Beta decays in investigations and searches for rare effects

Current status of experimental investigations of rare single beta decays (48Ca, 50V, 96Zr, 113Cd, 113mCd, 115In, 123Te, 180mTa, 222Rn) is reviewed. Nuclei which decay through single beta decay very often constitute backgrounds in studies of rare effects like double beta decay, solar neutrinos or dark matter. Summary of correction factors used in description of forbidden beta decays is also briefly given.Comment: 4 pages, contribution to the MEDEX'2017 conference, one more acknowledgment adde

False starts in history of searches for double beta decay, or Discoverless double beta decay

A collection of stories is presented on discoveries of double beta decay (including neutrinoless one) which were refuted in the subsequent investigations.Comment: 6 pages, contribution to the Workshop on Calculation of Double Beta Decay Matrix Elements (MEDEX'11), Prague, June 13-16, 201

Spontaneous double alpha decay: First experimental limit and prospects of investigation

Nuclear decays with simultaneous emission of two alpha particles are energetically possible for a number of nuclides. Prospects of searching for such kind of decay for nuclides present in the natural isotopic composition of elements are discussed here. The first experimental limit on half-life for 2alpha decay is set for 209Bi as T1/2 > 2.9e20 y at 90% C.L., using the data of work [P. de Marcillac et al., Nature 422 (2003) 876]. Theoretical T1/2 estimations for the process are also given. Using these values, which are on the level of 1e33 y or more, one can conclude that the prospects of experimental observation of 2alpha decay are very pessimistic.Comment: 8 p., submitted to Nuclear Physics and Atomic Energ

Quest for double beta decay of 160-Gd and Ce isotopes

The double beta decay study of 160-Gd has been performed in the Solotvina Underground Laboratory with the help of Gd_2SiO_5(Ce) crystal scintillator (volume 95 cc). The background of the detector in the vicinity of the 2 beta energy of 160-Gd was reduced to 1.0 cpd/keV kg. The new improved half-life limits have been established for neutrinoless 2 beta decay of 160-Gd to the ground and first excited levels of 160-Dy: T1/2 > 2.3(1.3)E21 yr at 68%(90%) C.L. The T1/2 bounds have been also set for two neutrino mode as well as for 2 beta decay with Majorons emission. Also the limits were established for different 2 beta decay processes in 136-Ce, 138-Ce and 142-Ce.Comment: 12 pages, 6 figures, submitted to Nucl. Phys.

Search for α\alpha decay of 151^{151}Eu to the first excited level of 147^{147}Pm using underground γ\gamma-ray spectrometry

The alpha decay of $^{151}$Eu to the first excited level of $^{147}$Pm ($J^\pi = 5/2^+$, $E_{exc}=91.1$ keV) was searched for at the HADES underground laboratory ($\approx 500$ m w.e.). A sample of high purity europium oxide with mass of 303 g and a natural isotopic composition has been measured over 2232.8 h with a high energy resolution ultra-low background n-type semi-planar HPGe detector (40 cm$^3$) with sub-micron deadlayer. The new improved half-life limit has been set as $T_{1/2} \geq 3.7\times 10^{18}$ yr at 68% C.L. Possibilities to improve the sensitivity of the experiment, which is already near the theoretical predictions, are discussed. New half-life limit for $\alpha$ decay of $^{153}$Eu is also set as $T_{1/2} \geq 5.5\times 10^{17}$ yr.Comment: 11 pages, 5 figures, 2 tables, 18 reference

Precise measurement of energy of the first excited state of 115Sn (Eexc = 497.3 keV)

Single beta decay of 115In to the first excited level of 115Sn (Eexc = 497.3 keV) is known as beta decay with the lowest Q value. To determine the Q precisely, one has to measure very accurately the Eexc value. A sample of tin enriched in 115Sn to 50.7% was irradiated by proton beam at the U-120 accelerator of INR, Kyiv. The 115Sb radioactive isotope, created in 115Sn(p,n)115Sb reaction, decays with T1/2 = 32 min to 115Sn populating the 497 keV level with ~ 96% probability. The total statistics of ~ 10^5 counts collected in the 497 keV peak in series of measurements, exact description of the peak shape and precisely known calibration points around the 497 keV peak allowed to obtain the value Eexc = 497.342(3) keV, which is the most precise to-date. This leads to the following Q* value for the decay 115In to 115Sn*: Q* = 147 +- 10 eV.Comment: 6 pages, 3 figure

Final results of an experiment to search for 2beta processes in zinc and tungsten with the help of radiopure ZnWO4 crystal scintillators

A search for the double beta decay of zinc and tungsten isotopes has been performed with the help of radiopure ZnWO4 crystal scintillators (0.1-0.7 kg) at the Gran Sasso National Laboratories of the INFN. The total exposure of the low background measurements is 0.529 kg yr. New improved half-life limits on the double beta decay modes of 64Zn, 70Zn, 180W, and 186W have been established at the level of 10^{18}-10^{21} yr. In particular, limits on double electron capture and electron capture with positron emission in 64Zn have been set: T_{1/2}(2\nu 2K) > 1.1 10^{19} yr, T_{1/2} (0\nu 2\epsilon) > 3.2 10^{20} yr, T_{1/2} (2\nu \epsilon \beta^+) > 9.4 10^{20} yr, and T_{1/2} (0\nu \epsilon \beta^+) > 8.5 10^{20} yr, all at 90% C.L. Resonant neutrinoless double electron capture in 180W has been restricted on the level of T_{1/2} (0\nu 2\epsilon) > 1.3 10^{18} yr. A new half-life limit on alpha transition of 183W to the metastable excited level 1/2^- 375 keV of 179Hf has been established: T_{1/2} > 6.7 10^{20} yr.Comment: This is an author-created, un-copyedited version of an article published in J. Phys. G: Nucl. Part. Phys. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher authenticated version is available online at doi: 10.1088/0954-3899/38/11/11510