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Experiment TGV-2 – Search for double beta decay of 106Cd
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Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 478 www.elsevier.com/locate/npbps
Experiment TGV-2 - search for double beta decay of 106 Cd ˇ N.I. Rukhadzea,1,∗, Ch. Brianc¸onc , V.B. Brudanina , P. Cerm´ akb , V.G. Egorova , A.A. Klimenkoa , A. Koval´ıka , a a a b ˇ ˇ , I. Stekl , V.V. Timkina E.N. Rukhadze , Yu.A. Shitov , F. Simkovic a Joint Institute for Nuclear Research, 141980 Dubna, Russia of Experimental and Applied Physics, CTU, 128 00 Prague, Czech Republic c Centre de Spectrom´ etrie Nucl´eaire et de Spectrom´etrie de Masse, Orsay, France
b Institute
Abstract New limits (at 90% C.L.) on double beta decay of 106 Cd - T1/2 (0νEC/EC) > 1.7 × 1020 yr and T1/2 (2νEC/EC) > 4.2 × 1020 yr were obtained in a preliminary calculation of data accumulated for 12900 h on the TGV-2 spectrometer. Keywords: double beta decay, neutrino, 106 Cd The ββ decay processes are of major importance for particle and nuclear physics as powerful tools for the study of lepton number conservation and neutrino properties. In contrast to the β− β− -decay, where 2ν mode of the process has been experimentally measured for several isotopes, other ββ processes have never been observed in direct experiments, neither for 2ν nor for 0ν modes. The 106 Cd isotope (QEC/EC =2770 keV) is one of the most favorable candidates for studying EC/EC decay. The 2νEC/EC decay of 106 Cd is characterized by emission of two Palladium (Pd) X-rays (∼21 keV). The 0νEC/EC resonant decay of 106 Cd is expected to 2741.0 keV excited state of 106 Pd and accompanied by emission of γ2741 keV or by γ2229 keV-γ512 keV cascade. Investigation of double beta decay of 106 Cd was performed at the Modane underground laboratory (4800 m w.e.) using a low-background spectrometer TGV-2 (Telescope Germanium Vertical) [1]. The detector part of the TGV-2 is composed of 32 HPGe planar type detectors with the sensitive volume of 2040 mm2 × 6 mm each. The total sensitive volume of detectors is as large as 400 cm3 . The total mass of the detectors is ∼3 kg. The detectors are mounted one over another together with double beta emitters in a common cryostat. Dou∗ Corresponding
author, E-mail: [email protected] 08-02-00790
1 The work was partly supported by RFBR, grant No.
0920-5632/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2012.09.115
ble beta emitters were ∼50 μm thick foils of 106 Cd (enrichment 75%) with a diameter of 52 mm inserted between the entrance windows of the neighboring detectors. The distance between the detectors and the emitters was ∼1.5 mm. The energy resolution of detectors ranged from 3.0 to 4.0 keV at 1332 keV (60 Co). The detector part of TGV-2 was surrounded by a copper shielding (> 20 cm), a steel airtight box against radon, a led shielding (> 10 cm), and an antineutron shielding made of borated polyethylene (16 cm). Two experimental runs were performed to search for ββ decay of 106 Cd. In the first run ∼ 10 g (12 samples) of 106 Cd and ∼ 3.2 g of natural Cd were measured during 8687 h [2]. In the second run ∼ 13.6 g (16 samples) of 106 Cd were studied during 12900 h. The coincidences between two X-rays of Pd detected in neighboring detectors were analyzed to search for 2νEC/EC decay of 106 Cd to the ground 0+ state of 106 Pd. The search for 0νEC/EC resonant decay of 106 Cd was based on the analysis of KX(Pd) -γ2741 keV and KX(Pd) γ2229 keV -γ511.9 keV coincidences. New limits (at 90% C.L.) on half-lives of 0νEC/EC resonant decay of 106 Cd - T1/2 > 1.7×1020 yr and 2νEC/EC decay of 106 Cd + (0g.s. − 0+g.s. ) - T1/2 > 4.2 × 1020 yr were obtained in a preliminary calculation of data accumulated in run II. [1] P. Beneˇs et al. Nucl. Instr. Meth. A 569 (2006) 737. [2] N.I. Rukhadze et al., Bull. Rus. Ac. Sci.: Phys. 72 (2008) 731.
Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 478 www.elsevier.com/locate/npbps
Experiment TGV-2 - search for double beta decay of 106 Cd ˇ N.I. Rukhadzea,1,∗, Ch. Brianc¸onc , V.B. Brudanina , P. Cerm´ akb , V.G. Egorova , A.A. Klimenkoa , A. Koval´ıka , a a a b ˇ ˇ , I. Stekl , V.V. Timkina E.N. Rukhadze , Yu.A. Shitov , F. Simkovic a Joint Institute for Nuclear Research, 141980 Dubna, Russia of Experimental and Applied Physics, CTU, 128 00 Prague, Czech Republic c Centre de Spectrom´ etrie Nucl´eaire et de Spectrom´etrie de Masse, Orsay, France
b Institute
Abstract New limits (at 90% C.L.) on double beta decay of 106 Cd - T1/2 (0νEC/EC) > 1.7 × 1020 yr and T1/2 (2νEC/EC) > 4.2 × 1020 yr were obtained in a preliminary calculation of data accumulated for 12900 h on the TGV-2 spectrometer. Keywords: double beta decay, neutrino, 106 Cd The ββ decay processes are of major importance for particle and nuclear physics as powerful tools for the study of lepton number conservation and neutrino properties. In contrast to the β− β− -decay, where 2ν mode of the process has been experimentally measured for several isotopes, other ββ processes have never been observed in direct experiments, neither for 2ν nor for 0ν modes. The 106 Cd isotope (QEC/EC =2770 keV) is one of the most favorable candidates for studying EC/EC decay. The 2νEC/EC decay of 106 Cd is characterized by emission of two Palladium (Pd) X-rays (∼21 keV). The 0νEC/EC resonant decay of 106 Cd is expected to 2741.0 keV excited state of 106 Pd and accompanied by emission of γ2741 keV or by γ2229 keV-γ512 keV cascade. Investigation of double beta decay of 106 Cd was performed at the Modane underground laboratory (4800 m w.e.) using a low-background spectrometer TGV-2 (Telescope Germanium Vertical) [1]. The detector part of the TGV-2 is composed of 32 HPGe planar type detectors with the sensitive volume of 2040 mm2 × 6 mm each. The total sensitive volume of detectors is as large as 400 cm3 . The total mass of the detectors is ∼3 kg. The detectors are mounted one over another together with double beta emitters in a common cryostat. Dou∗ Corresponding
author, E-mail: [email protected] 08-02-00790
1 The work was partly supported by RFBR, grant No.
0920-5632/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2012.09.115
ble beta emitters were ∼50 μm thick foils of 106 Cd (enrichment 75%) with a diameter of 52 mm inserted between the entrance windows of the neighboring detectors. The distance between the detectors and the emitters was ∼1.5 mm. The energy resolution of detectors ranged from 3.0 to 4.0 keV at 1332 keV (60 Co). The detector part of TGV-2 was surrounded by a copper shielding (> 20 cm), a steel airtight box against radon, a led shielding (> 10 cm), and an antineutron shielding made of borated polyethylene (16 cm). Two experimental runs were performed to search for ββ decay of 106 Cd. In the first run ∼ 10 g (12 samples) of 106 Cd and ∼ 3.2 g of natural Cd were measured during 8687 h [2]. In the second run ∼ 13.6 g (16 samples) of 106 Cd were studied during 12900 h. The coincidences between two X-rays of Pd detected in neighboring detectors were analyzed to search for 2νEC/EC decay of 106 Cd to the ground 0+ state of 106 Pd. The search for 0νEC/EC resonant decay of 106 Cd was based on the analysis of KX(Pd) -γ2741 keV and KX(Pd) γ2229 keV -γ511.9 keV coincidences. New limits (at 90% C.L.) on half-lives of 0νEC/EC resonant decay of 106 Cd - T1/2 > 1.7×1020 yr and 2νEC/EC decay of 106 Cd + (0g.s. − 0+g.s. ) - T1/2 > 4.2 × 1020 yr were obtained in a preliminary calculation of data accumulated in run II. [1] P. Beneˇs et al. Nucl. Instr. Meth. A 569 (2006) 737. [2] N.I. Rukhadze et al., Bull. Rus. Ac. Sci.: Phys. 72 (2008) 731.