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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Dense autoencoders, clustering techniques, and semi-supervised learning for HPGe $γ$-spectra

Classifying high-resolution gamma spectra by their isotopic content is an essential task in nuclear forensics and other applications. Traditional analysis methods are often time-intensive, but machine learning (ML) may help analysts quickly process many spectra. Such methods tend to rely on abundant, well-labeled data for training. Historical gamma data exists in various fields but is not uniformly useful for supervised ML due to inconsistent labeling. Here, to address some of these challenges, we present a method to classify and organize unlabeled data from high-purity germanium detectors using an autoencoding neural network (autoencoder). We trained dense autoencoders to compress gamma data into latent representations that enable efficient data characterization. By clustering the encoded spectra or lower-dimensional mappings of them, we identified and removed portions of over-abundant data categories, resulting in a more balanced dataset and improved autoencoder performance. This encoding and clustering pipeline also enabled the organization of spectra into self-consistent categories. Finally, we found that encoded representations showed potential as inputs for semi-supervised learning of nuclide identification (NID) labels, achieving an average F1 score of 0.85 ± 0.03 when mapping encodings to a set of 65 isotope labels.

Autoencoders↗
NASA NTRS1972

A tentative identification of /C-13/H4 and an estimate of C-12/C-13 in the atmosphere of Jupiter.

Laboratory spectra of the 3nu(sub 3) band of (C-13)H4 at 1.1 micron were analyzed along with high-resolution image-tube spectra of Jupiter in the appropriate spectral region. Comparison of several J-multiplets in these spectra resulted in the identification of (C-13)H4 in the atmosphere of Jupiter. A Jovian C-12/C-13 isotopic abundance ratio of 110 (plus or minus 35) has been derived from the equivalent width of the R(2) multiplet measured on the two best spectrograms.

Fox, K.↗
NASA NTRS1986

Primordial material in meteorites

Primordial is a term which applied to material that entered the solar system early and became incorporated into a meteorite without totally losing its identity. Identification of such material surviving in meteorites is so far solely through recognition of anomalous isotopic compositions of generally macroscopic entities contained within those meteorites. Isotopic anomalies are, by definition, isotopic compositions which differ from the canonical solar system abundances in ways which cannot be explained in terms of local processes such as mass dependent fractionation, cosmic ray induced spallation or decay of radionuclides. A comprehensive account of isotopic anomalies is impractical here, so it is necessary to be selective. Issues which are potentially addressable through the study of such primordial material are examined. Those issues will be illustrated with specific, but not exhaustive, examples.

Kerridge, J. F.↗
NASA NTRS1994

Penetration of multiple thin films in micrometeorite capture cells

As part of a continuing effort to develop cosmic dust detectors/collectors for use in space, we performed a series of hypervelocity impact experiments on combined sensor/capture-cell assemblies using 10-200-micron-diameter glass projectiles and olivine crystals at velocities of 0.9-14.4 km/s. The design objective of the space-flight instrument is to measure the trajectories of individual particles with sufficient accuracy to permit identification of their parent bodies and to capture enough impactor material to allow chemical and isotopic analyses of samples returned to Earth. Three different multiple-film small-particle capture cell designs (0.1-100-micron-thick Al foils with approx. 10, 100, and 1800 micron spacing) were evaluated for their ability to capture impactor fragments and residue. Their performances were compared to two other types of capture cells, foil covered Ge crystals, and 0.50 and 0.120 g/cu cm aerogels. All capture cells were tested behind multifilm (1.4-6.0-micron-thick) polyvinylidene fluoride (PVDF) velocity/trajectory sensor devices. Several tests were also done without the PVDF sensors for comparison. The results of this study were reported by Simon in a comprehensive report in which the morphology of impacts and impactor residues in various types of capture cells after passage through two PVDF sensor films is discussed. Impactor fragments in selected capture cells from impacts at velocities up to 6.4 km/s were identified using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS).

Simon, Charles G.↗
NASA NTRS1994

Distribution of siderophile and other trace elements in melt rock at the Chicxulub impact structure

Recent isotopic and mineralogical studies have demonstrated a temporal and chemical link between the Chicxulub multiring impact basin and ejecta at the Cretaceous-Tertiary boundary. A fundamental problem yet to be resolved, however, is identification of the projectile responsible for this cataclysmic event. Drill core samples of impact melt rock from the Chichxulub structure contain Ir and Os abundances and Re-Os isotopic ratios indicating the presence of up to approx. 3 percent meteoritic material. We have used a technique involving microdrilling and high sensitivity instrumental neutron activation analysis (INAA) in conjunction with electron microprobe analysis to characterize further the distribution of siderophile and other trace elements among phases within the C1-N10 melt rock.

Schuraytz, B. C.↗
NASA NTRS1987

The Diogene 4 pi detector at Saturne

Diogene, an electronic 4 pi detector, has been built and installed at the Saturne synchrotron in Saclay. The forward angular range (0 degree-6 degrees) is covered by 48 time-of-flight scintillator telescopes that provide charge identification. The trajectories of fragments emitted at larger angles are recorded in a cylindrical 0.4-m3 Pictorial Drift Chamber (PDC) surrounding the target. The PDC is inside a 1-T magnetic field; the axis of the PDC cylinder and the magnetic field are parallel to the beam. Good identification has been obtained for both positive and negative pi mesons and for hydrogen and helium isotopes. Multiplicities in relativistic nucleus-nucleus reactions up to 40 have been detected, limited mainly by the present electronics.

Non-NASA Center↗
NASA NTRS2011

Spatially Resolved, In Situ Carbon Isotope Analysis of Archean Organic Matter

Spatiotemporal variability in the carbon isotope composition of sedimentary organic matter (OM) preserves information about the evolution of the biosphere and of the exogenic carbon cycle as a whole. Primary compositions, and imprints of the post-depositional processes that obscure them, exist at the scale of individual sedimentary grains (mm to micron). Secondary ion mass spectrometry (SIMS) (1) enables analysis at these scales and in petrographic context, (2) permits morphological and compositional characterization of the analyte and associated minerals prior to isotopic analysis, and (3) reveals patterns of variability homogenized by bulk techniques. Here we present new methods for in situ organic carbon isotope analysis with sub-permil precision and spatial resolution to 1 micron using SIMS, as well as new data acquired from a suite of Archean rocks. Three analytical protocols were developed for the CAMECA ims1280 at WiscSIMS to analyze domains of varying size and carbon concentration. Average reproducibility (at 2SD) using a 6 micron spot size with two Faraday cup detectors was 0.4 %, and 0.8 % for analyses using 1 micron and 3 micron spot sizes with a Faraday cup (for C-12) and an electron multiplier (for C-13). Eight coals, two ambers, a shungite, and a graphite were evaluated for micron-scale isotopic heterogeneity, and LCNN anthracite (delta C-13 = -23.56 +/- 0.1 %, 2SD) was chosen as the working standard. Correlation between instrumental bias and H/C was observed and calibrated for each analytical session using organic materials with H/C between 0.1 and 1.5 (atomic), allowing a correction based upon a C-13H/C-13 measurement included in every analysis. Matrix effects of variable C/SiO2 were evaluated by measuring mm to sub-micron graphite domains in quartzite from Bogala mine, Sri Lanka. Apparent instrumental bias and C-12 count rate are correlated in this case, but this may be related to a crystal orientation effect in graphite. Analyses of amorphous Archean OM suggest that instrumental bias is consistent for 12C count rates as low as 10% relative to anthracite. Samples from the ABDP-9 (n=3; Mount McRae Shale, approximately 2.5 Ga), RHDH2a (n=2; Carrawine Dolomite and Jeerinah Fm, approximately 2.6 Ga), WRL1 (n=3; Wittenoom Fm, Marra Mamba Iron Formation, and Jeerinah Fm, approximately 2.6 Ga), and SV1 (n=1; Tumbiana Fm, approximately 2.7 Ga) drill cores, each previously analyzed for bulk organic carbon isotope composition, yielded 100 new, in situ data from Neoarchean sedimentary OM. In these samples, delta C-13 varies between -53.1 and -28.3 % and offsets between in situ and bulk compositions range from -8.3 to 18.8%. In some cases, isotopic composition and mode of occurrence (e.g. morphology and mineral associations) are statistically correlated, enabling the identification of distinct reservoirs of OM. Our results support previous evidence for gradients of oxidation with depth in Neoarchean environments driven by photosynthesis and methane metabolism. The relevance of these findings to questions of bio- and syngenicity as well as the alteration history of previously reported Archean OM will be discussed.

Williford, Kenneth H.↗
NASA NTRS2000

Participation in the Consolidated Infrared Spectrometer (CIRS) as Co-Investigator

During the period under review, Owen-pursued the question of a determination of N-15/N-14 in the atmosphere of Saturn, to be carried out by CIRS when Cassini is in orbit about the planet. There are presently no determinations of this important isotope ratio in Saturn, but a study of the 10 microns spectral region of Jupiter has led to the identification of (N-15)H3 lines with the short Wavelength Spectrometer (SWS) of ISO. The resulting determination was a value of N-15/N-14 = 1.9 (+0.9/-1.0) x 10(exp -3) for this giant planet. This number is decidedly lower than the terrestrial value of 3.66 x 10(exp -3) for molecular nitrogen in the Earth's atmosphere. It is much lower than a direct measurement of N-15/N-14 =5 (+2 /-1) x 10(exp -3) in the solar wind by Kallenbach et al. The latter discrepancy is especially surprising in that Jupiter and the sun are expected to have identical isotope ratios: deep mixing on the sun that would dredge up products of nucleosynthesis from the solar interior is not known to occur. Both Fouchet et al. and Kallenbach et al. suggested that some as yet unknown fractionation process in Jupiter's upper atmosphere might act to enrich N-14 above the NH3 clouds, at the 400 mb pressure level corresponding to the ISO observation. A new measurement of the nitrogen isotopes on Jupiter has just become available from the in situ mass spectra recorded by the Galileo Probe Mass Spectrometer. It is N-15/N-14 = 2.3 +/- 0.3 x 10(exp -3). This determination refers to a pressure level greater than 0.8 mb, weighted toward 2 bars. This new result validates the essential correctness of the Fouchet et al. measurement while greatly reducing the uncertainty. It thus appears that the Kallenbach et al. value must somehow be in error. Further support for this conclusion comes from the upper limit of N-15/N-14 less than 2.8 x 10(exp -3) set for solar wind nitrogen implanted in lunar grains.

Owen, Tobias C.↗
NASA NTRS2014

Assessing the Origins of Aliphatic Amines in the Murchison Meteorite from their Compound-Specific Carbon Isotopic Ratios and Enantiomeric Composition

The study of meteoritic organic compounds provides a unique window into the chemical inventory of the early Solar System and prebiotic chemistry that may have been important for the origin of life on Earth. Multiple families of organic compounds have been extracted from the Murchison meteorite, which is one of the most thoroughly studied carbonaceous chondrites. The amino acids extracted from Murchison have been extensively analyzed, including measurements of non-terrestrial stable isotopic ratios and discoveries of L-enantiomeric excesses for alpha-dialkyl amino acids, notably isovaline. However, although the isotopic signatures of bulk amine-containing fractions have been measured, the isotopic ratios and enantiomeric composition of individual aliphatic amines, compounds that are chemically related to amino acids, remain unknown. Here, we report a novel method for the extraction, separation, identification and quantitation of aliphatic monoamines extracted from the Murchison meteorite. Our results show a complete suite of structural isomers, with a larger concentration of methylamine and ethylamine and decreasing amine concentrations with increasing carbon number. The carbon isotopic compositions of fourteen meteoritic aliphatic monoamines were measured, with delta C-13 values ranging from +21% to +129%, showing a decrease in C-13 with increasing carbon number, a relationship that may be consistent with the chain elongation mechanism under kinetic control previously proposed for meteoritic amino acids. We also found the enantiomeric composition of sec-butylamine, a structural analog to isovaline, was racemic within error, while the isovaline extracted from the same Murchison piece showed an L-enantiomeric excess of 9.7; this result suggested that processes leading to enantiomeric excess in the amino acid did not affect the amine. We used these collective data to assess the primordial synthetic origins of these meteoritic aliphatic amines and their potential linkage to meteoritic amino acids.

prebiotic chemistry↗
DOE OSTI2023

Simulation studies for beam commissioning at FRIB Advanced Rare Isotope Separator

The Facility for Rare Isotope Beams (FRIB) includes a powerful superconducting driver accelerator and an Advanced Rare Isotope Separator (ARIS). The ARIS collects and purifies the rare isotope fragments of interest for experiments in nuclear physics, nuclear astrophysics, fundamental symmetries, etc. ARIS consists of a vertical pre-separator and downstream horizontal separator section (C-Bend). Each section can provide a high-resolution separation alternatively. The resolution reduction due to the emittance induced by momentum compression can be avoided by isotope separation in different dispersive planes. Beam commissioning of ARIS for the first experiments was completed and demonstrated particle identification of fragments. The beam tuning in ARIS largely relies on numerical simulations since the limited space for diagnostics. Here, we report the result of the beam trajectory correction, transverse matching, and beam-based misalignment studies at ARIS.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1988

Ureilites are not igneous differentiates

Although most all meteorites are as old as the solar system (4.5 billion years), they can be subdivided into primitive and evolved groups, depending on the extent of their chemical and physical processing. Primitive meteorites, most of which are chondrites, are assemblages of dust and millimeter-sized pellets from the presolar nebula, which were not extensively heated and processed since their assembly. Thus they provide information about the conditions in the nebular cloud. Many of the evolved meteorites are achondrites, which are igneous rocks produced by melting on or within an asteroidal object known as the parent body. A major unsolved problem in solar system studies is identification of the source of heat which led to melting of the achondrites. The role of oxygen isotopes in establishing genetic relationships among meteorites is examined.

Clayton, Robert N.↗
NASA NTRS2012

Status of the Stardust ISPE and the Origin of Four Interstellar Dust Candidates

Some bulk properties of interstellar dust are known through infrared and X-ray observations of the interstellar medium. However, the properties of individual interstellar dust particles are largely unconstrained, so it is not known whether individual interstellar dust particles can be definitively distinguished from interplanetary dust particles in the Stardust Interstellar Dust Collector (SIDC) based only on chemical, mineralogical or isotopic analyses. It was therefore understood from the beginning of the Stardust Interstellar Preliminary Examination (ISPE) that identification of interstellar dust candidates would rest on three criteria - broad consistency with known extraterrestrial materials, inconsistency with an origin as secondary ejecta from impacts on the spacecraft, and consistency, in a statistical sense, of observed dynamical properties - that is, trajectory and capture speed - with an origin in the interstellar dust stream. Here we quantitatively test four interstellar dust candidates, reported previously [1], against these criteria.

Westphal, A. J.↗
DOE OSTI2025

Direct Reactions and Spectroscopy with Hydrogen Targets at the RIBF

The implementation of MINOS, a liquid-hydrogen target and vertex-tracking system, at the Radioactive Isotope Beam Factory (RIBF) of the RIKEN Nishina Center has led to numerous nuclear physics discoveries. In experiments involving rare-isotope beams at intermediate energies, MINOS was integrated with the DALI2 + γ-ray spectrometer and other auxiliary devices. These were positioned in front of both the ZeroDegree Spectrometer and the SAMURAI magnetic spectrometers for the identification of ejectiles following quasi-free scattering direct reactions. Notable outcomes include the first spectroscopy of unstable doubly magic nucleus, investigations into multi-neutron decays, and the study of shell evolution along isotopic chains. These studies have significantly advanced our understanding of nuclear structure, as well as the mechanism of direct reactions with fast beams. Simultaneously, these direct reactions enabled raising new physics questions and paved the way for next-generation experimental setups to address them. Through the combination of particle- and γ-spectroscopy with a broad range of nuclear reactions, new frontiers will be established in our understanding of nuclear structure and reaction mechanisms. Here, we review the past ten years of studies on direct reactions and spectroscopy of exotic nuclei with liquid-hydrogen targets at the RIBF and define a vision for the future.

Bertulani, Carlos A [East Texas A & M Univ., Comme↗
NASA NTRS1988

Accretion and primary differentiation of Mars

In collecting samples from Mars to address questions such as whether Mars accreted homogeneously or heterogeneously, how Mars segregated into a metallic core and silicate mantle, and whether Mars outgassed catastrophically coincident with accretion or more serenely on a longer timescale, we must be guided by our experience in addressing these questions for the Earth, Moon, and igneous meteorite parent bodies. A key measurement to be made on any sample returned from Mars is its oxygen isotopic composition. A single measurement will suffice to bind the SNC meteorites to Mars or demonstrate that they cannot be samples of that planet. A positive identification of Mars as the SNC parent planet will permit all that has been learned from the SNC meteorites to be applied to Mars with confidence. A negative result will perhaps be more exciting in forcing us to look for another object that has been geologically active in the recent past. If the oxygen isotopic composition of Earth and Mars are established to be distinct, accretion theory must provide for different compositions for two planets now separated by only 0.5 AU.

Drake, Michael J.↗
NASA NTRS1976

Directory of aerospace safety specialized information sources, volume 2

A handbook of organizations and experts in specific and well-defined areas of safety technology is presented. It is designed for the safety specialist as an aid for locating both information sources and individual points of contact (experts) in engineering related fields. The file covers sources of data in aerospace design, tests, and operations, as well as information on hazard and failure cause identification, accident analysis, and materials characteristics. Other related areas include the handling and transportation of hazardous chemicals, radioactive isotopes, and liquified natural gases.

Rubinstein, R. I.↗
NASA NTRS2008

Exploration of the Habitability of Mars with the SAM Suite Investigation on the 2009 Mars Science Laboratory

The 2009 Mars Science Laboratory (MSL) with a substantially larger payload capability that any other Mars rover, to date, is designed to quantitatively assess a local region on Mars as a potential habitat for present or past life. Its goals are (1) to assess past or present biological potential of a target environment, (2) to characterize geology and geochemistry at the MSL landing site, and (3) to investigate planetary processes that influence habitability. The Sample Analysis at Mars (SAM) Suite, in its final stages of integration and test, enables a sensitive search for organic molecules and chemical and isotopic analysis of martian volatiles. MSL contact and remote surface and subsurface survey Instruments establish context for these measurements and facilitate sample identification and selection. The SAM instruments are a gas chromatograph (GC), a mass spectrometer (MS), and a tunable laser spectrometer (TLS). These together with supporting sample manipulation and gas processing devices are designed to analyze either the atmospheric composition or gases extracted from solid phase samples such as rocks and fines. For example, one of the core SAM experiment sequences heats a small powdered sample of a Mars rock or soil from ambient to -1300 K in a controlled manner while continuously monitoring evolved gases. This is followed by GCMS analysis of released organics. The general chemical survey is complemented by a specific search for molecular classes that may be relevant to life including atmospheric methane and its carbon isotope with the TLS and biomarkers with the GCMS.

Mahaffy, P. R.↗
NASA NTRS2016

In Situ Analysis of Martian Regolith with the SAM Experiment During the First Mars Year of the MSL Mission: Identification of Organic Molecules by Gas Chromatography from Laboratory Measurements

The Sample Analysis at Mars (SAM) instrument onboard the Curiosity rover, is specifically designed for in situ molecular and isotopic analyses of martian surface materials and atmosphere. It contributes to the Mars Science Laboratory (MSL) missions primary scientific goal to characterize the potential past, present or future habitability of Mars. In all of the analyses of solid samples delivered to SAM so far, chlorinated organic compounds have been detected above instrument background levels and identified by gas chromatography coupled to mass spectrometry (GC-MS) (Freissinet et al., 2015; Glavin et al., 2013). While some of these may originate from reactions between oxychlorines and terrestrial organic carbon present in the instrument background (Glavin et al., 2013), others have been demonstrated to originate from indigenous organic carbon present in samples (Freissinet et al., 2015). We present here laboratory calibrations that focused on the analyses performed with the MXT-CLP GC column (SAM GC-5 channel) used for nearly all of the GC-MS analyses of the martian soil samples carried out with SAM to date. Complementary to the mass spectrometric data, gas chromatography allows us to separate and identify the species analyzable in a nominal SAM-GC run time of about 21 min. To characterize the analytical capabilities of this channel within the SAM Flight Model (FM) operating conditions on Mars, and their implications on the detection of organic matter, it is required to perform laboratory experimental tests and calibrations on spare model components. This work assesses the SAM flight GC-5 column efficiency, confirms the identification of the molecules based on their retention time, and enables a better understanding of the behavior of the SAM injection trap (IT) and its release of organic molecules. This work will enable further optimization of the SAM-GC runs for additional samples to be analyzed during the MSL mission.

analysis↗
NASA NTRS1994

Acquisition and processing of data for isotope-ratio-monitoring mass spectrometry

Methods are described for continuous monitoring of signals required for precise analyses of 13C, 18O, and 15N in gas streams containing varying quantities of CO2 and N2. The quantitative resolution (i.e. maximum performance in the absence of random errors) of these methods is adequate for determination of isotope ratios with an uncertainty of one part in 10(5); the precision actually obtained is often better than one part in 10(4). This report describes data-processing operations including definition of beginning and ending points of chromatographic peaks and quantitation of background levels, allowance for effects of chromatographic separation of isotopically substituted species, integration of signals related to specific masses, correction for effects of mass discrimination, recognition of drifts in mass spectrometer performance, and calculation of isotopic delta values. Characteristics of a system allowing off-line revision of parameters used in data reduction are described and an algorithm for identification of background levels in complex chromatograms is outlined. Effects of imperfect chromatographic resolution are demonstrated and discussed and an approach to deconvolution of signals from coeluting substances described.

NASA Discipline Exobiology↗