Commissioning of a portable ionization chamber at high counting rate using heavy ion beams

A fast ionization chamber with a high counting rate was commissioned at the 8 MV tandem accelerator complex of Kyushu University in Japan. Heavy ion beams consisting of ¹²C and ¹⁶O with E_beam = 36 MeV were used to investigate the detector performance. By using various beam intensities ranging from 10³ to 10⁶ particles per second (pps), the maximum counting rate of the ion counter was measured to be about 8 × 10⁵ pps. The detector performance under different gases was also investigated using two common gases in the ionization chamber: isobutane and P-10 gases. The results show that the negative effects due to pileups, which are often observed at high counting rates, can be greatly reduced when P-10 gas is used.