Performance evaluation of multi sampling ionization chamber for heavy ion beams by comparison with GEANT4 simulation

In high-energy heavy-ion accelerator facilities, multi sampling ionization chambers are often used for the identification of the atomic number $Z$ by detecting the energy deposit in it [1,2]. In the study at GSI, the picture of the escape of secondary electrons, $\delta$ rays, from the ionization chamber explains the experimental data of pulse-height resolution [3]. If this picture is correct, the pulse-height resolution should depend on the effective area of the ionization chamber. The experiment have been performed at NIRS-HIMAC. The pulse-height resolutions of two ionization chambers with different effective area were compared by using a 400-MeV/u Ni beam and their fragments. The difference in the pulse-height resolutions was observed. By comparison with the GEANT4 simulation including the $\delta $-rays emission, the performance of the ionization chamber have been evaluated. \\[4pt] [1] K. Kimura et al., Nucl. Instr. and Meth. A, 538, 608 (2005).\\[0pt] [2] Y. Sato et al., Jpn. J. Appl. Phys., 53, 016401 (2014).\\[0pt] [3] M. Pfutzuner, et al., Nucl. Instr. and Meth. B, 86, 213 (1994).