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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Analysis of orbital occupancy of valence neutron in {sup 15}C through Coulomb breakup reactions

The Coulomb breakup reactions {sup 208}Pb({sup 15}C, {sup 14}C + n){sup 208}Pb and {sup 181}Ta({sup 15}C, {sup 14}C + n){sup 181}Ta have been studied at 68 and 85 A MeV beam energies, respectively, within the framework of the eikonal approximation to investigate the orbital occupancy of valence neutron in the {sup 15}C nucleus. The outcomes of the present work favor 0{sup +} ⊗ 2s{sub 1/2} as the core-neutron coupling for the ground-state structure with 0.91 as a spectroscopic factor.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Electron Captures on {sup 14}N as a Trigger for Helium Shell Detonations

White dwarfs (WDs) that accrete helium at rates ∼10{sup −8} M{sub ⊙} yr{sup −1}, such as those in close binaries with sdB stars, can accumulate large (≳0.1 M{sub ⊙}) helium envelopes, which are likely to detonate. We perform binary stellar evolution calculations of sdB+WD binary systems with MESA, incorporating the important reaction chain {sup 14}N(e{sup −},ν){sup 14}C(α,γ){sup 18}O (NCO), including a recent measurement for the {sup 14}C(α,γ){sup 18}O rate. In large accreted helium shells, the NCO reaction chain leads to ignitions at the dense base of the freshly accreted envelope, in contrast to 3α ignitions, which occur away from the base of the shell. In addition, at these accretion rates, the shells accumulate on a timescale comparable to their thermal time, leading to an enhanced sensitivity of the outcome on the accretion rate history. Hence, time dependent accretion rates from binary stellar evolution are necessary to determine the helium layer mass at ignition. We model the observed sdB+WD system CD −30{sup ∘}11223 and find that the inclusion of these effects predicts ignition of a 0.153 M{sub ⊙} helium shell, nearly a factor of two larger than previous predictions. A shell with this mass will ignite dynamically, a necessary condition for a helium shell detonation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The knockout reaction of {sup 15}C on a {sup 9}Be target at intermediate energies

In this work, neutron knockout reactions of {sup 15}C on a {sup 9}Be target at energy 103 and 250 MeV/nucleon are studied. Using the Eikonal approximation of the Glauber model, total neutron removal cross sections, the stripping and diffractive cross sections as well as {sup 14}C longitudinal momentum distributions are determined in both {sup 15}C ground state and exited states of the wave function. We compared the results of our calculations with the available experimental data obtained recently. The calculated cross sections of {sup 15}C and {sup 14}C reactions, as well as the momentum distribution are in relatively good agreement with available data.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2010

Electric dipole moments in {sup 230,232}U and implications for tetrahedral shapes

The nuclei {sup 230}U and {sup 232}U were populated in the compound nucleus reactions {sup 232}Th({alpha},6n) and {sup 232}Th({alpha},4n), respectively. Gamma rays from these nuclei were observed in coincidence with a recoil detector. A comprehensive set of in-band E2 transitions were observed in the lowest lying negative-parity band of {sup 232}U while one E2 transition was also observed for {sup 230}U. These allowed B(E1;I{sup -{yields}}I{sup +}-1)/B(E2;I{sup -{yields}}I{sup -}-2) ratios to be extracted and compared with systematics. The values are similar to those of their Th and Ra isotones. The possibility of a tetrahedral shape for the negative-parity U bands appears difficult to reconcile with the measured Q{sub 2} values for the isotone {sup 226}Ra.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Nuclear Data Sheets for A = 30

Evaluated spectroscopic data and level schemes from radioactive decay and nuclear reaction studies are presented for {sup 30}F, {sup 30}Ne, {sup 30}Na, {sup 30}Mg, {sup 30}Al, {sup 30}Si, {sup 30}P, {sup 30}S, and {sup 30}Cl. This evaluation for A=30 supersedes the previous evaluation 1998En04. However, some additional information for these nuclides can be found in earlier evaluations 1990En08 and 1978En02. Highlights of this publication are the following: The latest studies (2010StZZ, 2010De26) by fusion evaporation reaction of {sup 14}C and {sup 18}O using GAMMASPHERE array, consisted of 101 Compton-suppressed HPGe detectors, provided new data for {sup 30}Al, {sup 30}Si, and {sup 30}Mg nuclides and extended the level scheme to higher spin states. 2010Se07 reported a new level at 4814(3) keV for {sup 30}S nuclide studied by the {sup 32}S(p,t) reaction. It did not observe the 5168(6) keV level that was reported earlier as a possible doublet by 2007Ba69. In the absence of further experiment, 2010Se07 considers the level as one of the doublets.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Dissolved Organic Carbon 14C in Southern Nevada Groundwater and Implications for Groundwater Travel Times

Dissolved inorganic carbon (DIC) carbon-14 ( 14 C) ages must be corrected for complex chemical and physical reactions and processes that change the amount of 14 C in groundwater as it flows from recharge to downgradient areas. Because of these reactions, DIC 14 C can produce unrealistically old ages and long groundwater travel times that may, or may not, agree with travel times estimated by other methods. Dissolved organic carbon (DOC) 14 C ages are often younger than DIC 14 C ages because there are few chemical reactions or physical processes that change the amount of DOC 14 C in groundwater. However, there are several issues that create uncertainty in DOC 14 C groundwater ages including limited knowledge of the initial (A 0 ) DOC 14 C in groundwater recharge and potential changes in DOC composition as water moves through an aquifer. This study examines these issues by quantifying A 0 DOC 14 C in recharge areas of southern Nevada groundwater flow systems and by evaluating changes in DOC composition as water flows from recharge areas to downgradient areas. The effect of these processes on DOC 14 C groundwater ages is evaluated and DOC and DIC 14 C ages are then compared along several southern Nevada groundwater flow paths. Twenty-seven groundwater samples were collected from springs and wells in southern Nevada in upgradient, midgradient, and downgradient locations. DOC 14 C for upgradient samples ranged from 96 to 120 percent modern carbon (pmc) with an average of 106 pmc, verifying modern DOC 14 C ages in recharge areas, which decreases uncertainty in DOC 14 C A 0 values, groundwater ages, and travel times. The HPLC spectra of groundwater along a flow path in the Spring Mountains show the same general pattern indicating that the DOC compound composition does not change along this flow path. Although DOC concentration decreases from recharge-area to downgradient groundwater, the organic compounds are similar, indicating that DOC 14 C is unaffected by other processes such as microbial degradation. A small amount of organic carbon was leached from crushed volcanic and carbonate aquifer outcrop rock in rock-leaching experiments. The leached DOC was high in 14 C (75 pmc carbonate rocks, 91 pmc volcanic) suggesting that the leached DOC likely came from microbes in the rock samples. The small amount of DOC and high 14 C indicates that the amount of old organic carbon in these rocks is low so there should be minimal impact on groundwater DOC 14 C ages. Based on the results from this study, DOC 14 C ages do not require additional corrections. Several correction models were applied to DIC 14 C ages to correct for water-rock reactions along two carbonate and two volcanic flow paths and the corresponding travel times were compare to DOC 14 C travel times. The DOC 14 C travel times were hundreds to thousands of years shorter than uncorrected and corrected DIC 14 C travel times except for the upper section of one carbonate flow path. DOC 14 C travel times ranged from 400 to 5,400 years as compared to DIC 14 C that ranged from modern to 20,900 years. The DIC 14 C ages are greatly influenced by carbonate mineral and gas reactions and other processes such as matrix diffusion, isotope exchange, or adsorption, which are not always adequately accounted for in DIC 14 C groundwater age correction models.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2013

Detection and profiling of carbon via the {sup 13}C(P,{gamma}){sup 14}N resonant reaction

We have tested and standardized the profiling of {sup 13}C in various substrates, including silicon, by use of the {sup 13}C(p,{gamma}){sup 14}N resonance at 1.748 MeV. Depth resolution and interference factors will be shown. The large background due to silicon is not a significant difficulty for atomic concentrations of {sup 13}C which are greater than 1%. Background from elements heavier than Si are present but not significant. We show the mechanical details and results of the analysis program ALLPROF which also develops depth profiles for the light elements H, Li, {sup 11}B, {sup 13}C, {sup 14}N, {sup 15}N, F, Na, Al and P. By extension, the program and our system can profile natural B, C and N via the assumed natural ratio of isotopes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

The {sup 14}N(p,{gamma}){sup 15}O reaction studied with a composite germanium detector

The rate of the carbon-nitrogen-oxygen (CNO) cycle of hydrogen burning is controlled by the {sup 14}N(p,{gamma}){sup 15}O reaction. The reaction proceeds by capture to the ground states and several excited states in {sup 15}O. In order to obtain a reliable extrapolation of the excitation curve to astrophysical energy, fits in the R-matrix framework are needed. In an energy range that sensitively tests such fits, new cross-section data are reported here for the four major transitions in the {sup 14}N(p,{gamma}){sup 15}O reaction. The experiment has been performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) 400-kV accelerator placed deep underground in the Gran Sasso facility in Italy. Using a composite germanium detector, summing corrections have been considerably reduced with respect to previous studies. The cross sections for capture to the ground state and to the 5181, 6172, and 6792 keV excited states in {sup 15}O have been determined at 359, 380, and 399 keV beam energy. In addition, the branching ratios for the decay of the 278-keV resonance have been remeasured.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Effects of first-order correction to eikonal approximation in the analysis of {sup 9}Be({sup 15}C,{sup 14}C + n){sup 9}Be stripping reaction

We have studied the effects of the first-order correction to the eikonal approximation for {sup 9}Be({sup 15}C,{sup 14}C + n){sup 9}Be stripping reactions at 54A MeV incident energy and have found that the correction term slightly changes the tail of the longitudinal momentum distribution of the core fragment.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS2016

A DSMC Surface Chemistry Model for Carbon-Based Ablators

A detailed molecular surface chemistry model for the DSMC (Direct Simulation Monte Carlo) method is proposed and implemented into the SPARTA (Stochastic PArallel Rarefied-gas Time-accurate Analyzer) DSMC solver. Molchanova et al. constructed a molecular model for surface recombination in DSMC that includes different surface processes (adsorption, desoprtion, Eley-Rideal and Langmuir-Hinshelwood). All surface processes can be divided into two groups: surface mechanisms, which involve only the particle adsorbed by the surface (desorption and Langmuir-Hinshelwood), and impact mechanisms, which also involve gas-phase particles (adsorption, Eley-Rideal). Using a similar approach, the 14-reaction kinetic model of oxygen-carbon interaction suggested by Zhlukhtov and Abe, as well as more recent models by Alba et al., Poovathinghal et al., and a new model developed in the scope of this work, are implemented in SPARTA. The computational results for the different oxidation models are compared with experimental results from Murray et al. (oxidation of a vitreous carbon surface due to a hyperthermal beam of O and O2), with a particular focus on fluxes, angular and Time-Of-Flight distributions of scattered particles.

oxidation↗
DOE OSTI2011

Radiological Monitoring of Waste Treatment Plant

Scheduled waste in West Malaysia is handled by Concession Company and is stored and then is incinerated. It is known that incineration process may result in naturally occurring radioactive materials (NORM) to be concentrated. In this study we have measured three samples consist of by-product from the operation process such as slag, filter cake and fly ash. Other various environmental media such as air, surface water, groundwater and soil within and around the plant have also been analysed for their radioactivity levels. The concentration of Ra-226, Ac-228 and K-40 in slag are 0.062 Bq/g, 0.016 Bq/g and 0.19 Bq/g respectively. The total activity (Ra{sub eq}) in slag is 99.5 Bq/kg. The concentration in fly ash is 0.032 Bq/g, 0.16 Bq/g and 0.34 Bq/g for Ra-226, Ac-228 and K-40 respectively resulting in Raeq of 287.0 Bq/kg. For filter cake, the concentration is 0.13 Bq/g, 0.031 Bq/g and 0.33 Bq/g for Ra-226, Ac-228 and K-40 respectively resulting in Raeq of 199.7 Bq/kg. The external radiation level ranges from 0.08 {mu}Sv/h (Administrative building) to 0.35 {mu}Sv/h (TENORM storage area). The concentration level of radon and thoron progeny varies from 0.0001 to 0.0016 WL and 0.0006 WL to 0.002 WL respectively. For soil samples, the activity ranges from 0.11 Bq/g to 0.29 Bq/g, 0.06 Bq/g to 0.18 Bq/g and 0.065 Bq/g to 0.38 Bq/g for Ra-226, Ac-228 and K-40 respectively. While activity in water, except for a trace of K-40, it is non-detectable.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2011

Can-AMS: The New Accelerator Mass Spectrometry Facility At The University Of Ottawa

The Canadian Centre for Accelerator Mass Spectrometry (AMS) at the University of Ottawa will be equipped with a new, 3 MV tandem accelerator with peripheral equipment for the analysis of elements ranging from tritium to the actinides. This facility, along with a wide array of support instrumentation recently funded by the Canada Foundation for Innovation, will be located in a new science building on the downtown campus of the University of Ottawa. In addition to providing the standard AMS measurements on {sup 14}C, {sup 10}Be, {sup 26}Al, {sup 36}Cl and {sup 129}I for earth, environmental, cultural and biomedical sciences, this facility will incorporate the new technologies of anion isobar separation at low energies using RFQ chemical reaction cells for {sup 36}Cl and new heavy element applications, integrated sample combustion and gas ion source for biomedical and environmental {sup 14}C analysis and the use of novel target matrices for expanding the range of applicable elements and simplifying sample preparation, all currently being developed at IsoTrace. This paper will outline the design goals for the new facility, present some details of the new AMS technologies, in particular the Isobar Separator for Anions and discuss the design of the AMS system resulting from these requirements.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

PROPERTIES OF CARBON–OXYGEN WHITE DWARFS FROM MONTE CARLO STELLAR MODELS

We investigate properties of carbon–oxygen white dwarfs with respect to the composite uncertainties in the reaction rates using the stellar evolution toolkit, Modules for Experiments in Stellar Astrophysics (MESA) and the probability density functions in the reaction rate library STARLIB. These are the first Monte Carlo stellar evolution studies that use complete stellar models. Focusing on 3 M{sub ⊙} models evolved from the pre main-sequence to the first thermal pulse, we survey the remnant core mass, composition, and structure properties as a function of 26 STARLIB reaction rates covering hydrogen and helium burning using a Principal Component Analysis and Spearman Rank-Order Correlation. Relative to the arithmetic mean value, we find the width of the 95% confidence interval to be ΔM{sub 1TP} ≈ 0.019 M{sub ⊙} for the core mass at the first thermal pulse, Δt{sub 1TP} ≈ 12.50 Myr for the age, Δlog(T{sub c}/K) ≈ 0.013 for the central temperature, Δlog(ρ{sub c}/g cm{sup −3}) ≈ 0.060 for the central density, ΔY{sub e,c} ≈ 2.6 × 10{sup −5} for the central electron fraction, ΔX{sub c}({sup 22}Ne) ≈ 5.8 × 10{sup −4}, ΔX{sub c}({sup 12}C) ≈ 0.392, and ΔX{sub c}({sup 16}O) ≈ 0.392. Uncertainties in the experimental {sup 12}C(α,γ){sup 16}O, triple-α, and {sup 14}N(p,γ){sup 15}O reaction rates dominate these variations. We also consider a grid of 1–6 M{sub ⊙} models evolved from the pre main-sequence to the final white dwarf to probe the sensitivity of the initial–final mass relation to experimental uncertainties in the hydrogen and helium reaction rates.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Radiocarbon as a Reactive Tracer for Tracking Permanent CO 2 Storage in Basaltic Rocks

In view of concerns about the long-term integrity and containment of CO 2 storage in geologic reservoirs, many efforts have been made to improve the monitoring, verification and accounting methods for geologically stored CO 2 . Our project aimed to demonstrate that carbon-14 ( 14 C) could be used as a reactive tracer to monitor geochemical reactions and evaluate the extent of mineral trapping of CO 2 in basaltic rocks. The capacity of a storage reservoir for mineral trapping of CO 2 is largely a function of host rock composition. Mineral carbonation involves combining CO 2 with divalent cations including Ca 2+ , Mg 2+ and Fe 2+ . The most abundant geological sources for these cations are basaltic rocks. Based on initial storage capacity estimates, we know that basalts have the necessary capacity to store million to billion tons of CO 2 via in situ mineral carbonation. However, little is known about CO2-fluid-rock reactions occurring in a basaltic storage reservoir during and post-CO 2 injection. None of the common monitoring and verification techniques have been able to provide a surveying tool for mineral trapping. The most direct method for quantitative monitoring and accounting involves the tagging of the injected CO 2 with 14C because 14C is not present in deep geologic reservoirs prior to injection. Accordingly, we conducted two CO 2 injection tests at the CarbFix pilot injection site in Iceland to study the feasibility of 14C as a reactive tracer for monitoring CO 2 -fluid-rock reactions and CO 2 mineralization. Our newly developed monitoring techniques, using 14C as a reactive tracer, have been successfully demonstrated. For the first time, permanent and safe disposal of CO 2 as environmentally benign carbonate minerals in basaltic rocks could be shown. Over 95% of the injected CO 2 at the CarbFix pilot injection site was mineralized to carbonate minerals in less than two years after injection. Our monitoring results confirm that CO 2 mineralization in basaltic rocks is far faster than previously postulated.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2016

Rapid Production of Graphite Without Contamination for Biomedical AMS

The application of AMS to the detection of 14 C makes possible a new class of sensitive experiments in molecular biology. Such experiments inherently produce large numbers of samples for the determination of biological variability in molecular interactions. The samples vary in 14 C concentration over many orders of magnitude. We added TiH 2 to aid the reduction of CO 2 by zinc in a sealed tube to reproducibly make graphite without sample cross-contamination. The CO 2 is transferred from a combustion tube to the reaction tube through a disposable plastic manifold. The sealed tubes are heated to a single-reaction temperature in a muffle furnace. The process is complete within 5 h. Bulk isotopic fractionation in the finished graphite is less than 0.5%.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Carbon synthesis in steady-state hydrogen and helium burning on accreting neutron stars

Superbursts from accreting neutron stars probe nuclear reactions at extreme densities (ρ ≈ 10{sup 9} g cm{sup –3}) and temperatures (T > 10{sup 9} K). These bursts (∼1000 times more energetic than type I X-ray bursts) are most likely triggered by unstable ignition of carbon in a sea of heavy nuclei made during the rapid proton capture process (rp-process) of regular type I X-ray bursts (where the accumulated hydrogen and helium are burned). An open question is the origin of sufficient amounts of carbon, which is largely destroyed during the rp-process in X-ray bursts. We explore carbon production in steady-state burning via the rp-process, which might occur together with unstable burning in systems showing superbursts. We find that for a wide range of accretion rates and accreted helium mass fractions large amounts of carbon are produced, even for systems that accrete solar composition. This makes stable hydrogen and helium burning a viable source of carbon to trigger superbursts. We also investigate the sensitivity of the results to nuclear reactions. We find that the {sup 14}O(α, p){sup 17}F reaction rate introduces by far the largest uncertainties in the {sup 12}C yield.

79 ASTRONOMY AND ASTROPHYSICS↗