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

Low background scintillation setup to investigate radiopurity of materials

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

Low background scintillation setup to investigate radiopurity of materials

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

Neutrinoless double-electron capture

Indexación ScopusDouble-beta processes play a key role in the exploration of neutrino and weak interaction properties, and in the searches for effects beyond the standard model. During the last half century many attempts were undertaken to search for double-beta decay with emission of two electrons, especially for its neutrinoless mode 0?2ß-, the latter having still not been observed. Double-electron capture (2EC) was not yet in focus because of its in general lower transition probability. However, the rate of neutrinoless double-electron capture 0?2EC can experience a resonance enhancement by many orders of magnitude when the initial and final states are energetically degenerate. In the resonant case, the sensitivity of the 0?2EC process can approach the sensitivity of the 0?2ß- decay in the search for the Majorana mass of neutrinos, right-handed currents, and other new physics. An overview of the main experimental and theoretical results obtained during the last decade in this field is presented. The experimental part outlines search results of 2EC processes and measurements of the decay energies for possible resonant 0?2EC transitions. An unprecedented precision in the determination of decay energies with Penning traps has allowed one to refine the values of the degeneracy parameter for all previously known near-resonant decays and has reduced the rather large uncertainties in the estimate of the 0?2EC half-lives. The theoretical part contains an updated analysis of the electron shell effects and an overview of the nuclear-structure models, in which the nuclear matrix elements of the 0?2EC decays are calculated. One can conclude that the decay probability of 0?2EC can experience a significant enhancement in several nuclides. © 2020 American Physical Society.https://journals-aps-org.recursosbiblioteca.unab.cl/rmp/abstract/10.1103/RevModPhys.92.04500

Search for 2β processes in 64Zn with the help of ZnWO4 crystal scintillator

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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

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