Search for Double Beta Decay of 106Cd with an Enriched 106CdWO4 Crystal Scintillator in Coincidence with CdWO4 Scintillation Counters

Abstract

Studies on double beta decay processes in 106Cd were performed by using a cadmium tungstate scintillator enriched in 106Cd at 66% (106CdWO4) with two CdWO4 scintillation counters (with natural Cd composition). No effect was observed in the data that accumulated over 26,033 h. New improved half-life limits were set on the different channels and modes of the 106Cd double beta decay at level of limT1/2∼1020−1022 yr. The limit for the two neutrino electron capture with positron emission in 106Cd to the ground state of 106Pd, T1/22νECβ+≥2.1×1021 yr, was set by the analysis of the 106CdWO4 data in coincidence with the energy release 511 keV in both CdWO4 counters. The sensitivity approaches the theoretical predictions for the decay half-life that are in the range T1/2∼1021−1022 yr. The resonant neutrinoless double-electron capture to the 2718 keV excited state of 106Pd is restricted at the level of T1/20ν2K≥2.9×1021 yr.

Comparative Analysis of Nuclear Matrix Elements of 0νβ+β+ Decay and Muon Capture in 106Cd

“…In [16], the phase-space factors for the 2νβ + β + decay, as well as for the competing modes 2νβ + EC and 2νECEC were computed. In [8], the experimentally extracted lower limits for half-lives of the different modes for 106 Cd were given. These values, together with the corresponding phase-space factors and resulting experimental matrix elements, are listed in Table 1.…”

“…Of these isotopes, 106 Cd is a particularly promising candidate for the 2νβ + β + -decay searches since it has the biggest decay energy, Q ββ = 2775.39 (10) keV, as well as other experimentally favorable features. At present, there are three running experiments searching for the β + β + decay of 106 Cd, namely COBRA [5,6], TGV-2 [7], and 106 CdWO 4 crystal scintillator [8].…”

“…Phase-space factors[16], half-lives[8], and the resulting experimental NMEs of different decay modes of 106 Cd.…”

Enriched Crystal Scintillators for 2β Experiments

“…The best half-life limits (as well as the theoretical estimations) on some 2β processes in 106 Cd are presented in Table 2 [80]. In particular, new limits on 2ε, εβ + , and 2β + processes were set on the level of T 1/2 > (10 20 -10 22 ) years.…”

“…The passive shield consists of copper (8-some parts are shown), lead, polyethylene, and cadmium. The figure was taken from[80].…”