arXiv subjects

L. Shekhtman

Publications and source records attributed to L. Shekhtman.

At least 19 recordsLinked to original sources

arXiv2018

Revealing neutral bremsstrahlung in two-phase argon electroluminescence

Proportional electroluminescence (EL) in noble gases has long been used in two-phase detectors for dark matter search, to record ionization signals induced by particle scattering in the noble-gas liquid (S2 signals). Until recently, it was believed that proportional electroluminescence was fully due to VUV emission of noble gas excimers produced in atomic collisions with excited atoms, the latter being in turn produced by drifting electrons. In this work we consider an additional mechanism of proportional electroluminescence, namely that of bremsstrahlung of drifting electrons scattered on neutral atoms (so-called neutral bremsstrahlung); it is systemically studied here both theoretically and experimentally. In particular, the absolute EL yield has for the first time been measured in pure gaseous argon in the two-phase mode, using a dedicated two-phase detector with EL gap optically read out by cryogenic PMTs and SiPMs. We show that the neutral bremsstrahlung effect can explain two intriguing observations in EL radiation: that of the substantial contribution of the non-VUV spectral component, extending from the UV to NIR, and that of the photon emission at lower electric fields, below the Ar excitation threshold. Possible applications of neutral bremsstrahlung effect in two-phase dark matter detectors are discussed.

physics.ins-det↗

arXiv2017

Measurement of the ionization yield of nuclear recoils in liquid argon using a two-phase detector with electroluminescence gap

A measurement of ionization yields in noble-gas liquids is relevant to the energy calibration of nuclear recoil detectors for dark matter search and coherent neutrino-nucleus scattering experiments. In this work we further study the ionization yield of nuclear recoils in liquid Ar, using a two-phase detector with an electroluminescence gap and DD neutron generator. The ionization yields of nuclear recoils in liquid Ar were measured at 233 keV and electric fields of 0.56 and 0.62 kV/cm; their values amounted to 5.9 $\pm$ 0.8 and 7.4 $\pm$ 1 e$^-$/keV, respectively. The characteristic dependences of the ionization yield on energy and electric field were determined, while comparing the results obtained to those at lower energies and higher fields.

astro-ph.IM↗

arXiv2017

Further studies of proportional electroluminescence in two-phase argon

The study of proportional electroluminescence in two-phase argon is relevant in the field of noble-gas liquid detectors for dark matter search and low-energy neutrino experiments. In this work, we continued to study proportional electroluminescence (EL) in two-phase argon doped with a minor (9 ppm) admixture of nitrogen, in the VUV, UV and visible spectral ranges. We confirmed the effect of enhancement of the EL yield, as well as the presence of non-VUV component in addition to that of VUV, in proportional electroluminescence in two-phase Ar. On the other hand, the contribution of non-VUV component determined here within the model of N2 emission in the UV, turned out to be insufficient to explain the EL yield enhancement effect. Accordingly, the problem of proportional electroluminescence in two-phase Ar remains unresolved.

astro-ph.IM↗

arXiv2017

Study of cryogenic photomultiplier tubes for the future two-phase cryogenic avalanche detector

We report the results of a characterization study of several types of cryogenic photomultipliers manufactured by Hamamatsu Photonics and intended for operation in liquid Ar conditions, namely: compact 2-inch R6041-506MOD tubes, 3-inch R11065-10 and R11065-MOD tubes for operation in liquid Ar and 3-inch R11410-20 tubes originally designed for operation in liquid Xe. These types of PMT are proposed for installation into the future two-phase cryogenic avalanche detector that is developed in the Laboratory of Cosmology and Particle Physics of the Novosibirsk State University jointly with the Budker Institute of Nuclear Physics. Eight R11065 PMTs and seven R11410-20 tubes were tested and all demonstrated excellent performance in liquid Ar in terms of gain and relative single electron efficiency. All 3-inch PMTs showed a maximal gain in liquid Ar above 5x10^6 and relative single electron efficiency higher than 95%. Compact R6041-506MOD tubes have dynode system different from that of the 3-inch photomultipliers and thus their single electron energy resolution and relative efficiency is much worse than that of 3-inch tubes. From 21 2-inch PMTs only 12 tubes were selected with acceptable, i.e. higher than 75%, relative single electron efficiency and the maximal gain higher than 5x10^6. However, these PMTs are very attractive because they are the only compact type of tubes that can operate in liquid Ar.

astro-ph.IM↗

arXiv2016

Two-phase Cryogenic Avalanche Detector with electroluminescence gap operated in argon doped with nitrogen

A two-phase Cryogenic Avalanche Detector (CRAD) with electroluminescence (EL) gap, operated in argon doped with a minor (49$\pm$7 ppm) admixture of nitrogen, has been studied. The EL gap was optically read out using cryogenic PMTs located on the perimeter of the gap. We present the results of the measurements of the N$_2$ content, detector sensitivity to X-ray-induced signals, EL gap yield and electron lifetime in the liquid. The detector sensitivity, at a drift field in liquid Ar of 0.6 kV/cm, was measured to be 9 and 16 photoelectrons recorded at the PMTs per keV of deposited energy at 23 and 88 keV respectively. Such two-phase detectors, with enhanced sensitivity to the S2 (ionization-induced) signal, are relevant in the field of argon detectors for dark matter search and low energy neutrino detection.

physics.ins-det↗

arXiv2016

X-ray ionization yields and energy spectra in liquid argon

The main purpose of this work is to provide reference data on X-ray ionization yields and energy spectra in liquid Ar to the studies in the field of Cryogenic Avalanche Detectors (CRADs) for rare-event and other experiments, based on liquid Ar detectors. We present the results of two related researches. First, the X-ray recombination coefficients in the energy range of 10-1000 keV and ionization yields at different electric fields, between 0.6 and 2.3 kV/cm, are determined in liquid Ar based on the results of a dedicated experiment. Second, the energy spectra of pulsed X-rays in liquid Ar in the energy range of 15-40 keV, obtained in given experiments including that with the two-phase CRAD, are interpreted and compared to those calculated using a computer program, to correctly determine the absorbed X-ray energy. The X-ray recombination coefficients and ionization yields have for the first time been presented for liquid Ar in systematic way.

physics.ins-det↗

arXiv2015

Proportional electroluminescence in two-phase argon and its relevance to rare-event experiments

Proportional electroluminescence (EL) in gaseous Ar has for the first time been systematically studied in the two-phase mode, at 87 K and 1.00 atm. Liquid argon had a minor (56 ppm) admixture of nitrogen, which allowed to understand, inter alia, the effect of N2 doping on the EL mechanism in rare-event experiments using two-phase Ar detectors. The measurements were performed in a two-phase Cryogenic Avalanche Detector (CRAD) with EL gap located directly above the liquid-gas interface. The EL gap was optically read out in the Vacuum Ultraviolet (VUV), near 128 nm (Ar excimer emission), and in the near Ultraviolet (UV), at 300-450 nm (N2 Second Positive System emission), via cryogenic PMTs and a Geiger-mode APD (GAPD). Proportional electroluminescence was measured to have an amplification parameter of 109+-10 photons per drifting electron per kV overall in the VUV and UV, of which 51+-6% were emitted in the UV. The measured EL threshold, at an electric field of 3.7+-0.2 kV/cm, was in accordance with that predicted by the theory. The latter result is particularly relevant to DarkSide and SCENE dark matter search-related experiments, where the operation electric field was thereby on the verge of appearance of the S2 (ionization-induced) signal. The results obtained pave the way to the development of N2-doped two-phase Ar detectors with enhanced sensitivity to the S2 signal.

physics.ins-det↗

arXiv2015

Characterization of photo-multiplier tubes for the Cryogenic Avalanche Detector

New Cryogenic Avalanche Detector (CRAD) with ultimate sensitivity, that will be able to detect one primary electron released in the cryogenic liquid, is under development in the Laboratory of Cosmology and Particle Physics of the Novosibirsk State University jointly with the Budker Institute of Nuclear Physics. The CRAD will use two sets of cryogenic PMTs in order to get trigger signal either from primary scintillations in liquid Ar or from secondary scintillations in high field gap above the liquid. Two types of cryogenic PMTs produced by Hamamatsu Photonics were tested and the results are presented in this paper. Low background 3 inch PMT R11065- 10 demonstrated excellent performance according to its specifications provided by the producer. The gain measured with single electron response (SER) in liquid Ar reached 10^7, dark count rate rate did not exceed 300 Hz and pulse height resolution of single electron signals was close to 50%(FWHM). However, two R11065-10 PMTs out of 7 tested stopped functioning after several tens minutes of operation immersed completely into liquid Ar. The remaining 5 devices and one R11065-MOD were operated successfully for several hours each with all the parameters according to the producer specifications. Compact 2 inch PMT R6041-506-MOD with metal-channel dynode structure is a candidate for side wall PMT system that will look at electroluminescence in high field region above liquid. Four of these PMTs were tested in liquid Ar and demonstrated gain up to 2x10^7, dark count rate rate below 100 Hz and pulse height resolution of single electron signals of about 110% (FWHM).

physics.ins-det↗

arXiv2014

Measurement of the ionization yield of nuclear recoils in liquid argon at 80 and 233 keV

The energy calibration of nuclear recoil detectors is of primary importance to rare-event experiments such as those of direct dark matter search and coherent neutrino-nucleus scattering. In particular, such a calibration is performed by measuring the ionization yield of nuclear recoils in liquid Ar and Xe detection media, using neutron elastic scattering off nuclei. In the present work, the ionization yield for nuclear recoils in liquid Ar has for the first time been measured in the higher energy range, at 80 and 233 keV, using a two-phase Cryogenic Avalanche Detector (CRAD) and DD neutron generator. The ionization yield in liquid Ar at an electric field of 2.3 kV/cm amounted to 7.8+/-1.1 and 9.7+/-1.3 e-/keV at 80 and 233 keV respectively. The Jaffe model for nuclear recoil-induced ionization, in contrast to that Thomas-Imel, can probably consistently describe the energy dependence of the ionization yield.

physics.ins-det↗

arXiv2014

Performance degradation of Geiger-mode APDs at cryogenic temperatures

Two-phase Cryogenic Avalanche Detectors (CRADs) with THGEM multipliers, optically read out with Geiger-mode APDs (GAPDs), were proposed as potential technique for charge recording in rare-event experiments. In this work we report on the degradation of the GAPD performance at cryogenic temperatures revealed in the course of the study of two-phase CRAD in Ar, with combined THGEM/GAPD-matrix multiplier; the GAPDs recorded secondary scintillation photons from the THGEM holes in the Near Infrared. The degradation effect, namely the loss of the GAPD pulse amplitude, depended on the incident X-ray photon flux. The critical counting rate of photoelectrons produced at the 4.4 mm2 GAPD, degrading its performance at 87 K, was estimated as 10000 per second. This effect was shown to result from the considerable increase of the pixel quenching resistor of this CPTA-made GAPD type. Though not affecting low-rate rare-event experiments, the observed effect may impose some limitations on the performance of CRADs with GAPD-based optical readout at higher-rate applications.

physics.ins-det↗

arXiv2012

Study of infrared scintillations in gaseous and liquid argon - Part II: light yield and possible applications

We present here a comprehensive study of the light yield of primary and secondary scintillations produced in gaseous and liquid Ar in the near infrared (NIR) and visible region, at cryogenic temperatures. The measurements were performed using Geiger-mode avalanche photodiodes (GAPDs) and pulsed X-ray irradiation. The primary scintillation yield of the fast emission component in gaseous Ar was found to be independent of temperature in the range of 87-160 K; it amounted to 17000+/-3000 photon/MeV in the NIR in the range of 690-1000 nm. In liquid Ar at 87 K, the primary scintillation yield of the fast component was considerably reduced, amounting to 510+/-90 photon/MeV, in the range of 400-1000 nm. Proportional NIR scintillations (electroluminescence) in gaseous Ar were also observed; their amplification parameter at 160 K was measured to be 13 photons per drifting electron per kV. No proportional scintillations were observed in liquid Ar up to the electric fields of 30 kV/cm. The applications of NIR scintillations in dark matter search and coherent neutrino-nucleus scattering experiments and in ion beam radiotherapy are considered.

physics.ins-det↗

arXiv2006

Triple-GEM performance in He-based mixtures

The performance of triple-GEM detectors in He+N2 gas mixtures is studied in the range of 1-10 atm. The results obtained are relevant in the field of minimization of ionic space-charge effect in the TPC and neutron detection.

physics.ins-det↗

arXiv2005

Light multi-GEM detector for high-resolution tracking systems

Controlled etching of copper electrodes in Gas Electron Multiplier foils allows a reduction of the material budget by more than a factor of two for a triple-GEM detector. Detectors making use of thinned foils provide performances similar to those obtained with standard devices: a gain above 10^4 for a double-GEM, with energy resolution of 27 % fwhm for 5.9 keV X-rays.

physics.ins-det↗

arXiv2005

A Hadron Blind Detector for the PHENIX Experiment at RHIC

A Hadron Blind Detector (HBD) is being developed for the PHENIX experiment at RHIC. It consists of a Cherenkov radiator operated with pure CF4 directly coupled in a windowless configuration to a triple-GEM detector element with a CsI photocathode and pad readout. The HBD operates in the bandwidth 6-11.5 eV(110-200 nm). We studied the detector response to minimum ionizing particles and to electrons. We present measurements of the CsI quantum efficiency, which are in very good agreement with previously published results over the bandwidth 6-8.3 eV and extend them up to 10.3 eV. Discharge probability andaging studies of the GEMs and the CsI photocathode in pure CF4 are presented.

physics.ins-det↗

arXiv2004

Cryogenic avalanche detectors based on gas electron multipliers

We study the performances of gaseous and two-phase (liquid-gas) cryogenic detectors of ionizing radiation based on gas electron multipliers (GEMs) and operated in an avalanche mode in pure noble gases. The gas amplification in He, Ar and Kr is systematically studied at low temperatures, using triple-GEM multipliers. High gains, exceeding 10^4, were obtained in these gases in the range of 120-300 K. Stable electron avalanching was demonstrated in a saturated Kr vapor in the two-phase mode. These results are relevant for understanding basic mechanisms of electron avalanching at low temperatures and for applications in cryogenic particle detectors, in particular in dark matter and solar neutrino detectors.

physics.ins-det↗

arXiv2003

Development of a triple GEM UV-photon detector operated in pure CF4 for the PHENIX experiment

Results obtained with a triple GEM detector operated in pure CF4 with and without a reflective CsI photocathode are presented. The detector operates in a stable mode at gains up to 10^4. A deviation from exponential growth starts to develop when the total charge exceeds ~ 4 10^6 e leading to gain saturation when the total charge is ~ 2 10^7 e and making the structure relatively robust against discharges. No aging effects are observed in the GEM foils after a total accumulated charge of ~ 10 mC/cm^2 at the anode. The ion back-flow current to the reflective photocathode is comparable to the electron current to the anode. However, no significant degradation of the CsI photocathode is observed for a total ion back-flow charge of ~ 7 mC/cm^2.

physics.ins-det↗

arXiv2003

First results from cryogenic avalanche detectors based on gas electron multipliers

We study the performance of gaseous and two-phase (liquid-gas) cryogenic detectors of ionizing radiation, based on gas electron multipliers (GEMs). For the first time, high gas gains, exceeding 10^4, were obtained in pure He, Ar and Kr at low temperatures and the stable avalanche mode of operation was observed in the two-phase cryogenic detector in Kr. The electron avalanching at low temperatures, in the range of 120-300 K, is systematically studied.

physics.ins-det↗

arXiv2002

Further studies of GEM performance in dense noble gases

We further study the performance of single, double and triple Gas Electron Multiplier (GEM) detectors in pure noble gases at high pressures, in the range of 1-10 atm. We confirm that light noble gases, in particular He and its mixtures with Kr, have the highest gain, reaching 10^6, and an unusual gain dependence on pressure. Effects of the number of GEMs, GEM hole diameter and pitch are investigated in detail. In He, avalanche-induced secondary scintillations are observed at high gains, using the metal photocathode. These results are relevant in the field of avalanche mechanism in noble gases and X-ray, neutron and cryogenic particle detectors.

physics.ins-det↗