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Nelson, A.

Publications and source records attributed to Nelson, A..

16 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Normalization of stroboscopic neutron scattering experiments

Neutron scattering studies of kinetic processes are often flux limited. For processes which can be repeated many times, this can be mitigated by stroboscopic reintegration. The recorded scattering events are assigned to different time slices of the process and corresponding slices from all repetitions are summed up. The normalization of such data with respect to the incident beam spectrum can be challenging since the incident neutron flux may not necessarily be evenly distributed over all time slices. Here, in this paper, we discuss how this can result in misleading information and we expand on a technique to amend these issues.

Adlmann, Franz Alois↗
DOE OSTI2017

Future Nuclear Energy Factual Status Document: Resource Document for the Workshop on Basic Research Needs for Future Nuclear Energy, July 2017

Since commercialization in the mid-1950s, nuclear power has been widely deployed and provides an important clean source of energy, primarily through the generation of electricity. There are currently 449 commercial nuclear power reactors operating in 31 countries with over 390 GWe total capacity, with 99 operating units in the United States with a total generating capacity of about 100 GWe. Nuclear power plants provide over 11% of the world’s electricity production and, as of 2016, thirteen countries rely on nuclear energy to supply at least one-quarter of their total electricity. Virtually all of that power is generated with water-cooled reactor systems. A number of advanced nuclear energy system concepts have been developed to provide improved efficiency, greater fissile fuel utilization, reduced high level waste generation, and increased margins of safety over today’s water-cooled systems. However, there are a number of technical challenges that must be addressed to enable the broad deployment of these systems from concept to the electrical grid. This Technical Document is written to provide workshop participants with an overview of the current status of a number of advanced reactor systems: Key issues for advanced nuclear energy, including coolants, materials in extremes (irradiation, coolant, and/or high temperature) and interfaces; Nuclear fuel technologies for key reactor types and limitations in testing and design; State of science and understanding for nuclear systems, including characterization, testing, and modeling and simulation tools. For each of these technical areas, this document describes the technological challenge, current state of the art for the technology, and barriers to advanced nuclear concepts.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Thermal/epithermal experiments with hafnium (TEX-Hf)

Critical experiment benchmarks are essential for validating calculational techniques used by criticality safety engineers to guarantee safe fissile material operations, yet there remain significant areas of need where existing benchmarks are insufficient or entirely absent. There is a particularly notable shortage of intermediate benchmarks (where the majority of fissions are caused by neutrons with energy between 0.625 eV and 100 keV). This work describes the design of a set of critical experiments (TEX-Hf) that address this gap by developing a highly enriched uranium (HEU) test bed into which various materials of interest (diluents) can be substituted. The first diluent to be investigated with this test bed is hafnium, a neutron poison used in nuclear applications for which there are no sufficiently sensitive benchmarks. Twenty-one critical configurations made up of stacked disks of HEU, polyethylene, and hafnium were designed and simulated in MCNP6 to calculate their fission energy spectra and the sensitivity of k{sub eff} to changes in various cross sections. It was shown that configurations spanned the energy range from thermal (below 0.625 eV), through the intermediate energy range (0.625 eV to 100 keV), to fast (above 100 keV). Furthermore, it was determined that this set of experiments is sensitive to the hafnium and {sup 235}U cross section data. These test bed experiments were designed to allow substitution of various diluent plates and can therefore be used to quickly and easily produce many more benchmarks. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

The DarkSide-50 Experiment: a Liquid Argon Target for Dark Matter Particles

The DarkSide-50 experiment, located at the “Laboratori Nazionali del Gran Sasso (INFN)”, is based on low-radioactivity argon double phase time projection chamber, surrounded by an active liquid scintillator veto, designed for the zero background achievement. The liquid argon features sufficient self shielding and easy scalability to multi-tons scale. The impressive reduction of the 39 Ar isotope (compared to the atmospheric argon), along with the excellent pulse shape discrimination, make this technology a possible candidate for the forthcoming generation of multi-ton Dark Matter experiments.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The electronics and data acquisition system for the DarkSide-50 veto detectors

DarkSide-50 is a detector for dark matter candidates in the form of weakly interacting massive particles. It utilizes a liquid argon time projection chamber for the inner main detector, surrounded by a liquid scintillator veto (LSV) and a water Cherenkov veto detector (WCV). The LSV and WCV act as the neutron and cosmogenic muon veto detectors for DarkSide-50. This paper describes the electronics and data acquisition system used for these two detectors. The system is made of a custom built front end electronics and commercial National Instruments high speed digitizers. The front end electronics, the DAQ, and the trigger system have been used to acquire data in the form of zero-suppressed waveform samples from the 110 PMTs of the LSV and the 80 PMTs of the WCV. The veto DAQ system has proven its performance and reliability. This electronics and DAQ system can be scaled and used as it is for the veto of the next generation DarkSide-20k detector.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Current Status of the dark matter experiment DarkSide-50

DarkSide-50 is a dark matter direct search experiment at LNGS, searching for rare nuclear recoils possibly induced by WIMPs. It has two nested vetoes and a dual phase liquid argon TPC as dark matter detector. Key features of this experiment are the use of underground argon as radio-pure target and of muon and neutron active vetoes to suppress the background. The first data-taking campaign was running from November 2013 to April 2015 with an atmospheric argon target and a reduced efficiency neutron veto due to internal contamination. However, an upper limit on the WIMP-nucleon cross section of 6.1×10 -44 cm 2 at 90% CL was obtained for a WIMP mass of 100 GeV/c 2 and an exposure of (1422 ± 67) kg·d. At present DarkSide-50 started a 3 years run, intended to be background-free because the neutron veto was successfully recovered and underground argon replaced the atmospheric one. Additionally calibration campaigns for both the TPC and the neutron veto were completed. Thanks to the good performance of the background rejection, the results obtained so far suggest the scalability of DarkSide-50 to a ton-scale detector, which will play a key role into the dark matter search scenario.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Fabrication of advanced accident tolerant U-Si fuel forms

Prospective advanced accident tolerant UN-USi fuel forms for light-water reactors are being studied at Los Alamos National Laboratory. In this paper we present a recent effort to fabricate and characterize U{sub 3}Si{sub 5} and UN-U{sub 3}Si{sub 5} fuel. The U{sub 3}Si{sub 5} is prepared by arc-melting stoichiometric amounts of uranium and silicon metals. The arc melting process consists of cutting U metal plate into small pieces that can be placed in a tri-arc furnace for melting. The material is slowly heated until a uniform melt of the U and Si is achieved. The fabrication of the U{sub 3}Si{sub 5} pellets followed a conventional cold-press and sinter process. As for the fabrication of UN-U{sub 3}Si{sub 5}, the uranium nitride (UN) feedstock powder was synthesized using carbothermic reduction nitridation. The UN is milled and sieved to sub-74 μm. The UN was mixed with EBS (ethylene bis-stearamide) and milled for 45 minutes. The UN-EBS was combined with 10 wt.% U{sub 3}Si{sub 5} powder (equivalent to 15 vol.% in UN) and additional EBS. The fabrication of the UN-U{sub 3}Si{sub 5} pellets followed a conventional cold-press and sinter process similar to that used to fabricate the U{sub 3}Si{sub 5} pellets. A sample UN-U{sub 3}Si{sub 5} pellet was cross-sectioned, ground, and polished for optical microscopy. The UN and U{sub 3}Si{sub 5} phases are apparent as well as pores and micro-cracks. The affect of micro-cracking on fuel performance is unknown and should be assessed during post-irradiation examination.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Results From the First Use of Low Radioactivity Argon in a Dark Matter Search

Liquid argon is a bright scintillator with potent particle identification properties, making it an attractive target for direct-detection dark matter searches. The DarkSide-50 dark matter search here reports the first WIMP search results obtained using a target of low-radioactivity argon. DarkSide-50 is a dark matter detector, using a two-phase liquid argon time projection chamber, located at the Laboratori Nazionali del Gran Sasso. The underground argon is shown to contain Ar39 at a level reduced by a factor (1.4±0.2)×103 relative to atmospheric argon. We report a background-free null result from (2616±43) kg d of data, accumulated over 70.9 live days. When combined with our previous search using an atmospheric argon, the 90% C.L. upper limit on the WIMP-nucleon spin-independent cross section, based on zero events found in the WIMP search regions, is 2.0×10-44 cm2 (8.6×10-44 cm2, 8.0×10-43 cm2) for a WIMP mass of 100 GeV/c2 (1 TeV/c2, 10 TeV/c2).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

The veto system of the DarkSide-50 experiment

Nuclear recoil events produced by neutron scatters form one of the most important classes of background in WIMP direct detection experiments, as they may produce nuclear recoils that look exactly like WIMP interactions. In DarkSide-50, we both actively suppress and measure the rate of neutron-induced background events using our neutron veto, composed of a boron-loaded liquid scintillator detector within a water Cherenkov detector. This paper is devoted to the description of the neutron veto system of DarkSide-50, including the detector structure, the fundamentals of event reconstruction and data analysis, and basic performance parameters.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

The DarkSide project

DarkSide is a graded experimental project based on radiopure argon, and is now, and will be, used in direct dark matter searches. The present DarkSide-50 detector, operating at the Gran Sasso National Laboratory, is a dual-phase, 50 kg, liquid argon time-projection-chamber surrounded by an active liquid scintillator veto. It is designed to be background free in 3 years of operation. DS-50 performances, when filled with atmospheric argon, are reported. However DS-50 filled with underground argon, shows impressive reduction of the 39Ar isotope. The application of this powerful technology in a future generation of the DarkSide program is discussed.

Agnes, P.↗
DOE OSTI2016

A new ATLAS muon CSC readout system with system on chip technology on ATCA platform

The ATLAS muon Cathode Strip Chamber (CSC) backend readout system has been upgraded during the LHC 2013-2015 shutdown to be able to handle the higher Level-1 trigger rate of 100 kHz and the higher occupancy at Run-2 luminosity. The readout design is based on the Reconfigurable Cluster Element (RCE) concept for high bandwidth generic DAQ implemented on the Advanced Telecommunication Computing Architecture (ATCA) platform. The RCE design is based on the new System on Chip XILINX ZYNQ series with a processor-centric architecture with ARM processor embedded in FPGA fabric and high speed I/O resources. Together with auxiliary memories, all of these components form a versatile DAQ building block that can host applications tapping into both software and firmware resources. The Cluster on Board (COB) ATCA carrier hosts RCE mezzanines and an embedded Fulcrum network switch to form an online DAQ processing cluster. More compact firmware solutions on the ZYNQ for high speed input and output fiberoptic links and TTC allowed the full system of 320 input links from the 32 chambers to be processed by 6 COBs in one ATCA shelf. The full system was installed in September 2014. In conclusion, we will present the RCE/COB design concept, the firmware and software processing architecture, and the experience from the intense commissioning for LHC Run 2.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1988

Electrochemical and galvanic corrosion effects in thin-film photovoltaic modules

The electrochemical and galvanic corrosion properties of thin-film photovoltaic (TF-PV) modules and module subcomponents are determined and interpreted in the light of established corrosion science. Results of a detailed study of thin-film aluminum metallization corrosion are presented. Bar-graph corrosion, observed in fielded modules, has been induced experimentally and found to be electrochemical in nature. Corrosion rates and passivation techniques for TF-PV modules are discussed.

Mon, G.↗
NASA NTRS1979

Airborne laser induced fluorescence system for measuring OH and other trace gases in the parts-per-quadrillion to parts-per-trillion range

Described in detail is a laser induced fluorescence system which has been successfully interfaced with two aircraft sampling platforms (i.e., Sabreliner jet and an L-188C Electra). This system, which has been under development for four years, presently consists of the following major components: (1) a Nd-Yag laser driven oscillator-amplifier dye laser; (2) a sampling manifold with associated fluorescence detection optics; (3) an OH calibration chamber; (4) a laser beam steering assembly; and (5) sampling electronics and data processing hardware. During the last three years, this system has been flown some 50,000 air miles making tropospheric OH radical measurements over the latitude range of 70 N to 57 S. OH concentrations measured during these flights have ranged from 30 parts-per-quadrillion (3.7 x 10 to the 5th molecules/sq cm) at altitudes of 6 km to 0.8 parts-per-trillion (2.0 x 10 to the 7th molecules/sq cm) at 0.5 km. Computations have been completed which indicate that the existing aircraft system with modest modifications should also be capable of detecting natural tropospheric levels of NO, SO2, CH2O, NO2, HNO2, NO3, H2O2 and CS2 by using both conventional laser-induced fluorescence methodology and multiphoton techniques.

Davis, D. D.↗