Scintillation yield in liquid argon for non-relativistic protons and helium ions

Linear energy transfer dependence of the scintillation intensity in liquid Ar (LAr) is flat for the relativistic particles over the range from 1.8×102 to 5.5×103 MeV cm2/g. The data observed so far with non-relativistic light particles are very few compared to the data with relativistic particles. The scintillation yields have been measured in LAr for the non-relativistic protons (7.3–24.1 MeV, 67–28 MeV cm2/g). and helium ions (13.8–20.8 MeV, 4.4–3.4×102 MeV cm2/g). For non-relativistic protons, the yields normalized by the flat level of relativistic particles were about 0.81. From comparison of the data with the theoretical curve for relativistic particles, both effects of quenching and electron escape are found to occur for the non-relativistic protons. For non-relativistic helium ions, the scintillation yields were around 0.68.