RED-100 is a two-phase liquid xenon time projection chamber with an active volume containing 126 kg of liquid xenon. The detector was exposed to an antineutrino flux of about 1.4×1013 cm−2 s−1 at a distance of 19 m from the 3.1 GW Kalinin nuclear power plant reactor core. The comparison of data from 331 kg·days with the reactor on and 106 kg·days with the reactor off shows no statistically significant excess and the constraint on coherent elastic scattering of antineutrinos off xenon nuclei cross section is given.

The cryogenic system of the RED-100 two-phase emission detector has been modified to enable operation with liquid argon as a working medium with the aim of searching for the effect of coherent elastic scattering of reactor electron antineutrinos by argon nuclei.

RED-100 is a two-phase Xe detector designed and built for the study of coherent elastic neutrino-nucleus scattering CEvNS of reactor antineutrinos. A comprehensive calibration was performed in order to obtain important parameters of the detector during its exposition at the Kalinin Nuclear Power Plant (Tver, Russia). This paper describes the analysis of calibration data, position and energy reconstruction procedures, and evaluation of the efficiency of electron extraction from the liquid xenon to the gas phase.

Показано, что рабочий объем двухфазного эмиссионного детектора РЭД-100, работающего в условиях наземной лаборатории и использующего жидкий ксенон в качестве рабочего вещества, является источником одноэлектронных шумовых сигналов с характерной частотой ~200 кГц. Обсуждаются возможные механизмы генерации шумов такого рода и методы их подавления.

— It is shown that the working volume of the RED-100 two-phase emission detector, which operates in a ground-based laboratory with liquid xenon used as a working substance, is a source of single-electron noise signals with a characteristic frequency of ~200 kHz. Possible mechanisms of generation of these noises and methods for their suppression are discussed.

The RED-100 experiment with a liquid xenon target was carried out at Kalinin Nuclear Power Plant. The goal of the experiment is the detection and study of the coherent elastic neutrino nucleus scattering process (CEνNS) for the low-energy antineutrinos in close vicinity to a reactor core. A good understanding of the external radioactive background is needed to achieve this goal. This paper describes the external background conditions for the RED-100 experiment at Kalinin Nuclear Power Plant.

The RED-100 two-phase xenon emission detector has been deployed at 19-m distance from the reactor core of the Kalinin Nuclear Power Plant (KNPP) in 2021 - 2022 for investigation of the possibility to observe reactor antineutrinos using the effect of coherent elastic neutrino-nucleus scattering (CEνNS). The performance of the main systems of the RED-100 setup at operating nuclear power plant is described. There is no correlation of the radioactive background at the experimental setup site with ON and OFF states of the reactor. The data taking run was carried out at the beginning of the year 2022 and covered both the reactor OFF and ON periods.

RED-100 is a two-phase detector for study of coherent elastic scattering of reactor electron antineutrinos off xenon atomic nuclei. The detector contains a total of 200 kg of liquid xenon in a titanium cryostat with 160 kg of xenon in active volume inside a Teflon-made light collection cage associated with electrode system. The active volume is viewed by two arrays of nineteen 3''-diameter Hamamatsu R11410-20 PMTs assembled in two planes on top and bottom. The electrode system is equipped with an electron shutter (a patented device) to reduce a "spontaneous" single-electron noise. The detector was tested in a ground-level laboratory. The obtained results demonstrate that detection of coherent elastic scattering of reactor antineutrinos off xenon nuclei at Kalinin nuclear power plant with the RED-100 detector is feasible with a threshold of 4 ionization electrons.

An integral method is described for processing xenon used as a working medium in the RED-100 two-phase emission detector constructed in the NRNU MEPhI to study the process of elastic coherent neutrino scattering off atomic nuclei. The developed technology for purifying xenon and the detector has made it possible to increase the lifetime of quasi-free electrons in the 205-kg liquid xenon from ≤0.1 to ≥400 μs in fields of 50−500 V/cm. The entire procedure takes approximately 1000 h. The method can be used to process working media for new-generation two-phase emission detectors designed to conduct basic research, in particular, searching for dark matter in the form of weakly interacting massive particles, detecting boron solar neutrinos, and searching for neutrinoless double-beta decay.

The formation of titanium nanoparticles (NPs) in a high-voltage electric discharge between titanium electrodes in liquid xenon at a temperature of –105°C has been observed. It has been shown that these titanium nanoparticles have a spherical shape with an average diameter of <50 nm and they possess high chemical activity. This makes it possible when a relative mass concentration of NP reaches ~10 –6 to efficiently purify xenon from electronegative impurities for its use as a working medium for a new generation of high-efficiency nuclear radiation detectors.

AbstractThe formation of titanium nanoparticles (NPs) in a high-voltage electric discharge between titanium electrodes in liquid xenon at a temperature of –105°C has been observed. It has been shown that these titanium nanoparticles have a spherical shape with an average diameter of <50 nm and they possess high chemical activity. This makes it possible when a relative mass concentration of NP reaches ~10^–6 to efficiently purify xenon from electronegative impurities for its use as a working medium for a new generation of high-efficiency nuclear radiation detectors.

The current status of the RED-100 experiment is described. The detector is being prepared for the experiment on the first observation of a coherent elastic neutrino-nucleus scattering at the Kalinin Nuclear Power Plant (Russia). The estimation of the signal event rate for this process has been done by Monte Carlo with the use of the full detector geometry and the modern data on the ionisation yield for nuclear recoils in the liquid xenon. The simulation has shown very promising significant increase of it, by at least a factor of 2, in compare with our previous estimations.

A procedure for spark-discharge purification of a liquid xenon sample with a mass of 55 kg is described. The average lifetime of ionization electrons before capture by electronegative impurities in liquid xenon increased from ≤ 0.1 μs to ≥ 50 μs for an electric field of 50–500 V/cm as a result of the procedure. The xenon purified with this method is intended for use in the RED-100 detector for observation of the process of coherent elastic neutrino scattering off xenon nuclei.

A SensL MicroFC-SMT-60035 6 x 6mm(2) silicon photo-multiplier coated with a NOL-1 wavelength shifter have been tested in the liquid xenon to detect the 175-nm scintillation light. For comparison, a Hamamatsu vacuum ultraviolet sensitive MPPC VUV3 3 x 3mm(2) was tested under the same conditions. The photodetection efficiency of 13.1 +/- 2.5% and 6.0 +/- 1.0%, correspondingly, is obtained.

Krypton-85 is an anthropogenic beta-decaying isotope which produces low energy backgrounds in dark matter and neutrino experiments, especially those based upon liquid xenon. Several technologies have been developed to reduce the Kr concentration in such experiments. We propose to augment those separation technologies by first adding to the xenon an 85Kr-free sample of krypton in an amount much larger than the natural krypton that is already present. After the purification system reduces the total Kr concentration to the same level, the final 85Kr concentration will be reduced even further by the dilution factor. A test cell for measurement of the activity of various Kr samples has been assembled, and the activity of 25-year-old krypton has been measured. The measured activity agrees well with the expected activity accounting for the 85Kr abundance of the earth's atmosphere in 1990 and the half-life of the isotope. Additional tests with a Kr sample produced in the year 1944 (before the atomic era) have been done in order to demonstrate the sensitivity of the test cell.

Results of the experimental study of electron emission from liquid xenon via electroluminescence of the gas phase are presented. We report on observation of a peculiar kind of delayed electroluminescent signal following initial electroluminescence caused by ionizing particles. We also present the results of a study of spontaneous single electron emission following cosmic muon signals. It was found that the rate of spontaneous single electron signals strongly depends on the time passed since the initial electroluminescence happened. The analysis of experimental data showed that both spontaneous single electron signals and delayed electroluminescent signals are associated with ionization electrons which are trapped by the potential barrier at the interface.

The RED-100 (Russian Emission Detector) is being constructed for the experiment to search for elastic coherent neutrino scattering off atomic nuclei. This fundamental process was predicted several decades ago by the Standard Model of electroweak interactions but has not been discovered yet. The RED-100 is a two-phase emission xenon detector containing ∼200 kg of the liquid Xe (∼ 100 kg of that is in a fiducial volume). One of the possible sites to carry out the experiment is the SNS (Spallation Neutron Source) facility at Oak Ridge National Laboratory, USA. SNS is the world's most intense pulsed source of neutrinos and unique place to study neutrino properties. The energy spectrum of neutrinos produced at the SNS extends up to ∼ 50 MeV and satisfies coherence condition. These neutrinos give kinetic energies of Xe recoils up to a few tens of keV where the response of nuclear recoils is well-known from neutron calibrations of dark matter detectors. The detector will be deployed in the basement under the experimental hall at a distance of ∼30 meters from the SNS target. The expected signal and background (neutron and gamma) are estimated for this specific location. The detector details, current status and future plans are provided.