Pulse-shape discrimination and energy resolution of a liquid-argon scintillator with xenon doping

Abstract

Liquid-argon scintillation detectors are used in fundamental physics experiments and are being considered for security applications. Previous studies have suggested that the addition of small amounts of xenon dopant improves performance in light or signal yield, energy resolution, and particle discrimination. In this study, we investigate the detector response for xenon dopant concentrations from 9 ± 5 ppm to 1100 ± 500 ppm xenon (by weight) in 6 steps. The 3.14-liter detector uses tetraphenyl butadiene (TPB) wavelength shifter with dual photomultiplier tubes and is operated in single-phase mode. Gamma-ray-interaction signal yield of 4.0 ± 0.1 photoelectrons/keV improved to 5.0 ± 0.1 photoelectrons/keV with dopant. Energy resolution at 662 keV improved from (4.4 ± 0.2)% (σ) to (3.5 ± 0.2)% (σ) with dopant. Pulseshape discrimination performance degraded greatly at the first addition of dopant, slightly improved with additional additions, then rapidly improved near the end of our dopant range, with performance becoming slightly better than pure argon at the highest tested dopant concentration. Some evidence of reduced neutron scintillation efficiency with increasing dopant concentration was observed. Finally, the waveform shape outside the TPB region is discussed, suggesting that the contribution to the waveform from xenon-produced light is primarily in the last portion of the slow component.

Fast component re-emission in Xe-doped liquid argon

“…This improves position reconstruction since the re-emission occurs in the point of interaction.It was shown that gaseous xenon doped in LAr works as a volume-distributed WLS shifting the wave length from 128 nm to around 175 nm [14][15][16]. Currently several groups are studying its wavelength shifting parameters and the properties of the LAr+Xe mixture [17][18][19][20]. As shown previously [21], Xe doped in small concentrations (up to 260 ppm by mass) re-emits only the slow component of LAr scintillation.…”

“…As shown previously [21], Xe doped in small concentrations (up to 260 ppm by mass) re-emits only the slow component of LAr scintillation. Thus, at small concentrations it is impossible to use Xe as a single stage WLS and to keep PSD capability of the LAr+Xe mixture at the same time.In previous studies with a broad concentration range (up to 1000 ppm by mass) [19,20], it was shown that Xe-doping slightly improves the light yield and the energy resolution. Also they demonstrated that the PSD capability degrades with decreasing of Xe concentration in LAr.…”

“…Also they demonstrated that the PSD capability degrades with decreasing of Xe concentration in LAr. Both experiments [19,20] have shown that at the concentrations of Xe > 300 ppm the PSD capability of the LAr+Xe mixture is higher than that of pure LAr.One experimental study [20] indicated evidence of fast component re-emission at high Xe concentrations. However, the measurement scheme was very complicated, statistics were quite low, and the effect of the re-emission by Xe was obscured by the use of TPB.…”

“…One experimental study [20] indicated evidence of fast component re-emission at high Xe concentrations. However, the measurement scheme was very complicated, statistics were quite low, and the effect of the re-emission by Xe was obscured by the use of TPB.…”

Increasing the sensitivity of LXe TPCs to dark matter by doping with helium or neon

“…The amount of energy required to form these molecules decreases for increasing Z, and the wavelength of pure helium and neon scintillation is much deeper in the UV than xenon light [13]. Data from mixtures with ∼10 ppm xenon in liquid argon show that excitations can be efficiently transferred from argon to xenon, with the resulting light emission emitted at xenon wavelengths [14]; energy transfers from excitations of the heavy noble elements to lighter ones do not take place because they are not energetically favorable. Therefore, the wavelength of S1/S2 light in a doped LXe-TPC will be unchanged.…”