Search for double beta decay of 136^{136}Ce and 138^{138}Ce with HPGe gamma detector

Search for double $\beta$ decay of $^{136}$Ce and $^{138}$Ce was realized with 732 g of deeply purified cerium oxide sample measured over 1900 h with the help of an ultra-low background HPGe $\gamma$ detector with a volume of 465 cm$^3$ at the STELLA facility of the Gran Sasso National Laboratories of the INFN (Italy). New improved half-life limits on double beta processes in the cerium isotopes were set at the level of $\lim T_{1/2}\sim 10^{17}-10^{18}$~yr; many of them are even two orders of magnitude larger than the best previous results.Comment: 21 pages, 6 figures, 3 tables; version accepted for publication on Nucl. Phys.

New limits on 2ε2\varepsilon, εβ+\varepsilon\beta^+ and 2β+2\beta^+ decay of 136^{136}Ce and 138^{138}Ce with deeply purified cerium sample

A search for double electron capture ($2\varepsilon$), electron capture with positron emission ($\varepsilon\beta^+$), and double positron emission $2\beta^+$) in $^{136}$Ce and $^{138}$Ce was realized with a 465 cm$^3$ ultra-low background HP Ge $\gamma$ spectrometer over 2299 h at the Gran Sasso underground laboratory. A 627 g sample of cerium oxide deeply purified by liquid-liquid extraction method was used as a source of $\gamma$ quanta expected in double $\beta$ decay of the cerium isotopes. New improved half-life limits were set on different modes and channels of double $\beta$ decay of $^{136}$Ce and $^{138}$Ce at the level of $T_{1/2}>10^{17}-10^{18}$ yr.Comment: 19 pages, 6 figures, 2 table

High sensitivity double beta decay study of 116-Cd and 100-Mo with the BOREXINO Counting Test Facility (CAMEO project)

The unique features (super-low background and large sensitive volume) of the CTF and BOREXINO set ups are used in the CAMEO project for a high sensitivity study of 100-Mo and 116-Cd neutrinoless double beta decay. Pilot measurements with 116-Cd and Monte Carlo simulations show that the sensitivity of the CAMEO experiment (in terms of the half-life limit for neutrinoless double beta decay) is (3-5) 10^24 yr with a 1 kg source of 100-Mo (116-Cd, 82-Se, and 150-Nd) and about 10^26 yr with 65 kg of enriched 116-CdWO_4 crystals placed in the liquid scintillator of the CTF. The last value corresponds to a limit on the neutrino mass of less than 0.06 eV. Similarly with 1000 kg of 116-CdWO_4 crystals located in the BOREXINO apparatus the neutrino mass limit can be pushed down to m_nu<0.02 eV.Comment: 29 pages, LaTex, 9 eps figure

Investigation of β + β + and β + /EC decay of 106 Cd

A low background scintillation detector with a CdWO4 crystal of 1.046 kg was used to search for β+β+ and β+/EC processes in 106Cd. For the neutrinoless mode the limits T1/2(0νβ+β+) ≥ 2.2 · 1019 y and T1/2(0νβ+/EC) ≥ 5.5 · 1019 y were obtained with 90% C.L. For the possible two neutrino decay limits of T1/2(2νβ+β+) ≥ 9.2 · 1017 y and 1/2(2νβ+/EC) ≥ 2.6 · 1017 y have been determined with 99% C.L

New results of 116Cd double beta decay study with 116CdWO4 scintillators

A new phase of 116Cd double beta decay experiment is in progress in the Solotvina Underground Laboratory. Four enriched 116CdWO4 scintillators with total mass 339 g are used in a set up, whose active shield is made of 15 natural CdWO4 crystals (20.6 kg). The background rate in the energy interval 2.5-3.2 MeV is 0.03 counts/y*kg*keV. The half-life for 2-neutrino 2-beta decay of 116Cd is measured as T{1/2}(2-neutrino) = [2.6+-0.1(stat)-0.4+0.7}(syst)]*10**19 y. The T{1/2} limits for neutrinoless 2-beta decay of 116Cd are set as T{1/2} >= 0.7(2.5)*10**23 y at 90%(68%) C.L. for transition to ground state of 116Sn, while for decays to the first 2+ and second 0+ excited levels of 116Sn as T{1/2}>=1.3(4.8)*10**22 y and >=0.7(2.4)*10**22 y with 90%(68%) C.L., respectively. For 0-neutrino 2-beta decay with emission of one or two Majorons, the limits are T{1/2}(0-neutrino M1) >=3.7(5.8)*10**21 y and T{1/2}(0-neutrino M2)>=5.9(9.4)*10**20 y at 90%(68%) C.L. Restrictions on the value of the neutrino mass, right-handed admixtures in the weak interaction, and the neutrino-Majoron coupling constant are derived as: m(neutrino)<=2.6(1.4) eV, eta <=3.9*10**-8, lambda <=3.4*10**-6, and g{M}<= 12(9.5)*10**-5 at 90%(68%) C.L., respectively.Comment: 28 pages, 9 figures (LaTeX). Phys. Rev. C (in press

Development and properties of cadmium and lead tungstate low-background scintillators for double beta decay experiments

Methods of deep purification of natural and isotopically enriched cadmium (Cd, 106Cd, 116Cd), as well as of archaeological lead (archPb), to produce cadmium and lead tungstate crystal scintillators have been developed. The basic stages of development and characteristics of the scintillators are described. The developed methods of initial materials purification and crystal growth can be used for the production of scintillators for large-scale high sensitivity experiments to search for rare events (double beta decay, dark matter, rare alpha and beta decay)

New limits on double-beta decay of

A search for double-beta decay of $$^{190}$$Pt and $$^{198}$$Pt with emission of $$\gamma$$-ray quanta was realized at the HADES underground laboratory with a 148 g platinum sample measured by two ultralow-background HPGe detectors over 8946 h. The isotopic composition of the platinum sample has been measured with high precision using inductively coupled plasma mass spectrometry. New lower limits for the half-lives of $$^{190}$$Pt relative to different channels and modes of the decays were set on the level of $$\lim T_{1/2}\sim 10^{14}$$–$$10^{16}$$ year. A possible exact resonant $$0\nu KN$$ transition to the 1,2 1326.9 keV level of $$^{190}$$Os is limited for the first time as $$T_{1/2} \ge 2.5 \times 10^{16}$$ year. A new lower limit on the double-beta decay of $$^{198}$$Pt to the first excited level of $$^{198}$$Hg was set as $$T_{1/2} \ge 3.2\times 10^{19}$$ year, one order of magnitude higher than the limit obtained in the previous experiment

Effect of tungsten doping on ZnMoO4 scintillating bolometer performance

The introduction of a small quantity of tungsten oxide (in the range 0.2–0.5 wt%) into the melt improves the growth of ZnMoO4 crystals. No significant difference in the kinetics of scintillation decay, scintillation efficiency, emission spectra, optical transmittance was observed for three ZnMoO4 crystal samples grown from the melt of stoichiometric composition, with excess of molybdenum and doped with tungsten. Using CaWO4 as reference, the absolute light yield of ZnMoO4 is found to be equal to 3550±5503550±550 ph/MeV at 77 K. For two ZnMoO4 samples 20 mm in diameter and 40 mm in length (grown from the melt of stoichiometric composition and doped with tungsten) it is confirmed that scintillation and bolometric response are similar at milli-Kelvin temperature