Neutral bremsstrahlung in two-phase argon electroluminescence: further studies and possible applications

Abstract

We further study the effect of neutral bremsstrahlung (NBrS) in two-phase argon electroluminescence (EL), revealed recently in [1]. The absolute EL yield due to NBrS effect, in the visible and NIR range, was remeasured in pure gaseous argon in the two-phase mode, using a two-phase detector with EL gap read out directly by cryogenic PMTs and SiPMs. Possible applications of the NBrS effect in detection science are discussed, including those in two-phase dark matter detectors.

Electroluminescence and Electron Avalanching in Two-Phase Detectors

“…From Figures 4 and 9 one can see that NBrS EL, albeit being significantly weaker than ordinary EL above the Ar excitation threshold, has no threshold in electric field, in contrast to ordinary EL, and thus dominates below the threshold. Accordingly, the NBrS effect can explain two remarkable properties of proportional EL observed in experiment [9,13,19]: that of the photon emission below the Ar excitation threshold and that of the substantial contribution of the non-VUV spectral component above the threshold. ) and ionization ( ) (from [9], with permission from Elsevier).…”

“…Their time constants are of 4.2 ns and 3.1 μs respectively: Figure 5. Summary of experimental data on reduced electroluminescence (EL) yield in gaseous Ar for all known (EL) mechanisms: for NBrS EL below 1000 nm, measured in [9,13] at 87 K; for ordinary EL in the VUV, due to excimer emission going via Ar * (3p 5 4s 1 ) excited states, measured in [9,13] at 87 K and in [14] at 293 K; for EL in the NIR due to atomic transitions going via Ar * (3p 5 4p 1 ) excited states measured in [15] at 163 K.…”

“…Note that just in this field region, namely nominally at 4.6 Td, the DarkSide dark matter search experiment operates [22]. In [9,13] the NBrS contribution was measured, using dedicated spectral devices insensitive to the VUV, and appropriately subtracted from the data obtained with VUV-sensitive devices. The resulted EL yield of ordinary EL, shown in Figure 11, is in good agreement with the theory.…”

“…Figure13. Gallery of concepts of charge signal amplification in two-phase detectors, using electron avalanching in the gas phase and charge or optical readout, by 2012 in order of introduction.…”

SiPM-matrix readout of two-phase argon detectors using electroluminescence in the visible and near infrared range

“…In addition to the ordinary EL mechanism, a concurrent EL mechanism, based on bremsstrahlung of drifting electrons scattered on neutral atoms (so-called "neutral bremsstrahlung", NBrS), has been recently revealed [15,16]. It was shown that the NBrS effect can explain two remarkable properties of proportional electroluminescence: photon emission below the Ar excitation threshold and the substantial contribution of a non-VUV spectral component.…”