The proposed Majorana experiment is based on an array of segmented intrinsic Ge detectors with a total mass of 500 kg of Ge isotopically enriched to 86% in Ge-76. Background reduction will be accomplished by: material selection, detector segmentation, pulse shape analysis, electro-formation of copper parts, and granularity of detector spacing. The predicted experimental sensitivity for measurement of the neutrinoless double-beta decay mode of Ge-76, over a data acquisition period of 5000 kg(.)y, is T-1/2(0nu) similar to 4x 10(27) y.

Commercial high‐purity copper is an attractive material for constructing ultra‐low‐background radiation measurement devices. When even higher purity is desired, additional electrolytic and chemical purification can be combined with the final fabrication step. This process results in “electroformed” copper parts of extreme purity. Copper electroforming can be done underground, providing a way to eliminate cosmogenic activation products seen in copper that has had above‐ground exposure. A brief summary of the history, cosmogenics, process chemistry, cleaning, and passivation of this material is given. Examples of finished parts illustrate the method. The required infrastructure is summarized.

The Multiple-Element Gamma Assay (MEGA) is a low-background detector designed to support environmental monitoring and national security applications. MEGA also demonstrates technology needed for Majorana, a next generation neutrino mass experiment It will employ active and passive shielding to reduce backgrounds. It will also exploit multi-coincidence signatures to identify specific radioactive isotopes. MEGA is expected to begin operation in late 2003 at the Waste Isolation Pilot Plant in Carlsbad, NM.

A pulse shape analysis technique was implemented to determine the electron mobility /spl mu//sub e/ and the electron mobility lifetime product /spl mu//sub e//spl tau//sub e/ in cadmium zinc telluride detectors (CZT). The digital gamma finder (DGF-4C) a single-width CAMAC module produced by X-Ray Instrumentation Associates (XIA), was used to extract pulse height, pulse shape, and signal rise time information. Data analyses using the extracted information allowed measuring the /spl mu//sub e/ and /spl mu//sub e//spl tau//sub e/ in selected CZT samples. An almost linear relationship was observed for the signal rise time as a function of the inverse bias. This observed linear relationship was the basis for determination of /spl mu//sub e/ using a simple linear fit. The measured signal amplitude was also used to determine /spl mu//sub e//spl tau//sub e/ using the Hecht formulation. Repeated measurements confirmed the consistency of the method in determining /spl mu//sub e/ and /spl mu//sub e//spl tau//sub e/.

The cooled FET and associated feedback resistor and capacitor (the "cooled FET assembly") are part of resistive feedback preamplifiers often used with germanium spectrometers. This cooled FET assembly is placed close to the germanium crystal, usually in thermal contact with the crystal housing. In low-background applications, the remaining stages of the preamplifier are placed 10-100 cm away, isolating the trace radioactivity in the preamplifier from the germanium crystal. Its proximity to the crystal makes the cooled FET assembly a critical source of radioactive contamination in ultra-low background germanium spectrometers. The elimination of all materials not specifically checked for radiopurity leaves a very limited palette with which to construct the cooled FET assembly. This has lead, in the past, to serious compromises in the mechanical and thermal ruggedness of research ultra-low background germanium spectrometers. Additionally, with poor thermal design the FET operating temperature can be too high or, more likely, too low, increasing noise. The design goals were to create an assembly that was capable of withstanding repeated thermal cycles, was radiologically clean, had good noise performance, and supported the fast rise-times needed for pulse shape analysis applications for large ultra-low-background germanium spectrometer systems.

The automated radioxenon sampler/analyzer (ARSA) uses a highly compact, high efficiency beta-gamma coincidence detector to detect /sup 133/Xe, /sup 131m/Xe, /sup 133m/Xe and /sup 135/Xe for treaty monitoring and environmental sampling. This system has shown itself to he reliable and robust in several field exercises. However, from a maintenance and quality assurance/quality control (QA/QC) standpoint it suffers from a very detailed photo-multiplier-tube gain matching regime. In an effort to upgrade and simplify the current beta-gamma coincident detector, Pacific Northwest National Laboratory (PNNL) has developed a simplified but equally effective well-type detector. Initial comparison between three different well detectors has been performed. Along with the well gamma-ray detectors, a new plastic scintillation gas cell was constructed. The spectral resolution and efficiency obtained from this new design has been demonstrated to be as good as or better than the original ARSA design with greatly improved calibration and maintenance characteristics.

Pulse-shape discrimination (PSD) for germanium spectrometers has received attention for varied applications such as microphonic noise rejection, event localization in segmented detector systems, correction of ballistic deficit and trapping, and the separation of gamma events from nuclear recoil and beta decay. A new PSD method has been developed at Pacific Northwest National Laboratory (PNNL) having several unique characteristics. This PSD method: 1) Extracts a few key parameters from each preamplifier output pulse. 2) Is sensitive to interaction multiplicity - a new physical observable. 3) Can isolate various physical regions of a detector. 4) Is self-calibrating allowing optimal discrimination for any detector. 5) Is computationally cheap, requiring no computed libraries-of-pulses. 6) Leverages current state-of-the-art commercial digital spectroscopy hardware platforms. This paper describes the theory and operation of the method with attention to specific application areas in which this method could be useful. The challenge of sensing the neutrinoless double-beta decay of /sup 76/Ge (O/spl nu/ /spl beta//spl beta/-decay) is taken as an example of a single-site-interaction measurement. Experimental data is analyzed and the sensitivity increase expected from this method for neutrino mass probes based on O/spl nu/ /spl beta//spl beta/-decay is presented.

The ability to conduct automated trace radionuclide analysis at or near the sample collection point would provide a valuable tool for emergency response, environmental monitoring, and verification of treaties and agreements. Pacific Northwest National Laboratory is developing systems for this purpose based on dual gamma-ray spectrometers, e.g., NaI(TI) or HPGe, combined with thin organic scintillator sensors to detect light charged particles. Translating the coincident signatures recorded by these systems, which include beta gamma, gamma gamma, and beta gamma gamma, into the concentration of detectable radionuclides in the sample requires generalized multi-coincidence analysis tools. The development and validation of the Coincidence Lookup Library, which currently contains the probabilities of single and coincidence signatures from more than 420 isotopes, is described. Also discussed is a method to calculate the probability of observing a coincidence signature which incorporates true coincidence summing effects. These effects are particularly important for high-geometric-efficiency detection systems. Finally, a process for verifying the integrated analysis software package is demonstrated using GEANT 4 simulations of the prototype detector systems.

This paper is a response to the preceding Comment by Klapdor-Kleingrothaus, Dietz, and Krivosheina. The criticisms are confronted, and the questions raised are answered. We demonstrate that the lower limit quoted by IGEX, T-1/2(0nu)(Ge-76)greater than or equal to1.57x10(25) yr, is correct and that there was no "arithmetical error" as claimed in the "Critical View" article.

Multicoincidence radionuclide analysis systems consisting of light-charged-particle detectors operating in coincidence with photon spectrometers are being developed to improve the sensitivity of radionuclide analysis in field applications. Requiring charged-particle/photon coincidence provides active shielding from environmental photon sources, and mapping photon–photon events into a coincidence plane can remove photon spectroscopy interferences. List-mode data acquisition and flexible hardware design ensures that the most sensitive coincidence schemes involving β, atomic electron, γ and X-ray emissions can be used for radionuclide quantification. System hardware design and preliminary measurement data are discussed. A centerpiece component of this project, the development of analysis tools and data libraries required to perform automated multicoincidence analysis, is also described.

Pacific Northwest National Laboratory (PNNL) is currently developing multicoincidence systems to perform trace radionuclide analysis at or near the sample collection point, for applications that include emergency response, nuclear forensics, and environmental monitoring. Quantifying radionuclide concentrations with these systems requires a library of accurate emission intensities for each detected signature, for all candidate radionuclides. While such data are readily available for single gamma-ray emissions, no signature library has been found for coincident emissions such as /spl beta/-/spl gamma/, /spl gamma/-/spl gamma/, or /spl beta/-/spl gamma/-/spl gamma/. To meet this need, a Coincidence Lookup Library (CLL) is being developed to calculate the emission intensities of coincident signatures from a user-specified radionuclide, or conversely, to determine the radionuclides that may be responsible for a specific detected coincident signature. The algorithms used to generate absolute emission intensities and various user interfaces for the developmental CLL are described.

The IGEX experiment has been operating enriched germanium detectors in the Canfranc Underground Laboratory (Spain) in a search for the neutrinoless double decay of 76Ge. 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 2.5MeV), down to ∼0.09c/keVkgyr.

Interest in, and the relevance of, next-generation 0nu betabeta-decay experiments is increasing. Even with nonzero neutrino mass strongly suggested by SNO, Super Kamiokande, and similar experiments sensitive to deltam(2), 0nu betabeta- decay experiments are still the only way to establish the Dirac or Majorana nature of neutrinos by measuring effective electron neutrino mass, (m(nu)). Various theorists have recently argued in favor of a neutrino mass between 0.01 and 1 eV. The Majorana Project aims to probe this effective neutrino mass range, reaching a sensitivity of 0.02-0.07 eV. The experiment relies entirely on proven technology and has been devised based upon the materials, technology, and data analysis demonstrated to produce the lowest background per kilogram of fiducial germanium. The project plan includes 500 kg of germanium detector material enriched to 85% in Ge-76, specialized pulse-acquisition electronics and detector segmentation for background rejection, and underground electroformed copper support hardware.

One IGEX (76)Ge double-beta decay detector is currently operating in the Canfrane Underground Laboratory in a search for dark matter WIMPs, through the Ge nuclear recoil produced by the WIMP elastic scattering. A new exclusion plot, sigma (m), has been derived for WIMP-nucleon spin-independent interactions. To obtain this result, 40 days of data from the IGEX detector (energy threshold E(thr) similar to 4 keV), recently collected, have been analyzed. These data improve the exclusion limits derived from all the other ionization germanium detectors in the mass region from 20 to 200 GeV. where a WIMP supposedly responsible for the annual modulation effect reported by the DAMA experiment would be located. The new IGEX exclusion contour enters, by the first time, the DAMA region by using only raw data, with no background discrimination, and excludes its upper left part. It is also shown that with a moderate improvement of the detector performances, the DANA region could be fully explored. (C) 2002 Elsevier Science B.V. All rights reserved.

The International Germanium Experiment (IGEX) has analyzed 117 mol yr of Ge-76 data from its isotopically enriched (86% Ge-76) germanium detectors. Applying pulse-shape discrimination to the more recent data, the lower bound on the half-life for neutrinoless double-beta decay of Ge-76 is T-1/2(0nu) >1.57 x 10(25) yr (90% C.L.). This corresponds to an upper bound in the Majorana neutrino mass parameter, [m(nu)], between 0.33 and 1.35 eV, depending on the choice of theoretical nuclear matrix elements used in the analysis.

Pulse analysis techniques with the scintillator LiBaF3:Ce allow very clean separation of densely ionizing radiation (protons, deuterons, tritons, alphas, etc.) from less densely ionizing radiation (electrons). Consequently, pulse height spectra for each type of radiation can be obtained simultaneously. The pulse discrimination is based on the presence or absence of sub-nanosecond core-valence luminescence and in crystals doped with Ce 3 the presence or absence of Ce luminescence having a (-)35 ns lifetime. We are developing a pulse discrimination technique based on digital signal processing (DSP) using a CAMAC based module from XIA, Inc. Discrimination between electrons (gammas) and the light charged particles is based on the ratio of signal amplitude in the first 50 ns to signal amplitude at a longer time interval. We are evaluating more complicated algorithms to determine whether discrimination between hydrogen isotopes and alpha particles can be achieved. These techniques may allow determination of pulse height spectra for thermal neutron capture events, fast neutron capture events, fast-neutron-induced nuclear reactions, alpha events from Ra impurities in the scintillator, and gamma events simultaneously using a single scintillator.

A decommissioned LHC test magnet is being prepared as the CERN Axion Solar Telescope (CAST) experiment. The magnet has a field of 9.6 Tesla and length of 10 meters. It is being mounted on a platform to track the sun over ±8° vertically and ±45°, horizontally. A sensitivity in axion-photon coupling gαγγ < 5 × 10−11GeV−1 can be reached for mα ≤ 10−2eV, and with a gas filled tube-can reach gαγγ ≤ 10−10GeV−1 for axion masses mα < 2eV.

We comment on the recent claim for the experimental observation of neutrinoless double-beta decay. We discuss several limitations in the analysis provided in that paper and conclude that there is no basis for the presented claim.

Two germanium detectors are currently operating in the Canfranc Underground Laboratory at 2450 m.w.e looking for WIMP dark matter. One is a 2 kg 76Ge IGEX detector (RG-2) which has an energy threshold of 4 keV and a low-energy background rate of about 0.3 c/keV/kg/day. The other is a small (234 g) natural abundance Ge detector (COSME), of low energy threshold (2.5 keV) and an energy resolution of 0.4 keV at 10 keV which is looking for WIMPs and for solar axions. The analysis of 73 kg-days of data taken by COSME in a search for solar axions via their photon Primakoff conversion and Bragg scattering in the Ge crystal yields a 95% C.L. limit for the axion-photon coupling g < 2.8 10^-9 GeV^-1. These data, analyzed for WIMP searches provide an exclusion plot for WIMP-nucleon spin-independent interaction which improves previous plots in the low mass region. On the other hand, the exclusion plot derived from the 60 kg-days of data from the RG-2 IGEX detector improves the exclusion limits derived from other ionization (non thermal) germanium detector experiments in the region of WIMP masses from 30 to 100 GeV recently singled out by the reported DAMA annual modulation effect.

The IGEX Collaboration enriched 76Ge double-beta decay detectors are currently operating in the Canfranc Underground Laboratory with an overburden of 2450 m.w.e. A recent upgrade has made it possible to use them in a search for WIMPs. A new exclusion plot, σ(m), has been derived for WIMP-nucleon spin-independent interaction. To obtain this result, 30 days of data from one IGEX detector, which has an energy threshold Ethr∼4 keV, have been considered. These data improve the exclusion limits derived from other ionization (non-thermal) germanium detector experiments in the ∼50 GeV DAMA region, and show that with a moderate improvement of the background below 10 keV, the DAMA region may be tested with an additional 1 kg-year of exposure.