F. T. Avignone

The IGEX Ge-76 neutrinoless double beta decay experiment: Prospects for next generation experiments

The International Germanium Experiment (IGEX) has analyzed 117 mole yr of 76Ge data from its isotopically enriched (86% 76Ge) germanium detectors. Applying pulse-shape discrimination (PSD) to the more recent data, the lower bound on the half-life for neutrinoless double-beta decay of 76Ge is:

Two neutrino double-beta decay of 100Mo to the first excited 0+ state in 100Ru

T_{1/2}(0\nu)> 1.57 \times 10^{25}

Confirmation of the observation of 2v ββ decay of 76Ge

yr (90% C.L.). This corresponds to an upper bound in the Majorana neutrino mass parameter,

Next generation double-beta decay experiments: metrics for their evaluation

, between 0.33 eV and 1.35 eV, depending on the choice of theoretical nuclear matrix elements used in the analysis.

Theory for the direct detection of solar axions by coherent Primakoff conversion in germanium detectors

Abstract Double-beta decay of 100Mo to the 0+ excited sate at 1130.29 keV in 100ru has been observed. A 956g sample of molybdenum powder enriched to 98.468% 100Mo was counted in a “Marinelli” geometry with a well-shielded, ultralow-background germnium detector. The cascade gamma rays at 539.53 and 590.76 keV in 100Ru were observed. The resulting half-life is (6.1−1.1+1.8)×1020 yr at the 68% confidence limit in disagreement with a recently published limit.

Theoretical and experimental investigation of cosmogenic radioisotope production in germanium

Two previous independent reports of 2v ββ decay by the ITEP-YPI Collaboration, T122v = (9±1) × 1020 yr (1σ), and the PNL-USC Collaboration, T122v = (1.12−0.26+0.48) × 1021 yr (2σ), are confirmed. A 0.25 kg Ge(Li) detector, isotopically enriched to 85% in 76Ge, was operated in the PNL-USC ultralow-background facility in the Homestake gold mine. Following a single correction to the data, a spectrum resembling that observed in the earlier PNL-USC experiment, with about the same intensity per 76Ge atom per year, was observed. The measured half-life is T122v = (9.2−0.4+0.7) × 1020 yr (2σ).

New limit on the neutrinoless betabeta decay of 130Te.

The radioactive background in two 1.1-kg Ge detectors was significantly reduced by material selection and careful control of fabrication of both the germanium crystals. The isotopes 57,58Co and 65Zn, formed cosmogenically in the crystals, were reduced by minimizing the time between the final between the final zone refinement, crystal growth, installation in the cryostat, and placement underground. An attempt was made to reduce the background from the decay of 68Ge in the detectors by deep mining the ore, rushing it through the refinement, crystal growing, and detector fabrication processes, and storing the germanium underground at all times it was not “in process”. Cosmogenically formed 54Mn, 59Fe, and 56,57,58,60Co in the cryostat were minimized by electroforming the cryostat parts. The ubiquitous background from primordial 40K in electronic components was virtually eliminated by selecting low-background components and by hiding the first-stage preamplifier behind 2.5 cm of 450-yr-old lead in one unit and special low-background lead in the other. Details of the procedures used are discussed.

Diurnal modulation effects in cold dark matter experiments

We discuss the six most important parameters that should be used in the computation of figures of merit of various proposed searches for neutrinoless double-beta decay (0νββ-decay). We begin by discussing the connection of this decay mode to the effective Majorana mass of the electron neutrino and the expected experimental sensitivities of favoured techniques. We then discuss the proposed next generation 0νββ-decay experimental techniques in the context of an expression for the experimental figure-of-merit. Finally, we discuss the various proposed experiments in the context of their figure-of-merit parameters. We conclude that the important parameters are the nuclear structure (theoretical rate of decay), isotopic abundance of the parent nuclide and detection efficiency for 0νββ-decay. These enter the equation linearly. Also important are: the mass of the source, and the background rate, although these enter to the one-half power. Energy resolution, while also entering the figure-of-merit to the one half power, is crucial for the discovery potential.

Results from a search for the 0 ν ββ-decay of 130 Te

Abstract It is assumed that axion-like Nambu Goldstone bosons exist and are created in the sun by Primakoff conversion of photons in the Coulomb fields of nuclei. Detection rates are calculated in germanium detectors due to the coherent conversion of axions to photons in the lattice when the incident angle fulfills the Bragg condition for a given crystalline plane. The rates are correlated with the relative positions of the sun and detector yielding a definite recognizable sub-diurnal temporal pattern. A major experiment is proposed based on a large detector array.