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NASA NTRS1975

Air pollution source identification

The techniques available for source identification are reviewed: remote sensing, injected tracers, and pollutants themselves as tracers. The use of the large number of trace elements in the ambient airborne particulate matter as a practical means of identifying sources is discussed. Trace constituents are determined by sensitive, inexpensive, nondestructive, multielement analytical methods such as instrumental neutron activation and charged particle X-ray fluorescence. The application to a large data set of pairwise correlation, the more advanced pattern recognition-cluster analysis approach with and without training sets, enrichment factors, and pollutant concentration rose displays for each element is described. It is shown that elemental constituents are related to specific source types: earth crustal, automotive, metallurgical, and more specific industries. A field-ready source identification system based on time and wind direction resolved sampling is described.

Fordyce, J. S.↗

NASA NTRS1980

Fission xenon in troctolite 76535

Xenon released in stepwise heating of troctolite 76535 shows remarkable similarity to that from the gas-rich breccias. The low temperature fractions are highly enriched in fissiogenic xenon from Pu-244. Although the quantity of fission xenon is not inconsistent with reported age data, release patterns demonstrate that this component is not due to in situ decay. However, in contrast with the gas-rich breccias, the parentless radionuclear component in 76535 is not accompanied by solar wind xenon. Mechanisms for the emplacement of this component in 76535 cannot, therefore, involve exposure on the lunar surface but most likely involve adsorption along intergranular boundaries or thermally driven redistribution. The fact that xenon released from a gas-poor igneous cumulate can mimic that from gas-rich breccias, except for the presence of solar wind xenon in the latter, suggests that direct exposure to space is not required for the incorporation of these weakly bound, surface-correlated, parentless radionuclear components in lunar samples.

Hohenberg, C. M.↗

NASA NTRS1987

The effect of pressure and excitation energy on the isotopic fractionation in the formation of ozone by discharge of O2

Isotopic fractionation processes in the formation of O3 by discharge (at 20 kV and 3 MHz) of O2 in a fused silica container at 77 K are investigated experimentally, with a focus on the effects of changes in the isotopic abundances in the predischarge O2, the O2 pressure, and the excitation energy on the isotope abundances in the postdischarge O2 and O3. The results are presented in extensive tables and graphs and characterized in detail, and good general agreement is found with data obtained using 60-kHz excitation (Yang and Epstein, 1987). It is shown that O-17 and O-18 enrichment of the residual O2 (when the predischarge gas is enriched) or of the O3 (when atmospheric isotope abundances are used) can occur independently of one another. It is inferred that the rate of anharmonic predissociation of vibrationally hot O3 depends on the symmetry and mass of the O3 molecules. The significance of the present findings for studies of anomalous oxygen isotope abundances in meteorites is indicated.

Yang, Jongmann↗

NASA NTRS2005

The Martian Soil as a Geochemical Sink for Hydrothermally Altered Crustal Rocks and Mobile Elements: Implications of Early MER Results

Hydrothermal and aqueous alteration can explain some of the exciting results from the MER team s analyses of the martian soil, including the major elements, mobile elements, and the nickel enrichment. Published results from the five lander missions lead to the following conclusions: 1) The soil appears to be globally mixed and basaltic with only small local variations in chemistry. Relative to martian basaltic meteorites and Gusev rocks the soils are depleted in the fluid-mobile element calcium, but only slightly enriched to somewhat depleted in iron oxide. 2) The presence of olivine in the soils based on M ssbauer data argues that the soil is only partly weathered and is more akin to a lunar regolith than a terrestrial soil. 3) The presence of bromine along with sulfur and chlorine in the soils is consistent with addition of a mobile element component to the soil.

Newsom, H. E.↗

NASA NTRS1997

Smoldering News From STS-77 Endeavour

The Microgravity Smoldering Combustion (MSC) experiment lifted off aboard the Space Shuttle Endeavour for its second flight in May 1996, as part of the STS-77 mission. This experiment is part of a series of studies focused on the smolder characteristics of porous combustible materials in a microgravity environment. Smoldering is a nonflaming form of combustion that takes place in the interior of combustible materials. Common examples of smoldering are nonflaming embers, charcoal briquettes, and cigarettes. The objective of this study is to provide a better understanding of the controlling mechanisms of smoldering in microgravity and normal Earth gravity (1g). As with other forms of combustion, gravity affects the availability of air and transport of heat, and therefore, the rate of combustion. The results of the microgravity experiments will be compared with identical ones carried out in 1g. In addition, they will be used to verify present theories of smolder combustion and will provide new insights into the process of smoldering combustion, enhancing our fundamental understanding of this frequently encountered combustion process and guiding improvements in fire safety practices. Two smoldering combustion tests with polyurethane foam were successfully accomplished during the STS-77 mission. The tests investigated smoldering combustion in a quiescent (no-flow) enriched oxygen environment, and in an air environment with a 2-mm/sec airflow through the fuel sample. The primary data from the tests are the ignition characteristics, spread rate, smolder reaction temperature, and products of combustion (solid and gas). On both the first mission on STS-69 and the second mission on STS-77, a smolder front propagated the length of the forced-flow samples, with the spread rate between the corresponding upward and downward 1g smolder rates. Neither of the quiescent cases propagated combustion (the first case was due in part to a problem with the experiment electronics). These results show a dramatic difference from the normal gravity results, where smolder propagation is very rapid and complete for both of these conditions. The experiment was conceived by Prof. A. Carlos Fernandez-Pello at the University of California-Berkeley. The MSC hardware was designed and built at the NASA Lewis Research Center by a team of civil servants and contractors from NYMA, Inc., and Aerospace Design & Fabrication, Inc. (ADF). The hardware consists of two sealed aluminum combustion chambers (each being a half a cylinder). The chambers hold the MSC test section, data acquisition electronics, power distribution electronics, and instrumentation. The hardware is fitted into a 5-ft(sup 3) Get-Away-Special (GAS) canister that is mounted in the shuttle cargo bay. The test section consists of a quartz cylinder that contains the polyurethane foam sample and an igniter. This igniter, which is an electrically heated wire sandwiched between two porous ceramic disks, is mounted in contact with the end of the foam sample. An array of 12 thermocouples placed axially and radially along the foam sample provide temperature histories, which are used to determine the rate of smolder propagation, and the characteristics of the reaction.

Koudelka, John M.↗

NASA NTRS2020

A Multi-Sims Investigation of Water Content and D/H Ratios in Roberts Massif 04262 with Insight to Sources of Hydrogen in Maskelynite

We want to define the H2O content ([H2O]) and hydrogen (H) isotope composition of meteoritic material from Mars [1-3] with motivation to understand Mars’ volatile history, constrain geochemical signatures of interior water reservoirs (i.e. the Martian mantle) and explore effects of planetary (e.g. planet formation, magma ocean degassing) and local (e.g. volcanic degassing, impact melting and degassing) processes on H incorporated in minerals. Secondary ion mass spectrometry (SIMS) allows multiple avenues to address these questions. However, application to (1) precious astromaterials and (2) low level H measurements, pose specific challenges that are further complicated when combined. We present preliminary data of a multi-approach (SIMS vs. NanoSIMS) study of H in Roberts Massif 04262 (RBT 04262), an enriched lherzolitic shergottite with nonpoikilitic (NP) and poikilitic (P) lithologies [4]. We analyze olivine, pyrox-ene, and melt inclusions to compare indigenous mantle water, with impact-generated maskelynite to investigate H signatures due to shock.

Dudley, J. M.↗

DOE OSTI2022

AGR-5/6/7 Final Release-to-Birth Ratio Data Analysis

AGR-5/6/7 is the last of a series of Advanced Gas Reactor (AGR) experiments conducted in the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) in support of development and qualification of tristructural isotropic (TRISO) low-enriched fuel for use in the high-temperature gas cooled reactor (HTGR). AGR configuration and irradiation conditions are based on prismatic HTGR technology that is distinguished primarily through the use of helium coolant, a low-power-density ceramic core capable of withstanding very high temperatures, and TRISO-coated particle fuel. The AGR tests provide valuable irradiation-performance data to support fuel process development, qualify fuel for normal operation and accident conditions, and support development and validation of fuel performance and fission-product (FP) transport models and codes. Each AGR test consists of multiple independently controlled and monitored capsules containing fuel compacts placed in a graphite cylinder shrouded by a steel shell. Release-to-birth ratios (R/B) for fission-gas isotopes released from each capsule are calculated from release rates, measured by germanium detectors in the Fission Product Monitoring System (FPMS) installed downstream from each capsule, and birth rates calculated using numerical models of FG generation. The R/Bs are a critical measure of the ability of the fuel kernel, the particle coating layers, and the compact matrix to retain fission-gas atoms, preventing their release into the sweep-gas flow, and the impact of initially defective particles and/or particle-coating failures that occur during irradiation. For fission-gas isotopes, particle failure is defined as failure of all coating layers, allowing gaseous fission atoms to escape from a particle. During the first five cycles (162B ? 165A), R/Bs were stable in the 10-8?10-6 range, and no in-pile particle failures were observed, based on the gross gamma counts. The maximum R/B value of around 2 ? 10-6 for Kr-85m resulted from the presence of as-fabricated exposed kernels (based on the high exposed kernel fraction), the dispersed uranium, and high fuel particle temperatures in Capsule 1. Comparison of capsule-measured R/Bs from these early cycles to predictions using the previously developed AGR R/B model demonstrated FG release from the AGR-5/6/7 TRISO fuel was comparable to that of previous experiments. In addition, the Kr-85m R/B per-exposed-kernel values are comparable to R/B values obtained in AGR-3/4 irradiation experiment and four irradiation experiments performed during 1980s: (1) HRB-17/18, (2) COMEDIE-BD1, (3) HFR B1, and (4) HRB-21. In contrast, all measured R/B values are lower than predictions by the commonly used Richards and German models, which are intentionally conservative. A large number of in-pile particle failures occurred in Capsule 1 by the end of Cycle 166A. During the final four cycles (166A ? 168A), apparent damage to the Capsule 1 gas line appeared to cause FG leakage from that capsule into the other four capsules, resulting in an increase in fission gas (FG) detected in the effluent for all capsules. Isolation of the Capsule 1 gas line during the last three cycles also prevented measurement of its FG release. Thus, R/Bs in all capsules after Cycle 166A are highly uncertain because of undefined amount of leakage from Capsule 1, especially for long-lived isotopes. A few hundred in-pile particle failures were estimated for Capsule 1 before the end of Cycle 166A, but the total number of failures is unknown due to the lack of FG release data in the later cycles. Based primarily on evidence from the gross gamma counts during Cycle 168A, approximately 15 particles failed in Capsule 3 and four particles failed in Capsule 2. In-pile failures in Capsule 3 were anticipated because this capsule was designed to operate beyond the HTGR normal operating temperature range. In contrast, no in-pile failures were identified in the top two capsules (4 and 5) based on the absence of the typical spikes in gross gamma counts and low failure estimates using the AGR model, developed in INL/EXT-14-32970, for R/B of the short-lived isotopes (Kr-89 and Xe-137) with minimal leakage from Capsule 1.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

NASA NTRS1991

Analyzing remote sensing geobotanical trends in Quetico Provincial Park, Ontario, Canada, using digital elevation data

A 10 x 13-km area in Quetico Provincial Park, Canada has been studied using a digital elevation model to separate different drainage classes and to examine the influence of site factors and lithology on vegetation. Landsat Thematic Mapper data have been classified into six forest classes of varying deciduous-coniferous cover through nPDF, a procedure based on probability density functions. It is shown that forests growing on mafic lithologies are enriched in deciduous species, compared to those growing on granites. Of the forest classes found on mafics, the highest coniferous component was on north facing slopes, and the highest deciduous component on south facing slopes. Granites showed no substantial variation between site classes. The digital elevation derived site data is considered to be an important tool in geobotanical investigations.

Warner, Timothy A.↗

DOE OSTI2024

Improving streamflow predictions across CONUS by integrating advanced machine learning models and diverse data

Accurate streamflow prediction is crucial to understand climate impacts on water resources and develop effective adaption strategies. A global long short-term memory (LSTM) model, using data from multiple basins, can enhance streamflow prediction, yet acquiring detailed basin attributes remains a challenge. To overcome this, we introduce the Geo-vision transformer (ViT)-LSTM model, a novel approach that enriches LSTM predictions by integrating basin attributes derived from remote sensing with a ViT architecture. Applied to 531 basins across the Contiguous United States, our method demonstrated superior prediction accuracy in both temporal and spatiotemporal extrapolation scenarios. Geo-ViT-LSTM marks a significant advancement in land surface modeling, providing a more comprehensive and effective tool for better understanding the environment responses to climate change.

Tayal, Kshitij↗

NASA NTRS2002

Phosphorus Equilibria Among Mafic Silicate Phases

Phosphorus incorporation in major rock-forming silicate minerals has the following implications: (1) Reactions between phosphorus-hosting major silicates and accessory phosphates, which are also major trace element carriers, may control the stability of the latter and thus may affect the amount of phosphorus and other trace elements released to the coexisting melt or fluid phase. (2) Less of a phosphate mineral is needed to account for the bulk phosphorus of planetaty mantles. (3) During partial melting of mantle mineral assemblages or equilibrium fractional crystallization of basaltic magmas, and in the absence or prior to saturation with a phosphate mineral, silicate melts may become enriched in phosphorus, especially in the geochemically important low melt fraction regime, Although the small differences in the ionic radii of IVp5+, IVSi4+, and IV Al3+ makes phosphoms incorporation into crystalline silicates perhaps unsurprising, isostructural silicate and phosphate crystalline solids do not readily form solutions, e.g., (Fe, Mg)2SiO4 vs. LiMgPO4, SiO)2 VS. AlPO4. Nonetheless, there are reports of, poorly characterized silico-phosphate phases in angrites , 2-4 wt% P2O5 in olivine and pyroxene grains in pallasites and reduced terestrial basalts which are little understood but potentially useful, and up to 17 wt% P2O5 in olivine from ancient slags. However, such enrichments are rare and only underscore the likelihood of phosphoms incorporation in silicate minerals. The mechanisms that allow phosphorus to enter major rock-forming silicate minerals (e.g., Oliv, Px, Gt) remain little understood and the relevant data base is limited. Nonetheless, old and new high-pressure (5-10 GPa) experimental data suggest that P2O5 wt% decreases from silica-poor to silica-rich compositions or from orthosilicate to chain silicate structures (garnet > olivine > orthopyroxene) which implies that phosphorus incorporation in silicates is perhaps more structure-than site-specific. The data also indicate that DXVliQP2O5 decrease in the same order, but DOVLiQP2O5 and DOpx/LiQP205 are likely constant, respectively equal to 0.08(3) and 0.007(4), in contrast, DG1ILiQP205 increases from 0.15(3) to 0.36(10) as garnet becomes majoritic, thus silica-enriched, and may also depend on liquid composition (SiO2, P2O5 and Na2O wt%).

Berlin, Jana↗

NASA NTRS2003

Mars: Detaching of the Free Water Signature (FWS) Presence Regions on the Base of HEND/ODYSSEY Data and Their Correlation with Some Permafrost Features from MOC Data

The first results from global mapping of the neutron albedo from Mars by HEND instrument have shown the noticeable deficit of both the epithermal (EN) and the fast (FN) neutrons counts rate in the high latitudes regions of both hemispheres of the planet. The deficit is indicative for high enriching of the surface regolith by hydrogen, which may correspond to amount of any water phases and forms. The objectives of our study are the spatial and temporal variations of the free water (ice) signature in the Martian surface layer on the base of HEND/ODYSSEY data and their correlation with spatial spreading of some permafrost features, mapped on the base of MOC images. For the study we used the results of the global mapping (pixel 5 x5 ) of EN and FN albedo, realized by HEND/ODYSSEY in the period from 17 February to 10 December 2002 year.

Kuzmin, R. O.↗

DOE OSTI2022

Improved evaluation of safeguards parameters from spent fuel measurements with the Differential Die-Away (DDA) instrument

The Differential Die-Away (DDA) technique is a highly sensitive non-destructive assay method for characterizing and detecting the presence of fissile material within an item of interest. DDA utilizes a series of pulses from a neutron generator (NG) to actively interrogate an item of interest. The die-away time of the neutron population induced by this active interrogation and the integral of the total differential die-away signal can be used to characterize items such as nuclear waste drums and spent nuclear fuel assemblies. In this work, Los Alamos National Laboratory (LANL) conceptualized, designed, and fabricated a DDA instrument that was deployed for field test measurements at the Central Interim Storage Facility for Spent Nuclear Fuel (Clab) in Oskarshamn, Sweden. The instrument performed multiple static measurements at fixed locations and dynamic axial scans of 15 pressurized water reactor (PWR) and 10 boiling water reactor (BWR) spent fuel assemblies, collecting both passive and active measurement data. The static assays of the assemblies measured the differential die-away signal, die-away time, and total passive neutron emission rate to create calibration curves for the evaluation of assembly multiplication, burnup, initial enrichment, effective fissile mass, and total elemental plutonium mass. Each calibration curve was optimized by minimizing the relative root mean square error (RRMSE) of assembly assay results compared to declared assembly parameters. The same quantities were also measured with the axial scans, and the resulting data were applied in two ways: (1) in the creation of calibration curves to improve evaluation of the same safeguards parameters as static assays, and (2) for comparison to simulation. In most cases, across both PWR and BWR assemblies, axial scan data improved the estimation of the above parameters, quantified by decreasing the calibration curve RRMSE. These axial scan results demonstrate the ability of the DDA instrument and analysis method to characterize spent PWR and BWR fuel as well as, or better than, a static assay of the same assembly. Furthermore, the DDA instrument’s unique ability to obtain both active and passive data in a single, axial scan of an entire spent fuel assembly represents a more efficient and accurate way of assaying spent fuel for verification purposes. These results represent a significant advancement for characterizing spent nuclear fuel compared to current technologies.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2021

NPRL2 reduces the niraparib sensitivity of castration-resistant prostate cancer via interacting with UBE2M and enhancing neddylation

In this study, we explored the regulatory effects of nitrogen permease regulator 2-like (NPRL2) on niraparib sensitivity, a PARP inhibitor (PARPi) in castrate-resistant prostate cancer (CRPC). Data from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) program were retrospectively examined. Gene-set enrichment analysis (GSEA) was conducted between high and low NRPL2 expression prostate adenocarcinoma (PRAD) cases in TCGA. CCK-8 assay, Western blot analysis of apoptotic proteins, and flow cytometric analysis of apoptosis were applied to test niraparib sensitivity. Immunofluorescent (IF) staining and co-immunoprecipitation (co-IP) were conducted to explore the proteins interacting with NPRL2. Results showed that the upregulation of a canonical protein-coding transcript of NPRL2 (ENST00000232501.7) is associated with an unfavorable prognosis. Bioinformatic analysis predicts a physical interaction between NPRL2 and UBE2M, which is validated by a following Co-IP assay. This interaction increases NPRL2 stability by reducing polyubiquitination and proteasomal degradation. Depletion of NPRL2 or UBE2M significantly increases the niraparib sensitivity of CRPC cells and enhances niraparib-induced tumor growth inhibition in vivo. NPRL2 cooperatively enhances UBE2M-mediated neddylation and facilitates the degradation of multiple substrates of Cullin-RING E3 ubiquitin ligases (CRLs). In conclusion, this study identified a novel NPRL2-UBE2M complex in modulating neddylation and niraparib sensitivity of CRPC cells. Therefore, targeting NPRL2 might be considered as an adjuvant strategy for PARPi therapy.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2022

Constraining composition and temperature variations in the mantle transition zone

The mantle transition zone connects two major layers of Earth’s interior that may be compositionally distinct: the upper mantle and the lower mantle. Wadsleyite is a major mineral in the upper mantle transition zone. Here, we measure the single-crystal elastic properties of hydrous Fe-bearing wadsleyite at high pressure-temperature conditions by Brillouin spectroscopy. Our results are then used to model the global distribution of wadsleyite proportion, temperature, and water content in the upper mantle transition zone by integrating mineral physics data with global seismic observations. Our models show that the upper mantle transition zone near subducted slabs is relatively cold, enriched in wadsleyite, and slightly more hydrated compared to regions where plumes are expected. This study provides direct evidence for the thermochemical heterogeneities in the upper mantle transition zone which is important for understanding the material exchange processes between the upper and lower mantle.

58 GEOSCIENCES↗

DOE OSTI2022

TRIPOLI-4 neutronics calculations for IAEA-CRP benchmark of CEFR start-up tests using new libraries JEFF-3.3 and ENDF/B-VIII

Sodium-cooled Fast Reactors (SFR) are one of the promising Generation IV fast reactors. The China Experimental Fast Reactor (CEFR) is a 65 MWth pool-type SFR with a high neutron leakage core using high enriched uranium oxide fuel. The CEFR start-up tests in 2010 consist of series of neutronics experiments. Essential experimental data are available from the 2018 IAEA-CEFR-CRP benchmark document and useful for the validation of neutron transport codes and nuclear data libraries. The TRIPOLI-4 Monte Carlo transport code is a general-purpose neutronics code using continuous-energy nuclear data libraries. It has a rich validation database covering different computational and experimental benchmark data sets to assure the accuracy and credibility of numerical studies. Previous TRIPOLI-4 SFR core physics calculations used mainly MOX fuels. SFR control rod worth studies with TRIPOLI-4 were mainly on big-size cores. To test the modeling capability of TRIPOLI-4 on fuel loading patterns and on variable control rods positions for SFRs and to check recent nuclear data libraries, it is interesting to investigate the CEFR start-up tests in this work, including core states from subcritical to supercritical, control rods and rod group worth, point kinetics parameters, and radial foil activation measurements. TRIPOLI-4 calculation results using new data libraries JEFF-3.3, ENDF/B-VIII, and those of ENDF/B-VII.1 for different CEFR core states are reported here. By means of different options of TRIPOLI-4, control-rod SAs reactivity worth, point kinetics parameters, and radial {sup 237}Np(n,f) fission rate distribution were successfully evaluated. Both ENDF/B-VIII and JEFF-3.3 nuclear data libraries provided reliable results with a difference of 170 +/- 11 pcm in k{sub eff}.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

NASA NTRS1976

Agglutinates and carbon accumulation in Apollo 17 lunar soils

A critical review of maturity with respect to the abundance of implanted solar wind elements (SWE) in lunar soils indicates: (1) that the Rosiwal Principle has limited applicability in determining implantation of SWE in lunar soils, and (2) that despite a depletion of SWE in agglutinitic glass, agglutinates are enriched in SWE due to the presence of buried surfaces of numerous clasts within agglutinates. A statistical analysis of published data of several Apollo 17 soils indicates that the abundance of carbon and, by analogy, the abundance of other SWE are correlatable with the agglutinate content and the mean grain size of lunar soils. Microscopic examination of more than 5000 grains of agglutinates in polished thin sections reveals a wide range of variability in the mineralogy, grain size distribution, degree of recycling, etc., of the clast population in agglutinates. This indicates that the volume-correlated SWE content of agglutinates may vary and need not be constant.

Basu, A.↗

NASA NTRS1977

An XPS /ESCA/ study of lunar surface alteration profiles

We describe several important potential applications of surface analyses in planetology, and discuss some fundamental questions pertinent to the use of X-ray photoemission spectroscopy XPS or Auger electron spectroscopy AES to study complex powder samples. It appears that in addition to specific studies of surface chemistry, XPS may be able to provide useful major element analyses for all elements except hydrogen and perhaps helium and lithium. We provide data on the chemical changes associated with sputtering of a synthetic lunar glass. The surface is depleted in Si and enriched in Ca and Ti with Fe remaining nearly constant in parallel with changes observed during thermal volatilization. No Fe reduction was observed. Composition profiles obtained by sputtering 15301 fines suggest that surface alterations and reduced Fe are confined largely to depths of a few 100 A.

Housley, R. M.↗

NASA NTRS1983

Samarium-146 in the early solar system - Evidence from neodymiun in the Allende meteorite

A carbon-chromite fraction from the Allende C3V chondrite shows strikingly large isotopic enrichments of neodymium-142 (0.47 percent) and neodymium-143 (36 percent). Both apparently formed by alpha decay of samarium-146 and samarium-147 (half-lives 1.03 x 10 to the 8th and 1.06 x 10 to the 11th years), but the isotopic enrichment was greatly magnified by recoil of residual nuclei into a carbon film surounding the samarium-bearing grains. These data provide an improved estimate of the original abundance of extinct samarium-146 in the early solar system, Sm-146/Sm-144 = (4.5 + or - 0.5) x 10 to the -3rd, higher than predicted by some models of p-process nucleosynthesis. It may be possible to use this isotopic pair as a chronometer of the early solar system.

Lugmair, G. W.↗