Search for rare alpha and double beta decays of Yb isotopes to excited levels of daughter nuclei

A search for alpha and double beta decays of ytterbium isotopes was performed with an ultra low-background high purity germanium detector at Gran Sasso Underground Laboratory (Italy). A 194.7 g Yb2(C2O4)3 powder sample was measured for 11.3 days with a total Yb exposure of 1.25 kg× day. Half-life limits for α-decay modes of 168Y b, 170Y b, 171Y b, 172Y b, 173Y b, 174Y b and 176Y b into the first excited states have been obtained between 6 × 10 14 years and 2 × 10 16 years. These are the first experimental constraints of these decay modes. Double electron capture of 168Y b and double beta decay of 176Y b into the first excited 2+ and 0+ states could be excluded with limits between 1 × 10 14 years to 8 × 10 16 years. This improves the experimental information on some of the decay modes compared to previous constraints

ZnWO4 scintillators for cryogenic dark matter experiments

The scintillation properties of a zinc tungstate crystal, shaped as a hexagonal prism (height 40 mm, diagonal 40 mm) were determined. An energy resolution of 10.7% for the 662 keV γ-line of 137Cs was measured with the scintillator placed in a light collection setup similar to that used by the CRESST dark matter search. The light output and decay kinetics of ZnWO4 were examined over the temperature range 7-300 K and confirmed to be competitive with those of CaWO4. The radioactive contaminations of the ZnWO4 scintillator measured in the Solotvina Underground Laboratory do not exceed 0.1-10 mBq/kg (depending on radionuclide). Our study highlights the excellent feasibility of this ZnWO4 scintillator for a cryogenic dark matter experiment. © 2008 Elsevier B.V. All rights reserved

Limits and performances of a BaWO4 single crystal

A Barium Tungstate single crystal (BaWO4) was produced using the low thermal gradient Czochralski technique. In this paper the results concerning its light emission and radioactive contaminants are presented. The aim of this work is to investigate the possibility to realize BaWO4 crystals with suitably features to study the double beta decay of 130Ba and 132Ba isotopes by the “source=detector” approach. The results show the limitations of a BaWO4 crystal as a scintillator and give some idea on how to overcome them in order to take profit from the potentiality of this single crystal

Large Volume ZnWO4 Crystal Scintillators With Excellent Energy Resolution and Low Background

Large volume zinc tungstate crystal scintillators with improved scintillation characteristics were produced. Energy resolution and relative light output of samples with various sizes and shapes (cylinders, rectangular, and hexagonal prisms) were investigated. The energy resolutions of ZnWO 4 scintillator modules for the 662 keVγ line of 137Cs were 8.5% for a 1 cm3 sample and 10.7% for the large hexagonal module of dimensions ◇ 40 × 40 mm. A variation of the light output by 7%, depending on direction of observation was found for the 1 cm3 cubic crystal. Afterglow,measured 20 ms after termination of irradiation, was 0.002%. The relative light output of the scintillator and the decay kinetics were studied over the temperature range 7-300 K. The level of radioactive contamination of the ZnWO4 scintillator was determined in the Solotvina Underground Laboratory at a sensitivity of ≈0.1-10 mBq/kg. © 2006 IEEE

Effect of recrystallisation on the radioactive contamination of CaWO4 crystal scintillators

Minimising intrinsic radioactivity of crystal scintillators is of particular importance for experiments searching for rare events. We studied the impact of the crystal production process (recrystallisation) on the level of radioactive contamination of CaWO4 crystal scintillators. Several samples of single crystal scintillators were produced using the recrystallisation procedure. It is shown that this has a significant effect on the radioactive contamination of the crystals. Depending on the stage of recrystallisation the activity due to 210Po (product of 210Pb decay) varies in the range 0.031.32 Bq kg-1 while the activity of 238U varies from 0.04 to 0.33 Bq kg-1. We found that uranium is rejected by the crystal with a segregation coefficient ≈0.3. The improvement in radiopurity of CaWO4 by one order of magnitude due to recrystallisation has been demonstrated. The additional benefit of this process is the improvement in the energy resolution. A programme to develop radiopure CaWO4 crystal scintillators is discussed briefly. © 2010 Elsevier B.V. All rights reserved

First search for double beta decay of platinum by ultra-low background HP Ge spectrometry,

A search for double- processes in 190Pt and 198Pt was realized with the help of ultra-low background HP Ge 468cm^3 spectrometer in the underground Gran Sasso National Laboratories of the INFN (Italy). After 1815 h of data taking with 42.5g platinum sample, T 1/2 limits on 2 processes in 190Pt ( + and 2 have been established on the level of 1014-1016y, 3 to 4 orders of magnitude higher than those known previously. In particular, a possible resonant double-electron capture in 190Pt was restricted on the level of 2.9×1016 y at 90% C.L. In addition, T 1/2 limit on 2− decay of 198Pt (2 +0) to the 2+ 1 excited level of 198Hg has been set at the first time: T 1/2 > 3.5×1018 y. The radiopurity level of the used platinum sample is reported

Search for alpha decay of natural Europium

The indication for the α decay of 151Eu (Qα=1.964 MeV) with the half-life yr has been observed for the first time with the help of a low background CaF2(Eu) crystal scintillator (mass of 370 g) in measurement at the Gran Sasso National Laboratories of the INFN during 7426 h. In a conservative approach the lower limit on the half-life of 151Eu has been established as yr at 68% C.L

Search for double-beta decay processes in Cd-108 and Cd-114 with the help of the low-background CdWO4 crystal scintillator

The search for double- processes in 108Cd and 114Cd was realized by using data of the low-background experiment with the CdWO4 crystal scintillator at the Gran Sasso National Laborato- ries of the INFN. New improved half-life limits on double-beta processes were established, in particular T0 2" 1/2 (108Cd) ≥ 1.0(2.7)×1018 yr, T2 2 1/2 (114Cd) ≥ 1.3(2.1)×1018 yr, and T0 2 1/2 (114Cd) ≥ 1.1(2.5)×1021 yr at 90(68)% C.L