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Davis, J

Publications and source records attributed to Davis, J.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Search for Double Beta Decays of Xe134 with EXO-200 Phase II

EXO-200 was a leading double beta decay experiment consisting of a single-phase, enriched liquid xenon time projection chamber filled with an admixture of 80.672% ^{136}Xe and 19.098% ^{134}Xe. The detector operated at the Waste Isolation Pilot Plant between 2010 and 2018 and was designed to search for double beta decay of ^{136}Xe. Data were acquired in two phases separated by a period of detector upgrades. We report on the search for 0νββ and 2νββ decay of ^{134}Xe with Phase II EXO-200 data, with median 90% CL exclusion sensitivity to half-life T_{1/2}^{0ν}≥3.7×10^{23} yr and T_{1/2}^{2ν}≥2.6×10^{21} yr, respectively. No statistically significant signal is observed for either decay mode. We set a world-leading lower limit on the half-life of the neutrinoless decay mode of ^{134}Xe of T_{1/2}^{0ν}≥8.7×10^{23} (90% CL) and the second strongest constraint on the two-neutrino decay of T_{1/2}^{2ν}≥2.9×10^{21} (90% CL), a threefold improvement over the EXO-200 Phase I measurement. New constraints are also set for the 2νββ and 0νββ decays of ^{134}Xe to the lowest excited state of ^{134}Ba.

Al Kharusi, S↗
DOE OSTI2016

SU-C-204-02: Behavioral and Pathologic Differences in Mice Exposed to Proton Minibeam Arrays Versus Proton Broad Beams

Purpose: Minibeam therapy using protons or light-ions offers a theoretical reduction of biologic damage to tissues upstream of a tumor compared to broad-beam therapy while providing equal tumor control. The purpose of this study was to investigate behavioral and pathologic differences in mice after exposure of healthy brain to proton minibeam arrays versus proton broad beams. Methods: Twenty-four C57BL/6J juvenile mice were divided into 5 study arms: sham irradiation (NoRT), broad-beam 10 Gy (BB10), minibeam 10Gy (MB10), broad-beam 30 Gy (BB30), and minibeam 30 Gy (MB30), approximate integral entrance doses. Circular beams of 100 MeV protons with 7-mm diameter were delivered laterally through the brain, either as broad beams or as planar minibeam arrays having 300-micron beam width and 1-mm spacing on center. Mice were followed for 8 months using standard behavioral tests. Pathologic studies were carried out at 8 months after irradiation. Results: Peak entrance doses were 10.0, 23.8, 30.0, and 71.3 Gy for mice in BB10, MB10, BB30, and MB30, respectively. Despite the high single-fraction doses, no animals showed signs of radiation sickness or neurophysical impairment over the 8-month study duration. The Morris water maze alternate-starting-position trial showed significant evidence of better spatial learning for mice in MB10 versus BB10 (p=0.026), but other behavioral tests showed no significant differences. Glial fibrillary acidic protein stains showed gliosis in arms BB10, BB30, and MB30 but not in NoRT or MB10. A secondary finding was categorically higher epilation in broad-beam arms compared with their minibeam dose counterparts. Conclusion: Our findings indicate trends that, despite the higher peak doses, proton minibeam therapy can reduce radiation side effects in shallow tissue and brain compared to proton broadbeam therapy. As the behavioral findings were mixed, confirmation studies are needed with larger numbers of animals. AAPM Research Seed Funding Grant.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-T-634: Analysis of Volume Based GYN HDR Brachytherapy Plans for Dose Calculation to Organs At Risk(OAR)

Purpose: We have analyzed the dose volume histogram of 140 CT based HDR brachytherapy plans and evaluated the dose received to OAR ; rectum, bladder and sigmoid colon based on recommendations from ICRU and Image guided brachytherapy working group for cervical cancer . Methods: Our treatment protocol consist of XRT to whole pelvis with 45 Gy at 1.8Gy/fraction followed by 30 Gy at 6 Gy per fraction by HDR brachytherapy in 2 weeks . The CT compatible tandem and ovoid applicators were used and stabilized with radio opaque packing material. The patient was stabilized using special re-locatable implant table and stirrups for reproducibility of the geometry during treatment. The CT scan images were taken at 3mm slice thickness and exported to the treatment planning computer. The OAR structures, bladder, rectum and sigmoid colon were outlined on the images along with the applicators. The prescription dose was targeted to A left and A right as defined in Manchester system and optimized on geometry . The dosimetry was compared on all plans using the parameter Ci.sec.cGy-1 . Using the Dose Volume Histogram (DVH) obtained from the plans the doses to rectum, sigmoid colon and bladder for ICRU defined points and 2cc volume were analyzed and reported. The following criteria were used for limiting the tolerance dose by volume (D2cc) were calculated. The rectum and sigmoid colon doses were limited to <75Gy. The bladder dose was limited to < 90Gy from both XRT and HDR brachytherapy. Results: The average total (XRT+HDRBT) BED values to prescription volume was 120 Gy. Dose 2cc to rectum was 70Gy +/− 17Gy, dose to 2cc bladder was 82+/−32 Gy. The average Ci.sec.cGy-1 calculated for the HDR plans was 6.99 +/− 0.5 Conclusion: The image based treatment planning enabled to evaluati volume based dose to critical structures for clinical interpretation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2012

Generation of high-energy (>15 MeV) neutrons using short pulse high intensity lasers

A roadmap is suggested and demonstrated experimentally for the production of high-energy (>15 MeV) neutrons using short pulse lasers. Investigation with a 3D Monte Carlo model has been employed to quantify the production of energetic neutrons. Numerical simulations have been performed for three nuclear reactions, d(d,n){sup 3}He, {sup 7}Li(d,n){sup 8}Be, and {sup 7}Li(p,n){sup 7}Be, driven by monoenergetic ion beams. Quantitative estimates for the driver ion beam energy and number have been made and the neutron spectra and yield in the ion propagation direction have been evaluated for various incident ion energies. In order to generate neutron fluence above a detection limit of 10{sup 6} neutrons/sr, either {approx}10{sup 10} protons with energy 20-30 MeV or comparable amount of deuterons with energy 5-10 MeV are required. Experimental verification of the concept with deuterons driven by the Titan laser (peak intensity 2 Multiplication-Sign 10{sup 19} W/cm{sup 2}, pulse duration of 9 ps, wavelength 1.05 {mu}m, and energy of 360 J) is provided with the generation of neutrons with energy of up to 18 MeV from {sup 7}Li(d,n){sup 8}Be reactions. Future research will focus on optimized schemes for ion acceleration for production of high-energy neutrons, which will involve efficient target design, laser parameter optimization, and converter material.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Soft X-Ray Spectroscopic Study of Dense Strontium-Doped Lanthanum Manganite Cathodes for Solid Oxide Fuel Cell Applications

The evolution of the Mn charge state, chemical composition, and electronic structure of La{sub 0.8}Sr{sub 0.2}MnO{sub 3} (LSMO) cathodes during the catalytic activation of solid oxide fuel cell (SOFC) has been studies using X-ray spectroscopy of as-processed, exposed, and activated dense thin LSMO films. Comparison of O K-edge and Mn L{sub 3,2}-edge X-ray absorption spectra from the different stages of LSMO cathodes revealed that the largest change after the activation occurred in the Mn charge state with little change in the oxygen environment. Core-level X-ray photoemission spectroscopy and Mn L{sub 3} resonant photoemission spectroscopy studies of exposed and as-processed LSMO determined that the SOFC environment (800 C ambient pressure of O{sub 2}) alone results in La deficiency (severest near the surface with Sr doping >0.55) and a stronger Mn{sup 4+} contribution, leading to the increased insulating character of the cathode prior to activation. Meanwhile, O K-edge X-ray absorption measurements support Sr/La enrichment nearer the surface, along with the formation of mixed Sr{sub x}Mn{sub y}O{sub z} and/or passive MnO{sub x} and SrO species.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2011

Production of neutrons up to 18 MeV in high-intensity, short-pulse laser matter interactions

The generation of high-energy neutrons using laser-accelerated ions is demonstrated experimentally using the Titan laser with 360 J of laser energy in a 9 ps pulse. In this technique, a short-pulse, high-energy laser accelerates deuterons from a CD{sub 2} foil. These are incident on a LiF foil and subsequently create high energy neutrons through the {sup 7}Li(d,xn) nuclear reaction (Q = 15 MeV). Radiochromic film and a Thomson parabola ion-spectrometer were used to diagnose the laser accelerated deuterons and protons. Conversion efficiency into protons was 0.5%, an order of magnitude greater than into deuterons. Maximum neutron energy was shown to be angularly dependent with up to 18 MeV neutrons observed in the forward direction using neutron time-of-flight spectrometry. Absolutely calibrated CR-39 detected spectrally integrated neutron fluence of up to 8 x 10{sup 8} n sr{sup -1} in the forward direction.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Comparison of bulk and pitcher-catcher targets for laser-driven neutron production

Laser-driven d(d, n)-{sup 3}He beam-target fusion neutron production from bulk deuterated plastic (CD) targets is compared with a pitcher-catcher target scheme using an identical laser and detector arrangement. For laser intensities in the range of (1-3) x 10{sup 19} W cm{sup -2}, it was found that the bulk targets produced a high yield (5 x 10{sup 4} neutrons per steradian) beamed preferentially in the laser propagation direction. Numerical modeling shows the importance of considering the temperature adjusted stopping powers to correctly model the neutron production. The bulk CD targets have a high background target temperature leading to a reduced stopping power for the deuterons, which increases the probability of generating neutrons by fusion. Neutron production from the pitcher-catcher targets was not as efficient since it does not benefit from the reduced stopping power in the cold catcher target. Also, the inhibition of the deuteron acceleration by a proton rich contamination layer significantly reduces the pitcher-catcher neutron production.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Broad Overview of Energy Efficiency and Renewable Energy Opportunities for Department of Defense Installations

The Strategic Environmental Research and Developmental Program (SERDP)/Environmental Security Technology Certification Program (ESTCP) is the Department of Defense?s (DOD) environmental science and technology program focusing on issues related to environment and energy for the military services. The SERDP/ESTCP Office requested that the National Renewable Energy Laboratory (NREL) providetechnical assistance with strategic planning by evaluating the potential for several types of renewable energy technologies at DOD installations. NREL was tasked to provide technical expertise and strategic advice for the feasibility of geothermal resources, waste-to-energy technology, photovoltaics (PV), wind, microgrids, and building system technologies on military installations. Thistechnical report is the deliverable for these tasks.

14 SOLAR ENERGY↗
DOE OSTI2011

A generalized implicit algorithm for multi-dimensional particle-in-cell simulations in Cartesian geometry

An implicit multi-dimensional particle-in-cell (PIC) code is developed to study the interaction of ultrashort pulse lasers with matter. The algorithm is based on current density decomposition and is only marginally more complicated compared to explicit PIC codes, but it completely eliminates grid heating and possesses good energy conserving properties with relaxed time step and grid resolution. This is demonstrated in a test case study, in which high-energy protons are generated from a thin carbon foil at solid density using linear and circular polarizations. The grid heating rate is estimated to be 1-10 eV/ps.

36 MATERIALS SCIENCE↗