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Varner, Jr, Robert L

Publications and source records attributed to Varner, Jr, Robert L.

16 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

The Majorana Demonstrator for 0νββ: Current Status and Future Plans

The Majorana Demonstrator will search for neutrinoless-double-beta decay (0νββ) in 76Ge, while establishing the feasibility of a future tonne-scale germanium-based 0νββ experiment, and performing searches for new physics beyond the Standard Model. The experiment, currently under construction at the Sanford Underground Research Facility in Lead, SD, will consist of a pair of modular high-purity germanium detector arrays housed inside of a compact copper, lead, and polyethylene shield. Through a combination of strict materials qualifications and assay, low-background design, and powerful background rejection techniques, the Demonstrator aims to achieve a background rate in the 0νββ region of interest (ROI) of no more than 3cnts/(ROI-t-y). The current status of the Demonstrator is discussed, as are plans for its completion.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Nuclear Structure Studies in the 132 Sn Region: Safe Coulex with Carbon Targets

The collective and single-particle structure of nuclei in the 132 Sn region was recently studied by Coulomb excitation and heavy-ion induced transfer reactions using carbon, beryllium, and titanium targets. In particular, Coulomb excitation was used determine a complete set of electromagnetic moments for the first 2 + states and one-neutron transfer was used to probe the purity and evolution of single-neutron states. These recent experiments were conducted at the Holifield Radioactive Ion Beam Facility at ORNL using a CsI-HPGe detector array (BareBall- CLARION) to detect scattered particles and emitted gamma rays from the in-beam reactions. A Bragg-curve detector was used to measure the energy loss of the various beams through the targets and to measure the radioactive beam compositions. A sample of the Coulomb excitation results is presented here with an emphasis placed on 116 Sn. In particular, the safe Coulex criterion for carbon targets will be analyzed and discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

First results with a microcavity plasma panel detector

A new type of gaseous micropattern particle detector based on a closed-cell microcavity plasma panel sensor is reported. The first device was fabricated with 1 x 1 x 2 mm cells. It has shown very clean signals of 0.6-2.5 V amplitude, fast rise time of approximately 2 ns and FWHM of about 2 ns with very uniform signal shapes across all pixels. From initial measurements with beta particles from a radioactive source, a maximum pixel efficiency greater than 95% is calculated, for operation of the detector over a 100 V wide span of high voltages (HV). Over this same HV range, the background rate per pixel was measured to be 3-4 orders of magnitude lower than the rate with which the cell was illuminated by the beta source. Pixel-to-pixel count rate uniformity is within 3% and stable within 3% for many days. The time resolution is 2.4 ns, and a very low cell-to-cell crosstalk has been measured between cells separated by 2 mm. (C) 2014 Elsevier B.V. All rights reserved.

Ball, Robert↗
DOE OSTI2014

The MAJORANA DEMONSTRATOR Neutrinoless Double-Beta Decay Experiment

The MAJORANA DEMONSTRATOR will search for the neutrinoless double-beta (ββ(0ν)) decay of the isotope 76 Ge with a mixed array of enriched and natural germanium detectors. The observation of this rare decay would indicate that the neutrino is its own antiparticle, demonstrate that lepton number is not conserved, and provide information on the absolute mass scale of the neutrino. The DEMONSTRATOR is being assembled at the 4850-foot level of the Sanford Underground Research Facility in Lead, South Dakota. The array will be situated in a low-background environment and surrounded by passive and active shielding. Here we describe the science goals of the DEMONSTRATOR and the details of its design.

Abgrall, N.↗
DOE OSTI2014

High-precision B(E2) measurements of semi-magic 58,60,62,64Ni by Coulomb excitation

High-precision reduced electric-quadrupole transition probabilities B(E2) have been measured from single-step Coulomb excitation of semi-magic 58,60,62,64 Ni (Z = 28) beams at 1.8 MeV per nucleon on a natural carbon target. The energy loss of the nickel beams through the carbon target were directly measured with a zero-degree Bragg detector and the absolute B(E2) values were normalized by Rutherford scattering. The B(E2) values disagree with recent lifetime studies that employed the Doppler-shift attenuation method. The present high-precision B(E2) values reveal an asymmetry about 62 Ni, midshell between N = 28 and 40, with larger values towards 56 Ni (Z = N = 28). The experimental B(E2) values are compared with shell-model calculations in the full pf model space and the results indicate a soft 56 Ni core.

Allmond, James M↗
DOE OSTI2013

Plasma Panel Based Radiation Detectors

The plasma panel sensor (PPS) is a gaseous micropattern radiation detector under current development. It has many operational and fabrication principles common to plasma display panels (PDPs). It comprises a dense matrix of small, gas plasma discharge cells within a hermetically sealed panel. As in PDPs, it uses non-reactive, intrinsically radiation-hard materials such as glass substrates, refractory metal electrodes, and mostly inert gas mixtures. We are developing these devices primarily as thin, low-mass detectors with gas gaps from a few hundred microns to a few millimeters. The PPS is a high gain, inherently digital device with the potential for fast response times, fine position resolution (< 50 m RMS) and low cost. In this paper we report here on prototype PPS experimental results in detecting betas, protons and cosmic muons, and we extrapolate on the PPS potential for applications including detection of alphas, heavy-ions at low to medium energy, thermal neutrons and X-rays.

Friedman, Dr. Peter S.↗
DOE OSTI2013

Sub-barrier fusion enhancement with radioactive 134Te

The fusion cross sections of radioactive 134Te + 40Ca were measured at energies above and below the Coulomb barrier. The evaporation residues produced in the reaction were detected in a zero-degree ionization chamber providing high efficiency for inverse kinematics. Both coupled-channel calculations and comparison with similar Sn + Ca systems indicate an increased sub-barrier fusion probability that is correlated with the presence of positive Q-value neutron transfer channels. In comparison, the measured fusion excitation functions of 130Te + 58,64Ni, which have positive Q-value neutron transfer channels, were accurately reproduced by coupled-channel calculations including only inelastic excitations. The results demonstrate that the coupling of transfer channels can lead to enhanced sub-barrier fusion but this is not directly correlated with positive Q-value neutron transfer channels in all cases.

Kohley, Zachary W↗
DOE OSTI2012

Fusion probability for neutron-rich radioactive Sn induced reactions

Evaporation residue cross sections for $^{124,126,127,128}$Sn+$^{64}$Ni and $^{132}$Sn+$^{58}$Ni have been measured to study the effects of neutron excess in neutron-rich radioactive nuclei on fusion. For the reactions with $^{64}$Ni, the fusion probability does not decrease with increasing neutron excess in Sn, contrary to the result of the stable beam Sn+Zr measurement. A comparison of the reduced evaporation residue cross sections for $^{126}$Sn+$^{64}$Ni and $^{132}$Sn+$^{58}$Ni, which make the same compound nucleus, shows that the fusion probability is indistinguishable for reactions involving the same atomic elements but different isotope combinations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Fusion of 124,132Sn with 40,48Ca

Fusion excitation functions for the reactions of {sup 124,132}Sn with {sup 40,48}Ca were measured at energies near and below the Coulomb barrier. Weak sub-barrier fusion enhancement accounted for by coupling to the first 2{sup +} and 3{sup -} states in the target and projectile was observed for {sup 124,132}Sn+{sup 48}Ca. However, the {sup 124,132}Sn+{sup 40}Ca fusion cross sections are very strongly enhanced below the barrier and this difference survives even after correcting for trivial size effects. Although the enhancement appears to be related to the existence of large positive Q values for neutron transfer reactions, it is not proportional to the magnitudes of those Q values, which are much larger for {sup 132}Sn+{sup 40}Ca than for {sup 124}Sn+{sup 40}Ca.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

ISOL science at the Holifield Radioactive Ion Beam Facility

The Holi eld Radioactive Ion Beam Facility, located in Oak Ridge, Tennessee, is operated as a National User Facility for the U.S. Department of Energy, producing high quality ISOL beams of short-lived, radioactive nuclei for studies of exotic nuclei, astrophysics research, and various societal applications. The primary driver, the Oak Ridge Isochronous Cyclotron, produces rare isotopes by bombarding highly refractory targets with light ions. The radioactive isotopes are ionized, formed into a beam, mass selected, injected into the 25-MV Tandem, accelerated, and used in experiments. This article reviews HRIBF and its science.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

The MAJORANA Experiment

The Majorana Collaboration is assembling an array of HPGe detectors to search for neutrinoless double-beta decay in {sup 76}Ge. Initially, Majorana aims to construct a prototype module to demonstrate the potential of a future 1-tonne experiment. The design and potential reach of this prototype Demonstrator module are presented.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Near-barrier fusion of Sn+Ni and Te+Ni Systems: Examining the influence of neutron transfer couplings

The fusion excitation functions for radioactive 132Sn+58Ni and stable 130Te+58;64Ni were measured at energies near the Coulomb barrier. The role of transfer couplings in heavy-ion fusion was examined through a comparison of Sn+Ni and Te+Ni systems, which have large variations in the number of positive Q-value nucleon transfer channels. In contrast with previous comparisons, where increased sub-barrier fusion cross sections were observed in the systems with positive Q-value neutron transfer channels, the reduced excitation functions were equivalent for the different Sn+Ni and Te+Ni systems. The present results suggest a significant change in the influence of transfer couplings on the fusion process for the Sn+Ni and Te+Ni systems.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗