Pressure dependence of secondary NIR scintillation in Ar and Ar/CF 4

The variation with charge gain of the total number of photons emitted per electron, in the visible and near-infrared (NIR) regions (400<λ<1000 mm), in Ar/CF₄, mixtures, is investigated for CF₄ concentrations below 15%. Measurements were performed in a uniform field configuration and results are presented for charge gains below 100, under X-ray excitation. The maximum number of photons emitted per drifting electron (0.7 and 0.2 ph/e^- for Ar⁺ 2% CF₄ and Ar+10% CF₄, respectively) is obtained for a charge gain G~4. The spectral distribution of the emitted light in Ar/CF₄ mixtures is also analyzed. The pressure dependence (1-4 atm) of the secondary light output, in the visible and near infrared regions is studied as a function of the reduced electric field E/P for pure argon and Ar/CF₄ mixtures. Above the charge multiplication threshold, the maximum number of photons emitted per electron decreases by a factor of about 1.5 when the pressure increases from 1 to 2 atms