Search

The cosmogenic production of long-lived radioactive isotopes in materials is an hazard for experiments demanding ultra-low background conditions. Although NaI(Tl) scintillators have been used in this context for a long time, very few activation data were available. We present results from two 12.5 kg NaI(Tl) detectors, developed within the ANAIS project and installed at the Canfranc Underground Laboratory. The prompt data taking starting made possible a reliable quantification of production of some I, Te and Na isotopes with half-lives larger than ten days. Tnitial activities underground were measured and then production rates at sea level were estimated following the history of detectors; a comparison of these rates with calculations using typical cosmic neutron flux at sea level and a selected description of excitation functions was also carried out. After including the contribution from the identified cosmogenic products in the detector background model, we found that the presence of ³H in the crystal bulk would help to fit much better our background model and experimental data. We have analyzed the cosmogenic production of ³H in NaI, and although precise quantification has not been attempted, we can conclude that it could imply a very relevant contribution to the total background below 15 ke in NaI detectors. [ABSTRACT FROM AUTHOR]

ANAIS (Annual modulation with NaI Scintillators) is a project aiming to set up at the new facilities of the Canfranc Underground Laboratory (LSC), a large scale NaI(Tl) experiment in order to explore the DAMA/LIBRA annual modulation positive result using the same target and technique. Two 12.5 kg each NaI(Tl) crystals provided by Alpha Spectra took data at the LSC in the ANAIS-25 set-up. The comparison of the background model for the ANAIS-25 prototypes with the experimental results is presented. ANAIS crystal radiopurity goals have been achieved for 232Th and 238U chains, but a 210Pb contamination out-of-equilibrium was identified, whose origin has been studied. The high light collection efficiency obtained with these prototypes allows to anticipate an energy threshold of the order of 1 keVee. A new detector, with improved performances, was received in March 2015 and very preliminary results are shown. [ABSTRACT FROM AUTHOR]

Several large NaI(Tl) detectors, produced by different companies, have been operated in the Canfranc Underground Laboratory (LSC) in the frame of the ANAIS (Annual modulation with NaI Scintillators) project devoted to the direct detection of dark matter. A complete background model has been developed for a 9.6 kg detector (referred as ANAIS-0 prototype) after a long data taking at LSC. Activities from the natural chains of 238U and 232Th, and 40K in the NaI(Tl) crystal were evaluated applying different methods: discrimination of alpha particles vs beta/gamma background by Pulse Shape Analysis for quantifying the content of the natural chains and coincidence techniques for 40K. Radioactive contaminations in the detector and shielding components were also determined by HPGe spectrometry. Monte Carlo simulations using Geant4 package were carried out to evaluate their contribution. At high energies, most of the measured background is nicely reproduced; at low energy some non-explained components are still present, although some plausible background sources have been analyzed. The 40K content of the NaI(Tl) crystal has been confirmed to be the dominant contributor to the measured background with this detector. In addition, preliminary results of the background characterization, presently underway at the LSC, of two recently produced NaI(Tl) detectors, with 12.5 kg mass each, will be presented: cosmogenic induced activity has been clearly observed and is being quantified, and 40K activity at a level ten times lower than in ANAIS-0 has been determined. [ABSTRACT FROM AUTHOR]

A lasting Dark Matter Search Program is being carried out in the facilities of the Canfranc Underground Laboratory since 1990 with the participation of the University of Zaragoza (UZ) Nuclear and Astroparticle Physics group. A brief summary of the most relevant experiments will be followed by the report on the status of the present experimental efforts at Canfranc: ANAIS and ROSEBUD. ANAIS (Annual modulation with NAI) will look for the annual modulation effect in the WIMP signal with about 100 kg sodium iodide as target. In the framework of the ROSEBUD (Rare Objects SEarch with Bolometers UnDerground) collaboration, the particle discrimination capability of different scintillating bolometers has been tested. These detectors are showing excellent performances for their application in dark matter searches and enable a multi-target strategy in the search for WIMPs, which is planned to be used in the near future at the Canfranc Underground Laboratory. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The problem of cosmogenic activation produced at sea level in materials typically used in underground experiments looking for rare events is being studied. Several nuclear data libraries have been screened looking for relevant isotope production cross-sections and different codes which can be applied to activation studies have been reviewed. The excitation functions for some problems of interest like production of 60Co and 68Ge in germanium and production of 60Co in tellurium have been obtained taking into account both measurements and calculations and a preliminary estimate of the corresponding rates of production at sea level has been performed. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]