40 research outputs found
First bolometric measurement of the two neutrino double beta decay of Mo with a ZnMoO crystals array
The large statistics collected during the operation of a ZnMoO array, for
a total exposure of 1.3 kg day of Mo, allowed the first
bolometric observation of the two neutrino double beta decay of Mo. The
observed spectrum of each crystal was reconstructed taking into account the
different background contributions due to environmental radioactivity and
internal contamination. The analysis of coincidences between the crystals
allowed the assignment of constraints to the intensity of the different
background sources, resulting in a reconstruction of the measured spectrum down
to an energy of 300 keV. The half-life extracted from the data is
T= [7.15 0.37 (stat) 0.66 (syst)] 10
y.Comment: 6 pages, 2 figure, Accepted for publication in Journal of Physics G:
Nuclear and Particle Physic
Radioactive contamination of ZnWO4 crystal scintillators
The radioactive contamination of ZnWO4 crystal scintillators has been
measured deep underground at the Gran Sasso National Laboratory (LNGS) of the
INFN in Italy with a total exposure 3197 kg x h. Monte Carlo simulation,
time-amplitude and pulse-shape analyses of the data have been applied to
estimate the radioactive contamination of the ZnWO4 samples. One of the ZnWO4
crystals has also been tested by ultra-low background gamma spectrometry. The
radioactive contaminations of the ZnWO4 samples do not exceed 0.002 -- 0.8
mBq/kg (depending on the radionuclide), the total alpha activity is in the
range: 0.2 - 2 mBq/kg. Particular radioactivity, beta active 65Zn and alpha
active 180W, has been detected. The effect of the re-crystallization on the
radiopurity of the ZnWO4 crystal has been studied. The radioactive
contamination of samples of the ceramic details of the set-ups used in the
crystals growth has been checked by low background gamma spectrometry. A
project scheme on further improvement of the radiopurity level of the ZnWO4
crystal scintillators is briefly addressed.Comment: 15 pages, 8 figures, 6 tables, submitted for publicatio
Search for double beta decay processes in 106Cd with the help of 106CdWO4 crystal scintillator
A search for the double beta 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 processes in 106Cd
were established at the level of 10^{19}-10^{21} yr; in particular,
T_{1/2}(2\nu \epsilon \beta^+) > 2.1 10^{20} yr, T_{1/2}(2\nu 2\beta^+) > 4.3
10^{20} yr, and T_{1/2}(0\nu 2\epsilon) > 1.0 10^{21} yr. The resonant
neutrinoless double electron captures to the 2718 keV, 2741 keV and 2748 keV
excited states of 106Pd are restricted to T_{1/2}(0\nu 2K) > 4.3 10^{20} yr,
T_{1/2}(0\nu KL1) > 9.5 10^{20} yr and T_{1/2}(0\nu KL3) > 4.3 10^{20} yr,
respectively (all limits at 90% C.L.). A possible resonant enhancement of the
0\nu 2\epsilon processes is estimated in the framework of the QRPA approach.
The radioactive contamination of the 106CdWO4 crystal scintillator is reported.Comment: Minor changes of half-life limits after improving the data analysis;
version accepted for publication on Phys. Rev.
Low background detector with enriched 116CdWO4 crystal scintillators to search for double beta decay of 116Cd
A cadmium tungstate crystal boule enriched in Cd 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 CdWO
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 CdWO
sample (326 g) was tested with the help of ultra-low background high purity
germanium detector. Monte Carlo simulations of double
processes in Cd were used to estimate the sensitivity of an experiment
to search for double decay of Cd.Comment: 24 pages, 13 figures, 3 tables, accepted for publication on Journal
of Instrumentatio
Searches for neutrinoless resonant double electron captures at LNGS
Several experiments were performed during last years at underground (3600 m
w.e.) Laboratori Nazionali del Gran Sasso (LNGS) of the INFN (Italy) to search
for resonant 2 captures in 96Ru, 106Cd, 136Ce, 156Dy, 158Dy,
180W, 184Os, 190Pt with the help of HP Ge semiconductor detectors, and ZnWO4
and 106CdWO4 crystal scintillators. No evidence for r-2 decays
was found, and only T_{1/2} limits were established in the range of
10^{14}-10^{21} yr.Comment: Proceedings of TAUP 2011 Conferenc
Low thermal gradient Czochralski growth of large MWO4 (M = Zn, Cd) crystals, and microstructural and electronic properties of the (010) cleaved surfaces
The large optical-quality MWO4 (M = Zn, Cd) crystals of mass up to 14 (ZnWO4) and 20 (CdWO4) kg were grown by Low Thermal Gradient Czochralski Technique (LTG Cz). Crystallographic properties of MWO4(010) cleaved surface were evaluated by AFM and RHEED, and electronic structure of the surface was studied using XPS. A system of Kikuchi lines has been observed for cleaved MWO4(010) by RHEED confirming high crystallographic quality of the surface. The XPS valence-band and core-level spectra of MWO4(010) have been measured. The XPS measurements reveal that W and M atoms are in the formal valences 6+ and 2+, respectively, on cleaved MWO4(010) surface