D. Zinatulina

DANSS: Detector of the reactor AntiNeutrino based on Solid Scintillator

The DANSS project is aimed at creating a relatively compact neutrino spectrometer which does not contain any flammable or other dangerous liquids and may therefore be located very close to the core of an industrial power reactor. As a result, it is expected that high neutrino flux would provide about 15,000 IBD interactions per day in the detector with a sensitive volume of 1 m3. High segmentation of the plastic scintillator will allow to suppress a background down to a ~1% level. Numerous tests performed with a simplified pilot prototype DANSSino under a 3 GWth reactor of the Kalinin NPP have demonstrated operability of the chosen design. The DANSS detector surrounded with a composite shield is movable by means of a special lifting gear, varying the distance to the reactor core in a range from 10 m to 12 m. Due to this feature, it could be used not only for the reactor monitoring, but also for fundamental research including short-range neutrino oscillations to the sterile state. Supposing one-year measurement, the sensitivity to the oscillation parameters is expected to reach a level of sin2(2θnew) ~ 5 × 10−3 with Δ m2 ⊂ (0.02–5.0) eV2.

Negative-muon capture in 150Sm

The energy and time spectra of γ rays emitted during negative-muon capture in 150Sm were studied. The total muon lifetime in 150Sm was measured. The yields of several radioactive isotopes in this reaction were determined. The partial γ-ray yield upon muon capture by a 150Sm nucleus were measured.

New search for 0νEC/EC and 2νEC/EC decay of 106Cd

The studies aimed at decreasing the background of the TGV-2 spectrometer have led to constructive changes in the cryostat and increased the sensitivity of the 32-detector spectrometer. New search for 0νEC/EC, 2νEC/EC) decays of 106Cd was started with ∼13.6 g of 106Cd with enrichment of 75%. The evaluation of the experimental data accumulated for 4800 h was performed. Limits (at 90% CL) on the half-lives of 0νEC/EC resonant decay of 106Cd to the 2741 keV excited state of 106Pd (T1/2 ≥ 6.5 × 1019 y) and on t 2νEC/EC decay to the ground state of 106Pd (0+ → 0+, g.s.) (T1/2 ≥ 1.7 × 1020 y) were obtained. The limits on the other branches of 106Cd decay—2νEC/EC decay to the 2+, 512 keV and 01+, 1334 keV excited states of 106Pd and 2νβ+β+ and 2νβ+EC decays of 106Cd to the ground and excited states of 106Pd were improved.

Search for sterile neutrinos at the DANSS experiment

Abstract DANSS is a highly segmented 1 m3 plastic scintillator detector. Its 2500 one meter long scintillator strips have a Gd-loaded reflective cover. The DANSS detector is placed under an industrial 3.1 G W th reactor of the Kalinin Nuclear Power Plant 350 km NW from Moscow. The distance to the core is varied on-line from 10.7 m to 12.7 m. The reactor building provides about 50 m water-equivalent shielding against the cosmic background. DANSS detects almost 5000 ν ˜ e per day at the closest position with the cosmic background less than 3%. The inverse beta decay process is used to detect ν ˜ e . Sterile neutrinos are searched for assuming the 4ν model (3 active and 1 sterile ν). The exclusion area in the Δ m 14 2 , sin 2 ⁡ 2 θ 14 plane is obtained using a ratio of positron energy spectra collected at different distances. Therefore results do not depend on the shape and normalization of the reactor ν ˜ e spectrum, as well as on the detector efficiency. Results are based on 966 thousand antineutrino events collected at three different distances from the reactor core. The excluded area covers a wide range of the sterile neutrino parameters up to sin 2 ⁡ 2 θ 14 0.01 in the most sensitive region.

Neutrino Physics at Kalinin Nuclear Power Plant: 2002 – 2017

The results of the research in the field of neutrino physics obtained at Kalinin nuclear power plant during 15 years are presented. The investigations were performed in two directions. The first one includes GEMMA I and GEMMA II experiments for the search of the neutrino magnetic moment, where the best result in the world on the value of the upper limit of this quantity was obtained. The second direction is tied with the measurements by a solid scintillator detector DANSS designed for remote on-line diagnostics of nuclear reactor parameters and search for short range neutrino oscillations. DANSS is now installed at the Kalinin Nuclear Power Plant under the 4-th unit on a movable platform. Measurements of the antineutrino flux demonstrated that the detector is capable to reflect the reactor thermal power with an accuracy of about 1.5% in one day. Investigations of the neutrino flux and their energy spectrum at different distances allowed to study a large fraction of a sterile neutrino parameter space indicated by recent experiments and perform the reanalysis of the reactor neutrino fluxes. Status of the short range oscillation experiment is presented together with some preliminary results based on about 170 days of active data taking during the first year of operation.

OMC studies for the matrix elements in ββ decay

Energy and time spectra of gamma-rays following μ-capture in natural Kr, Se, Cd and Sm, as well as isotopic enriched 82Kr, 76Se, 106Cd and 150Sm, have been measured. Total life-times of muons in different isotopes, as well as partial μ-capture rates to the excited states of 48Sc, 76As and 106Ag, were extracted. These results are discussed in the context of the double-beta decay matrix elements. The data are also compared with data from theoretical calculations and with data from charge-exchange reactions on 48Ti. It is the first time that μ-capture and charge-exchange reaction data are being compared in the context of ββ decay.

Muon capture rates in Se and Cd isotopes

Energy and time spectra of γ rays following nuclear capture of negative muons in natural Se and Cd and isotopically enriched 76Se and 106Cd targets have been measured with HPGe detectors. Total muon lifetimes in Se and Cd isotopes and partial μ capture rates to excited levels of 76As and 106Ag are obtained. These results are necessary for calculation of nuclear matrix elements of the 2β decay of 76Ge and 106Cd respectively.

Muon capture in Ti, Se, Kr, Cd and Sm

Energy and time spectra of gamma‐rays following μ‐capture in natural Kr, Se, Cd and Sm, as well as isotopic enriched 82Kr, 76Se, 106Cd and 150Sm, have been measured. Total life‐times of muons in 150Sm and different Kr isotopes, as well as partial μ‐capture rates to the excited states of 48Sc, 76As and 106Ag, were extracted. These results are important for calculation of nuclear matrix elements of the 48Ca, 76Ge and 106Cd 2β‐decay, respectively.

Search for double beta decay of 106Cd in the TGV-2 experiment

An investigation of double beta decay (β+β+, β+/EC, EC/EC) of 106Cd was performed at the Modane underground laboratory (at a water equivalent depth of 4800 m) using a TGV-2 spectrometer with 32 detectors. Evaluation of the experimental data accumulated over 12 400 h of measuring ∼13.6 g of 106Cd with an enrichment of 75% was performed. New limits (at a confidence level of 90%) on the half-lives of the 0νEC/EC resonant decay of 106Cd to the 2741 keV excited state of 106Pd − T1/2 ≥ 1.5 × 1020 y and on 2νEC/EC decay to the ground state of 106Pd (0+ → 0+, g.s.) − T1/2 ≥ 3.9 × 1020 y were obtained. The limits of the 2νEC/EC decay of 106Cd to the 2+, 512 keV and 01+, 1334 keV excited states of 106Pd and 2νβ+β+- and the 2νβ+EC decays of 106Cd to the ground and excited states of 106Pd were improved.

Low-background multi-HPGe spectrometer TGV II used for the study of double electron capture of 106 Cd

The TGV II (Telescope Germanium Vertical) facility is a low background spectrometer operated in Modane Underground Laboratory (France). It aims at the study of double beta electron capture of 106Cd. The spectrometer is composed of 32 HPGe planar detectors (total mass of Ge ∼3 kg) interleaved with thin-foil samples made of enriched 106Cd. In 2007 the Phase I of the experiment (1 year measurement) was finished and the new limit on half-life for two-neutrino double electron capture (g.s. → g.s.) of 106Cd was obtained as 3.2 × 1020 years. This limit is significantly higher (by almost three orders of magnitude) than those already published. From December 2007 the Phase II of the experiment continues with more enriched material (13.6 grams instead of 8 grams) and with significantly suppressed background of the cryostat.