A. V. Shakirov

RED-100 detector for the first observation of the elastic coherent neutrino scattering off xenon nuclei

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 worlds 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.

Noise characteristics of low-background Hamamatsu R11410-20 photomultiplier tubes

The RED-100 two-phase liquid xenon emission detector is developed today for the experiment aimed at searching for elastic coherent neutrino scattering off atomic nuclei. The main elements of the photodetector system of the RED-100 detector are Hamamatsu R11410-20 photomultiplier tubes (PMTs) dedicated for low-background experiments and liquid xenon environment. The basic characteristics of the PMTs are investigated, in particular, noise pulses and afterpulses, which may cause difficulties in searching for rare events. Amplitude distributions of the noise pulses and time distributions of the afterpulses, as well as the dependences of the noise pulse rate on the PMT bias voltage and the temperature are presented.

A controllable voltage divider for Hamamatsu R11410-20 photomultipliers for use in the RED 100 emission detector

A control circuit for the operation of Hamamatsu R11410-20 photomultiplier tubes (PMTs), which is intended for use in the RED 100 liquid-xenon emission detector, was developed. To prevent the photocathode degradation due to intense flashes that are associated with signals from high-energy cosmic-ray muons, the circuit forms a voltage pulse that is fed to the PMT photocathode and “blocks” the interelectrode gap between the photocathode and the first dynode. Thus, electron current through this gap is stopped for some time, which suffices for the complete collection of ionization electrons in the RED 100 detector after a cosmic muon passes its sensitive volume. The parameters of the circuit are selected such that the PMT relaxation time after the termination of a blocking pulse, which is determined by the transient processes in the divider, is ∼200 μs for a divider with a total resistance of 20 MΩ. This is acceptable for the intended application of the RED 100 detector in an experiment on the search for coherent neutrino scattering off xenon nuclei.

The RED-100 two-phase emission detector

The RED-100 experimental setup, which is designed to detect elastic coherent neutrino scattering off xenon nuclei, is described. One specific feature of this setup is the possibility of using it in above ground experiments. The setup is based on the RED-100 two-phase emission detector in which liquid xenon is used as a working medium for detection of rare events. The results of the technical run with the setup are presented. These are the evidence of the normal operation of all systems and the readiness of the setup for carrying out an experiment.

Purification of liquid xenon with the spark discharge technique for use in two-phase emission detectors

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.

Performance of Hamamatsu R11410-20 PMTs under intense illumination in a two-phase cryogenic emission detector

Hamamatsu R11410-20 PMTs are used in the RED-100 two-phase xenon emission detector built to search for the rare process of coherent elastic neutrino-nucleus scattering using intense artificial neutrino flux. We demonstrate how to adapt the PMTs for their operation under strong illumination caused by electroluminescent signals from gamma and cosmogenic muon backgrounds which are significant at shallow depth experimental sites. The PMT linearity is demonstrated for signals in the dynamic range from 1 to 2*104 photoelectrons. Impact of a photoelectric effect at the PMT first dynode to the capabilities of the RED-100 photodetection system is studied and quantified.

Synthesis of Titanium Nanoparticles in Liquid Xenon by a High-Voltage Discharge

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.

Thermostatting of the RED-100 liquid-xenon emission detector

The thermal stabilization system of the RED-100 liquid-xenon two-phase emission detector for the experiment aimed at detecting the effect of coherent neutrino scattering off xenon nuclei has been tested. The system is based on thermosyphons (closed two-phase heat pipes) that are filled with nitrogen and use liquid nitrogen boiling at atmospheric pressure as a cooler. The system is capable of keeping the working medium of the RED-100 detector at a temperature of 167 K with a precision of <1 K.