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Reedy, Robert C.

Publications and source records attributed to Reedy, Robert C..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Distribution of rare earth and other critical elements in lignites from the Eocene Jackson Group, Texas

Coal is increasingly evaluated as a source of rare earth elements (REEs) in the United States to address the overreliance on imported REEs. The objective of this study was to assess the distribution of REEs in lignites from selected mining areas in the Texas Gulf Coastal Plain region. Thirty-one archived lignite and rock samples previously collected by the U.S. Geological Survey were analyzed for their rare earth element and critical mineral content. These include samples from one core (5400 and 5500 lignite horizons) and two opencast lignite mines (Gibbons Creek 3500 and 4500 horizons, and San Miguel horizons A to D) in the Eocene Jackson Group of the Texas Gulf of Mexico Coastal Plain. Some lithologies in the Gibbons Creek 3500 and 4500 lignite-bearing sections have high total rare earth, yttrium (Y), and scandium (Sc) (REYSc) values, up to 7800 ppm (ash basis) REYSc. The lignite lithologies show an enrichment in rare earths, [samarium (Sm) through gadolinium (Gd)]. The basal Gibbons Creek 3500 lignite bench shows a heavy rare earth element enrichment pattern resembling that often seen in peats through high volatile A bituminous coals. The 5500 lignite sequence, overlying the latter lignite sections, shows a light rare earth enrichment. The San Miguel lignite benches have heavy rare earth enrichments with a negative europium (Eu) anomaly.

58 GEOSCIENCES↗
DOE OSTI2018

Fingerprinting groundwater salinity sources in the Gulf Coast Aquifer System, USA

Understanding groundwater salinity sources in the Gulf Coast Aquifer System (GCAS) is a critical issue due to depletion of fresh groundwater and concerns for potential seawater intrusion. The study objective was to assess sources of groundwater salinity in the GCAS using ∼1,400 chemical analyses and ∼90 isotopic analyses along nine well transects in the Texas Gulf Coast, USA. Salinity increases from northeast (median total dissolved solids (TDS) 340 mg/L) to southwest (median TDS 1,160 mg/L), which inversely correlates with the precipitation distribution pattern (1,370– 600 mm/yr, respectively). Molar Cl/Br ratios (median 540–600), depleted δ{sup 2}H and δ{sup 18}O (−24.7‰, −4.5‰) relative to seawater (Cl/Br ∼655 and δ{sup 2}H, δ{sup 18}O 0‰, 0‰, respectively), and elevated {sup 36}Cl/Cl ratios (∼100), suggest precipitation enriched with marine aerosols as the dominant salinity source. Mass balance estimates suggest that marine aerosols could adequately explain salt loading over the large expanse of the GCAS. Evapotranspiration enrichment to the southwest is supported by elevated chloride concentrations in soil profiles and higher δ{sup 18}O. Secondary salinity sources include dissolution of salt domes or upwelling brines from geopressured zones along growth faults, mainly near the coast in the northeast. The regional extent and large quantities of brackish water have the potential to support moderate-sized desalination plants in this location. These results have important implications for groundwater management, suggesting a current lack of regional seawater intrusion and a suitable source of relatively low TDS water for desalination.

58 GEOSCIENCES↗
DOE OSTI2017

Energy Intensity and Greenhouse Gas Emissions from Oil Production in the Eagle Ford Shale

A rapid increase in horizontal drilling and hydraulic fracturing in shale and “tight” formations that began around 2000 has resulted in record increases in oil and natural gas production in the U.S. This study examines energy consumption and greenhouse gas (GHG) emissions from crude oil and natural gas produced from ~8,200 wells in the Eagle Ford Shale in southern Texas from 2009 to 2013. Our system boundary includes processes from primary exploration wells to the refinery entrance gate (henceforth well-to-refinery or WTR). The Eagle Ford includes four distinct production zones—black oil (BO), volatile oil (VO), condensate (C), and dry gas (G) zones—with average monthly gas-to-liquids ratios (thousand cubic feet per barrel—Mcf/bbl) varying from 0.91 in the BO zone to 13.9 in the G zone. Total energy consumed in drilling, extracting, processing, and operating an Eagle Ford well is ~1.5% of the energy content of the produced crude and gas in the BO and VO zones, compared with 2.2% in the C and G zones. On average, the WTR GHG emissions of gasoline, diesel, and jet fuel derived from crude oil produced in the BO and VO zones in the Eagle Ford play are 4.3, 5.0, and 5.1 gCO2e/MJ, respectively. Comparing with other known conventional and unconventional crude production where upstream GHG emissions are in the range 5.9–30 gCO2e/MJ, oil production in the Eagle Ford has lower WTR GHG emissions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Investigation of Sb-Containing Precursors for Cu(In, Ga)Se2 Thin Films Through Design of Experiments

The Design of Experiments (DoE) module in JMP statistical software was used to determine the best parameters for Sb-containing CIGS precursors with a fixed selenization step. Solar cells were fabricated and measured for all completed films. The most important factor influencing the current-voltage device parameters was identified as the temperature and antimony flux interaction. The DoE prediction profiler and predictive contour plots provided guidance to further improve the device parameters. In one follow-up run, we increased device efficiency from 14.9% to 15.5% Additional gains in efficiency to 16.9% were realized by introducing an intentional Ga gradient and an antireflective coating.

14 SOLAR ENERGY↗
DOE OSTI2015

Tunnel oxide passivated contacts formed by ion implantation for applications in silicon solar cells

Passivated contacts (poly-Si/SiO{sub x}/c-Si) doped by shallow ion implantation are an appealing technology for high efficiency silicon solar cells, especially for interdigitated back contact (IBC) solar cells where a masked ion implantation facilitates their fabrication. This paper presents a study on tunnel oxide passivated contacts formed by low-energy ion implantation into amorphous silicon (a-Si) layers and examines the influence of the ion species (P, B, or BF{sub 2}), the ion implantation dose (5 × 10{sup 14 }cm{sup −2} to 1 × 10{sup 16 }cm{sup −2}), and the subsequent high-temperature anneal (800 °C or 900 °C) on the passivation quality and junction characteristics using double-sided contacted silicon solar cells. Excellent passivation quality is achieved for n-type passivated contacts by P implantations into either intrinsic (undoped) or in-situ B-doped a-Si layers with implied open-circuit voltages (iV{sub oc}) of 725 and 720 mV, respectively. For p-type passivated contacts, BF{sub 2} implantations into intrinsic a-Si yield well passivated contacts and allow for iV{sub oc} of 690 mV, whereas implanted B gives poor passivation with iV{sub oc} of only 640 mV. While solar cells featuring in-situ B-doped selective hole contacts and selective electron contacts with P implanted into intrinsic a-Si layers achieved V{sub oc} of 690 mV and fill factor (FF) of 79.1%, selective hole contacts realized by BF{sub 2} implantation into intrinsic a-Si suffer from drastically reduced FF which is caused by a non-Ohmic Schottky contact. Finally, implanting P into in-situ B-doped a-Si layers for the purpose of overcompensation (counterdoping) allowed for solar cells with V{sub oc} of 680 mV and FF of 80.4%, providing a simplified and promising fabrication process for IBC solar cells featuring passivated contacts.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Impact of implanted phosphorus on the diffusivity of boron and its applicability to silicon solar cells

Boron diffusivity reduction in extrinsically doped silicon was investigated in the context of a process combination consisting of BBr{sub 3} furnace diffusion and preceding Phosphorus ion implantation. The implantation of Phosphorus leads to a substantial blocking of Boron during the subsequent Boron diffusion. First, the influences of ion implantation induced point defects as well as the initial P doping on B diffusivity were studied independently. Here, it was found that not the defects created during ion implantation but the P doping itself results in the observed B diffusion retardation. The influence of the initial P concentration was investigated in more detail by varying the P implantation dose. A secondary ion mass spectrometry (SIMS) analysis of the BSG layer after the B diffusion revealed that the B diffusion retardation is not due to potential P content in the BSG layer but rather caused by the n-type doping of the crystalline silicon itself. Based on the observations the B diffusion retardation was classified into three groups: (i) no reduction of B diffusivity, (ii) reduced B diffusivity, and (iii) blocking of the B diffusion. The retardation of B diffusion can well be explained by the phosphorus doping level resulting in a Fermi level shift and pairing of B and P ions, both reducing the B diffusivity. Besides these main influences, there are probably additional transient phenomena responsible for the blocking of boron. Those might be an interstitial transport mechanism caused by P diffusion that reduces interstitial concentration at the surface or the silicon/BSG interface shift due to oxidation during the BBr{sub 3} diffusion process. Lifetime measurements revealed that the residual (non-blocked) B leads to an increased dark saturation current density in the P doped region. Nevertheless, electrical quality is on a high level and was further increased by reducing the B dose as well as by removing the first few nanometers of the silicon surface after the BBr{sub 3} diffusion.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2012

Geochemistry at 4 Vesta: Observations Using Fast Neutrons

Dawn is currently in orbit around the asteroid 4 Vesta, and one of the major objectives of the mission is to probe the relationship of Vesta to the Howardite, Eucrite, and Diogenite (HED) meteorites. As Vesta is an example of a differentiated planetary embryo, Dawn will also provide fundamental information about planetary evolution in the early solar system [1]. To help accomplish this overall goal, the Dawn spacecraft carries the Gamma-Ray and Neutron Detector (GRaND). GRaND uses planetary gamma-ray and neutron spectroscopy to measure the surface elemental composition of Vesta and will provide information that is unique and complementary to that provided by the other Dawn instruments and investigations. Gamma-ray and neutron spectroscopy is a standard technique for measuring planetary compositions [2], having successfully made measurements at near-Earth asteroids, the Moon, Mars, Mercury and now Vesta. GRaND has made the first measurements of the neutron spectrum from any asteroid (previous asteroid measurements were only made with gamma-rays). Dawn has been collecting data at Vesta since July 2011. The prime data collection period for GRaND is the Low-Altitude Mapping Orbit (LAMO), which started on 12 December 2011 and will last through spring 2012. During LAMO, the Dawn spacecraft orbits at an average altitude of ~210 km above the surface of Vesta, which allows good neutron and gamma-ray signals to be detected from Vesta. A description of the overall goals of GRaND and a summary of the initial findings are given elsewhere [3,4]. The subject of this study is to present the information that will be returned from GRaND using fast neutron measurements. Here, we discuss what fast neutrons can reveal about Vesta s surface composition, how such data can address Dawn science goals, and describe fast neutron measurements made in the early portion of the Vesta LAMO phase.

Lawrence, David J.↗
NASA NTRS2011

Geochemical Mapping of 4 Vesta Begins

By December, the NASA Dawn spacecraft will have descended to a low altitude mapping orbit (LAMO), where the Gamma Ray and Neutron Detector (GRaND) will acquire global mapping data for up to four months. Measurements by GRaND will help answer elusive questions about how Vesta differentiated and the nature of processes that shaped Vesta s surface. The data will be analyzed to determine the abundances of Mg, Si, Fe, K, Th, and H at a spatial resolution of roughly 300 km full-width-at-half-maximum from a 465 km radius orbit. Thermal and fast neutron counting data will be analyzed to determine the neutron macroscopic absorption cross section and average atomic mass, providing constraints on additional elements, such as Ca and Al. GRaND will quantify the elemental composition of coarse spatial units identified by Dawn s Framing Camera (FC) and the Visible & Infrared Spectrometer (VIR). In addition, GRaND will map the mixing ratio of compositional end members selected from the howardite, eucrite and diogenite (HED) meteorites, determine the relative proportions of plagioclase and mafic minerals, and search for compositions that are absent or under-represented in the meteorite collection. While it is generally thought that Vesta s crust on a regional scale should be well-represented by linear mixing of HED whole-rock compositions, there are hints that Vesta may be more diverse than implied by this model. For example, the discovery of K-rich impact glasses in howardites suggests that K-rich rocks may be present on a portion of Vesta s surface, and the analysis of diogenites indicates considerable variability in the magmatic processes that formed them. The chemical composition of materials within Vesta s south polar structure may provide further clues to how it formed. An impact might have exposed mantle and lower crustal materials, which should have a distinctive compositional signature. We present the analysis of data acquired by GRaND from cruise through the descent to LAMO, including GRaND s sensitivity to different elements and geochemical processes.

Prettyman, Thomas H.↗
NASA NTRS2003

Extraterrestrial Studies Using Nuclear Interactions

Cosmogenic nuclides were used to study the recent histories of the aubrite Norton County and the pallasite Brenham using calculated production rates. Calculations were done of the rates for making cosmogenic noble-gas isotopes in the Jovian satellite Europa by the interactions of galactic cosmic rays and especially trapped Jovian protons. Cross sections for the production of cosmogenic nuclides were reported and plans made to measure additional cross sections. A new code, MCNPX, was used to numerically simulate the interactions of cosmic rays with matter and the subsequent production of cosmogenic nuclides. A review was written about studies of extraterrestrial matter using cosmogenic radionuclides. Several other projects were done. Results are reviewed here with references to my recent publications for details.

Reedy, Robert C.↗
NASA NTRS2003

Numerical Simulations of Cosmogenic Neutron Production and Transport in Planetary Surfaces

The numerical simulation code MCNPX was used to calculate the production and transport of cosmic-ray-produced neutrons in Mars and meteorites. These calculations help to understand the processes involved and the parameters that control the neutron fluxes. Results are presented here for neutrons in Mars and for the distribution of cosmic-ray neutrons and protons in a 50 cm-radius L-chondrite.

Kim, Kyeong J.↗
NASA NTRS2000

Solar-Cosmic-Ray-Produced Nuclides in Extraterrestrial Matter

There are two main types of cosmic rays that have sufficient energy to induce nuclear reactions -- the galactic cosmic rays (GCR) and solar cosmic rays (also called solar energetic particles). Both types of particles can have production rates and production ratios in the small objects often found in cold and hot deserts that are different from those seen for most meteorites, which typically have radii of approx.10-100 centimeters. GCR production rates are often lower than those for most meteorites. GCR production ratios, such as Ne-22/Ne-21, are also often different in small objects. Smaller meteoroids also are more likely to have nuclides made by solar-cosmic-ray (SCR) particles than typically-sized meteorites. The very small meteorite Salem had large amounts of SCR-produced radionuclides. Meteorites recovered in Antarctica are more likely to contain SCR-produced nuclides than other meteorites. Martian and lunar meteorites are also likely to have SCR-produced nuclides. Production rates and profiles for SCR-produced nuclides in meteoroids have been calculated previously. However, the cross sections for the nuclear reactions making many SCR-produced nuclides, such as Be-10, were not well measured then. New rates and profiles are calculated here using good cross sections for the reactions making these nuclides.

Reedy, Robert C.↗
NASA NTRS1999

Solar-Cosmic-Ray-Produced Nuclides in Extraterrestrial Matter

There are two main types of cosmic rays that have sufficient energy to induce nuclear reactions -- the galactic cosmic rays (GCR) and solar cosmic rays (also called solar energetic particles). Both types of particles can have production rates and production ratios in the small objects often found in cold and hot deserts that are different from those seen for most meteorites, which typically have radii of approx. 10-100 centimeters. GCR production rates are often lower than those for most meteorites. GCR production ratios, such as Ne-22/Ne-21, are also often different in small objects. Smaller meteoroids also are more likely to have nuclides made by solar-cosmic-ray (SCR) particles than typically-sized meteorites. The very small meteorite Salem had large amounts of SCR-produced radionuclides. Meteorites recovered in Antarctica are more likely to contain SCR-produced nuclides than other meteorites. Martian and lunar meteorites are also likely to have SCR-produced nuclides. Production rates and profiles for SCR-produced nuclides in meteoroids have been calculated previously. However, the cross sections for the nuclear reactions making many SCR-produced nuclides, such as Be-10 were not well measured then. New rates and profiles are calculated here using good cross sections for the reactions making these nuclides.

Reedy, Robert C.↗
NASA NTRS1993

Radioactivities induced in some LDEF samples

Radioactivities induced in several Long Duration Exposure Facilities (LDEF) samples were measured by low-level counting at Los Alamos and elsewhere. These radionuclides have activities similar to those observed in meteorites and lunar samples. Some trends were observed in these measurements in terms of profiles in trunnion layers and as a function of radionuclide half-life. Several existing computer codes were used to model the production by the protons trapped in the Earth's radiation belts and by the galactic cosmic rays of some of these radionuclides, Mn-54 and Co-57 in steel, Sc-46 in titanium, and Na-22 in alloys of titanium and aluminum. Production rates were also calculated for radionuclides possibly implanted in LDEF, Be-7, Be-10, and C-14. Enhanced concentrations of induced isotopes in the surfaces of trunnion sections relative to their concentrations in the center are caused by the lower-energy protons in the trapped radiation. Secondary neutrons made by high-energy trapped protons and by galactic cosmic rays produce much of the observed radioactivities, especially deep in an object. Comparisons of the observed to calculated activities of several radionuclides with different half-lives indicate that the flux of trapped protons at LDEF decreased significantly at the end of the mission.

Reedy, Robert C.↗
NASA NTRS1993

Effects of bulk composition on production rates of cosmogenic nuclides in meteorites

The bulk chemical composition of meteorites has been suggested as a main factor influencing the production of cosmogenic nuclides. Numerical simulations with Los Alamos Monte Carlo production and transport codes were done for Ne-21/Ne-22 ratios and Ar-38 production rates in meteorites with a wide range of compositions. The calculations show that an enhanced flux of low-energy secondary particles in metal-rich phases is the essential key for the explanation of experimentally observed differences in nuclide production processes in various meteorite classes.

Masarik, Jozef↗
NASA NTRS1992

Radioactivities induced in some LDEF samples

Final activities are reported for gamma ray emitting isotopes measured in 35 samples from LDEF. In 26 steel trunnion samples, activities of Mn-54 and Co-57 were measured and limits set on other isotopes. In five Al end support retainer plates and two Al keel plate samples, Na-22 was measured. In two Ti clip samples, Na-22 was measured, limits for Sc-46 were obtained, and high activities for impurity Uranium and daughter isotopes were observed. Four sets of depth vs activity profiles were measured for the D sections of the trunnion. For all 4 profiles, the activities first decreased with increasing distance from the surface of the trunnion but were fairly flat near the center. These profiles are consistent with production by both the lower energy (approx. 100 MeV) trapped particles and high energy (approx. 10 GeV) galactic-cosmic ray particles. For the near surface samples, the earth quadrant had more Mn-54 than the space quadrant. For the D sections, there was less Mn-54 in the east trunnion than in the west trunnion. Comparisons are made among the samples and with activities measured by others. The limit for Sc-46 in the Ti clips is compared with the activities of Mn-54 produced in the steel pieces by similar reactions. Activities predicted by several models are compared with the measured activities.

Reedy, Robert C.↗