Measurement of lineal energy distribution of 290 MeV/u carbon beam using a wall-less tissue equivalent proportional counter

Tsuda, Shuichi  ; Sato, Tatsuhiko   ; Satoh, Daiki   ; Takahashi, Fumiaki  ; Sasaki, Shinichi*; Namito, Yoshihito*; Iwase, Hiroshi*; Ban, Shuichi*; Takada, Masashi*

The frequency distribution of the lineal energy, y, of 290 MeV/u carbon beam was measured to obtain the dosed-mean of y and compare it with the linear energy transfer, LET. In the experiment a wall-less tissue equivalent proportional counter, TEPC, in a cylindrical volume with simulated diameter 0.72 micrometer was used. The measured frequency distribution of y as well as its dose-mean value agrees fairly well with the corresponding data from microdosimetric calculations using the PHITS code within the experimental uncertainty. The ratio of the measured dose-mean lineal energy to the LET of the 290 MeV/u carbon beam is 0.73, which is much smaller than the corresponding data obtained by a wall TEPC. This result demonstrates that a wall-less TEPC is necessary to precisely measure the dose-mean of y for energetic heavy ion beams.