Absolute number of scintillation photons emitted by alpha particles in rare gases

To determine absolute scintillation yields due to alpha particles in high-pressure rare gases, the number of scintillation photons N-p was measured using a vacuum ultraviolet (VUV) sensitive photodiode with spectral quantum efficiency q(e)(lambda) measured as a function of wavelength lambda. The absolute number of photoelectrons from the photocathode N-p. was measured using a charge-sensitive preamplifier calibrated with respect to charge number. The collection efficiency for scintillation photons F-ce at the photocathode was determined from the solid angle subtended by the photocathode at a scintillation point under the condition that there are no photons reflected off the surrounding walls. N-p was determined from N-p = N-pe/(Q(e)F(ce)), where Q(e) is the average quantum efficiency calculated from q(e)(lambda) and a relative intensity I(lambda) of scintillation in rare gases. We measured the luminescence spectra using a VUV monochromator of known efficiency in order to obtain I(lambda). Measurements were performed in gaseous argon, krypton, and xenon in the pressure range from 1.01 x 10(5) Pa to 1.01 x 10(6) Pa. N-p in xenon at 1.01 x 10(5) Pa is 1.60 x 10(5) for 5.49-MeV alpha particles.