Secondary scintillation in CF4: emission spectra and photon yields for MSGC and GEM

Abstract

Secondary scintillation (defined here as photon emission originating from electron avalanches) was studied for two gaseous micropattern detectors: MSGC (MicroStrip Gas Chamber) and GEM (Gas Electron Multiplier) operated in pure CF4. For MSGC, the study was performed in the pressure range from 1 to 5 bar; for GEM all experiments were carried out at a fixed pressure of 1 bar. Charge gains from ∼ 10 to ∼ 150 were used in both cases. The primary ionization of the gas was produced by alpha particles from an Am-241 source. Emission spectra of the secondary scintillation were recorded in the wavelength range from 200 to 800 nm and corrected for the response of the detection system. Photon yields (number of photons generated per electron collected at MSGC or GEM) were measured for the integrated UV (200–500 nm) and visible (500–800 nm) emission bands. The obtained emission spectra and photon-per-electron ratios were compared to the corresponding data for the primary scintillation.