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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Nuclear Data Sheets for A=31

Nuclear spectroscopic information for the known nuclides of mass 31 (F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar) has been evaluated. A useful source of many of the Adopted Levels for {sup 31}P and {sup 31}S is presented in Endt's evaluations (1998En04,1990En08,1978En02,1973EnVA), however all the adopted properties of levels and gamma rays have been re-evaluated in this work. The data sets for reactions and decays, including all available gamma–ray data, are based mostly on the original literature. The 31Mg nuclide is a prime candidate for the study of ‘island-of-inversion’ as its ground state and first excited state can only be explained by intruder orbitals in a deformed shell-model approach. {sup 31}S is of importance in astrophysics rp-process as a possible ‘bottleneck’ nuclide. There are no data available for excited states in {sup 31}F, {sup 31}Ne and {sup 31}Ar. No gamma transitions are known in {sup 31}Cl. For {sup 31}Na, only one excited state is known. The radioactive decay characteristics of {sup 31}F and {sup 31}Ne isotopes have not yet been investigated. The {sup 31}S and {sup 31}Mg nuclei are currently being pursued intensively by various experimental groups, including recent work by Nuclear Astrophysics group at McMaster, the results of which will soon become available.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Proton-Rich Sulphur and Nucleosynthesis in Classical Novae

The structure of proton-unbound states in {sup 30}{sub S} and {sup 31}{sub S} is important for determining the {sup 29}P(p,{gamma}){sup 30}S and {sup 30}P(p,{gamma}){sup 31}S reaction rates, which influence explosive hydrogen burning in classical novae. The former reaction rate in this temperature regime had been previously predicted to be dominated by two low-lying, unobserved, J{sup {pi}} = 3{sup +} and 2{sup +} resonances in {sup 30}S. To search for evidence for these levels, the structure of {sup 30}{sub S} was studied using the {sup 32}S(p,t){sup 30}S reaction with a magnetic spectrograph. We provide an update on the status of the ongoing analysis and some preliminary results.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

The {sup 30}P(p, γ){sup 31}S reaction in classical novae: progress and prospects

The unknown thermonuclear rate of the {sup 30}P(p, γ){sup 31}S reaction at classical-nova temperatures currently prohibits the accurate modeling of nova nucleosynthesis in the A ⩾ 30 region. This is hindering the calibration of nova thermometers based on observed O/S, S/Al, O/P, and P/Al abundance ratios in nova ejecta, the calibration of a meter to probe mixing at the core-envelope interface in novae based on the observed Si/H abundance ratio, and the identification of candidate pre-solar nova grains found in primitive meteorites based on laboratory measurements of their {sup 30}Si/{sup 28}Si isotopic ratios. Each of these diagnostics could address key questions in our understanding of classical novae if the {sup 30}P(p, γ){sup 31}S rate were known. We review progress on the determination of the {sup 30}P(p, γ){sup 31}S rate leading to a critical assessment of current interpretations of published data and prospects for future work.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

NUCLEAR MIXING METERS FOR CLASSICAL NOVAE

Classical novae are caused by mass transfer episodes from a main-sequence star onto a white dwarf via Roche lobe overflow. This material possesses angular momentum and forms an accretion disk around the white dwarf. Ultimately, a fraction of this material spirals in and piles up on the white dwarf surface under electron-degenerate conditions. The subsequently occurring thermonuclear runaway reaches hundreds of megakelvin and explosively ejects matter into the interstellar medium. The exact peak temperature strongly depends on the underlying white dwarf mass, the accreted mass and metallicity, and the initial white dwarf luminosity. Observations of elemental abundance enrichments in these classical nova events imply that the ejected matter consists not only of processed solar material from the main-sequence partner but also of material from the outer layers of the underlying white dwarf. This indicates that white dwarf and accreted matter mix prior to the thermonuclear runaway. The processes by which this mixing occurs require further investigation to be understood. In this work, we analyze elemental abundances ejected from hydrodynamic nova models in search of elemental abundance ratios that are useful indicators of the total amount of mixing. We identify the abundance ratios ΣCNO/H, Ne/H, Mg/H, Al/H, and Si/H as useful mixing meters in ONe novae. The impact of thermonuclear reaction rate uncertainties on the mixing meters is investigated using Monte Carlo post-processing network calculations with temperature-density evolutions of all mass zones computed by the hydrodynamic models. We find that the current uncertainties in the {sup 30}P(p, γ){sup 31}S rate influence the Si/H abundance ratio, but overall the mixing meters found here are robust against nuclear physics uncertainties. A comparison of our results with observations of ONe novae provides strong constraints for classical nova models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

NUCLEAR THERMOMETERS FOR CLASSICAL NOVAE

Classical novae are stellar explosions occurring in binary systems, consisting of a white dwarf and a main-sequence companion. Thermonuclear runaways on the surface of massive white dwarfs, consisting of oxygen and neon, are believed to reach peak temperatures of several hundred million kelvin. These temperatures are strongly correlated with the underlying white dwarf mass. The observational counterparts of such models are likely associated with outbursts that show strong spectral lines of neon in their shells (neon novae). The goals of this work are to investigate how useful elemental abundances are for constraining the peak temperatures achieved during these outbursts and determine how robust 'nova thermometers' are with respect to uncertain nuclear physics input. We present updated observed abundances in neon novae and perform a series of hydrodynamic simulations for several white dwarf masses. We find that the most useful thermometers, N/O, N/Al, O/S, S/Al, O/Na, Na/Al, O/P, and P/Al, are those with the steepest monotonic dependence on peak temperature. The sensitivity of these thermometers to thermonuclear reaction rate variations is explored using post-processing nucleosynthesis simulations. The ratios N/O, N/Al, O/Na, and Na/Al are robust, meaning they are minimally affected by uncertain rates. However, their dependence on peak temperature is relatively weak. The ratios O/S, S/Al, O/P, and P/Al reveal strong dependences on temperature and the poorly known {sup 30}P(p, {gamma}){sup 31}S rate. We compare our model predictions to neon nova observations and obtain the following estimates for the underlying white dwarf masses: 1.34-1.35 M {sub Sun} (V838 Her), 1.18-1.21 M {sub Sun} (V382 Vel), {<=}1.3 M {sub Sun} (V693 CrA), {<=}1.2 M {sub Sun} (LMC 1990 no. 1), and {<=}1.2 M {sub Sun} (QU Vul).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

CRADA Final Report, 2011S003, Faraday Technologies

This Phase I SBIR program addressed the need for an improved manufacturing process for electropolishing niobium RF superconducting cavities for the International Linear Collider (ILC). The ILC is a proposed particle accelerator that will be used to gain a deeper understanding of the forces of energy and matter by colliding beams of electrons and positrons at nearly the speed of light. The energy required for this to happen will be achieved through the use of advanced superconducting technology, specifically ~16,000 RF superconducting cavities operating at near absolute zero. The RF superconductor cavities will be fabricated from highly pure Nb, which has an extremely low surface resistance at 2 Kelvin when compared to other materials. To take full advantage of the superconducting properties of the Nb cavities, the inner surface must be a) polished to a microscale roughness < 0.1 µm with removal of at least 100 µm of material, and b) cleaned to be free of impurities that would degrade performance of the ILC. State-of-the-art polishing uses either chemical polishing or electropolishing, both of which require hydrofluoric acid to achieve breakdown of the strong passive film on the surface. In this Phase I program, Faraday worked with its collaborators at the Thomas Jefferson National Accelerator Facility (JLab) to demonstrate the feasibility of an electropolishing process for pure niobium, utilizing an environmentally benign alternative to chemical or electrochemical polishing electrolytes containing hydrofluoric acid. Faraday utilized a 31 wt% aqueous sulfuric acid solution (devoid of hydrofluoric acid) in conjunction with the FARADAYICSM Process, which uses pulse/pulse reverse fields for electropolishing, to demonstrate the ability to electropolish niobium to the desired surface finish. The anticipated benefits of the FARADAYICSM Electropolishing process will be a simpler, safer, and less expensive method capable of surface finishing high purity niobium cavities. Another potential benefit would be for the medical industry that uses hydrofluoric acid to electropolish niobium-alloy materials. The FARADAYICSM Electropolishing process will eliminate the environmental hazards posed by the use of hydrofluoric acid employed by chemical polishing and conventional electropolishing. Further, improved performance benefits may be possible. The overall objective of the Phase I program was to demonstrate that FARADAYIC Electropolishing of niobium cavities in electrolytes free of hydrofluoric acid can meet the RF superconducting performance criteria of those cavities. The FARADAYIC Electropolishing Process developed in the Phase I program was used to polish 50 mm Nb disks to a surface roughness (RA) of < 1 nm over a small area through process and post-processing optimization. An excellent level of surface cleanliness was achieved. While the desired 2K RF performance has not yet been achieved, Faraday believes that surface oxide state can be controlled through manipulation of the process parameters, to meet the 2K RF standard. Faraday is establishing apparatus and facilities infrastructure for single-cell SRF cavity electropolishing, through a synergistic effort with the Fermi National Accelerator Facility (Fermilab) to scale-up electropolishing of superconducting RF cavities. Faraday proposes to commercialize the subject technology via an IP based strategic relationship with a partner with established market channels within two primary commercialization avenues: 1) the superconducting particle accelerator community, 2) the medical device and implant market. Faraday will initially maintain Low Rate Initial Production capabilities for an application, but latterly seek a strategic partner who is solely dedicated to high rate production.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Massively parallel implementations of coupled-cluster methods for electron spin resonance spectra. I. Isotropic hyperfine coupling tensors in large radicals

Coupled cluster (CC) methods provide highly accurate predictions of molecular properties, but their high computational cost has precluded their routine application to large systems. Fortunately, recent computational developments in the ACES III program by the Bartlett group [the OED/ERD atomic integral package, the super instruction processor, and the super instruction architecture language] permit overcoming that limitation by providing a framework for massively parallel CC implementations. In that scheme, we are further extending those parallel CC efforts to systematically predict the three main electron spin resonance (ESR) tensors (A-, g-, and D-tensors) to be reported in a series of papers. In this paper inaugurating that series, we report our new ACES III parallel capabilities that calculate isotropic hyperfine coupling constants in 38 neutral, cationic, and anionic radicals that include the {sup 11}B, {sup 17}O, {sup 9}Be, {sup 19}F, {sup 1}H, {sup 13}C, {sup 35}Cl, {sup 33}S,{sup 14}N, {sup 31}P, and {sup 67}Zn nuclei. Present parallel calculations are conducted at the Hartree-Fock (HF), second-order many-body perturbation theory [MBPT(2)], CC singles and doubles (CCSD), and CCSD with perturbative triples [CCSD(T)] levels using Roos augmented double- and triple-zeta atomic natural orbitals basis sets. HF results consistently overestimate isotropic hyperfine coupling constants. However, inclusion of electron correlation effects in the simplest way via MBPT(2) provides significant improvements in the predictions, but not without occasional failures. In contrast, CCSD results are consistently in very good agreement with experimental results. Inclusion of perturbative triples to CCSD via CCSD(T) leads to small improvements in the predictions, which might not compensate for the extra computational effort at a non-iterative N{sup 7}-scaling in CCSD(T). The importance of these accurate computations of isotropic hyperfine coupling constants to elucidate experimental ESR spectra, to interpret spin-density distributions, and to characterize and identify radical species is illustrated with our results from large organic radicals. Those include species relevant for organic chemistry, petroleum industry, and biochemistry, such as the cyclo-hexyl, 1-adamatyl, and Zn-porphycene anion radicals, inter alia.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1999

Aerosol Transport Over Equatorial Africa

Long-range and inter-hemispheric transport of atmospheric aerosols over equatorial Africa has received little attention so far. Most aerosol studies in the region have focussed on emissions from rain forest and savanna (both natural and biomass burning) and were carried out in the framework of programs such as DECAFE (Dynamique et Chimie Atmospherique en Foret Equatoriale) and FOS (Fires of Savanna). Considering the importance of this topic, aerosols samples were measured in different seasons at 4420 meters on Mt Kenya and on the equator. The study is based on continuous aerosol sampling on a two stage (fine and coarse) streaker sampler and elemental analysis by Particle Induced X-ray Emission. Continuous samples were collected for two seasons coinciding with late austral winter and early austral spring of 1997 and austral summer of 1998. Source area identification is by trajectory analysis and sources types by statistical techniques. Major meridional transports of material are observed with fine-fraction silicon (31 to 68 %) in aeolian dust and anthropogenic sulfur (9 to 18 %) being the major constituents of the total aerosol loading for the two seasons. Marine aerosol chlorine (4 to 6 %), potassium (3 to 5 %) and iron (1 to 2 %) make up the important components of the total material transport over Kenya. Minimum sulfur fluxes are associated with recirculation of sulfur-free air over equatorial Africa, while maximum sulfur concentrations are observed following passage over the industrial heartland of South Africa or transport over the Zambian/Congo Copperbelt. Chlorine is advected from the ocean and is accompanied by aeolian dust recirculating back to land from mid-oceanic regions. Biomass burning products are transported from the horn of Africa. Mineral dust from the Sahara is transported towards the Far East and then transported back within equatorial easterlies to Mt Kenya. This was observed during austral summer and coincided with the dying phase of 1997/98 El Nino.

Gatebe, C. K.↗
NASA NTRS1997

Sulfuric Acid and Soot Particle Formation in Aircraft Exhaust

A combination of CN counts, Ames wire impactor size analyses and optical particle counter data in aircraft exhaust results in a continuous particle size distribution between 0.01 micrometer and 1 micrometer particle radius sampled in the exhaust of a Boeing 757 research aircraft. The two orders of magnitude size range covered by the measurements correspond to 6-7 orders of magnitude particle concentration. CN counts and small particle wire impactor data determine a nucleation mode, composed of aircraft-emitted sulfuric acid aerosol, that contributes between 62% and 85% to the total aerosol surface area and between 31% and 34% to its volume. Soot aerosol comprises 0.5% of the surface area of the sulfuric acid aerosol. Emission indices are: EIH2SO4 = 0.05 g/kgFUEL and (0.2-0.5) g/kgFUEL (for 75 ppmm and 675 ppmm fuel-S, respectively), 2.5E4<EISOOT<1.3E-3 g/kgFUEL, and EICN 8E14 and 1.3E16 particles/kgFUEL (for 75 and 675 ppmm fuel-S). The sulfur (gas) to H2SO4 (particle) conversion efficiency is between 10% and 25%.

Pueschel, Rudolf F.↗
DOE OSTI2017

γ spectroscopy of states in Cl 32 relevant for the S 31 ( p , γ ) Cl 32 reaction rate

Background: The 31 S(p,gamma) 32 Cl reaction becomes important for sulfur production in novae if the P-31(p, alpha)Si-28 reaction rate is somewhat greater than currently accepted. The rate of the S-31(p,gamma) Cl-32 reaction is uncertain, primarily due to the properties of resonances at E-c.m. = 156 and 549 keV. Purpose: We precisely determined the excitation energies of states in Cl-32 through high-resolution. spectroscopy including the two states most important for the S-31(p,gamma) Cl-32 reaction at nova temperatures. Method: Excited states in Cl-32 were populated using the B-10(Mg-24, 2n) Cl-32 reaction with a Mg-24 beam from the ATLAS facility at Argonne National Laboratory. The reaction channel of interest was selected using recoils in the Fragment Mass Analyzer, and we determined precise level energies by detecting. rays with Gammasphere. Results: We also observed. rays from the decay of six excited states in Cl-32. The excitation energies for two unbound levels at E-x = 1738.1 (6) keV and 2130.5 (10) keV were determined and found to be in agreement with a previous high-precision measurement of the S-32(He-3, t) Cl-32 reaction [1]. Conclusions: An updated 31 S(p,gamma) Cl-32 reaction rate is presented. With the excitation energies of important levels firmly established, the dominant uncertainty in the reaction rate at nova temperatures is due to the strength of the resonance corresponding to the 2131-keV state in Cl-32.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Sulfur Pellets Responses to a Bare and Steel Reflected Pulse of the Oak Ridge National Laboratory Health Physics Research Reactor

The experiments analyzed in this report were conducted at the Health Physics Research Reactor (HPRR), also known as the $\textit{Fast Burst Reactor}$. The reactor was designed and built at Oak Ridge National Laboratory (ORNL) in 1961. The HPRR was an unmoderated, unshielded fast reactor that used highly enriched uranium and molybdenum alloy as fuel. The reactor was initially sent to the Nevada Test Site in 1962, where it was used to evaluate radiation doses received as a result of the Hiroshima and Nagasaki bombings during World War II. A few years later, the reactor was sent back to ORNL to be part of the Dosimetry Application Research (DOSAR) facility shown in Figure 1, which included a reactor building shown on the left (west) of the picture and a control and laboratory building in the upper right corner (northeast). The critical assembly was used for numerous technical studies, including systems calibration, dosimetry, radiobiology of plants and animals, testing of radiation alarms, as well as teaching and training in radiation dosimetry and nuclear engineering. Between 1963 and 1987, the HPRR was operated for thousands of hours, achieving criticality close to 10,000 times and motivating many publications. The HPRR was decommissioned in 1987. The goal of this effort was to use historical data from operation of the HPRR to create a criticality accident alarm system (CAAS) benchmark to be included in the $\textit{International Handbook of Evaluated Criticality Safety Benchmark Experiments}$ (ICSBEP Handbook). A thorough inspection was performed of all available documentation and information available. The most promising experiments that were selected for evaluation were those described in the 1987 ORNL report entitled $\textit{Health Physics Research Reactor Reference Dosimetry}$, ORNL-6240. The report includes reference dosimetry results of the shielded and unshielded configurations of the HPRR after burst operations. Because of changes to the reactor positioning and storage systems that were made in 1985, the previous dosimetry reports became obsolete, and the newly designed experiments were needed to create the HPRR’s adjusted dosimetry data. The various results reported in ORNL-6240 include reference doses and dose equivalents from different conventions at different distances and elevations as determined using the detected neutron fluence and conversion factors. The HPRR neutron fluence was obtained through different methods, including sulfur pellet analysis and threshold detector unit data. Information about the HPRR spectrum was also obtained through Bonner sphere measurements. This benchmark is focused on a part of the measured sulfur fluences reported in Appendix H of ORNL-6240. Standard commercial sulfur pellets were placed at different distances from the HPRR centerline during burst operation and were activated due to the 32 S(n,p) 32 P reaction. The resulting 32 P activity was then measured and the information about the corresponding sulfur fluence and/or neutron dose could be extracted. Many of those measurements have 7 been performed with the HPRR in its bare configuration or with different shields (combinations of Lucite, concrete, steel). All the necessary, precise information about material and/or dimensions of the different shields was not found, so it was decided to focus only on the unshielded and steel-shielded configurations to minimize the benchmark uncertainty. A total of 31 cases (24 unshielded and 7 shielded cases at different positions) of sulfur fluence were selected before evaluation to develop the benchmark.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2014

Sulfur vacancies in photorefractive Sn{sub 2}P{sub 2}S{sub 6} crystals

A photoinduced electron paramagnetic resonance (EPR) spectrum in single crystals of Sn{sub 2}P{sub 2}S{sub 6} (SPS) is assigned to an electron trapped at a sulfur vacancy. These vacancies are unintentionally present in undoped SPS crystals and are expected to play an important role in the photorefractive behavior of the material. Nonparamagnetic sulfur vacancies are formed during the initial growth of the crystal. Subsequent illumination below 100 K with 442 nm laser light easily converts these vacancies to EPR-active defects. The resulting S = 1/2 spectrum shows well-resolved and nearly isotropic hyperfine interactions with two P ions and two Sn ions. Partially resolved interactions with four additional neighboring Sn ions are also observed. Principal values of the g matrix are 1.9700, 1.8946, and 1.9006, with the corresponding principal axes along the a, b, and c directions in the crystal. The isotropic parts of the two primary {sup 31}P hyperfine interactions are 19.5 and 32.6 MHz and the isotropic parts of the two primary Sn hyperfine interactions are 860 and 1320 MHz (the latter values are each an average for {sup 117}Sn and {sup 119}Sn). These hyperfine results suggest that singly ionized sulfur vacancies have a diffuse wave function in SPS crystals, and thus are shallow donors. Before illumination, sulfur vacancies are in the doubly ionized charge state because of compensation by unidentified acceptors. They then trap an electron during illumination. The EPR spectrum from the sulfur vacancy is destroyed when a crystal is heated above 120 K in the dark and reappears when the crystal is illuminated again at low temperature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗