Simultaneous measurements of absolute numbers of electrons and scintillation photons produced by 5.49 MeV alpha particles in rare gases

The absolute numbers of scintillation photons and electrons produced by 5.49 MeV alpha particles were measured simultaneously in argon, krypton and xenon in the gas pressure range from 1.01×10⁵ Pa to 1.01×10⁶ Pa. The ratio of the number of excited atoms to the number of electron-ion pairs is an important quantity for understanding the energy pathway of the absorbed radiation energy and was found to be 0.52, 0.55, and 0.60 in argon, krypton and xenon, respectively. The ratios were determined by measuring the number of scintillation photons originating from the excited atoms and the number of electrons. The value of W_s, which is defined as the average energy to produce one photon, in the case that all of the electron-ion pairs recombine was estimated to be 17.5, 15.4, and 13.0 eV in argon, krypton and xenon, respectively. From the relation between the numbers of electrons escaping from the recombination with ions and the numbers of scintillation photons, it is confirmed experimentally that one scintillation photon is emitted from one recombination process. This means that an excited molecule caused by three-body collisions is not de-excited without emitting a scintillation photon in the vacuum ultraviolet region.