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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

MRI of the lung gas-space at very low-field using hyperpolarized noble gases

In hyperpolarized (HP) noble-gas magnetic resonance imaging, large nuclear spin polarizations, about 100,000 times that ordinarily obtainable at thermal equilibrium, are created in 3He and 129Xe. The enhanced signal that results can be employed in high-resolution MRI studies of void spaces such as in the lungs. In HP gas MRI the signal-to-noise ratio (SNR) depends only weakly on the static magnetic field (B(0)), making very low-field (VLF) MRI possible; indeed, it is possible to contemplate portable MRI using light-weight solenoids or permanent magnets. This article reports the first in vivo VLF MR images of the lungs in humans and in rats, obtained at a field of only 15 millitesla (150 Gauss).

NASA Discipline Life Sciences Technologies↗
NASA NTRS1998

Envelope structure on 700 AU scales and the molecular outflows of low-mass young stellar objects

Aperture synthesis observations of HCO+ J = 1-0, 13CO 1-0, and C18O 1-0 obtained with the Owens Valley Millimeter Array are used to probe the small-scale (5" approximately 700 AU) structure of the molecular envelopes of a well-defined sample of nine embedded low-mass young stellar objects in Taurus. The interferometer results can be understood in terms of: (1) a core of radius approximately or less than 1000 AU surrounding the central star, possibly flattened and rotating; (2) condensations scattered throughout the envelope that may be left over from the inhomogeneous structure of the original cloud core or that may have grown during collapse; and (3) material within the outflow or along the walls of the outflow cavity. Masses of the central cores are 0.001-0.1 M (solar), and agree well with dust continuum measurements. Averaged over the central 20" (3000 AU) region, an HCO+ abundance of 4 x 10(-8) is inferred, with a spread of a factor of 3 between the different sources. Reanalysis of previously presented single-dish data yields an HCO+ abundance of (5.0 +/- 1.7) x 10(-9), which may indicate an average increase by a factor of a few on the smaller scales sampled by the interferometer. Part of this apparent abundance variation could be explained by contributions from extended cloud emission to the single-dish C18O lines, and uncertainties in the assumed excitation temperatures and opacities. The properties of the molecular envelopes and outflows are further investigated through single-dish observations of 12CO J = 6-5, 4-3, and 3-2, 13CO 6-5 and 3-2, and C18O 3-2 and 2-1, obtained with the James Clerk Maxwell and IRAM 30 m telescopes, along with the Caltech Submillimeter Observatory. Ratios of the mid-J CO lines are used to estimate the excitation temperature, with values of 25-80 K derived for the gas near line centre. The outflow wings show a similar range, although Tex is enhanced by a factor of 2-3 in at least two sources. In contrast to the well-studied L1551 IRS 5 outflow, which extends over 10' (0.4 pc), seven of the remaining eight sources are found to drive 12CO 3-2 outflows over < or = 1' (0.04 pc); only L1527 IRS has a well-developed outflow of some 3'(0.12 pc). Estimates are obtained for the outflow kinetic luminosity, Lkin, and the flow momentum rate, FCO, applying corrections for line opacity and source inclination. The flow force FCO correlates with the envelope mass and with the 2.7 mm flux of the circumstellar disk. Only a weak correlation is seen with Lbol, while none is found with the relative age of the object as measured by integral Tmb(HCO+ 3-2)dV/Lbol. These trends support the hypothesis that outflows are driven by accretion through a disk, with a global mass infall rate determined by the mass and density of the envelope. The association of compact HCO+ emission with the walls of the outflow cavities indicates that outflows in turn influence the appearance of the envelopes. It is not yet clear, however, whether they are actively involved in sweeping up envelope material, or merely provide a low-opacity pathway for heating radiation to reach into the envelope.

NASA Discipline Exobiology↗
NASA NTRS1995

Climatic forcing of carbon-oxygen isotopic covariance in temperate-region marl lakes

Carbon and oxygen stable isotopic compositions of lacustrine carbonate from a southeastern Michigan marl lake display linear covariance over a range of 4.0% Peedee belemnite (PDB) in oxygen and 3.9% (PDB) in carbon. Mechanisms of delta 13 C-delta 18 O coupling conventionally attributed to lake closure in arid-region basins are inapplicable to hydrologically open lake systems. Thus, an alternative explanation of isotopic covariance in temperate region dimictic marl lakes is required. We propose that isotopic covariance is a direct record of change in regional climate. In short-residence-time temperate-region lake basins, summer meteoric precipitation is enriched in 18O relative to winter values, and summer organic productivity enriches epilimnic dissolved inorganic carbon in 13C. Thus, climate change toward longer summers and/or shorter winters could result in greater proportions of warm-month meteoric precipitation, longer durations of warm-month productivity, and net long-term enrichment in carbonate 18O and 13C. Isotopic covariance observed in the Michigan marl lake cores is interpreted to reflect postglacial warming from 10 to 3 ka followed by cooler mean annual temperature, a shift toward greater proportions of seasonal summer precipitation, a shortening of the winter season, or some combination of these three factors.

NASA Discipline Number 52-30↗
DOE OSTI2025

Internal-Gelation Production of Uranium Oxide Sol-Gel Particles for Forensic Applications

The purpose of this project was to develop and demonstrate a novel method for the production of uranium oxide microsphere particles with tunable chemical compositions via a sol-gel process using a 3D-printer setup. These particles can serve several purposes in research and development as a forensic training tool or as standard reference materials. A key component of the project was to demonstrate the ability to control physical and chemical parameters of the particles created. First, we demonstrated the ability to employ an internal gelation sol-gel process to create individual uranium oxide particles. The particles were successfully dispensed using a unique 3D-printing setup onto a substrate to react and then were collected and thermally processed. A series of temperatures for the annealing process was tested on individual samples to investigate the effect on the sol-gel chemical composition and physical integrity. Next, we demonstrated the ability to control matrix composition of the particles by separately incorporating fission product isotopes as well as Np-237 into the sol-gel solution. It was shown by gamma-ray spectroscopy that these matrix elements were successfully retained during the gelation process. We studied the retention of the elements across a series of annealing temperatures. Additionally, we demonstrated the ability to quantitatively control the isotopic composition of the particles by altering the U-237/U-238 ratio to a controlled value. Finally, X-ray diffraction analysis (XRD) was used to investigate the oxidation state of the sol-gel after annealing at different temperatures.

37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL C↗
DOE OSTI2025

Neutron capture signatures determined from gadolinium isotope compositions of uranium ore concentrates using MC-ICPMS

We present Gd isotope compositions on 25 well-characterized uranium ore concentrates (UOCs). About half the UOCs have isotope depletions in 157 Gd coupled with anticorrelated excesses in 158 Gd due to neutron capture effects. UOCs from older ore bodies and with higher U contents show larger neutron capture effects than UOCs from younger ore bodies with lower U contents. These Gd data are correlated with their previously measured Sm isotope compositions, and we use the Sm data to estimate the neutron fluence of these samples. In conclusion, this work demonstrates how Gd isotope signatures can be employed as a new tool for nuclear forensics.

Earth Sciences↗
NASA NTRS1994

Primitive Xe in the atmospheres of Earth and mars

Published data on Xe isotope compositions in primitive carbonaceous meteorites are examined using multidimensional correlation analysis. Distribution of the Xe data in multidimensional data space, except for (129)Xe, can be characterized by a single component, whose isotope composition is identical to 'H plus L minus Xe'. Additional small contributions to the data variations, less than 1 percent of total variations, can be attributed to 'S minus Xe' as well as atmospheric contamination. Isotopic composition of primitive Xe common to the Earth's atmosphere and carbonaceous meteorites are determined with the same assumption as adopted by Pepin and Phinney: primitive Xe is precisely related to fission-free Xe in the Earth's atmosphere by mass fractionation. The determined isotopic composition of primitive Xe is closer to Solar-type Xe, rather than U-Xe (and the primitive Xe estimated from chondrite-achondrite correlation. Hence, the present published data on Xe isotope compositions in meteorites do not seem to require any special component for the primitive Xe common to the Earth's atmosphere and carbonaceous meteorites. Thus Earth's accreting planetesimals would have trapped Xe from the surrounding nebula gases where Xe isotope composition is identical to Solar-type Xe. The trapped Xe was subsequently subject to isotopic fractionation due to gravitational separation as planetesimals grew. Finally fissiogenic Xe from (244)Pu was added to form the present Xe isotope composition of the Earth's atmosphere. The amount of fissiogenic (136)Xe is estimated to be 2.6 percent of the total amount of (136)Xe in the atmosphere, which is about a half of that estimated by Pepin and Phinney (4.65 percent).

Igarashi, G.↗
DOE OSTI2025

Distinguishing fissile uranium isotopes using an active well neutron coincidence counter

Proposed thorium-based nuclear fuel cycles are likely to require quantification and verification of 233 U within nuclear material. Because of their similar fission cross sections, active neutron nondestructive assay (NDA) systems may respond similarly to 233 U and 235 U. Traditional safeguards equipment has been optimized for 235 U and 238 U quantification associated with conventional uranium/plutonium fuel cycles and may not be directly applicable to 233 U quantification when mixed with other actinides. This work used models of the large volume active well coincidence counter (LV-AWCC) at Oak Ridge National Laboratory to evaluate the performance of this neutron NDA system to differentiate fissile uranium isotopes. The models were developed to simulate NDA system performance in response to a number of triangular radiation signature training device sources within the central cavity or well. This work predicted that the LV-AWCC can effectively differentiate 233 U from 235 U in certain modes of operation. In active mode, the LV-AWCC with the cadmium liner results in different doubles count rates between the fissile isotopes for a given fissile uranium mass. Without the cadmium liner, the uranium isotopes provide a statistically indistinguishable doubles count rate response for the fissile masses considered in this work (up to approximately 150 g). The cadmium liner serves to harden the neutron interrogation spectrum, which better exploits the notable difference in the 233 U and 235 U fission cross sections at approximately 1 eV. In passive mode, the two fissile isotopes exhibit different doubles and singles count rates regardless of liner presence because the passive source strength of 233 U is approximately 2 orders of magnitude stronger than that of 235 U due to the shorter half-life and correspondingly higher (α, n) yield. We conclude that using neutron interrogation in the LV-AWCC, two measurements are needed to quantify 233 U content in mixed uranium items. The first measurement is used to determine the total fissile uranium mass using a mode that cannot distinguish fissile isotopes (i.e., where a similar response is observed for both fissile uranium isotopes such as active doubles without cadmium or using a thermal neutron interrogation source). In conclusion, the second measurement is used to determine the 233 U content by using a differentiating technique (e.g., passive doubles, passive doubles to singles ratio, active doubles with cadmium).

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Comparison of the sensitivity of 236 U measurements in environmental samples by MC-ICP-MS and ATONA based high precision U TIMS measurements

The ATONA project is focused upon exploring the improvements in uranium isotope ratio measurements by thermal ionization mass spectrometry (TIMS) provided by a new, capacitor-based, amplifier technology. These “ATONA” Faraday amplifiers (Isotopx Ltd, UK) promise accurate, low-noise measurements of very small signals (< 1 femto-amp) in a traditional Faraday cup, which was only previously possible using an ion counter. This report outlines a series of experiments that were performed to assess the performance of the system in samples that test our rapid analysis procedures, and then compare the results against other mass spectrometry techniques currently available for environmental analyses. The following major goals were achieved: (1) illustrated the importance of 236 U measurements for the screening and analysis of environmental samples; (2) improved sensitivity for 236 U, and then identified 236 U in the 4350B standard at ultra-trace levels (3) Provided comparison of the 236 U sensitivity to multi-collector inductively coupled mass spectrometry techniques (4) Illustrated high TRL for the ATONA based measurement technique. This completes the reporting requirements for task 4 in the project LCP and highlights the utility of the system to make highly sensitive 236 U measurements in programmatically relevant sample matrices and at relevant uranium concentrations.

07 ISOTOPE AND RADIATION SOURCES↗
NASA NTRS1988

Geochronological and lead-isotope evidences for rapid crust formation in middle-proterozoic time: The Labrador example

Extensive U-Pb geochronological studies in the Grenville and Makkovik provinces have shown that eastern Labrador is underlain by two distinct crustal blocks. In order to substantiate the juvenile character of the middle-Proterozoic crustal block, the isotopic compositon of lead in leached k-feldspars from the same rocks were analyzed. The results of the analysis are briefly discussed.

Schaerer, Urs↗
DOE OSTI2023

Fission with Exotic Nuclei (Abbreviated Report)

Nuclear fission is a key mechanism involved in the synthesis of heavy elements in the Cosmos and is the primary explanation for the stability of superheavy elements. Nevertheless, our knowledge of fission remains extremely fragmented. Most experiments have been conducted only on a tiny number of stable actinide nuclei and are often incomplete, leading to gaps in our basic understanding of the process. For many radioactive isotopes, basic fission data such as the charge or mass distribution of the fragments is unknown. These gaps cannot always be filled by simulation alone. Common fission models contain too many free parameters and lack predictive power. In contrast, the fundamental theory of fission under development at LLNL is much more predictive, but its current computational cost is too high to be used extensively for data evaluations. A unique window of opportunity to resolve these limitations has recently opened: the U.S. nuclear science community is ramping up major experimental programs at the Facility for Rare Isotope Beams (FRIB, the DOE flagship facility in low-energy nuclear science), and techniques from machine learning have shown great potential to simplify the use of a fundamental, quantum-mechanical theory of fission. This project has two components. On the experimental side, we acquired and deployed at the HIGS facility a new dual Frisch-Grid ionization chamber to measure correlated fragment-mass, kinetic energy, and angular distributions of fission fragments from induced fission. This new device was used to perform measurements of charge, mass and total kinetic energy of fission fragments in the photofission of 238 U and eight gamma-ray beam energies between 6.2 and 13 MeV, which allowed extracting high-precision independent yields for this reaction. The device was also used to perform measurements of the same quantities in the neutron-induced fission of 234 U with monoenergetic beams of energy between 5 and 8 MeV. In parallel, we collaborated with a team at Commissariat à l’énergie atomique et aux énergies alternatives (CEA) to perform a series of measurements of fission yields in inverse kinematics for the two isotopes of 236 U and 240 Pu. The experiment took place at the Grand Accélérateur National d’Ions Lourds in France in June 2023. The deployment of the VAMOS spectrometer with a new array called PISTA allowed determining the excitation energy of the fissioning system within 1 Mega-electronvolts. The second component of the project involved using deep neural networks to build fast and reliable emulators of our current fission models. In an invited paper published in Frontier in Physics, we showed that autoencoders could successfully compress nuclear wavefunctions in nuclear density functional theory. We achieved a dimensionality reduction of the order of two orders of magnitude while keeping the error in the total energy to less than 0.01%. In a second paper submitted to Physical Review Letters in June 2023 with our collaborators at CEA, we showed that variational autoencoders can learn the collective degrees of freedom driving the fission process.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Complex exposure-burial history and Pleistocene sediment recycling in the dead sea rift with implications for the age of the Acheulean site of ‘Ubeidiya

Here, we present early Pleistocene burial ages of the ‘Ubeidiya Formation sediments in the Jordan Valley, a segment of the Dead Sea Rift Valley. A minimum age of ∼1.1 Ma is constrained both by paleomagnetic analysis and U-Pb dating of Melanopsis shells. Simple cosmogenic burial ages (i.e., one very long exposure period followed by one period of burial) calculated from the ratios of 26 Al to 10 Be and 10 Be concentrations indicate ages of ∼3 Ma, contradicting the geological and paleomagnetic constraints as well as a reasonable age of the ‘Ubeidiya archeological site, as it contains human remains. A more sophisticated way of treating the results, by combining numerical modeling of cosmogenic nuclide build up during repeated burial-exposure cycles, paleomagnetic analysis (indicating reverse polarity) and a minimum burial age of 1.1 Ma set by U-Pb dating of Melanopsis shells, suggests two most probable time slots (1.19-1.77 and 1.93- 2.14 Ma) for the absolute age of the ‘Ubeidiya Formation. However, the skewed distribution of cosmogenic isotope burial ages, with a median age of 2.05 Ma, indicates a much higher probability of the older ages, most likely >1.9 Ma. The exposure-burial history that emerges from the model implies recycling of sediments previously deposited and buried in the rift valley, between 4.5 and 3.2 Ma, and subsequently exhumed, eroded, transported and then redeposited along the ‘Ubeidiya paleo lake shoreline.

Acheulean↗
DOE OSTI2023

Microstructure and microchemistry changes at U-10Mo fuel/AA6061 cladding interfaces with varying hot isostatic pressing conditions

Monolithic uranium - 10 wt.% molybdenum (U-10Mo) is a promising high-assay low-enriched uranium fuel system for nuclear reactors used in research, medical isotope production, and remote power applications. During manufacturing, AA6061 cladding is bonded to the U-10Mo fuel plate via hot isostatic pressing, during which diffusion and fuel/cladding chemical interaction occurs at plate edges. Furthermore, the microstructure and microchemistry changes that occur at fuel/cladding interfaces are important to understand as a function of process parameters to develop a reliable fuel fabrication process and to meet the desired specifications. Here, microstructural and microchemical changes are studied using complementary electron microscopy and atom probe tomography for two manufactured fuel plates with varied hot isostatic pressing (HIP) parameters. Results highlight that modifying thermomechanical processing parameters significantly changed the interaction layer thickness between U-10Mo and AA6061 by an order of magnitude. In addition to this the distribution and concentration of elements (i.e., Al, Si, Mg) from cladding to fuel was also investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Excited states in semi-magic 82 Ge populated in the βn-decay of 83 Ga

For this work, the βn and β-decay of the neutron-rich 83 Ga isotopes produced in proton-induced fission of 238 U were studied at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory using on-line mass separation and the hybrid-3Hen neutron-γ detector array. Excited states in semi-magic 82 Ge populated in βn decay of 83 Ga were identified using neutron-γ coincidences. The measured relative population of excited states in 82 Ge is compared with a βn emission model, where the neutron emission model combines the strength distribution obtained from the shell-model calculations with the statistical Hauser-Feshbach model.

3HEN↗
DOE OSTI2020

β -decay half-lives of 55 neutron-rich isotopes beyond the N = 82 shell gap

The β -decay half-lives of 55 neutron-rich nuclei Sn 134 - 139 , Sb 134 - 142 , Te 137 - 144 , I 140 - 146 , Xe 142 - 148 , Cs 145 - 151 , Ba 148 - 153 , and La 151 - 155 were measured at the Radioactive Isotope Beam Factory employing the projectile fission fragments of U 238 . The nuclear level structure, which relates to deformation, has a large effect on the half-lives. The impact of newly measured half-lives on modeling the astrophysical origin of the heavy elements is studied in the context of r process nucleosynthesis. For a wide variety of astrophysical conditions, including those in which fission recycling occurs, the half-lives have an important local impact on the second ( A ≈ 130) peak.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Impact of Spontaneous Fission Neutron Emission Energy on Neutron Detector Response

A parametric study was simulated in MCNP to investigate the impact of spontaneous fission neutron energy on neutron detector response. A total of 880 configurations were simulated by varying 3 He pressure and polyethylene reflector thickness for 8 different isotopes. Results showed that deviations between the simulated isotopes become more prevalent at higher energies with 238 U showing the greatest deviation. It was also observed that configurations comparable to most detection setups, 10 atm and 6 - 8 cm polyethylene, were closer to the upper bound of deviations from a 252 Cf. 240 Pu, a common spontaneous fission source of interest, ranged from 2% - 3% within this space. This suggests that further investigation is required to determine exact correction factors when calibrating neutron detectors with a 252 Cf. Although demonstrated here for a 4π-detection system, future plans include simulating a more detailed model of the MC-15 detection setup to determine exact correction factors for future experiments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Survey of Neutron Induced Fission Experimental and Evaluated Data for 233 U, 238 Pu, 240 Pu, and 242 Pu between 100 keV and 20 MeV

We review data and evaluations for neutron-induced fission for the actinides 233 U, 238 Pu, 240 Pu and 242 Pu. These isotopes are part of common nuclear fuel cycles, especially for modern fast reactors. We focus on incident neutrons in the energy range of 100 keV to 20 MeV and compare the experimental data from the literature to the major evaluated libraries ENDF/B-VIII.1, JENDL-5, and JEFF-3.3, as well as to LLNL’s ENDL-2009.5 library. Based on the assessment of the fission cross sections, we provide recommendations on which library to use. Additional assessments covering other reaction channels will be provided separately.

07 ISOTOPE AND RADIATION SOURCES↗