Absorbed dose in ion beams: Comparison of ionisation- and fluence-based measurements

Abstract

A direct comparison measurement of fluorescent nuclear track detectors (FNTDs) and a thimble ionisation chamber is presented. Irradiations were performed using monoenergetic protons (142.66 MeV, Φ=3×106 cm-2) and carbon ions (270.55 MeV u-1, Φ=3×106 cm-2). It was found that absorbed dose to water values as determined by fluence measurements using FNTDs are, in case of protons, in good agreement (2.4 %) with ionisation chamber measurements, if slower protons and Helium secondaries were accounted for by an effective stopping power. For carbon, however, a significant discrepancy of 4.5 % was seen, which could not be explained by fragmentation, uncertainties or experimental design. The results rather suggest aW-value of 32.10 eV±2.6 %. Additionally, the abundance of secondary protons expected from Monte-Carlo transport simulation was not observed.