CdWO4 crystal scintillators from enriched isotopes for double beta decay experiments

CdWO₄ crystal scintillators from enriched isotopes for double beta decay experiments

D.V. Poda^a, A.S. Barabash^b, P. Belli^c, R. Bernabei^c,d, R.S. Boiko^a, V.B. Brudanin^e, F. Cappella^f,g, V. Caracciolo^h, S. Castellano^h, R. Cerulli^h, D.M. Chernyak^a, F.A. Danevich^a, S. d’Angelo^c,d, V.Ya. Degodaⁱ, M.L. Di Vacri^h, A.E. Dossovitskiy^j, E.N. Galashov^k, A. Incicchitti^f,g, V.V. Kobychev^a, S.I. Konovalov^b, G.P. Kovtun^l, M. Laubenstein^h, A.L. Mikhlin^j, V.M. Mokina^a, A.S. Nikolaiko^a, S. Nisi^h, R.B. Podviyanuk^a, O.G. Polischuk^a,f, A.P. Shcherban^l, V.N. Shlegel^k, D.A. Solopikhin^l, V.I. Tretyak^a, V.I. Umatov^b, Ya.V. Vasiliev^k, V.D. Virich^l

^aInstitute for Nuclear Research, MSP 03680 Kyiv, Ukraine
^bInstitute of Theoretical and Experimental Physics, 117218 Moscow, Russia
^cINFN, sezione Roma “Tor Vergata”, I-00133 Rome, Italy
^dDipartimento di Fisica, Università di Roma “Tor Vergata”, I-00133 Rome, Italy
^eJoint Institute for Nuclear Research, 141980 Dubna, Russia
^fINFN, sezione Roma “La Sapienza”, I-00185 Rome, Italy
^gDipartimento di Fisica, Università di Roma “La Sapienza”, I-00185 Rome, Italy
^hINFN, Laboratori Nazionali del Gran Sasso, I-67100 Assergi (AQ), Italy
ⁱKyiv National Taras Shevchenko University, MSP 03680 Kyiv, Ukraine
^jJoint Stock Company NeoChem, 117647 Moscow, Russia
^kNikolaev Institute of Inorganic Chemistry, 630090 Novosibirsk, Russia
^lNational Science Center “Kharkiv Institute of Physics and Technology”, 61108 Kharkiv, Ukraine

Keywords: CdWO₄ crystal scintillator, enriched isotope, ¹⁰⁶Cd, ¹¹⁶Cd, low counting experiment, radiopurity, double beta decay

Abstract

Cadmium tungstate crystal scintillators enriched in ¹⁰⁶Cd and ¹¹⁶Cd were developed. The produced scintillators exhibit good optical and scintillation properties, and a low level of radioactive contamination. Experiments to search for double beta decay of ¹⁰⁶Cd and ¹¹⁶Cd are in progress at the Gran Sasso National Laboratories of the INFN (Italy). Prospects to further improve the radiopurity of the detectors by recrystallization are discussed.

1. Introduction

Two neutrino double beta (2ʋ2β) decay is the rarest nuclear transformation ever observed; the half-lives are in the range of T_1/2 ~ 10¹⁸ - 10²⁴ yr (see e.g. (Tretyak and Zdesenko, 1995, 2002; Barabash, 2010a)). As regards the neutrinoless mode (0ʋ) of the decay, a particular analysis of the data collected by the Heidelberg-Moscow collaboration, exploiting the ⁷⁶Ge isotope, was presented in (Klapdor-Kleingrothaus and Krivosheina, 2006); several experiments are now in progress on the same and on other isotopes to further investigate the process. Published limits on the half-life of this process in various isotopes are at level of lim T_1/2 ~ 10²³ - 10²⁵ yr (see e.g. (Tretyak and Zdesenko, 1995, 2002; Barabash, 2010b; Gomez-Cadenas et al., 2012)). Investigations of the 0ʋ2β decay are related with several fundamental topics of particle physics: the lepton number violation, the nature of neutrino (Majorana or Dirac particle), an absolute scale of neutrino mass and the neutrino mass hierarchy (see (Rodejohann, 2011; Elliott, 2012; Vergados et al., 2012; Gomez-Cadenas et al., 2012) and references therein).

One of the most sensitive 2β experiments was realized in the Solotvina underground laboratory (Ukraine) with the help of ≈0.3 kg radiopure cadmium tungstate scintillators enriched in ¹¹⁶Cd (¹¹⁶CdWO₄) (Danevich et al., 2003). CdWO₄ crystal scintillators were also successfully used to search for 2β processes in ¹⁰⁶Cd (Danevich et al., 1996, 2003) and ^108,114Cd (Belli et al., 2008). The experiments showed that CdWO₄ scintillator is a promising detector thanks to possibility to realize calorimetric “source=detector” experiment with a high detection efficiency, low level of intrinsic radioactivity, good scintillation properties, ability of pulse-shape discrimination in order to suppress background caused by intrinsic radioactive contamination, and long operation stability. In addition, ¹¹⁶Cd and ¹⁰⁶Cd isotopes are favorable candidates for 2β experiments thanks to the high energy of decay (≈2.8 MeV (Tretyak and Zdesenko, 1995, 2002)), promising theoretical estimations (e.g. see in (Tretyak and Zdesenko, 1995, 2002)), relatively large isotopic abundance (Berglund and Wieser, 2011) and possibility of enrichment by ultra-centrifugation (Artyukhov et al., 1997).

Полный текст статьи представлен в журнале «Radiation Measurements», 2013, №56, р. 66-69