A technique for searching for the 2 K capture in 124 Xe with a copper proportional counter
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ORS AND METHODS OF INVESTIGATION
A Technique for Searching for the 2K Capture in 124Xe with a Copper Proportional Counter Yu. M. Gavrilyuka, A. M. Gangapsheva, V. V. Kazalova, V. V. Kuzminova, S. I. Panasenkob, S. S. Ratkevichb, D. A. Tekuevaa *, and S. P. Yakimenkoa a Institute
for Nuclear Research, Russian Academy of Sciences, pr. 60letiya Oktyabrya 7a, Moscow, 117312 Russia b Karazin Kharkiv National University, pl. Svobody 4, Kharkiv, 61077 Ukraine *email: [email protected] Received January 23, 2015
Abstract—An experimental technique for searching for the 2K capture in 124Xe with a large lowbackground copper proportional counter is described. Such an experiment is conducted at the Baksan Neutrino Obser vatory of the Institute for Nuclear Research of the Russian Academy of Sciences. The experimental setup is located in the LowBackground DeepLevel 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 lowbackground 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 pre sented. A new limit on the halflife of 124Xe with respect to the 2K capture is set at the level of 2.5 × 1021 years. Keywords: double beta decay, 2K capture, proportional counter. DOI: 10.1134/S1063778815130098
A 124Te** atom with two vacancies at the K shell is produced in the 124Xe(2eK, 2νe)124Te reaction with total transition energy Q = 2866 keV. The technique for searching for this reaction is based on the fact that the double Kvacancy filling in the daughter 124Te** atom is accompanied by the emission of two characteristic photons with an energy of 31.81 keV and a total energy release of 63.6 keV in ~73.4% of all cases. The residual shell excitation is removed via the emission of a single Auger electron ea (or several Auger electrons). If both characteristic photons are absorbed in the sensitive volume of the counter, the total energy release becomes distributed over three local regions within the volume of the counter (a threepoint event). The sig nals from such events have certain specific character istics and are investigated in the present study. Theoretical calculations for the 2K capture per formed using different models (QRPA and MCM) yield the following halflives of 124Xe with respect to the 2K capture: 1.08 × 1022 years [1] and 3.9 × 1023 years [2]. Using the XENON100 data, the authors of [3] determined a limit for the halflife of 124Xe with respect to the 2K capture (1.66 × 1021 years) and calcu lated a sensitivity value at the level of 2.9 × 1021 years for a threeyearlong experiment. The present experiment on searching for the 2K capture in 124Xe is conducted in the LowBackground DeepLevel Laboratory at the Baksan Neutrino Observatory of the Institute for Nuclear Research of
the Russian Academy of Sciences. This laboratory is located at a depth of 4900 m.w.
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