Cosmogenic-neutron activation of TeO2 and implications for neutrinoless double- β decay experiments

Flux-averaged cross sections for cosmogenic-neutron activation of natural tellurium were measured using a neutron beam containing neutrons of kinetic energies up to ∼800 MeV and having an energy spectrum similar to that of cosmic-ray neutrons at sea level. Analysis of the radioisotopes produced reveals that Ag110m will be a dominant contributor to the cosmogenic-activation background in experiments searching for neutrinoless double-β decay of Te130, such as the Cryogenic Underground Observatory for Rare Events (CUORE) and the Sudbury Neutrino Observatory Plus (SNO+). An estimate of the cosmogenic-activation background in the CUORE experiment has been obtained using the results of this measurement and cross-section measurements of proton activation of tellurium. Additionally, the measured cross sections in this work are also compared with results from semiempirical cross-section calculations

Half-life of Ge71 and the gallium anomaly

Recent discussions about the origin of the so-called gallium anomaly have motivated a remeasurement of the half-life of Ge71. We have conducted three separate measurements using dedicated planar Ge detectors - one with Fe55 as a standard, one with Co57 as a standard, and one standalone Ge71 measurement. Our results yield a half-life of 11.468±0.008 days, which is consistent with, but significantly more precise than, the currently accepted value. With this experiment, the potential explanation of the gallium anomaly being due to an unexpectedly long Ge71 half-life has been ruled out, leaving the anomaly's origin as an open question

Q value of the superallowed decay of Mg-22 and the calibration of the Na-21(p,gamma) experiment

Journals published by the American Physical Society can be found at http://publish.aps.org/The masses of the radioactive nuclei Mg-22 and Na-22 have been measured with the Canadian Penning trap on-line mass spectrometer to a precision of 3x10(-8) and 1x10(-8), respectively. A Q(EC) value of 4124.39(73) keV for the superallowed beta decay of Mg-22 is obtained from the difference of these two masses. With this precise Q value, the Ft value for this decay is determined with improved precision and is found to be consistent with the existing precision data set of superallowed Fermi emitters. This provides an important test of the isospin symmetry-breaking corrections. If the mass of Mg-22 determined here is used in the calibration of a recent Na-21(p,gamma)Mg-22 measurement, part of the discrepancy observed in that measurement is removed

Particle- γ coincidence spectroscopy of the N = 90 nucleus 154Gd by (p, tγ)

A segmented Si-telescope and HPGe array, STARS-LIBERACE, was used to study the 156Gd(p, tγ)154Gd direct reaction by particle- γ coincidence spectroscopy. New cross sections with a 25MeV proton beam are reported and compared to previous (p,t) and (t,p) studies. Furthermore, additional evidence for coexisting Kπ=01+,21+ and 02+, 22+ configurations at N = 90 is presented. Direct and indirect population patterns of the low-lying states are also explored. Review of the new and existing evidence favors an interpretation based on a configuration-dependent pairing interaction. The weakening of monopole pairing strength and an increase in quadrupole pairing strength could bring 2p-2h 0 + states below 2 Δ. This may account for a large number of the low-lying 0 + states observed in two-nucleon transfer reactions. A hypothesis for the origin of the 02+ and 03+ states is provided

Enriched TeO2 bolometers with active particle discrimination: Towards the CUPID experiment

We present the performances of two 92% enriched 130TeO2 crystals operated as thermal bolometers in view of a next generation experiment to search for neutrinoless double beta decay of 130Te. The crystals, 435 g each, show an energy resolution, evaluated at the 2615 keV γ-line of 208Tl, of 6.5 and 4.3 keV FWHM. The only observable internal radioactive contamination arises from 238U (15 and 8 μBq/kg, respectively). The internal activity of the most problematic nuclei for neutrinoless double beta decay, 226Ra and 228Th, are both evaluated as <3.1 μBq/kg for one crystal and <2.3 μBq/kg for the second. Thanks to the readout of the weak Cherenkov light emitted by β/γ particles by means of Neganov–Luke bolometric light detectors we were able to perform an event-by-event identification of β/γ events with a 95% acceptance level, while establishing a rejection factor of 98.21% and 99.99% for α particles