Response of a tissue equivalent proportional counter to different ions having a similar linear energy transfer

Abstract

The Tissue Equivalent Proportional Counter (TEPC) is a part of the active dosimetry of current space missions, measuring high-energy charged particles making up the proton and galactic cosmic radiation (GCR) fields, as well as the fragmentation products produced when these radiations interact with shielding. It is also used to characterize high-energy charged particle beams produced by accelerators used at many tumor treatment facilities throughout the world. A proper understanding of its response to these types of radiation fields is required before an assessment of radiation quality and dose equivalent may be made with confidence. Past studies have characterized detector response to a single high-energy ion, 56Fe, with energies ranging from 200 to 1,000 MeV/nucleon. It was found that the TEPC could be used to accurately determine the average quality of high-energy charged particles, and therefore dose equivalent, if the dose mean lineal energy, yd, were used. The present study is an analysis of TEPC response to several high-energy ions having different charge and velocity, the square of their ratio, Z2/V2, chosen such that all ions have a similar Linear Energy Transfer (LET). Four ions, 14N, 16O, 20Ne and 28Si, all having an LET of about 43 keV/?m were measured at the Heavy Ion Medical Accelerator (HIMAC) in Chiba, Japan with a spherical TEPC having a physical diameter of 1.27 cm. Results of this study indicate that the proper choice of using yf or yd to determine radiation quality and absorbed dose may depend on the associated momentum of the ion.