Systematic measurement of lineal energy distributions for proton, He and Si ion beams over a wide energy range using a wall-less tissue equivalent proportional counter
Tsuda, Shuichi
; Sato, Tatsuhiko
; Takahashi, Fumiaki
; Satoh, Daiki
; Sasaki, Shinichi*; Namito, Yoshihito*; Iwase, Hiroshi*; Ban, Shuichi*; Takada, Masashi*
Deposit energy distribution in microscopic site is basic information for understanding of biological effects of energetic heavy ion beams. To estimate RBE, lineal energy,
, can be an appropriate physical index. In this work, a wall-less tissue equivalent proportional counter has been designed and used for the measurement of
distributions, 
(
), for 160 MeV H, 150 MeV/u He, 290 MeV/u C, 490 MeV/u Si and 500 MeV/u Ar. Data of 
(
) were also obtained in the wide range of LET. The dose-means of
, 
, were compared with those calculated by the microdosimetric function of PHITS. It is found that the calculated 
(
) and 
agree fairly well with those measured. The values of 
are larger than those of LET less than
10 keV/
m because of the discrete energy deposition by delta rays, while the relation is reversed above 10 keV/
m. The results indicate that care should be taken in the difference between 
and LET when the values of RBE of energetic heavy ions are estimated.