The influence of the chemical environment on the decay constant of90mNb

An influence of the chemical environment on the decay constant λ of the 2.38 keV isomeric transition of^90mNb was investigated. The relative difference of the decay constants for Nb atoms in Zr metal and in a fluorine complex was determined to be ¦λ_complex-λ_Zr¦/λ_zr<1.8·10^?3. This result is discussed in view of other experimental results and on theoretical estimates.     

Subshell closure effects on the collectivity of 36 88 Kr52 and the beta decay of88Br to levels in88Kr

The level structure of⁸⁸Kr has been investigated by measurements on chemically separated bromine samples. A total of 146γ-rays have been assigned to the decay of⁸⁸Br, and a level scheme with 58 levels is proposed. The collectivity of⁸⁸Kr has been investigated within the framework of the Interacting Boson Approximation (IBA-2 model). Comparison of our detailedγ-ray data and calculations have led to the establishment of a protonhole boson desciption rather than protonparticle nature. This supports recent works establishingZ=40 as a major subshell closure.     

The beta decay of139I

With the⁹⁶Ru(⁵⁸Ni,2pn) reaction we produced¹⁵¹Yb₈₁ and studied its decay after online mass separation by γ-spectroscopic techniques. The decay populates the four positive parity single proton levels in the N=82 daughter nucleus¹⁵¹Tm and establishes I^π=1/2⁺ for the so far unknown¹⁵¹Tm low spin isomer. Using BCS theory proton single particle energies for¹⁵¹Tm were extracted from the observed excitation energies.     

Double beta decay

Double beta decay is a rare nuclear process changing the nuclear charge by two units leaving atomic number unchanged. The detection of the neutrino accompanied mode (A,Z)→(A,Z + 2) + 2e^? + &;2v^? ₂ with half-lives around 10²⁰ years is among the rarest decays ever observed. Of outmost importance for particle physics and especially neutrino physics, is the neutrinoless mode (A,Z)→(A,Z + 2) + 2e^?. This process is violating lepton number by two units and requires massive Majorana neutrinos, i.e. neutrino and antineutrino are identical. The current experimental status is reviewed and an outlook towards future activities is given.     

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 beta decay of176m Lu

The shape factors of the 1^?→2⁺ and 1^?→0⁺ beta transitions and theβ-γ directional correlation of^176m Lu have been measured. An analysis in terms of nuclear matrix elements is given.     

The anisotropy of inverse beta decay and antineutrino detection

The anisotropy of the positrons emitted in the reaction has to be taken into account for extracting an antineutrino signal in Superkamiokande. For the Sun, this effect allows a sensitivity to transition probability at the 3% level already with the statistics collected in the first hundred days. For a supernova in the Galaxy, the effect is crucial for extracting the correct ratio of events.     

The beta decay of neutron-deficient rhodium and ruthenium isotopes

The very neutron-deficient ^91,92,93Rh and ^90,91Ru nuclei were produced in ⁵⁸Ni(^36,40Ar, xn yp) fusion-evaporation reactions. Reaction products leaving the target were stopped in a gas cell and selectively laser ionised before mass separation using the LISOL setup. Data were collected in singles and coincidence formats to investigate -delayed and isomeric decays. Ground-state decays of ^91,93 Rh to excited states in the daughter nucleus were identified for the first time and the decay schemes of ^90,91 Ru were expanded. The low-spin isomeric decay of ⁹²Rh was identified for the first time and detail added to the decay scheme of the known high-spin state. Results are discussed in terms of comparison with shell model calculations. -delayed proton activity in the lighter ⁹⁰Rh and ⁸⁹Ru isotopes was also investigated and upper limits for this decay mode in these two nuclei have been included.Received: 26 November 2003, Revised: 12 January 2004, Published online: 10 August 2004PACS: 23.40.-s decay; double decay; electron and muon capture - 21.10.-k Properties of nuclei; nuclear energy levels - 21.10.Tg Lifetimes - 21.60.Cs Shell modelM. Górska: Present address: Gesellschaft für Schwerionenforschung, Planckstrasse 1, D-64291 Darmstadt, Germany.K. Van de Vel: Present address: VITO, IMS, Mol, Belgium.     

The first forbidden beta decay of Pb209

The 9/2⁺→9/2^? first forbidden β-transition of Pb²⁰⁹→Bi²⁰⁹ has been investigated. The end point energy has been determined to (644.6±1.2) keV, the half life to (3.253±0.014) h. For the shape factor no deviation from the allowed form has been found within an accuracy of 1%. Shape factor andft-value can be excellently interpreted by the shell model injj-coupling.     

The isospin mixing and the superallowed Fermi beta decay

In the present work, the isospin admixtures in the nuclear ground states of the parent nuclei and isospin structure of the isobar analog resonance (IAR) states have been investigated by studying the 0^?+???0^?+? superallowed Fermi ?? decays using Pyatov??s restoration method. Within the random phase approximation (RPA), in this method, the effect of isospin breaking due to the Coulomb forces has been evaluated, taking into account the effect of pairing correlations between nucleons.     

Double beta decay experiments

The present status of double beta decay experiments is reviewed. The results of the most sensitive experiments are discussed. Proposals for future double beta decay experiments with a sensitivity to the 〈m _ν〉 at the level of (0.01–0.1) eV are considered.     

Neutrinoless double beta decay

The physics potential of neutrinoless double beta decay is discussed. Furthermore, experimental considerations as well as the current status of experiments are presented. Finally, an outlook towards the future, work on nuclear matrix elements and alternative processes is given.     

The pionic beta decay in chiral perturbation theory

Within the framework of chiral perturbation theory with virtual photons and leptons, we present an updated analysis of the pionic beta decay including all electromagnetic contributions of order e ² p ² . We discuss the extraction of the Cabibbo-Kobayashi-Maskawa matrix element |V _ud | from the experimental data. The method employed here is consistent with the analogous treatment of the decays and the determination of |V _us |. Received: 19 September 2002 / Published online: 24 January 2003     

Double beta decay and all that

This review illustrates the present state of knowledge and directions of interest in infrared spectroscopy through the discussion of a number of examples of recent work. After a brief introduction the survey falls into three parts. The first is concerned with problems of assignment and interpretation of the spectra of polyatomic molecules, and the calculation of force constants. The second deals with the study of some chemical systems by infrared methods, and in the final section mention is made of a number of specialized topics such as matrix-isolation techniques.     

The beta decay of 137Cs

Evidence is presented to support the view that the approximate shape factor $\text{C = q}{}^2\text{+}\text{b}\text{?}\text{p}{}^2$ does not adequately describe the second-forbidden beta decay of ¹³⁷Cs. An improved formula is given, with single-particle estimates of the nuclear matrix-element ratios. According to this model the coefficient of p² involves considerable cancellation between matrix elements; when due allowance is made for this, good fits to the experimental data are obtained, leading to better estimates of the decay scheme parameters.     

Constraining neutrinoless double beta decay

A class of discrete flavor-symmetry-based models predicts constrained neutrino mass matrix schemes that lead to specific neutrino mass sum-rules (MSR). We show how these theories may constrain the absolute scale of neutrino mass, leading in most of the cases to a lower bound on the neutrinoless double beta decay effective amplitude.     

Bremsstrahlung spectrum in beta decay

The spectrum of the bremsstrahlung due to the complete slowing down in aluminium of beta particles belonging to the continuous spectrum, was calculated for an arrangement, in which the beta emitter is completely enclosed in an absorber. The Bethe-Heitler cross-section, corrected by an empirical factor, was used. A table is given which makes it possible to calculate bremsstrahlung spectra of beta emitters with their maximal energy between 0·6 MeV and 2·0 MeV; the necessary additional calculations are quite simple. The error in the calculation is practically determined by the uncertainty in the determination of the cross-section and is equal to about 10%.

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