James R. Beene

The MAJORANA demonstrator: A search for neutrinoless double-beta decay of germanium-76

The observation of neutrinoless double-beta decay would determine whether the neutrino is a Majorana particle and provide information on the absolute scale of neutrino mass. The MAJORANA Collaboration is constructing the DEMONSTRATOR, an array of germanium detectors, to search for neutrinoless double-beta decay of 76-Ge. The DEMONSTRATOR will contain 40 kg of germanium; up to 30 kg will be enriched to 86% in 76-Ge. The DEMONSTRATOR will be deployed deep underground in an ultra-low-background shielded environment. Operation of the DEMONSTRATOR aims to determine whether a future tonne-scale germanium experiment can achieve a background goal of one count per tonne-year in a 4-keV region of interest around the 76-Ge neutrinoless double-beta decay Q-value of 2039 keV.

Studies of laser wakefield structures and electron acceleration in underdense plasmas

Experiments on electron acceleration and optical diagnostics of laser wakes were performed on the HERCULES facility in a wide range of laser and plasma parameters. Using frequency domain holography we demonstrated single shot visualization of individual plasma waves, produced by 40TW, 30fs laser pulses focused to the intensity of 1019W∕cm2 onto a supersonic He gas jet with plasma densities ne<1019cm−3. These holographic “snapshots” capture the variation in shape of the plasma wave with distance behind the driver, and resolve wave front curvature seen previously only in simulations. High-energy quasimonoenergetic electron beams were generated using plasma density in the range 1.5×1019≤ne≤3.5×1019cm−3. These experiments demonstrated that the energy, charge, divergence, and pointing stability of the beam can be controlled by changing ne, and that higher electron energies and more stable beams are produced for lower densities. An optimized quasimonoenergetic beam of over 300MeV and 10mrad angular divergence i...

Isobar suppression by photodetachment in a gas-filled rf quadrupole ion guide

A novel technique based on selective non-resonant laser photodetachment in a radio frequency quadrupole ion guide is demonstrated for efficient suppression of isobaric contaminants in negative ion beams. The use of the quadrupole ion guide substantially increases the interaction time of the ions with the laser, significantly increasing the efficiency of the photodetachment process. In a proof–of-principle experiment, we achieved 95% suppression of59Co-ions by photodetachment while under identical conditions only 10% of58Ni-ions were neutralized.

Compton suppression tests on Ge and BGO prototype detectors for gammasphere

During the last decade the application of arrays of 10--30 Compton Suppressed germanium (CSG) detectors in the field of {gamma}-ray spectroscopy has led to a number of significant advances in studies of nuclear structure. Despite the success of these instruments, most of them are limited to detecting two-fold (and in a few cases three-fold) coincidences from highmultiplicity cascades. To increase the detection sensitivity for weak cascades, proposals have recently emerged for construction of much larger arrays. In the USA, the proposed array, called GAMMASPHERE, is to have 110 large CSG detectors which will subtend a solid angle of almost 2{pi} steradians, sufficient to permit routine acquisition of up to 5-fold coincidences from high-multiplicity cascades. This together with other improvements, will yield a resolving power several orders of magnitude greater than currents arrays. In Europe, an array of similar size and power, called EUROGAM, is currently being constructed. In this paper, we report on measurements of the Compton suppression and overall P/T ratio of two Ge detectors in a BGO shield of the honeycomb pattern. These were the first prototype CSG detector assemblies for GAMMASPHERE

Enhancing the performances of traditional electron cyclotron resonance ion sources with multiple-discrete-frequency microwave radiation

The performances of electron cyclotron resonance (ECR) ion sources, in terms of high-charge-state yields and intensities within a particular charge state, can be enhanced by increasing the physical sizes of the ECR zones in relation to the sizes of their plasma volumes. The creation of a large ECR plasma “volume” permits coupling of more power into the plasma, resulting in the heating of a much larger electron population to higher energies, the effect of which is to produce higher charge-state distributions and higher intensities within a particular charge state than possible in present forms of the ECR source. The ECR plasma “volumes” of traditional B-minimum ECR sources can be increased by injecting broadband microwave radiation (multiple-discrete-frequency, variable frequency, or broad-band-width frequency microwave radiation) derived from standard klystron, gyrotron, or traveling-wave-tube (TWT) technologies (frequency domain). To demonstrate that the frequency domain technique can be used to enhance ...

Breeding 10{sup 10}/s Radioactive Nuclei in a Compact Plasma Focus Device

In the early 90s, it was discovered that a Plasma Focus (PF) system self-creates a plasma-tarp in which high energy-threshold nuclear-reactions occur at high reaction rates. Short life radioisotopes (SLR)s such as {sup 18}F, {sup 17}F, {sup 15}O, {sup 14}O, {sup 13}N have been generated (10{sup 6} - 10{sup 8} per pulse) with a PF-machine using 7 kJ energy storage to produce the plasmas. {beta}{sup -} radioactivity from the SLRs is measured with rugged, Geiger counters inserted into the PF-chamber, and a specific SLR is identified by its half-life. The PF chamber (before discharge) is filled with a mixture of gases that constitutes the latter plasma-target--beam system, e.g., the elements required to produce specific SLRs through nuclear reactions. In this paper, arguments are presented showing that a modest sized PF-machine, using a 50-75 kJ fast capacitor-bank, when operated at pulse frequencies of 1-10 Hz can produce {ge} 10{sup 9} SLRs/pulse. This paper reports the result s of testing a PF as a breeder of SLRs with dual applications for: (1) Secondary Radioactive Nuclear Beams ion-sources (Z < 35), and (2) as a breeder of radioisotopes for biomedicine (Z {le} 10) and/or PET imaging.

The MAJORANA DEMONSTRATOR: An R&D project towards a tonne-scale germanium neutrinoless double-beta decay search

The MAJORANA collaboration is pursuing the development of the so‐called MAJORANA DEMONSTRATOR. The DEMONSTRATOR is intended to perform research and development towards a tonne‐scale germanium‐based experiment to search for the neutrinoless double‐beta decay of 76Ge. The DEMONSTRATOR can also perform a competitive direct dark matter search for light WIMPs in the 1–10 GeV/c2 mass range. It will consist of approximately 60 kg of germanium detectors in an ultra‐low background shield located deep underground at the Sanford Underground Laboratory in Lead, SD. The DEMONSTRATOR will also perform background and technology studies, and half of the detector mass will be enriched germanium. This talk will review the motivation, design, technology and status of the Demonstrator.

Population of the entry states in heavy-ion fusion reactions☆

Abstract The excitation energy and angular momentum dependence of the population of the entry states following fusion of 136 MeV 20Ne with 146Nd has been measured with a new type of instrument. Statistical-model calculations reproduce the main features of the data. Structure effects for J⪆45 are evident in the entry lines. The entrance-channel orbital angular momentum distribution leading to fusion has been deduced.

Photonuclear Fission with Quasimonoenergetic Electron Beams from Laser Wakefields

Recent advancements in laser wakefield accelerators have resulted in the generation of low divergence, hundred MeV, quasimonoenergetic electron beams. The bremsstrahlung produced by these highly energetic electrons in heavy converters includes a large number of MeV γ rays that have been utilized to induce photofission in natural uranium. Analysis of the measured delayed γ emission demonstrates production of greater than 3×105 fission events per joule of laser energy, which is more than an order of magnitude greater than that previously achieved. Monte Carlo simulations model the generated bremsstrahlung spectrum and compare photofission yields as a function of target depth and incident electron energy.

Resonant Ionization Laser Ion Source for Radioactive Ion Beams

A resonant ionization laser ion source based on all‐solid‐state, tunable Ti:Sapphire lasers is being developed for the production of pure radioactive ion beams. It consists of a hot‐cavity ion source and three pulsed Ti:Sapphire lasers operating at a 10 kHz pulse repetition rate. Spectroscopic studies are being conducted to develop ionization schemes that lead to ionizing an excited atom through an auto‐ionization or a Rydberg state for numerous elements of interest. Three‐photon resonant ionization of 12 elements has been recently demonstrated. The overall efficiency of the laser ion source measured for some of these elements ranges from 1 to 40%. The results indicate that Ti:Sapphire lasers could be well suited for laser ion source applications. The time structures of the ions produced by the pulsed lasers are investigated. The information may help to improve the laser ion source performance.