Spectroscopic analysis of the gaseous argon scintillation with a wavelength sensitive particle detector

Abstract

We performed a time-resolved spectroscopic study of the VUV/UV scintillation of gaseous argon as a function of pressure and electric field, by means of a wavelength sensitive detector operated with different radioactive sources. Our work conveys new evidence of distinctive features of the argon light which are in contrast with the general assumption that, for particle detection purposes, the scintillation can be considered to be largely monochromatic at 128 nm (second continuum). The wavelength and time-resolved analysis of the photon emission reveal that the dominant component of the argon scintillation during the first tens of ns is in the range [160, 325] nm. This light is consistent with the third continuum emission from highly charged argon ions/molecules. This component of the scintillation is field-independent up to 25 V/cm/bar and shows a very mild dependence with pressure in the range [1, 16] bar. The dynamics of the second continuum emission is dominated by the excimer formation time, whose variation as a function of pressure has been measured. Additionally, the time and pressure-dependent features of electron-ion recombination, in the second continuum band, have been measured. This study opens new paths toward a novel particle identification technique based on the spectral information of the noble-elements scintillation light.

Time and band-resolved scintillation in time projection chambers based on gaseous xenon

“…Data acquisition was performed with a CAEN DT5725 board having 14 bits, 125 MHz bandwidth and a sampling time of 4 ns. Experience shows that, with 10's of thousands events, this bandwidth and binning is sufficient to reconstruct exponential time constants down to at least 4 ns (e.g., [39]), as needed for present studies. The acquisition window was set to 5 µs for S1 data (in order to account for the charge recombination tail at high pressures) and to 12 µs for S2 data (in order to fully include the spatial extent of the ionization trail for all conditions studied).…”

“…[38]), attention has been brought recently to a number of subdominant and intriguing scintillation mechanisms, hitherto neglected. The '3rd continuum' emission, for instance, has been proposed in [39] as a means to perform electron/nucleus separation in argon TPCs, with potential use in direct dark matter searches. Along the same line, for TPCs that are strongly reliant on keV/MeV-electron scintillation such as NEXT [40], the absolute scintillation yield and spectral content is crucial, as it determines for instance how far from the cathode a krypton event can be reconstructed during energy calibrations [41].…”

“…In practice, and given the higher quantum efficiency and better optical properties involved in their detection (less absorption to gas impurities and better reflectivity at surfaces), it can be expected that the 3rd continuum emission represents a substantial fraction of the primary scintillation in noble-gas TPCs, dominating even over the fast component in some conditions (e.g. in argon in the range 1-5 bar [39]). On another front, the NEXT collaboration recently discussed the possible presence of charge recombination for MeV-electron tracks at pressures as high as 10 bar [43] and, despite measurements for X-rays have excluded recombination effects up to 10 bar in [44] , and the work of the collaboration points to the absence of delayed recombination light, the impact of the phenomenon for calorimetry in ββ0ν experiments is important enough that it requires further elucidation , e.g., by studying the effect as a function of electric field.…”

Performance of Hamamatsu VUV4 SiPMs for detecting liquid argon scintillation

“…In addition to observing only a small amount of light, the windowed S13371 also recorded signals that feature a dominant prompt component with a much suppressed delayed tail. This observation suggests that the prompt argon scintillation may include a component with a longer wavelength than that of the delayed triplet de-excitation light (128 nm), possibly in the longer wavelength UV as reported for gaseous argon in [28]. The total triplet state light measured by the windowed SiPM is less than 1% of that measured by the windowless SiPM, and may have originated from VUV light leakage into the SiPM around the quartz window, gamma interactions in the liquid argon between the quartz window and the SiPM sensitive face, optical crosstalk from the windowless SiPM units (photons produced by an active SiPM during avalanches leaving the SiPM [29]), or some unknown wavelength shifting process in the detector.…”

Real-time processing system for cavity ring down signal based on ZYNQ chip

“…With the rapid development of cavity ring-down(CRD) technology in recent years, its application has ranged from solving the problem of ultra-high reflectivity measurement to the most widely used cavity ring-down spectroscopy technology. It covers the fields of spectroscopy, atomic and molecular chemistry, applied chemistry, and biochemistry [1,2,3,4,5,6]. The decay time constant of the ring-down process is a core physical information of the cavity ring-down technology [7,8,9,10,11], and its measurement accuracy directly affects the reliability of the entire system.…”