Xenon-Gas Ionization Chamber to Improve the <i>Z</i> Identification of Heavy-Ion Beams with <i>Z</i> &amp;gt; 70

Abstract An ionization chamber (IC) is employed in nuclear experiments to measure energy deposits and provide crucial information for identifying nuclei in flight after undergoing nuclear reactions or decay. In ICs using P-10 (Ar+CH$_4$) gas, the atomic number (Z) identification capability deteriorates significantly when $Z&amp;gt;70$ at an energy range of 150–300 MeV/u. This degradation is caused by the substantial energy straggling caused by charge-state fluctuation when the beams pass through a gaseous medium. This study used a xenon-based gas (Xe+CH$_4$), with a large charge-state changing cross section, to improve the Z identification. The responses of ICs with P-10 and xenon-based gases were examined using $^{238}_{\,\,\,\,92}\rm {U}^{}$ beams and cocktail radioactive isotope (RI) beams with $Z=40$–90, which were produced in the BigRIPS separator at the RI Beam Factory. For $^{238}_{\,\,\,\,}\rm {U}^{}$ beams at 344 MeV/u, incident-charge dependence was observed in the energy deposits in the P-10 gas IC, whereas it was not observed in the xenon-based gas IC. When using cocktail RI beams, the P-10 gas IC failed to separate ions with the same mass-to-charge ratio but differing by one in Z within $Z=70$–84 at 210–220 MeV/u. However, the xenon-based gas IC successfully separated these ions. The xenon-based gas IC demonstrated Z identification with separations better than 3$\sigma$ across a wide Z range ($Z=40$–90) and emerged as a practical solution for the Z identification of heavy-ion beams.