First results for the measurement of double-electron capture of 106Cd in the experiment TGV II

Present status of the experiment TGV II which is devoted to the measurement of double-beta decay of ¹⁰⁶Cd is given. The low background spectrometer TGV II is installed in the Modane Underground Laboratory and has been running from February 2005 with approx 10 grams of ¹⁰⁶Cd enriched at 75%. After an analysis of 3736 hours of experimental data the new improved half-life limit for 2νEC/EC decay of ¹⁰⁶Cd (0 _g.s. ⁺ → 0 _g.s. ⁺ ) is given as T ₁ ^2/2ν > 4.8 × 10¹⁹ years (90% CL). The search for 2νEC/EC decay of ¹⁰⁶Cd to the excited states of ¹⁰⁶Pd allows to determine the limits of the half-lives T ₁ ^2/2ν (0 _g.s. ⁺ → 2 ₁ ⁺ ) > 3.9 × 10¹⁹ years (90% CL) and T ₁ ^2/2ν (0 _g.s. ⁺ → 0 ₁ ⁺ ) > 5.8 × 10¹⁹ years (90% CL). Presented by I. Štekl at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’05), Corfu, Greece, September 26–29, 2005.     

The 0+ → 0+ positron double- β decay with emission of two neutrinos in the nuclei 96Ru, 102Pd, 106Cd and 108Cd

Theoretical results for two neutrinos in the nuclei ⁹⁶Ru, ¹⁰²Pd, ¹⁰⁶Cd and ¹⁰⁸Cd are presented. The study employs the Hartree-Fock-Bogoliubov model to obtain the wave functions of the parent and daughter nuclei, in conjunction with the summation method to estimate the double-beta decay nuclear matrix elements. The reliability of the intrinsic wave functions of ^{96, 102}Ru, ⁹⁶Mo, ^{102, 106, 108}Pd and ^{106, 108}Cd nuclei is tested by comparing the theoretically calculated spectroscopic properties with the available experimental data. The calculated half-lives T_1/2^2ν of ⁹⁶Ru, ¹⁰²Pd, ¹⁰⁶Cd and ¹⁰⁸Cd nuclei for 2ν β⁺β⁺, 2ν β⁺EC and 2ν ECEC modes are presented. The effect of deformation on the nuclear transition matrix element M_2ν is also studied.     

Two-neutrino double beta decay to excited states

Both doubleβ ⁻ and doubleβ ⁺/EC decay transitions to excited final states in the two-neutrino mode are discussed, their gross properties reviewed and a compilation of recent calculations presented. A brief presentation of the involved nuclear models is given. The close connection between the single and double beta decays is discussed. Presented at Workshop on calculation of double-beta-decay matrix elements (MEDEX’97), Prague, May 27–31, 1997.     

Fine structure of the strength function for the β<Superscript>+</Superscript>/EC decay of the <Superscript>160<Emphasis Type="Italic">m</Emphasis></Superscript>Ho (5.02 h) isomer

The strength function for the β⁺/EC decay of the deformed nucleus of the ^160m Ho (5.02 h) isomer is obtained from the experimental data, The fine structure of the strength function S _β(E) is analyzed. It has a pronounced resonance structure for Gamow-Teller transitions and is found to exhibit a resonance structure for first-forbidden transitions. It is shown that for some excitation energies of the 160Dy daughter nucleus the probability of first-forbidden β⁺/EC transitions in the decay of the ^160m Ho isomer is comparable with the probability of Gamow-Teller β⁺/EC transitions.     

Two-neutrino double β decay of96Zr to excited 2+ state of96Mo

The two-neutrino double beta decay of⁹⁶Zr isotope for 0⁺ → 2⁺ transition has been studied in the PHFB model. In our earlier work, the reliability of the intrinsic wave functions of⁹⁶Zr and⁹⁶Mo isotopes has been established by obtaining an overall agreement between a number of theoretically calculated spectroscopic properties as well as half-lives of 2vββ decay for 0⁺ → 0⁺ transition and the available experimental data. In the present work, the half-life of 2vββ decay for 0⁺ ar 2⁺ transition T ₁ ^2/2v (0⁺ →²⁺) has been calculated using the same set of intrinsic wave functions.     

(EC + β<Superscript>+</Superscript>) decays of the 11/2<Superscript>-</Superscript> isomer and 1/2<Superscript>+</Superscript> ground state of <Superscript>143</Superscript>Dy

The 1/2⁺ ground state and a 11/2^- isomer of very neutron-deficient isotope ¹⁴³Dy were produced by irradiation of an enriched target of ¹⁰⁶Cd with ⁴⁰Ca and studied by using a helium-jet fast tape-transport system in combination with proton-γ, X-γ and γ-γ coincidence measurements. A simple ( EC + β⁺) decay scheme of ^143mDy with a half-life of 3.0(3) s and a tentative ( EC + β⁺) decay scheme of ^143gDy with a half-life of 5.6(10) s are proposed. As a by-product, the 347- and 545-keV γ transitions in ¹³⁸Sm following the β-delayed proton emission of ¹³⁹Gd decay and the 323-keV γ transition in ¹³⁹Eu following the β-delayed proton emission of ¹⁴⁰Tb decay could be observed for the first time. Received: 20 August 2002 / Accepted: 28 October 2002 / Published online: 11 February 2003 RID="a" ID="a"e-mail: xsw@ns.lzb.ac.cn Communicated by D. Schwalm     

Search for double beta decay of 106Cd

A search for the β⁺β⁺, β⁺/EC, and EC/EC decays of ¹⁰⁶Cd was performed at the Modane Underground Laboratory (France) located at a depth of 4800 m w.e. using a TGV-2 multidetector germanium spectrometer. A preliminary evaluation is performed of the experimental data accumulated during the measurements (12 900 h) of ～13.6 g of ¹⁰⁶Cd (with an enrichment of 75%) and the spectrometer background without samples and with samples of natural Cd. New limits (at a 90% confidence level) of half-lives are obtained: T _1/2 ? 1.7 × 10²⁰ yr and T _1/2 ? 1.6 × 10²⁰ yr for the 0νEC/EC resonant decay of ¹⁰⁶Cd to the 2741 keV and 2718 keV excited states of the daughter nucleus ¹⁰⁶Pd and T _1/2 ? 4.2 × 10²⁰ yr for the 2νEC/EC decay to the ground state of ¹⁰⁶Pd (0⁺ → 0⁺, g.s.). The limits for other branches of the double beta decay of ¹⁰⁶Cd with transitions to the ground and excited states of ¹⁰⁶Pd are improved.     

On the limit of nuclear stability — The region of double magic100Sn and bound-state β-decay of187Re75+

Experiments which led to the discovery of the heaviest, self-conjugated double magic nucleus¹⁰⁰Sn and the bound-state β-decay of completely ionized¹⁸⁷Re are presented.¹⁰⁰Sn was produced by fragmentation of 1.1 A GeV¹²⁴Xe beams, separated and implanted in a 4π Si-stack detector. From its decay a half-lifeT _1/2=0.94(+0.54, −0.27) s and a β⁺ endpoint energy ofE _β=3.4(+0.7, −0.3) MeV were determined for the 0⁺−1⁺ Gamov-Teller transition. Completely stripped¹⁸⁷Re⁷⁵⁺ was produced and stored in a coolerring with an energy of 351 A MeV for several hours. The products of bound-state β-decay of¹⁸⁷Re⁷⁵⁺ were detected by two independent methods, which allowed to determine a half-life ofT _1/2=33±6 y for this decay, which is of importance for the calibration of the Re/Os nucleosynthesis chronometer.     

Issues and status of “basic divertor and SOL physics” from papers and discussions

⁴⁸Ca, the lightest double beta decay candidate, has been until now the only one simple enough to be treated exactly in the nuclear shell model. Thus, theββ(2ν) half-life measurement, reported here, provides a unique test of the nuclear physics involved in theββ matrix element calculation. Enriched⁴⁸Ca sources of two different thicknesses have been exposed in a time projection chamber, and yieldT ₁ ^2/2ν =(4.3 _−1.1 ^+2.4 [stat.] ± 1.4[syst.]) × 10¹⁹ years, compatible with the shell model calculations. The consequences of this result for the shell model calculation of theββ(2ν) rate are briefly discussed. Presented by P. Vogel at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’97), Prague, May 27–31, 1997. This work was funded by the US Department of Energy under contracts DE-FG03-01ER40679 and DE-FG03-88ER40397.     

Search for double electron capture of 106Cd

A search for double electron capture of ¹⁰⁶Cd was performed at the Modane Underground Laboratory (4800 m w.e.) using a low-background and high-sensitivity multidetector spectrometer TGV-2 (Telescope Germanium Vertical). New limits on β ⁺/EC, EC/EC decays of ¹⁰⁶Cd were obtained from preliminary calculations of experimental data accumulated for 4800 h of measurement of 10 g of ¹⁰⁶Cd with enrichment of 75%. They are > 9.1 × 10¹⁸ yr, > 1.9 × 10¹⁹ yr for transitions to the first 2⁺, 511.9 keV excited state of ¹⁰⁶Pd, and > 1.3 × 10¹⁹ yr, > 6.2 × 10¹⁹ yr for transitions to the ground 0⁺ state of ¹⁰⁶Pd. All limits are given at 90% C.L. The text was submitted by the authors in English.     

Search for double beta decay of <Superscript>106</Superscript>Cd in the TGV-2 experiment

An investigation of double beta decay (β⁺β⁺, β⁺/EC, EC/EC) of ¹⁰⁶Cd was performed at the Modane underground laboratory (at a water equivalent depth of 4800 m) using a TGV-2 spectrometer with 32 detectors. Evaluation of the experimental data accumulated over 12 400 h of measuring ～13.6 g of ¹⁰⁶Cd with an enrichment of 75% was performed. New limits (at a confidence level of 90%) on the half-lives of the 0νEC/EC resonant decay of ¹⁰⁶Cd to the 2741 keV excited state of ¹⁰⁶Pd ? T _1/2 ≥ 1.5 × 10²⁰ y and on 2νEC/EC decay to the ground state of ¹⁰⁶Pd (0⁺ → 0⁺, g.s.) ? T _1/2 ≥ 3.9 × 10²⁰ y were obtained. The limits of the 2νEC/EC decay of ¹⁰⁶Cd to the 2⁺, 512 keV and 0 ₁ ⁺ , 1334 keV excited states of ¹⁰⁶Pd and 2νβ⁺β⁺- and the 2νβ⁺ EC decays of ¹⁰⁶Cd to the ground and excited states of ¹⁰⁶Pd were improved.     

β-delayed proton decay of the proton drip-line nucleus142Ho in the rare-earth region

New β-delayed proton precursor¹⁴²Ho was produced via heavy ion induced reaction¹⁰⁶Cd(⁴⁰Ca, p3n), and identified for the first time by using a He-jet fast tape transport system in combination with “p-γ” coincidence measurements. The β-delayed proton decay of¹⁴²Ho was observed and its half life was determined to be (0.4±0.1) s. By fitting the experimental relative branching ratios to final states in the proton daughter nucleus¹⁴¹Tb and the energy spectrum of β-delayed protons with a statistical model calculation, the ground-state spin of¹⁴²Ho was assigned as 5, 6 or 7. Nuclear energy-potential-surface (EPS) calculations were performed using the Woods-Saxon Strutinsky method. The calculated results favored the assignments of 7⁻ to¹⁴²Ho. As the by-products, some γ-transitions in the proton daughter nuclei following the β-delayed proton decays of precursors¹³⁹Gd,¹⁴⁰Tb,¹⁴²Tb, and¹⁴³Dy were reported here for the first time.     

On-line orientation of bromine isotopes

Assignments for the principal Nilsson configuration in light β⁺-decaying bromine isotopes were proposed in a contribution to the OLNO-1 conference. These assignments were made on the basis of magnetic moments derived from the temperature dependence of anisotropies in daughter Se isotopes observed in the DOLIS-COLD facility at Daresbury. Anisotropy measurements have since been extended to a lower base temperature in^74m Br and^72g Br decay, leading to more stringent limits on the ground state moment of⁷²Br. The proposed π[312]3/2 configuration for⁷⁵Br has also now been confirmed by a measurement of the sign of its magnetic moment. This was done by observing the β-asymmetry in⁷⁵Br decay using high purity Si detectors mounted within the dilution refrigerator.     

Structure of low-spin states in the doubly-odd 182Ir nucleus

Low-spin states of ¹⁸²Ir were populated through the β⁺ /EC decay of ¹⁸²Pt . Two strong E2 transitions were observed for the first time: a 25.7keV transition in ¹⁸²Ir and a 34.0keV transition in Re of probable mass A = 178 . Spin and parity, I ^π = 3⁺ , are firmly assigned to the ¹⁸²Ir ground state (g.s.). For the excited states, the parity is established and the spin determined or restricted. These assignments support most of the interpretations of the level structure previously suggested. The systematics for the known 5⁺ → 3⁺ transitions in π h _9/2 ⊗ ν 1/2^-[521] bands is presented. Using a semi-microscopic two-quasiparticle axial-rotor coupling model, particle configurations have been attributed or suggested for most of the coupled states lying at low energy in ¹⁸²Ir .     

The sign of the magnetic dipole moment of the ground state of122I

The sign of the nuclear magnetic dipole moment of the ground state of¹²²I has been determined to be positive using a novel experimental technique. The technique investigates the asymmetry of positron emission by detecting the 511 keV gamma-rays produced on the annihilation of the positrons. The method would appear to have general validity for studying the sign of the magnetic moment in other cases where theβ ⁺ decay is relatively simple.     

Decay of the very neutron-deficient isotope 131Pm

The decay of ¹³¹Pm has been investigated by means of γ-ray spectroscopy. The ¹³¹Pm nuclei were produced by fusion-evaporation reaction of ¹⁰⁶Cd(³²S,3p4n) at the beam energy of 170 MeV. A helium-jet technique and a tape transport system were used to collect the activities and transfer them to a detecting position for X and γ rays measurement. Two γ rays of 185.0 and 220.0 keV were unambiguously identified to follow the β⁺ decay of ¹³¹Pm by results of X-γ and γ–γ coincidence. A growth-decay feature of the decay curve for 87.8 keV γ-ray of ¹³¹Nd confirmed the production of ¹³¹Pm nuclei. The half-life of ¹³¹Pm was measured to be 6.3 ± 0.8 s. A partial decay scheme of ¹³¹Pm is proposed on the basis of X-γ and γ–γ coincidence data in this experiment and the known structure information deduced from in-beam experiments of the daughter nucleus ¹³¹Nd. Received: 11 January 1999 / Revised version: 20 May 1999     

β-delayed proton decays and spin assignments for 133Sm and 149Yb

The proton-rich isotope ¹³³Sm was produced via the fusion evaporation reaction ⁴⁰Ca + ⁹⁶Ru. Its β-delayed proton decay was studied by p-γ coincidence in combination with a He-jet tape transport system, and half-lives, proton energy spectra, γ-transitions following the proton emission, as well as β-delayed proton branching ratios to the low-lying states in the grand-daughter nucleus were determined. Comparing the observed β-delayed proton branching ratios with statistical model calculations, the best agreement is found assuming that only one level with the spin of 3/2 in ¹³³Sm decays or two levels with the spins of 1/2 and 5/2 decay with similar half-lives. The configuration-constrained nuclear potential energy surfaces of ¹³³Sm were calculated using the Woods-Saxon-Strutinsky method, which suggests a 1/2^- ground state and a 5/2⁺ isomer with an excitation energy of 120keV. Therefore, the simple (EC+β⁺) decay scheme of ¹³³Sm in Eur. Phys. J. A 11, 277 (2001) has been revised. In addition, our previous experimental data on the β-delayed proton decay of ¹⁴⁹Yb reported in Eur. Phys. J. A 12, 1 (2001) was also analyzed using the same method. The spin-parity of ¹⁴⁹Yb is suggested to be 1/2^-.     

Decay rate measurements of upper laser level in He-Cd+ laser

The decay rate of² D _5/2 level of Cd II has been measured by the magnetic-field power-dip method. The decay rate at the zero-pressure limit is found to be 2.4·10⁶s⁻¹. The calculated collision cross section for excited Cd ions with He atoms equals 0.91·10⁻¹⁵ cm². This work was supported by the Institute of Quantum Electronics. WAT Warszawa, within the project 06.2.3.