S. I. Panasenko

Working characteristics of the New Low-Background Laboratory(DULB-4900)

The Baksan Neutrino Observatory (BNO) of Institute for Nuclear Research of the Russian Academy of Science is one of major old underground laboratories in the world for experiments in the field of a nuclear physics, particle and astroparticle physics. A concise technical characteristic of a new lowbackground laboratory DULB-4900 of the BNO is presented. The laboratory is located at a distance of 3700 m from the main entry to the Observatory tunnel, in the hall of 6 6 40 m 3 . Thickness of the mountain rock over DULB corresponds to 4900 m:w:e:, thereby decreasing cosmic ray flux by 10 7 times. The technique and the results of background measurements in the Hall, ordinary box and low-background box are presented. 222 Rn contamination in the laboratory air has been measured by direct detection of -radiation of its daughter 214 Bi distributed over the volume of the lowbackground box. The results of the data analysis are presented.

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.

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 stage of search for 2K(2ν) capture of 78Kr

A technique to search for 2K capture of 78Kr with a large low-background proportional counter filled with a sample of krypton enriched in 78Kr up to 99.8% at a pressure of 4.51 atm is described in this paper. The results of first measurements are presented. An analysis of data collected for 159 h yielded a new limit to the half-life of 78Kr with regard to 2K capture (T1/2 ≥ 1.5 × 1021 yr (90% C.L.)). The sensitivity of the facility to the process for one year of measurement was evaluated to be S = 1.0 × 1022 yr (90% C.L.).

Results of a search for 2β decay of 136Xe with high-pressure copper proportional counters in Baksan Neutrino Observatory

A search for 2β decay of 136Xe with two high-pressure copper proportional counters was carried out in the Baksan Neutrino Observatory. The experiment is based on comparison of spectra measured with natural and enriched xenon. No evidence was found for 2β(2ν) and 2β(0ν) decay. The decay half-life limit based on data measured for 8000 h is T1/2 ≥ 8.5 × 1021 yr for 2ν mode and T1/2 ≥ 3.1 × 1023 yr for 0ν mode (90% 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.

Comparative study of the double- K -shell-vacancy production in single- and double-electron-capture decay

We carried out the comparative study of the signal from the decay of double

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

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