Absolute Scintillation Yields in Liquid Argon and Xenon for Various Particles

Abstract

For the determination of the absolute scintillation yields -the number of scintillation photons per unit absorbed energy-for a variety of particles in liquid argon, a series of simultaneous ionization and scintillation measurements were performed. The results verified that scintillation yields for relativistic heavy particles from Ne to La are constant despite their extensive range of linear energy transfer. Such a constant level, called ''flat top response'' level, manifests the maximum absolute scintillation yield in liquid argon. The maximum absolute scintillation yield is defined by the average energy to produce a single photon, W ph ðmaxÞ ¼ 19:5 AE 1:0 eV. In liquid xenon, the existence of the same flat top response level was also found by conducting scintillation measurements on relativistic heavy particles. The W ph (max) in liquid xenon was evaluated to be 13:8 AE 0:9 eV using the W ph for 1 MeV electrons, obtained experimentally. The ratio between the two maximum scintillation yields at the flat top response level obtained in liquid argon and xenon is in good agreement with the estimation by way of the energy resolutions of scintillation due to alpha particles in both liquids.

Scintillation response of liquid xenon to low energy nuclear recoils

“…The result of a fit with this empirical function to the alpha ionization data shown in Figure 6 gives a = 0.021 ± 0.004 and b = 0.52 ± 0.14, consistent with values obtained from fitting previous alpha ionization data in LXe [30]. Using the fitted parameters, we estimate the number of electrons collected by an external field E, for the case of a nuclear recoil of energy E r , to be Q(E) = (E r q nc /W )aE b , where W = 15.6 eV is the average energy required to produce an electron and ion pair [31] and q nc is the nuclear quenching factor from Lindhard theory. For a 56.5 keV nuclear recoil in LXe, under a field of 5 kV/cm, we would then expect about 50 ionization electrons.…”

“…Even at the highest field of 4 kV/cm, recombination is very strong and the light yield is suppressed by less than 5 %. The field dependence of the scintillation and the charge yields are related [31],…”

Properties of liquid xenon scintillation for dark matter searches

“…A value determined by the optical approximation using the oscillator strength data for solid Xe. The electric field dependences of ionization and scintillation yields have given N ex /N i =0.13-0.2 [52]. Solid circles represent efficiencies observed for relativistic heavy ions [24].…”

Tritium calibration of the LUX dark matter experiment

“…Starting with a W -value of 13.7 eV, we assume that α, the initial ratio of excitons-to-ions prior to recombination, is 0.2 independent of energy and electric field [28,29]. Then the initial number of ions prior to recombination (N ion , equivalent to the initial number of electrons), and the initial number of excitons prior to recombination (N ex ), and their sum (the total number of quanta), all increase linearly with energy as shown by the solid lines in Fig.…”