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/sub p/ was measured using a vacuum ultraviolet (VUV) sensitive photodiode with spectral quantum efficiency q/sub e/(/spl lambda/) measured as a function of wavelength /spl lambda/. The absolute number of photoelectrons from the photocathode N/sub pe/ was measured using a charge-sensitive preamplifier calibrated with respect to charge number. The collection efficiency for scintillation photons F/sub 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. NP was determined from N/sub p/ = N/sub pe//(Q/sub e/F/sub ce/), where Q/sub e/ is the average quantum efficiency calculated from q/sub e/(/spl lambda/) and a relative intensity I(/spl lambda/) of scintillation in rare gases. We measured the luminescence spectra using a VUV monochromator of known efficiency in order to obtain I(/spl lambda/). Measurements were performed in gaseous argon, krypton, and xenon in the pressure range from 1.01 /spl times/ 10/sup 5/ Pa to 1.01 /spl times/ 10/sup 6/ Pa. N/sub p/ in xenon at 1.01 /spl times/ 10/sup 5/ Pa is 1.60 /spl times/ 10/sup 5/ for 5.49-MeV alpha particles.