VUV emissions in gaseous detectors

The authors describe the time evolution of VUV photons emitted in Ar/CH4 and Ar/CO2 mixtures, during the development of electron avalanches occurring in cylindrical coaxial radiation detectors. Particular attention is paid to emissions considered as relevant to the photon feedback mechanisms, namely the C I atomic lines at 156.1, 165.7 and 193.1 nm. A correlation is obtained between the time spectra and the corresponding mean anode current signals, both for the proportional and the self-quenching streamer modes of operation. A comparison is also made between the data obtained with two detectors having different cathode diameters (16 and 30 mm).