Proton instability of73Rb

The study of the stability of an astrophysically interesting nucleus⁷³Rb was performed by searching itsβ ⁺ and proton decay at the ISOLDE facility at CERN. Light rubidium isotopes were produced in a spallation reaction of a niobium target induced by a pulsed 1 GeV proton beam. The previously reported proton-unbound character of⁷³Rb was confirmed and the upper limit for its production cross-section was reduced by more than one order of magnitude.     

CP violation in t → W + b decays in two-Higgs doublet model

Due to the large mass of top quark, CP violation in the top-quark decay is sensitive to the interactions mediated by Higgs bosons. We consider CP violation in t → W ⁺ b decay by calculating consistently in unitary gauge the CP-violating up-down asymmetry of the leptons from W boson decays in t → W ⁺ b, defined by Grz?dkowski and Gunion, in the two-Higgs doublet model with CP-violating neutral sector. The asymmetry is shown to be at most of the order of (1–4) × 10^-4 for tan β = 1.0, where tan β is the ratio of vacuum expectation values for the two neutral Higgs bosons.     

Theβ + decay of the new isotope86Mo and the first observation of86m Nb

Theβ ⁺ decay of⁸⁶Mo has been firstly investigated by means ofβγ spectroscopy. The⁸⁶Mo nuclei were produced by fusion-evaporation reactions of⁵⁴ Fe (³⁵Cl, 1 p2n) and⁵⁸Ni (³²S,2p 2n) at beam energies of 103 and 120 MeV, respectively. Threeγ rays of 47.3, 49.8 and 187.0 keV were unambiguously identified to follow theβ ⁺ decay of⁸⁶Mo by results ofXγ andβγ coincidence and cross-bombardment. A half life and a maximumβ ⁺-ray energy of⁸⁶Mo were determined to be 19.6±1.1 s and 3.9±0.4 MeV, respectively. A decay scheme of⁸⁶Mo is proposed in this article. Furthermore, a decay of⁸⁶Nb has been studied using the same combinations of projectiles and targets, and a newβ-decaying isomer^86m Nb was observed with a half life of 56.3±8.3 s.     

Messung von fünf β-γ-Zirkularpolarisationskorrelationen beim Zerfall Eu152→Gd152

In the decay Eu¹⁵²→Gd¹⁵² fiveβ(circularly polarizedγ) correlations have been measured (Table). The Fermi matrix element of the 3^?–3^? β transition is small or vanishing. The levels of 344 and 755 keV (I=2⁺ and 4⁺, respectively) seem to be collective states.     

Gamow-Teller strength in the β+ decay of104In

Theβ-strength function of¹⁰⁴Cd is studied in theβ ⁺/EC decay of mass-separated¹⁰⁴In. The determination of theβ ⁺ feeding and theβ ⁺/β ⁺EC ratio is the result of the simultaneous measurement of beta and gamma rays in one semiconductor beta-spectrometer. Information on the strength function near theQ _EC value is obtained from the detection of high-energyγ rays. The total observedβ strength amounts up to 10% of the Extreme Single-Particle Shell Model value. A strong enhancement in theβ ⁺/EC feeding to a group of levels around 5.6 MeV shows the influence of the Gamow-Teller Resonance.     

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.     

Remeasurement of capture to positron decay ratios in22Na and65Zn and comparison with theory

In the decay of²²Na theEC/β ⁺ ratio for theβ-transition to the 1275 keV-level was measured to beEC/β ⁺=0.1050 (29). Single and coincidence counting was performed using a 16% Ge(Li) and an NaI well-type detector. For⁶⁵Zn theK/β ⁺ ratio for the ground state transitionK ₁/β ⁺=30.3 (10) was obtained using the same apparatus and in addition a 10 mm diam. × 5.4 mm Si(Li) detector. The results are compared with earlier experiments and with theory.     

Spin-flipβ − decay of even-even deformed nuclei110Ru and112Ru

Neutron-rich nuclides¹¹⁰Ru and¹¹²Ru produced in symmetric fission of²³⁸U by 20 MeV protons have been studied at the IGISOL facility by means ofβ-ray,γ-ray and conversion electron spectroscopy. A total of 12 and 6γ-transitions were observed in the decays of¹¹⁰Ru and¹¹²Ru, respectively. Multipolarities were determined for a few transitions. The beta decay half-life was determined to be 11.6±0.6 s for¹¹⁰Ru and 1.75±0.07 s for¹¹²Ru. As a side product, a new value of 2.1±0.3 s for theβ half-life of the¹¹²Rh 1⁺ state was obtained. The decay energy measured with the plastic scintillator was 2.81 ±0.05 MeV for¹¹⁰Ru and 4.52 ±0.08 MeV for¹¹²Ru. The beta decay schemes of¹¹⁰Ru and¹¹²Ru isotopes indicate that the main fraction of their beta strength resides in two 0⁺→1⁺ spin-flip transitions with their logf t values between 4.4 and 4.7. The decay energies and the energies of the 1⁺ GT states are compared with the macroscopic-microscopic model calculations. The observed GT-strengths are discussed in the framework of the deformed single-particle model.     

Investigation ofβ + β + andβ +/EC decay of106Cd

A low background scintillation detector with a CdWO₄ crystal of 1.046 kg was used to search forβ ⁺ β ⁺ andβ ⁺/EC processes in¹⁰⁶Cd. For the neutrinoless mode the limits T_1/2(0νβ ⁺ β ⁺)≥2.2·10¹⁹ y and T_1/2(0νβ ⁺/EC)≥5.5·10¹⁹ y were obtained with 90% C.L. For the possible two neutrino decay limits of T_1/2(2νβ ⁺ β ⁺)≥9.2·10¹⁷ y and T_1/2(2νβ ⁺/EC)≥2.6·10¹⁷ y have been determined with 99% C.L.     

Das Positronenspektrum von22Na und die Ruhemasse des Neutrinos aus dem β+-Zerfall

Theβ ⁺ spectrum of²²Na has been measured with the Heidelberg (π/2) √13 iron-freeβ-ray spectrometer. Particular attention was paid to the upper end of the continuum. The maximum energy was found to beE _max=(545.7 ±0.5) keV. The rest mass of the neutrino connected withβ ⁺ decay was found to be zero with an upper limit of 4.1 keV (67 per cent confidence).     

Improved limits on β− and β−β− decays of 48Ca

New limits on ⁴⁸Caβ^? and β^?β^? decays to excited states of ⁴⁸Ti have been obtained using a 400 cm³ low-background HPGe detector and an external source of 24.558 g enriched CaF₂ powder (9.822 g of ⁴⁸Ca). The limits for β^? decay to the 6⁺ ground state and excited 5⁺ and 4⁺ states in ⁴⁸Sc are 1.6×10²⁰ yr, 2.5×10²⁰ yr, and 1.9×10²⁰ yr at the 90% confidence level. For the β?β? decay to ⁴⁸Ti, the limits to the first 2⁺, second 2⁺, and first 0⁺ excited states are 1.8×10²⁰ yr, 1.5×10²⁰ yr, and 1.5×10²⁰ yr, again at the 90% confidence level.     

The decay properties of 3.25 min 169Hf and 2.05 min 167Hf

The decays of 3.25 min ¹⁶⁹Hf and 2.05 min ¹⁶⁷Hf have been studied with high-resolution Ge(Li) and Si(Li) detectors. The total decay energy of ¹⁶⁹Hf determined from our experimental $\text{K}\text{β}{}^{\mathrm{+}}$ ratio is 3.29^+0.05_?0.13 MeV. The allowed unhindered character of the main β-branches in the decay of both isotopes allows unique Nilsson model assignments.     

Level structure of106Mo

The level scheme of the very neutron rich nucleus ₁₀₆ ⁴² Mo₆₄ has been studied for the first time through theβ decay of¹⁰⁶Nb. Six new excited states were observed inγ singles andγ-γ coincidence experiments in addition to the 2⁺, 4⁺ and 6⁺ members of the ground state band. The excitation energies and the deexcitation pattern suggest the interpretation of the levels at 710, 885 and 956 keV as the 2 ₂ ⁺ , 3 ₁ ⁺ and 0 ₂ ⁺ states, respectively. The data support the assumption of a non-axial deformation of¹⁰⁶Mo. A half-life of (1.02±0.05) s has been determined for theβ decay of¹⁰⁶Nb.     

Average excited state lifetimes in 73Br

Lifetimes in the region of 10^?16 s have been measured for excited states between 4 and 6.6 MeV in ⁷³Br. The states were produced by the β⁺(EC) decay of a mass-separated source of ⁷³Kr, and they decayed by the emission of protons or γ-rays; their lifetimes were measured by the particle X-ray coincidence technique. The data yield information on both γ-ray and proton partial widths as well as on the level density, a level density parameter-a = 13.7 MeV^?1 is obtained. With the level widths so determined, a statistical model calculation yields excellent agreement with the delayed proton spectrum if a smooth gaussian β-strength function is employed. It is concluded, however, that without the lifetime data, β-strength function information could not have been reliably extracted.     

Levels in182W populated in the decay of182Ta

Theγ-rays emitted in theβ-decay of¹⁸²Ta have been reinvestigated with improved statistics in attempting to clarify the reported new levels at 1460.41, 1592.98, 1620.36, 1712.29 and 1762.91 keV in¹⁸²W observed in theβ-decay of¹⁸²Ta. The present study demonstrated that the fifteen newγ-rays, which were used to support the existence of the five new levels, are not relevant to theγ-decay of¹⁸²Ta. Therefore the five new levels are not populated in this decay. Additionally, theγ-ray with an energy of 1035.6 keV (0 ₂ ⁺ →2 ₁ ⁺ ) deexciting theβ-band head in¹⁸²W is observed for the first time in the present decay study and the previous tentative placement of the 351.0 keVγ-ray in the level scheme is confirmed by the present coincidence measurements.     

The Gamow-Teller beta decay of100Cd

Neutron-deficient isotopes of cadmium were produced in thep(600 MeV)+^natSn spallation reaction. The ISOLDE facility provided mass-separated beams of these isotopes. The production yield was 10³ to 10⁴ atoms/s for¹⁰⁰Cd and roughly two orders of magnitude less for⁹⁸Cd. The properties of the¹⁰⁰Cd→¹⁰⁰Ag decay were studied in detail by X-ray,γ-ray and conversion electron spectroscopy. Forty nineγ-transitions were assigned to this decay, and all but five of them were placed in the decay scheme. The half-life was determined to be 49.1±0.5 s. TheQ _EC value of 3890±70 keV was deduced from a comparison of experimental and theoreticalβ ⁺/(EC+β ⁺ probability ratios. Seven 0⁺→1⁺ Gamow-Teller transitions with log ft values between 3.5 and 4.9 were identified. The total (summed) strength is about five times smaller than predicted by the shell model for the transformation of ag _9/2 proton into ag _7/2 neutron. The quenching of the Gamow-Teller strength and other questions of nuclear structure are discussed for the¹⁰⁰Cd decay. The properties of⁹⁸Cd are inferred by extrapolation of^104,102,100Cd data, and some preliminary experimental results on⁹⁸Cd decay are presented.     

The decay of174Ta

Levels in¹⁷⁴Hf excited in the decay of¹⁷⁴Ta have been studied. Measurements of gamma-rays, conversion electrons and gamma-gamma-time coincidences were performed. The ground state band, the beta-vibrational band, the gamma-vibrational band with its head at 1226.81 keV, aK=3⁺ band at 1303.42 keV and aK=2^? octupole band at 1308.67 keV were observed. Several 2⁺ levels withK=0 are excited. The mainβ ⁺-branches proceed through allowed or first-forbidden transitions to the 2⁺ and 4⁺ levels of the ground state band. The character of theI ^π=3⁽⁺⁾ ground state of¹⁷⁴Ta is discussed.     

Decay of the134Cs isomers and the levels of134Xe,134Cs,and134Ba

A precision study of the decay of¹³⁴Cs ^g and¹³⁴Cs ^m has been made, using ordinary Ge(Li) spectrometers and ā Compton-suppression spectrometer. The logft value of the second forbidden nonuniqueβ-decay to¹³⁴Xe has been measured to be 13.0±0.2. TheM4γ-ray transition in¹³⁴Cs^m(8^?) decay has been measured to haveα _K= 73±7 and a hindrance of 7.0 over the Moskowski estimate. This is discussed in terms of the level configurations and the analogous transition in¹³³Xe. A new intensity limit of 2×10^?6 has been set for the zero-phonon transition between the 4⁺ and 2⁺ members of the two-phonon triplet. This leads to an upper limit forB(E2)_4→2′, greater than 905. This and the more preciseγ-ray intensity values are discussed in relation to presently available nuclear models.