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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,729 records · Page 96
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Interpretation of Urinary Excretion Data From Plutonium Wound Cases Treated With DTPA: Application of Different Models and Approaches

After a chelation treatment, assessment of intake and doses is the primary concern of an internal dosimetrist. Using the urinary excretion data from two actual wound cases encountered at Los Alamos National Laboratory (LANL), this study discusses several methods that can be used to interpret intakes from the urinary data collected after one or multiple chelation treatments. One of the methods uses only the data assumed to be unaffected by chelation (data collected beyond 100 d after the last treatment). This method, used by many facilities for official dose records, was implemented by employing maximum likelihood analysis and Bayesian analysis methods. The impacts of an improper assumption about the physicochemical behavior of a radioactive material and the importance of the use of a facility-specific biokinetic model when available have also been demonstrated. Another method analyzed both the affected and unaffected urinary data using an empirical urinary excretion model. This method, although case-specific, was useful in determining the actual intakes and the doses averted or the reduction in body burdens due to chelation treatments. Finally, this approach was important in determining the enhancement factors, the behavior of the chelate, and other observations that may be pertinent to several DTPA compartmental modeling approaches being conducted by the health physics community.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Mitigating the Psychological Harm from Actinide Intakes

We report that investigations into possible actinide intakes, as well as the intakes themselves, may result in significant psychological harm that should be mitigated by the internal dosimetrist. Many aspects of this psychological impact are unique to actinide intakes and have not been discussed in the literature. This paper discusses some of these unique considerations and describes how the Internal Dosimetry Team at Los Alamos National Laboratory (LANL) has, with input and guidance from LANL psychologists, tried to address them. Lastly, we feel that much of the psychological harm can be mitigated by educating employees specifically about internal dosimetry and internal doses, and by improving communication with radiation workers.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2022

Applying ALARA Principles in the Design of New Radiological Facilities

The application of ALARA (As Low As Reasonably Achievable) principles to the design of new radiological facilities at Argonne National Laboratory provides a consistent radiation safety basis for future facility operations. The Department of Energy Rule 10 CFR 835 specifies design objectives to be adopted during the design of new facilities for controlling personal radiation exposure. One is to keep exposure levels below 20% of the applicable standards in 10 CFR 835.202. For a radiation worker 20% of the standard corresponds to 5 µSv hr -1 for a 2,000 hour work year. For a member of the public the DOE design objective corresponds to 0.2 mSv in a calendar year. For a new facility worst case radionuclides and their source strengths are chosen. Local shielding is specified to reduce exposure rates to less than 50 µSv hr -1 at 30 cm from the shielding. The current version MCNP6 of the Los Alamos radiation shielding computer program MCNP is then used to calculate the exposure rates elsewhere. Design modifications are made to meet the criteria. The calculations and resulting facility design modifications are discussed for two new radiological facilities.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2018

Quality control for community-based sea-ice model development

A new collaborative organization for sea-ice model development, the CICE Consortium, has devised quality control procedures to maintain the integrity of its numerical codes' physical representations, enabling broad participation from the scientific community in the Consortium's open software development environment. Using output from five coupled and uncoupled configurations of the Los Alamos Sea Ice Model, CICE, we formulate quality control methods that exploit common statistical properties of sea-ice thickness, and test for significant changes in model results in a computationally efficient manner. New additions and changes to CICE are graded into four categories, ranging from bit-for-bit amendments to significant, answer-changing upgrades. These modifications are assessed using criteria that account for the high level of autocorrelation in sea-ice time series, along with a quadratic skill metric that searches for hemispheric changes in model answers across an array of different CICE configurations. These metrics also provide objective guidance for assessing new physical representations and code functionality.

58 GEOSCIENCES↗
DOE OSTI2018

Imaging the dome of Santa Maria del Fiore using cosmic rays

The dome of Santa Maria del Fiore, Florence Cathedral, was built between 1420 and 1436 by architect Filippo Brunelleschi and it is now cracking under its own weight. Engineering efforts are under way to model the dome's structure and reinforce it against further deterioration. According to some scholars, Brunelleschi might have built reinforcement structures into the dome itself; however, the only known reinforcement is a wood chain 7.75 m above the springing of the Cupola. Multiple scattering muon radiography is a non-destructive imaging method that can be used to image the interior of the dome's wall and therefore ascertain the layout and status of any iron substructure in it. A demonstration measurement was performed at the Los Alamos National Laboratory on a mock-up wall to show the feasibility of the work proposed, and a lightweight and modular imaging system is currently under construction. Here, we will discuss here the results of the demonstration measurement and the potential of the proposed technique, describe the imaging system under construction and outline the plans for the measurement.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Influence of the plasma environment on atomic structure using an ion-sphere model

Plasma environment effects on atomic structure are analyzed using various atomic structure codes. To monitor the effect of high free-electron density or low temperatures, Fermi-Dirac and Maxwell-Boltzmann statistics are compared. After a discussion of the implementation of the Fermi-Dirac approach within the ion-sphere model, several applications are considered. In order to check the consistency of the modifications brought here to extant codes, calculations have been performed using the Los Alamos Cowan Atomic Structure (cats) code in its Hartree-Fock or Hartree-Fock-Slater form and the parametric potential Flexible Atomic Code (fac). The ground-state energy shifts due to the plasma effects for the six most ionized aluminum ions have been calculated using the fac and cats codes and fairly agree. For the intercombination resonance line in Fe 22+ , the plasma effect within the uniform electron gas model results in a positive shift that agrees with the MCDF value of B. Saha et al .

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Optical properties of highly compressed polystyrene: An ab initio study

Using all-electron density functional theory, we have performed an ab initio study on x ray absorption spectra of highly compressed polystyrene (CH). Here, we found that the K-edge shifts in strongly coupled, degenerate polystyrene cannot be explained by existing continuum-lowering models adopted in traditional plasma physics. To gain insights into the K edge shift in warm, dense CH, we have developed a model designated as “single-mixture-in-a-box” (SMIAB), which incorporates both the lowering of continuum and the rising of Fermi surface resulting from high compression. This simple SMIAB model correctly predicts the K-edge shift of carbon in highly compressed CH in good agreement with results from quantum-molecular-dynamics (QMD) calculations. Traditional opacity models failed to give the proper K-edge shifts as the CH density increased. Based on QMD calculations, we have established a first-principles opacity table (FPOT) for CH in a wide range of densities and temperatures [p = 0.1 to 100 g/cm 3 and T = 2000 to 1,000,000 K]. The FPOT gives much higher Rosseland mean opacity compared to the cold-opacity–patched astrophysics opacity table for warm, dense CH and favorably compares to the newly improved Los Alamos ATOMIC model for moderately compressed CH (pCH ≤10 g/cm 3 ) but remains a factor of 2 to 3 higher at extremely high densities (pCH ≥ 50 g/cm 3 ). We anticipate the established FPOT of CH will find important applications to reliable designs of high-energy-density experiments. Moreover, the understanding of K-edge shifting revealed in this study could provide guides for improving the traditional opacity models to properly handle the strongly coupled and degenerate conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Prompt-fission-neutron spectra in the 239 Pu( n,f ) reaction

Prompt-fission-neutron spectra from Pu 239 ( n , f ) were measured with respect to Cf 252 spontaneous fission for incident neutron energies from 0.7 to 700 MeV at the Weapons Neutron Research facility (WNR) of the Los Alamos Neutron Science Center. A newly designed high-efficiency fission chamber was coupled to the highly segmented Chi-Nu neutron liquid scintillator array to detect neutrons emitted in fission events. The double time-of-flight technique was used to deduce the incident neutron energies from the spallation target and the outgoing-neutron energies from the fission chamber. Prompt-fission-neutron spectra (PFNS) were measured with respect to Cf 252 spontaneous fission down to 200 keV and up to about 12 MeV for all the incident neutron energies with typical total uncertainties well below 2 % up to about 7-MeV outgoing-neutron energy. The general trend of PFNS is well reproduced by JEFF3.3 and ENDF evaluations, although a better agreement is found with JEFF3.3. Discrepancies were observed for the low-energy part of the spectra, especially around the opening of the second-, third- and fourth-chance fission. Additionally, neutron average kinetic energies as a function of incident neutron energy are obtained experimentally with reported total uncertainties below 0.5 % . The measured values agree with the most recent data. The trend is fairly well reproduced by the JEFF3.3 evaluation, although it fails to reproduce the experimental values within their uncertainties.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

γ-ray measurements in fast-neutron-induced reactions on 203 Tl

Fast-neutron-induced reactions can be used to characterize reaction mechanisms, investigate nuclear structure, and impose constraints on nuclear models. Because of the difficulty in predicting such effects, experimental data are important to constrain models. Thallium isotopes located close to the doubly magic Pb 208 nucleus are important for comparison with shell-model calculations. Study the population of excited states in Tl 203 and lighter isotopes in such reactions. Our methods are as follows. γ -ray cross sections were measured. The data were taken by using the Germanium Array for Neutron-Induced Excitations spectrometer. The pulsed neutron source of the Los Alamos Neutron Science Center's Weapons Neutron Research facility provided neutrons in the energy range from 1 to 300 MeV. The time-of-flight technique was used to determine the incident neutron energies. Cross sections for emission of several γ rays in 20 reaction channels were determined. Candidates for the intruder 9 / 2 - state in Tl 203 , from the odd proton in the h 9 / 2 orbital, and the first 5 + states in Tl 202 , 204 , from admixture of configurations, were identified. The excitation energy of the candidate 9 / 2 - , π h 9 / 2 state is in good agreement with the theoretical prediction from a semi-empirical weak-coupling model and its half-life is in the range of tens of nanoseconds. The feeding of a previously known isomer in Tl 202 exhibits similarities with the feeding of other isomers in this mass region.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Nonstatistical fluctuations in the 35 Cl(n,p) 35 S reaction cross section at fast-neutron energies from 0.6 to 6 MeV

The lack of experimental data on the 35 Cl(n,p) 35 S reaction above 100 keV has led to nuclear data evaluations that are relatively unconstrained at fast neutron energies. As a result, efforts to explore, develop, and potentially certify next generation reactor designs that incorporate chloride salts as a coolant material have been hindered. Here, we report partial cross section data for the 35 Cl(n,p) 35 S and 35 Cl(n,α) 32 P reactions at incident neutron energies between 0.6 MeV and 6 MeV. The measurement was performed using the pulsed beam of neutrons at the unmoderated WNR spallation neutron source at the Los Alamos Neutron Science Center, with the outgoing charged particles detected by the LENZ experimental setup, consisting of annular silicon detectors. Nonstatistical fluctuations in the 35 Cl(n,p 0 ) cross section were observed up to around 3 MeV, and the magnitude of the cross section was systematically lower than all available data evaluations at energies above 1 MeV. Modifications to the ENDF/B-VIII.0 data evaluation are suggested to better reproduce the energy averaged experimental data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Isotopically resolved neutron total cross sections at intermediate energies

The neutron total cross sections σ tot of 16,18 O, 58 64 Ni, 103 Rh, and 112,124 Sn have been measured at the Los Alamos Neutron Science Center from low to intermediate energies (3 ≤ E lab ≤ 450 MeV) by leveraging wave-form-digitizer technology. The σ tot relative differences between isotopes are presented, revealing additional information about the isovector components needed for an accurate optical-model description away from stability. Digitizer-enabled σ tot -measurement techniques are discussed and a series of uncertainty-quantified dispersive optical model (DOM) analyses using these new data is presented, validating the use of the DOM for modeling light systems ( 16,18 O) and systems with open neutron shells ( 58,64 Ni and 112,124 Sn). Here, the valence-nucleon spectroscopic factors extracted for each isotope reaffirm the usefulness of high-energy proton reaction cross sections for characterizing depletion from the mean-field expectation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Measurement of the 239 Pu$(n, f$) prompt fission neutron spectrum from 10 keV to 10 MeV induced by neutrons of energy 1–20 MeV

Although the prompt fission neutron spectrum (PFNS) is an essential component of neutron-driven systems that has been measured for decades, there are still multiple glaring unknowns regarding the PFNS of major actinides in the fission neutron incident energy range, specifically with regard to multichance fission and pre-equilibrium neutron emission processes. The only impactful experimental 239 Pu PFNS measurements included in recent nuclear data evaluations were measured over a limited outgoing neutron energy range at thermal and 1.5-MeV average incident neutron energy, while other potentially impactful measurements have been shown to contain errors that resulted in either large uncertainty increases or in complete exclusion from nuclear data evaluation. Here, we report a measurement of the 239 Pu PFNS over a wide range of incident neutron energy (1–20 MeV) and three orders of magnitude in outgoing neutron energy (0.01–10 MeV) resulting from the Chi-Nu experiment at the Los Alamos Neutron Science Center. These results are the combination of separate PFNS measurements in the same experimental area, one using a Li-glass and the other a liquid scintillator detector array. Covariances between all PFNS data points from each detector and within each incident energy range were generated between all other data in both detector arrays and within all other incident neutron energy bins, yielding a single covariance matrix for all 1300 PFNS data points reported here. These covariances are based on a thorough assessment of systematic bias and uncertainties associated with the measurement, PFNS extraction technique, combination of data from each detector type, and other aspects of the analysis. The existence of covariances between PFNS data points in different incident neutron energy ranges yielded covariances between average PFNS energy values at each incident energy to be reported here as well, which allowed for firm statements to be made regarding a shape of a purely experimental mean PFNS energy trend for the first time. Although minor PFNS shape differences exist between the results reported here and recent nuclear data evaluations, the ENDF/B-VIII.0 and JEFF-3.3 PFNS evaluations agree reasonably well with the present results from 1-to 10-MeV incident neutron energy, which spans the well-measured 1.5-MeV incident neutron energy PFNS from Lestone and Shores as well as the onset of second-chance fission. However, while the pre-equilibrium component of the PFNS above 12-MeV incident neutron energy roughly agrees in position and magnitude with ENDF/B-VIII.0 and JEFF-3.3, clear differences relating to the relative magnitude of third-chance fission PFNS features are present in the PFNS shape and in the mean PFNS energy trends.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Total kinetic energy release in the fast-neutron-induced fission of Np 237

The total kinetic energy (TKE) release in the fast neutron-induced fission of 237Np was measured for neutron energies from En = 2.6–100 MeV at the Los Alamos Neutron Science Center at the Weapons Neutron Research facility. The post-TKE release decreases nonlinearly with increasing incident neutron energy and can be represented as TKE(MeV) = (174.38 ± 0.72) – (5.11 ± 0.5821) log 10 E n for En > 1 MeV. Analysis of the fragment mass distributions indicates that the decrease in TKE with increasing E n is a consequence of the fading out of shell effects at high excitation energies (resulting in an increase of symmetric fission) and the decrease of the total kinetic energy associated with asymmetric fission with increasing E n .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Structure in the event-by-event energy-dependent neutron-$γ$ multiplicity correlations in 252 Cf(sf)

The emission of neutrons and γ rays by fission fragments reveal important information about the properties of fragments immediately following scission. The initial fragment properties, correlations between fragments, and emission competition give rise to correlations in neutron-γ emission. Recent theoretical and experimental advances have been proposed to explain the mechanism of angular momentum generation in fission, which would result in observable signature in neutron-γ emission correlations. In this paper, we present a novel analysis method of neutrons and γ rays emitted by fission fragments that allows us to discern structure in the observed correlations. We have analyzed data collected on 252 Cf (sf) at the Chi-Nu array at the Los Alamos Neutron Science Center. Through our analysis of the energy-differential neutron-γ multiplicity covariance, we have observed enhanced neutron-γ correlations, corresponding to rotational band γ-ray transitions, at γ-ray energies of 0.7 and 1.2 MeV. To shed light on the origin of this structure, we compare the experimental data with the predictions of three model calculations. The origin of the observed correlation structure is understood in terms of a positive spin-energy correlation in the generation of angular momentum in fission.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Measurement of the U 235 ( n , f ) prompt fission neutron spectrum from 10 keV to 10 MeV induced by neutrons of energy from 1 MeV to 20 MeV

The characterization of fission-driven nuclear systems primarily relies on calculations of neutron-induced chain reactions, and these calculations require evaluated nuclear data as input. Calculation accuracy heavily depends on input nuclear data evaluation accuracy, and thus high precision on the experimental input to the nuclear data evaluation is essential for fundamental quantities like the energy spectrum of neutrons emitted from neutron-induced fission (i.e., the prompt fission neutron spectrum, PFNS). Despite decades of measurement efforts, prior to the measurements described in this work there were only three literature data sets for the 235 U(n,f) PFNS at incident neutron energies above 1.0 MeV considered reliable for inclusion in nuclear data evaluations and no reliable data sets above 3.0 MeV incident neutron energy. In this work we report on new measurements of the 235 U(n,f) PFNS spanning a grid of 1.0–20.0 MeV in incident neutron energy and 0.01–10.0 MeV in outgoing (PFNS) neutron energy. These measurements were carried out at the Weapons Neutron Research facility at the Los Alamos Neutron Science Center and used a multifoil parallel-plate avalanche counter target with both a Li-glass and a liquid scintillator detector array in separate experiments to span the quoted outgoing neutron energy ranges. The PFNS results are shown in terms of the energy spectra themselves as well as the average PFNS energy $(\langle{E}\rangle)$ and ratios of $\langle{E}\rangle$ at forward and backward angles. Here, the results are compared with literature data and selected nuclear data evaluations. Generally, the data agree with the ENDF/B-VIII.0 evaluation below 5.0-MeV incident neutron energy and more closely with the JEFF-3.3 evaluation above 5.0 MeV, though no evaluations considered for comparison in this work agree with the data across all of the incident and outgoing neutron energies shown, especially in regions where the third-chance fission process becomes available. Additionally, we show a ratio of the present PFNS results for 235 U(n, f) with a recent and highly correlated experiment to measure the 239 Pu(n, f) PFNS at the same experimental facility and with nearly identical equipment and analysis procedures. Many observations reported in this work are the first of their kind and represent significant advancements for knowledge of the 235 U(n, f) PFNS.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Study of charged-particle emission in neutron reactions on 10 B

The 10 B + n system has been studied by measuring charged particles from neutron-induced reactions in the 1 to 20 MeV energy range. Protons, deuterons, tritons, and α particles were measured at four angles using the pulsed white neutron spectrum at the Los Alamos Neutron Science Center Weapons Neutron Research facility. Differential cross sections for each species are reported. These new data are combined with literature data in an R-matrix analysis of the 11 B compound system. Furthermore, a comparison is made to the molecular and cluster states candidates observed in these reactions.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Fill and dump measurement of the neutron lifetime using an asymmetric magneto-gravitational trap

The past two decades have yielded several new measurements and reanalysis of older measurements of the neutron lifetime. These have led to a 4.4 standard deviation discrepancy between the most precise measurements of the neutron decay rate producing protons in cold neutron beams and the most precise lifetime measured in neutron storage experiments. Measurements using different techniques are important for investigating whether there are unidentified systematic effects in any of the measurements. In this paper we report a new measurement using the Los Alamos asymmetric magneto-gravitational trap where the surviving neutrons are counted external to the trap using the fill and dump method. In this work, the new measurement gives a free neutron lifetime of $τ_n$ = 876.3(2.4) stat (0.8) syst . Although this measurement is not as precise, it is in statistical agreement with previous results using in situ counting in the same apparatus.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗