Measured 129I concentration profiles in southeastern United States soil are examined by means of a six-compartment model to estimate accumulation and downward migration in undisturbed surface soil. Effective mean residence half-times in the top 30-cm-depth interval averaged 30 +/- 6 y, based on estimated annual 129I deposition rates in the vicinity of a chemical separations facility for nuclear material over a 25-y period. The model demonstrates the need for subdividing the soil into small depth intervals of 5 cm or less near the surface. The results of this study differ significantly with other surface soil residence time studies where a large single depth interval was assumed. The conclusions do, however, compare favorably with distribution coefficient studies in the surface hydrosphere. Application of the results are graphically demonstrated.

The proposed Majorana double-beta decay 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 76 Ge. A discussion is given of background reduction by: material selection, detector segmentation, pulse shape analysis, and electro-formation of copper parts and granularity. Predictions of the experimental sensitivity are given. For an experimental running time of 10 years over the construction and operation of Majorana, a sensitivity of T 1/ 2 0 ~4 10 27 y is predicted. This corresponds to m ~0.03 0.04 eV according to recent QRPA and RQRPA matrix element calculations.

The objective of the Majorana Experiment is to study neutrinoless double beta decay (0νββ) with an effective Majorana-neutrino mass sensitivity below 50 meV in order to characterize the Majorana nature of the neutrino, the Majorana mass spectrum, and the absolute mass scale. An experimental study of the neutrino mass scale implied by neutrino oscillation results is now technically within our grasp. This exciting physics goal is best pursued using the well-established technique of searching for 0νββ of 76 Ge, augmented with recent advances in signal processing and detector design. The Majorana Experiment will consist of a large mass of 76 Ge in the form of high-resolution intrinsic germanium detectors located deep underground within a low-background shielding environment. Observation of a sharp peak at the ββ endpoint will quantify the 0νββ half-life and thus the effective Majorana mass of the electron neutrino. In addition to the modest R&D program, we present here an overview of the entire project in order to help put in perspective the scope, the low level of technical risk, and the readiness of the Collaboration to immediately begin the undertaking.

The energy dependence of the ionization produced in germanium by energetic germanium atoms was measured. Germanium solid-state detectors served simultaneously as crystalline Ge sample, neutron target, and ionization detector. The spectrum of ionization produced by prompt Ge recoil atoms energized by monoenergetic neutron bombardment was observed in a pulse-height analyzer, and the edge of the spectrum was identified with the ionization produced by Ge recoil atoms having the calculated maximum recoil energy. The electron-hole pair production of Ge recoils was measured in this manner from 21.4 to 997 keV, using monoenergetic neutrons from 400 keV to 18.6 MeV. In this energy range, the ratio of the ionization produced by a Ge recoil relative to that of an electron of the same energy increased from ~0.15 to ^0.7. At very low Ge recoil energies, most of the energy goes into atomic processes. At high recoil energies, where electronic processes become important, the ionization produced by a Ge recoil appears to approach that for an electron of the same energy. The corresponding partition of energy between electronic processes and atomic processes for an energetic Ge atom in a Ge lattice agrees favorably with predictions of the theory of Lindhard et al. These data together with the earlier results of ionization produced by energetic Si atoms within a Si lattice agree with the A and Z dependence of the partition of energy predicted by Lindhard.

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