The Response of a Spherical Tissue-Equivalent Proportional Counter to Different Ions Having Similar Linear Energy Transfer

The response of a tissue-equivalent proportional counter (TEPC) to different ions having a similar linear energy transfer (LET) has been studied. Three ions, ¹⁴N, ²⁰Ne and ²⁸Si, were investigated using the HIMAC accelerator at the National Institute of Radiological Sciences at Chiba, Japan. The calculated linear energy transfer (LET_∞) of all ions was 44 ± 2 keV/μm at the sensitive volume of the TEPC. A particle spectrometer was used to record the charge and position of each incident beam particle. This enabled reconstruction of the location of the track as it passed though the TEPC and ensured that the particle survived without fragmentation. The spectrum of energy deposition events in the TEPC could be evaluated as a function of trajectory through the TEPC. The data indicated that there are many events from particles that did not pass through the sensitive volume. The fraction of these events increased as the energy of the particle increased due to changes in the maximum energy of the δ rays. Even though the LET of the incident particles was nearly identical, the frequency-averaged lineal energy, ȳ_F, as well as the dose-averaged lineal energy, ȳ_D, varied with the velocity of the incident particle. However, both values were within 15% of LET in all cases.