Dosimetry and microdosimetry of monoenergetic neutrons using recombination chamber – Measurements and Monte Carlo simulations

Abstract

The REM-2 tissue-equivalent recombination chamber was used for dosimetry measurements performed in monoenergetic neutron reference fields at National Physical Laboratory, UK for the neutron energy range from 144 keV to 5 MeV. Measurement data were used for the determination of the recombination index of radiation quality, ambient dose, and finally ambient dose equivalent, H*(10). Results justify the relevance of the application of this measuring method in mixed radiation fields with dominant neutron component, which are present, for example, at photon and proton radiotherapy facilities. The relative response of the chamber in terms of H*(10) in the investigated neutron energy range, resulted in the correction factor at the maximum level of 1.25. Analysis of the saturation curves and use of the recombination microdosimetric method, RMM resulted in the determination of dose distribution at a nanometric level in terms of restricted linear energy transfer, LΔ. Monte Carlo simulations performed with the FLUKA code allowed to obtain double-differential distributions of L which were compared with those obtained during measurements. Comparison between measured and simulated data showed that RMM is a reliable method for microdosimetric investigations in mixed neutron-gamma fields present around medical radiotherapeutic units.