O. G. Polischuk

Low background detector with enriched 116CdWO4 crystal scintillators to search for double beta decay of 116Cd

A cadmium tungstate crystal boule enriched in 116Cd to 82% with mass of 1868 g was grown by the low-thermal-gradient Czochralski technique. The isotopic composition of cadmium and the trace contamination of the crystal were estimated by High Resolution Inductively Coupled Plasma Mass-Spectrometry. The crystal scintillators produced from the boule were subjected to characterization that included measurements of transmittance and energy resolution. A low background scintillation detector with two 116CdWO4 crystal scintillators (586 g and 589 g) was developed. The detector was running over 1727 h deep underground at the Gran Sasso National Laboratories of the INFN (Italy), which allowed to estimate the radioactive contamination of the enriched crystal scintillators. The radiopurity of a third 116CdWO4 sample (326 g) was tested with the help of ultra-low background high purity germanium γ detector. Monte Carlo simulations of double β processes in 116Cd were used to estimate the sensitivity of an experiment to search for double β decay of 116Cd.

Search for double beta decay processes in 106Cd with the help of 106CdWO4 crystal scintillator

A search for the double processes in 106Cd was carried out at the Gran Sasso National Laboratories of the INFN (Italy) with the help of a 106CdWO4 crystal scintillator (215 g) enriched in 106Cd up to 66%. After 6590 h of data taking, new improved half-life limits on the double beta decay processes in 106Cd were established at the level of 10^{19} - 10^{21} yr. A possible resonant enhancement of the neutrinoless2EC processes is estimated in the framework of the QRPA approach. The radioactive contamination of the 106CdWO4 crystal scintillator is reported.

CdWO4 crystal scintillators from enriched isotopes for double beta decay experiments

Abstract Cadmium tungstate crystal scintillators enriched in 106 Cd and 116 Cd were developed. The produced scintillators exhibit good optical and scintillation properties, and a low level of radioactive contamination. Experiments to search for double beta decay of 106 Cd and 116 Cd are in progress at the Gran Sasso National Laboratories of the INFN (Italy). Prospects to further improve the radiopurity of the detectors by recrystallization are discussed.

Search for

A radiopure cadmium tungstate crystal scintillator, enriched in Cd106 to 66%, with mass of 216 g (Cd106WO4), was used to search for double-β decay processes in Cd106 in coincidence with four ultra-low-background high-purity germanium detectors in a single cryostat. Improved limits on the double-β processes in Cd106 have been set on the level of 1020−1021 yr after 13 085 h of data taking. In particular, the half-life limit on the two-neutrino electron capture with positron emission, T2νɛβ+1/2≥1.1×1021 yr, has reached the region of theoretical predictions. With this half-life limit the effective nuclear matrix element for the 2νɛβ+ decay is bounded as M2νɛβ+eff≤1.1. The resonant neutrinoless double-electron captures to the 2718-, 2741-, and 2748-keV excited states of Pd106 are restricted at the level of T1/2≥(8.5×1020−1.4×1021) yr.

2\beta

An experiment to search for double-β decay processes in 96Ru and 104Ru, which are accompanied by γ rays, has been realized in the underground Gran Sasso National Laboratories of the I.N.F.N. (Italy). Ruthenium samples with masses of ≈0.5–0.7 kg were measured with the help of ultralow-background high-purity Ge γ-ray spectrometry. After 2162 h of data taking the samples were deeply purified to reduce the internal contamination of 40K. The last part of the data has been accumulated over 5479 h. New improved half-life limits on 2β+/ɛβ+/2ɛ processes in 96Ru have been established on the level of 1020 yr, in particular for decays to the ground state of 96Mo: T1/22ν2β+≥1.4×1020 yr, T1/22νɛβ+≥8.0×1019 yr, and T1/20ν2K≥1.0×1021 yr (all limits are at 90% C.L.). The resonant neutrinoless double-electron captures to the 2700.2 and 2712.7 keV excited states of 96Mo are restricted as T1/20νKL≥2.0×1020 yr and T1/20ν2L≥3.6×1020 yr, respectively. Various two-neutrino and neutrinoless 2β half-lives of 96Ru have been estimated in the framework of the quasiparticle random-phase approximation approach. In addition, the T1/2 limit for 0ν2β− transitions of 104Ru to the first excited state of 104Pd has been set as ≥6.5×1020 yr.

decay of

A search for double-

^{106}

\beta

Cd with an enriched

processes in 190Pt and 198Pt was realized with the help of ultra-low background HP Ge 468cm^3

^{106}

\gamma

CdWO

spectrometer in the underground Gran Sasso National Laboratories of the INFN (Italy). After 1815 h of data taking with 42.5g platinum sample, T1/2 limits on 2