Walter K. Hensley

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:

Pulse shape discrimination in the IGEX experiment

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

Ambient 133Xe levels in the Northeast US

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

SYNTH: A spectrum synthesizer

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

An Ultralow Background Germanium Gamma-Ray Spectrometer Using Superclean Materials and Cosmic Ray Anticoincidence

Abstract The IGEX experiment has been operating enriched germanium detectors in the Canfranc Underground Laboratory (Spain) in a search for the neutrinoless double decay of 76 Ge . The implementation of pulse-shape discrimination techniques to reduce the radioactive background is described in detail. This analysis has been applied to a fraction of the IGEX data, leading to a rejection of ∼60% of their background, in the region of interest (from 2 to 2.5 MeV ), down to ∼0.09 c/ keV kg yr .

Adaptation and implementation of the RAYGUN gamma-ray analysis code on the IBM PC

Measurements of 133Xe (τ12 = 5.2 days) atmospheric concentrations were performed during the fall of 1993 and throughout 1995 on ‘noble gas concentrates’ from the northeastern US. These samples were obtained from a commercial air-reduction plant in Allentown, Pennsylvania. Following Chromatographic purification of the xenon gas, the 133Xe activity was determined using a high-purity germanium gamma-ray spectrometer. The average 133Xe concentrations were in the range 1–3 mBq m−3, which is consistent with nuclear power plant noble gas releases in the region surrounding the sampling point, but approximately 50–100 times lower than those reported in Albany, NY approximately 300 km to the northeast from 1975 through 1984. The lower atmospheric concentrations are also consistent with the 100-fold reduction in radioxenon release from 25 nuclear reactors in that region. Only an upper limit could be established for the 135Xe level (τ12 = 9.1 h), which was about 0.03 of the 133Xe level. These background levels are of concern in monitoring for atmospheric radioxenons to assure compliance with a Comprehensive nuclear Test Ban Treaty (CTBT).

Naturally Occurring Radioactive Materials in Cargo at US Borders

The International Germanium Experiment (IGEX) operated with 3 detectors of approximately 700 gm fiducial mass and 3 detectors of approximately 2 kg fiducial mass each. They were fabricated from germanium isotopically enriched to 86% in 76Ge. The total fiducial mass was 8.4 kg. They were mounted in ultra-low radioactive background cryostats electroformed from purified CuSO4 solution.

Efficiency of germanium detectors as a function of energy and incident geometry : Comparison of measurements and calculations

A computer code has been written at the Pacific Northwest Laboratory (PNL) to synthesize the results of typical gamma-ray spectroscopy experiments. The code, dubbed SYNTH1, allows users to specify physical characteristics of a gamma-ray source, the quantity of the nuclides producing the radiation, the source-to-detector distance, the type and thickness of absorbers, the size and composition of the detector (Ge or NaI), and the electronic set up used to gather the data. In the process of specifying the parameters needed to synthesize a spectrum, several interesting intermediate results are produced, including a photopeak transmission function vs. energy, a detector efficiency curve, and a weighted list of gamma and x rays produced from a set of nuclides. All of these intermediate results are available for graphical inspection and for printing. SYNTH runs on personal computers, is menu driven and can be customized to user specifications. SYNTH contains robust support for coaxial germanium detectors and some support for sodium iodide detectors. SYNTH is not a finished product. A number of additional developments are planned. However, the existing code has been carefully compared to spectra obtained from National Institute for Standards and Technology (NIST) certified standards with very favorable results.

Current IGEX results for neutrinoless double-beta decay of 76Ge

Efforts to measure the double beta decay of /sup 76/Ge as predicted by Grand Unified Theories have resulted in the development of a high resolution germanium diode gamma-ray spectrometer with an exceptionally low background. This paper describes the development of this system and how these techniques can be utilized to significantly reduce the background in high resolution photon spectrometers at only a moderate cost.