On the alpha activity of natural tungsten isotopes

The indication for the alpha decay of 180-W with a half-life T1/2=1.1+0.8-0.4(stat)+-0.3(syst)x10^18 yr has been observed for the first time with the help of the super-low background 116-CdWO_4 crystal scintillators. In conservative approach the lower limit on half-life of 180-W has been established as T1/2>0.7x10^18 yr at 90% C.L. Besides, new T1/2 bounds were set for alpha decay of 182-W, 183-W, 184-W and 186-W at the level of 10^20 yr.Comment: 16 pages, 8 figures, accepted in Phys. Rev.

Response of CdWO4 crystal scintillator for few MeV ions and low energy electrons

The response of a CdWO4 crystal scintillator to protons, alpha particles, Li, C, O and Ti ions with energies in the range 1 - 10 MeV was measured. The non-proportionality of CdWO4 for low energy electrons (4 - 110 keV) was studied with the Compton Coincidence Technique. The energy dependence of the quenching factors for ions and the relative light yield for low energy electrons was calculated using a semi-empirical approach. Pulse-shape discrimination ability between gamma quanta, protons, alpha particles and ions was investigated.Comment: 20 pages, 8 figs, accepted in Nucl. Instrum. Meth.

Search for double beta decay of Zinc and Tungsten with the help of low-background ZnWO4 crystal scintillators

Double beta processes in 64-Zn, 70-Zn, 180-W, and 186-W have been searched for with the help of large volume (0.1-0.7 kg) low background ZnWO4 crystal scintillators at the Gran Sasso National Laboratories of the INFN. Total time of measurements exceeds 10 thousands hours. New improved half-life limits on double electron capture and electron capture with positron emission in 64-Zn have been set, in particular (all the limits are at 90% C.L.): T1/2(0nu2EC)> 1.1e20 yr, T1/2(2nuECbeta+)>7.0e20 yr, and T1/2(0nuECbeta+)>4.3e20 yr. The different modes of double beta processes in 70-Zn, 180-W, and 186-W have been restricted at the level of 1e17-1e20 yr.Comment: 20 p., submitted to Phys. Rev.

Pulse-shape discrimination with PbWO4_4 crystal scintillators

The light output, $\alpha/\beta$ ratio, and pulse shape have been investigated at $-25^\circ$ C with PbWO$_4$ crystal scintillators undoped, and doped by F, Eu, Mo, Gd and S. The fast $0.01-0.06 \mu$s and middle $0.1-0.5 \mu$s components of scintillation decay were observed for all the samples. Slow components of scintillation signal with the decay times $1-3 \mu$s and $13-28 \mu$s with the total intensity up to $\approx50$ have been recognized for several samples doped by Molybdenum. We found some indications of a pulse-shape discrimination between $\alpha$ particles and $\gamma$ quanta with PbWO$_4$ (Mo doped) crystal scintillators.Comment: 12 pages, 5 figures, submitted to NIM

Pulse Shape Analysis and Identification of Multipoint Events in a Large-Volume Proportional Counter in an Experimental Search for 2K Capture Kr-78

A pulse shape analysis algorithm and a method for suppressing the noise component of signals from a large copper proportional counter in the experiment aimed at searching for 2K capture of Kr-78 are described. These signals correspond to a compound event with different numbers of charge clusters due to from primary ionization is formed by these signals. A technique for separating single- and multipoint events and determining the charge in individual clusters is presented. Using the Daubechies wavelets in multiresolutional signal analysis, it is possible to increase the sensitivity and the resolution in extraction of multipoint events in the detector by a factor of 3-4.Comment: 10 pages, 8 figures. submitted to Instruments and Experimental Techniques; ISSN 0020/441

Additional Nucleon Current Contributions to Neutrinoless Double Beta Decay

We have examined the importance of momentum dependent induced nucleon currents such as weak-magnetism and pseudoscalar couplings to the amplitude of neutrinoless double beta decay in the mechanisms of light and heavy Majorana neutrino as well as in that of Majoron emission. Such effects are expected to occur in all nuclear models in the direction of reducing the light neutrino matrix elements by about 30%. To test this we have performed a calculation of the nuclear matrix elements of the experimentally interesting nuclei A = 76, 82, 96, 100, 116, 128, 130, 136 and 150 within the pn-RQRPA. We have found that indeed such corrections vary somewhat from nucleus to nucleus, but in all cases they are greater than 25 percent. In the case of heavy neutrino the effect is much larger (a factor of 3). Combining out results with the best presently available experimental limits on the half-life of the neutrinoless double beta decay we have extracted new limits on the effective neutrino mass (light and heavy) and the effective Majoron coupling constant.Comment: 31 pages, RevTex, 3 Postscript figures, submitted to Phys. Rev.

What can we learn from neutrinoless double beta decay experiments?

We assess how well next generation neutrinoless double beta decay and normal neutrino beta decay experiments can answer four fundamental questions. 1) If neutrinoless double beta decay searches do not detect a signal, and if the spectrum is known to be inverted hierarchy, can we conclude that neutrinos are Dirac particles? 2) If neutrinoless double beta decay searches are negative and a next generation ordinary beta decay experiment detects the neutrino mass scale, can we conclude that neutrinos are Dirac particles? 3) If neutrinoless double beta decay is observed with a large neutrino mass element, what is the total mass in neutrinos? 4) If neutrinoless double beta decay is observed but next generation beta decay searches for a neutrino mass only set a mass upper limit, can we establish whether the mass hierarchy is normal or inverted? We base our answers on the expected performance of next generation neutrinoless double beta decay experiments and on simulations of the accuracy of calculations of nuclear matrix elements.Comment: Added reference

Recent advances in neutrinoless double beta decay search

Even after the discovery of neutrino flavour oscillations, based on data from atmospheric, solar, reactor, and accelerator experiments, many characteristics of the neutrino remain unknown. Only the neutrino square-mass differences and the mixing angle values have been estimated, while the value of each mass eigenstate still hasn't. Its nature (massive Majorana or Dirac particle) is still escaping. Neutrinoless double beta decay ($0\nu$-DBD) experimental discovery could be the ultimate answer to some delicate questions of elementary particle and nuclear physics. The Majorana description of neutrinos allows the $0\nu$-DBD process, and consequently either a mass value could be measured or the existence of physics beyond the standard should be confirmed without any doubt. As expected, the $0\nu$-DBD measurement is a very difficult field of application for experimentalists. In this paper, after a short summary of the latest results in neutrino physics, the experimental status, the R&D projects, and perspectives in $0\nu$-DBD sector are reviewed.Comment: 36 pages, 7 figures, To be publish in Czech Journal of Physic

Низкофоновая сцинтилляционная установка для исследования радиоактивной чистоты материалов

Background of 2.128 kg CdWO₄ scintillation detector was reduced by 3 orders of magnitude in the energy region 0.5…2.6 MeV, and one order of magnitude above 3 MeV in the low background scintillation setup located in the basement floor of a laboratory building at the Institute for Nuclear Research (Kyiv, Ukraine). It was achieved by application of radiopure passive shield, plastic scintillators to veto cosmic rays, and pulse-shape discrimination to reject fast Cherenkov signals in the quartz light-guide of the detector. Sensitivity of the setup to radioactive contamination of different materials were estimated. For instance, for a 3.36 kg titanium sample over 30 days of measurements detection limits are on the level of 2.9 mBq/kg (⁴⁰K); 0.6 mBq/kg (¹³⁷Cs); 2 mBq/kg (²²⁶Ra), and 0.5 mBq/kg (²²⁸Th).Зниження фону низькофонової сцинтиляційної установки із сцинтиляційним кристалом CdWO₄ масою 2,128 кг складає три порядки в області енергій 0,5…2,6 МеВ і один порядок для енергій більше 3 МеВ. Придушення фону було досягнуто встановленням радіоактивно чистого пасивного захисту, пластикових сцинтиляторів для відкидання сигналів від космічних частинок і розділенням сигналів від черенковського свічення у світловоді детектора за формою. Оцінено чутливість установки до радіоактивних забруднень різних матеріалів (з довірчою ймовірністю 68%), наприклад, на рівні 2,9 мБк/кг (⁴⁰K); 0,6 мБк/кг (¹³⁷Cs); 2 мБк/кг (²²⁶Ra) і 0,5 мБк/кг (²²⁸Th) для зразку титану масою 3,36 кг протягом 30 діб вимірювання.Снижение фона низкофоновой сцинтилляционной установки со сцинтилляционным кристаллом CdWO₄ массой 2,128 кг составило три порядка в области энергий 0,5…2,6 МэВ и один порядок при энергиях больше 3 МэВ. Подавление фона было достигнуто путем установки радиоактивно чистой пассивной защиты, пластиковых сцинтилляторов для отбрасывания сигналов от космических частиц и разделением сигналов от черенковского свечения в световоде детектора по форме. Оценена чувствительность установки к радиоактивным загрязнениям разных материалов (с доверительной вероятностью 68%), например, на уровне 2,9 мБк/кг (⁴⁰K); 0,6 мБк/кг (¹³⁷Cs); 2 мБк/кг (²²⁶Ra) и 0,5 мБк/кг (²²⁸Th) для образца титана массой 3,36 кг за время измерения 30 сут