K. Grotz

Calculation of double beta decay of 76Ge, 82Se, 128,130Te

Abstract Calculations of double beta decay rates of 76Ge, 82Se, 128,130Te, including Δh excitations and collective effects arising from spin-isospin and quadrupole-quadrupole forces are presented. The serious discrepancy between previous shell model calculations and experimental rates for 128,130Te is markedly reduced. The persisting discrepancy of a factor 10 for these nuclei and for 82Se could raise the question of a possible non-nuclear structure origin of the disagreement.

THE NEUTRINO MASS FROM DOUBLE BETA DECAY

Abstract New and more stringent limits for the mass of a Majorana neutrino are deduced from the existing experimental data on double beta decay by new calculations of the matrix elements for neutrinoless double beta decay.

Predictions of 2ν and 0ν double beta decay rates for nuclei with A ⩾ 70

Abstract Microscopic calculations of double beta ( ββ ) decay matrix elements are presented for the first time for all potential ββ decaying nuclei with A ⩾ 70. This replaces previous phase-space estimates for most of these nuclei. It is found that nuclear structure effects considerably influence the ββ decay rates. The best candidates for 2 ν as well as 0 ν ββ decay experiments are selected.

The quenching of low-energetic nuclear Gamow-Teller strength by δ-excitations

Abstract It is found in shell model calculations including ground state correlations, that δ-nucleon hole ( δ − h ) mixing affects the low-lying β − Gamow-Teller transitions much less than the Gamow-Teller giant resonance (GTGR). This can be understood in a simple perturbation treatment as a destructive interference of first and second order contributions. It is therefore not possible to describe the δ-quenching mechanism by a constant renormalization of the axial vector current.

Double beta decay of 128Te/130Te and the question of a neutrino Majorana mass

The 2 nu double beta ( beta beta ) decay of 30Te and 128Te is calculated in the PBCS pairing model. A correct treatment of the phase-space integral shows that the Pontecorvo (1968) argument leads to an incorrect half-life ratio. This has severe impact on the discussion of neutrinoless beta decay and a possible neutrino mass.

Beta Decay far from Stability and the Decay Heat of Nuclear Reactors

The interest in the β-decay properties of nuclides far (and not so far) from stability has increased in recent years. Since the calculation of the half-lives of neutron-rich nuclei published in [1], about 70 new isotopes have been discovered, and this number will increase rapidly with new experimental possibilities (see, e.g.[2–5]). The theoretical predictions [1] thus can be tested now on a rather large number of nuclei unknown at the time of the calculations. Fig. 1 compares the half-lives of the latter nuclides with the predictions of [1]. The theoretical values are found reliable within the expected limits. This is of importance in particular for the astrophysical conclusions on element synthesis, age of galaxy and more recently the value of the cosmological constant and the corresponding energy density of the vacuum [6–8]. The new data allow on the other hand to improve the calculations.