A measurement of scintillation in CFf4 using GEM foils and a CsI photocathode

The absolute photon yield of scintillation light produced by highly ionizing particles in pure CF₄ has been measured using a photosensitive GEM detector. The detector consists of two standard GEMs and a Csl coated GEM that acts as a photocathode and is sensitive to the scintillation light produced in CF₄ at 160 nm. The light yield is determined in terms of the number of scintillation photons produced per MeV of energy deposited in the gas by a 5.5 MeV alpha particle using the measured gain and quantum efficiency of the GEM detector, the solid angle acceptance of the detector, and the measured energy loss in the gas. Preliminary measurements show that the yield determined using this method is in very good agreement with other measurements. Scintillation light in CF₄ can potentially play an important role in the performance of the PHENIX Hadron Blind Detector (HBD) as well as other Cherenkov detectors, and its effect on the operation of the HBD at RHIC will be discussed.