heavy ions.