Yu. M. Gavrilyuk

Pulse shape analysis and identification of multipoint events in a large-volume proportional counter in an experimental search for 2K capture of 78Kr

Abstract57-69A pulse shape analysis algorithm and a method for suppressing the noise component of signals from a large copper proportional counter in the experiment aimed at searching for 2K capture of 78Kr are described. These signals correspond to a compound event with different numbers of charge clusters from primary ionization. A technique for separating single-and multipoint events and determining the charge in individual clusters is presented. Using the Daubechies wavelets in multiresolutional signal analysis, it is possible to increase the sensitivity and the resolution in extraction of multipoint events in the detector by a factor of 3–4.A pulse shape analysis algorithm and a method for suppressing the noise component of signals from a large copper proportional counter in the experiment aimed at searching for 2K capture of Kr are described. These signals correspond to a compound event with different numbers of charge clusters due to from primary ionization is formed by these signals. A technique for separating singleand multipoint events and determining the charge in individual clusters is presented. Using the Daubechies wavelets in multiresolutional signal analysis, it is possible to increase the sensitivity and the resolution in extraction of multipoint events in the detector by a factor of 3÷ 4.

Results of experiments devoted to searches for 2K capture on 78Kr and for the double-beta decay of 136Xe with the aid of proportional counters

A brief description of two low-background setups deployed at the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences) and intended for searches for two types of double-beta decay of inert-gas isotopes—2K capture on 78Kr and the double-beta decay of 136Xe—is given. The two setups in question have similar structures and employ identical large high-pressure copper proportional counters as detectors. Upon a treatment of data from measurements with krypton samples differing in the content of the isotope 78Kr, the spectrum for an enriched sample revealed an excess of events at a statistical-significance level of about two standard deviations (2σ). If one attributes this excess to 2K(2ν) capture on 78Kr, the respective half-life is T1/2 = 1.4−0.7+2.3 × 1022 yr at a 90% C.L. A treatment of data from measurements with xenon samples differing in content of the isotope 136Xe led to the appearance of an excess of events in the spectrum for an enriched sample at a statistical-significance level of about 2.2σ. If one assumes that this excess is due to the two-neutrino double-beta decay of 136Xe, then the respective half-life is T1/2 = 5.8−1.8+4.7 × 1021 yr.

Correlation of variations in the thermal neutron flux from the Earth’s crust with the Moon’s phases and with seismic activity

The results of the long-term recording of thermal neutron flux near the Earth’s surface with the use of an unshielded scintillation thermal-neutron detector are presented. The data obtained indicate the presence of periodic variations in the thermal neutron flux with the lunar diurnal and the lunar monthly periods. A hypothesis about the existence in the Earth’s crust of radon-neutron tidal variations in the concentration of thermal neutrons, correlated with the Moon’s phases and which have the gravitational origin, is formulated and confirmed experimentally. A simple mathematical model is proposed, which satisfactorily describes the observed variations. The case of the anomalous behavior of thermal neutrons is presented, which correlates with the high local seismic activity.

Sources of the systematic errors in measurements of 214Po decay half-life time variations at the Baksan deep underground experiments

The design changes of the Baksan low-background TAU-1 and TAU-2 set-ups allowed to improve a sensitivity of 214Po half-life (τ) measurements up to the 2.5 × 10−4 are described. Different possible sources of systematic errors influencing on the τ-value are studied. An annual variation of 214Po half-life time measurements with an amplitude of A = (6.9 ± 3) × 10−4 and a phase of φ = 93 ± 10 days was found in a sequence of the week-collected τ-values obtained from the TAU-2 data sample with total duration of 480 days. 24 hours’ variation of the t-value measurements with an amplitude of A = (10.0 ± 2.6) × 10−4 and phase of φ = 1 ± 0.5 hours was found in a solar day 1 hour step t-value sequence formed from the same data sample. It was found that the 214Po half-life averaged at 480 days is equal to 163.45 ± 0.04 μs.

New experiment on search for the resonance absorption of solar axion emitted in the M1 transition of 83Kr nuclei

Axions with an energy of 9.4 keV emitted in the M1 transition of 83Kr nuclei in the Sun have been sought in the resonance absorption reaction A + 83Kr → 83Kr* → 83Kr + γ, e (9.4 keV). A proportional gas chamber filled with krypton and placed in a low-background setup at the underground laboratory of the Baksan neutrino observatory was used to detect γ-ray photons and electrons appearing after the decay of a nuclear level. As a result, a new constraint has been determined on the isoscalar and isovector coupling constants of the axion with nucleons: |gAN3– gAN0| ≤ 1.29 × 10–6. This constraint results in the following new bound on the mass of the axion in the hadronic axion model: mA ≤ 100 eV (95% C.L.).

First result of the experimental search for the 2K-capture of 124Xe with the copper proportional counter

First result of experiment for searching of 2K-capture of 124Xe with the large-volume copper proportional counter (LPC) is given. The 12 liters sample with 63.3% (44 g) of 124Xe was used in measurements. The limit on the half-life of 124Xe with regard to 2K(2ν)-capture for the ground state of 124Te (0+ → 0+, g.s.) has been found: T1/2 ≥ 4.67 × 1020 yr (90% C.L.). A sample with volume 52 liters comprising of 124Xe (10.6L - 58.6 g) and 126Xe (14.1L - 79.3 g) will used at the next step of the experiment to increase a sensitivity of 2K-caption of 124Xe registration. In this case sensitivity to the investigated process will be at the level of S = 1.46 × 1021 yr (90% C.L.) for 1 year measurement.

A technique for searching for the 2K capture in 124Xe with a copper proportional counter

An experimental technique for searching for the 2K capture in 124Xe with a large low-background copper proportional counter is described. Such an experiment is conducted at the Baksan Neutrino Observatory of the Institute for Nuclear Research of the Russian Academy of Sciences. The experimental setup is located in the Low-Background Deep-Level Laboratory at a depth of 4900 m.w.e., where the flux of muons of cosmic rays is suppressed by a factor of 107 relative to that at the Earth’s surface. The setup incorporates a proportional counter and low-background shielding (18 cm of copper, 15 cm of lead, and 8 cm of borated polyethylene). The results of processing the data obtained in 5 months of live measurement time are presented. A new limit on the half-life of 124Xe with respect to the 2K capture is set at the level of 2.5 × 1021 years.

Large-Volume Detector at the Baksan Neutrino Observatory for Studies of Natural Neutrino Fluxes for Purposes of Geo- and Astrophysics

At the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences, Moscow) deployed in the Caucasus mountains, it is proposed to create, at a depth corresponding to 4760 mwe, a large-volume neutrino detector on the basis of a liquid scintillator with a target mass of 10 kt. The detector in question is intended for recording natural fluxes of neutrinos whose energy may be as low as 100MeV. Neutrino fluxes from various sources are considered in the present study, and the expected effect in the proposed detector is estimated. The detector hat is being developed at the Baksan Neutrino Observatorywill become part of the world network of neutrino detectors for studying natural neutrino fluxes.

Results of a search for daily and annual variations of the 214Po half-life at the two year observation period

The brief description of installation TAU-2 intended for long-term monitoring of the half-life value

Analysis of the “Ulitka” noise background as an anti-coincidence filter for the OGRAN gravitational-wave antenna

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