New limits on the β+\beta^{+}EC and ECEC processes in 120^{120}Te

New limits on the double beta processes for $^{120}$Te have been obtained using a 400 cm$^3$ HPGe detector and a source consisting of natural Te0$_2$ powder. At a confidence level of 90% the limits are $0.19\times 10^{18}$ y for the $\beta^+$EC$(0\nu + 2\nu)$ transition to the ground state, $0.75\times 10^{18}$ y for the ECEC$(0\nu + 2\nu)$ transition to the first 2$^+$ excited state of $^{120}$Sn (1171.26 keV) and $(0.19-0.6)\times 10^{18}$ y for different ECEC($0\nu$) captures to the ground state of $^{120}$Sn.Comment: 9 pages, 4 figures; v2: minor change

Investigation of ββ\beta\beta decay in 150^{150}Nd and 148^{148}Nd to the excited states of daughter nuclei

Double beta decay of $^{150}$Nd and $^{148}$Nd to the excited states of daughter nuclei have been studied using a 400 cm$^3$ low-background HPGe detector and an external source consisting of 3046 g of natural Nd$_2$O$_3$ powder. The half-life for the two-neutrino double beta decay of $^{150}$Nd to the excited 0$^+_1$ state in $^{150}$Sm is measured to be $T_{1/2}=[1.33^{+0.36}_{-0.23}(stat)^{+0.27}_{-0.13}(syst)]\cdot 10^{20}$ y. For other $(0\nu + 2\nu)$ transitions to the 2$^+_1$, 2$^+_2$, 2$^+_3$, and 0$^+_2$ levels in $^{150}$Sm, limits are obtained at the level of $\sim (2-8)\cdot 10^{20}$ y. In the case of $^{148}$Nd only limits for the $(0\nu + 2\nu)$ transitions to the 2$^+_1$, 0$^+_1$, and 2$^+_2$ excited states in $^{148}$Sm were obtained and are at the level of \sim (4-8)\cdot 10^{20}$ y.Comment: 13 pages, 6 figure

Search for β+\beta^+EC and ECEC processes in 112^{112}Sn

Limits on $\beta^+$EC (here EC denotes electron capture) and ECEC processes in $^{112}$Sn have been obtained using a 380 cm$^3$ HPGe detector and an external source consisting of 53.355 g enriched tin (94.32% of $^{112}$Sn). A limit with 90% C.L. on the $^{112}$Sn half-life of $4.7\times 10^{20}$ y for the ECEC(0$\nu$) transition to the $0^+_3$ excited state in $^{112}$Cd (1871.0 keV) has been established. This transition is discussed in the context of a possible enhancement of the decay rate by several orders of magnitude given that the ECEC$(0\nu)$ process is nearly degenerate with an excited state in the daughter nuclide. Prospects for investigating such a process in future experiments are discussed. The limits on other $\beta^+$EC and ECEC processes in $^{112}$Sn were obtained on the level of $(0.6-8.7)\times 10^{20}$ y at the 90% C.L.Comment: 14 pages, 4 figure

First test of an enriched 116^{116}CdWO4_4 scintillating bolometer for neutrinoless double-beta-decay searches

For the first time, a cadmium tungstate crystal scintillator enriched in $^{116}$Cd has been succesfully tested as a scintillating bolometer. The measurement was performed above ground at a temperature of 18 mK. The crystal mass was 34.5 g and the enrichment level ~82 %. Despite a substantial pile-up effect due to above-ground operation, the detector demonstrated a high energy resolution (2-7 keV FWHM in 0.2-2.6 MeV $\gamma$ energy range), a powerful particle identification capability and a high level of internal radiopurity. These results prove that cadmium tungstate is an extremely promising detector material for a next-generation neutrinoless double-beta decay bolometric experiment, like that proposed in the CUPID project (CUORE Upgrade with Particle IDentification)

Improvement of radiopurity level of enriched 116^{116}CdWO4_4 and ZnWO4_4 crystal scintillators by recrystallization

As low as possible radioactive contamination of a detector plays a crucial role to improve sensitivity of a double beta decay experiment. The radioactive contamination of a sample of $^{116}$CdWO$_4$ crystal scintillator by thorium was reduced by a factor $\approx 10$, down to the level 0.01 mBq/kg ($^{228}$Th), by exploiting the recrystallization procedure. The total alpha activity of uranium and thorium daughters was reduced by a factor $\approx 3$, down to 1.6 mBq/kg. No change in the specific activity (the total $\alpha$ activity and $^{228}$Th) was observed in a sample of ZnWO$_4$ crystal produced by recrystallization after removing $\approx 0.4$ mm surface layer of the crystal.Comment: 14 pages, 5 figures and 2 table

Search for β+\beta^+EC and ECEC processes in 74^{74}Se

For the first time, limits on double-beta processes in $^{74}$Se have been obtained using a 400 cm$^3$ HPGe detector and an external source consisting of natural selenium powder. At a confidence level of 90%, they are $1.9\times 10^{18}$ y for the $\beta^+$EC$(0\nu + 2\nu)$ transition to the ground state, $7.7\times 10^{18}$ y for the ECEC($2\nu$) transition to the $2^+_1$ excited state in $^{74}$Ge (595.8 keV), $1.1\times 10^{19}$ y for the ECEC($0\nu$) transition to the $2^+_1$ excited state in $^{74}$Ge (595.8 keV) and $5.5\times 10^{18}$ y for the ECEC($2\nu$) and ECEC($0\nu$) transitions to the $2^+_2$ excited state in $^{74}$Ge (1204.2 keV). The last transition is discussed in association with a possible enhancement of the decay rate, in this case by several orders of magnitude, because the ECEC$(0\nu)$ process is nearly degenerate with an excited state in the daughter nuclide. Prospects for investigating such processes in future experiments are discussed.Comment: 13 pages, 2 figures; presented at the 2-nd Symposium on "Neutrino and Dark Matter in Nuclear Physics" (Paris, September 3-9, 2006); v3: minor change

Study of 2 beta-decay of Mo-100 and Se-82 using the NEMO3 detector

After analysis of 5797 h of data from the detector NEMO3, new limits on neutrinoless double beta decay of Mo-100 (T-1/2 > 3.1 x 10(23) y, 90% CL) and Se-82 (T-1/2 > 1.4 x 10(23) y, 90% CL) have been obtained. The corresponding limits on the effective majorana neutrino mass are: 1.4 x 10(22) y (90% CL) for Mo-100 and T-1/2 > 1.2 x 10(22) y (90% CL) for Se-82. Corresponding bounds on the Majoron-neutrino coupling constant are < (0.5-0.9) x 10(- 4) and <(0.7-1.6) x 10(- 4). Two-neutrino 2beta-decay half-lives have been measured with a high accuracy, (T1/2Mo)-Mo-100 = [7.68 +/- 0.02(stat) +/- 0.54(syst)] x 10(18) y and (T1/2Se)-Se-82 = [10.3 +/- 0.3(stat) +/- 0.7(syst)] x 10(19) y. (C) 2004 MAIK "Nauka/Interperiodica"