Thermonuclear reaction rates - On the nucleosynthesis of the S and P elements.
Nuclear physics of neutron producing reactions combined with stellar evolution models
Reeves, H.↗
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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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X-ray pulsar spectroscopy - Observational prospects
Three experimental concepts have been suggested to advance the study of X-ray pulsar spectroscopy. They are: (1) a higher bit rate for pulse phase spectroscopy; (2) an emphasis on the 10 keV 'pulsar surface' emission, and (3) an improved resolution to understand the nature of broadened iron lines in pulsars. It is shown that for conventional X-ray spectroscopy at least 5 KB/s are needed to substantially improve pulse phase spectroscopy; the broadened iron line emission in the pulsar spectra will require improved spectral resolution at 6.7 keV to discriminate among the models for this emission. It is concluded that this work will elucidate the physics of neutron star surface and circumstellar X-ray emission.
Pravdo, S. H.↗
Some observational tests of X-ray pulsar emission models
The understanding of neutron star physics which relies heavily on knowing values of their mass, radius and magnetic field strength was studied. The only information about these till now comes from the surface radiation. Major uncertainties concerning the nature of the mass exchange and the accretion flow, the magnetopause structure, the infall deceleration, the actual pulsation mechanism and the atmosphere geometry are examined. The alternatives and several possible observational tests are discussed.
Meszaros, P.↗
Chandra Observations of Neutron Stars: An Overview
We present a brief review of Chandra X-ray Observatory observations of neutron stars. The outstanding spatial and spectral resolution of this great observatory have allowed for observations of unprecedented clarity and accuracy. Many of these observations have provided new insights into neutron star physics. We present an admittedly biased and overly brief overview of these observations, highlighting some new discoveries made possible by the Observatory's unique capabilities. We also include our analysis of recent multiwavelength observations of the putative pulsar and its pulsar-wind nebula in the IC 443 SNR.
Weisskopf, Martin C.↗
Chandra Observations of Isolated Neutron Stars
We present a review of the first six years of Chandra X-ray Observatory observations of isolated neutron stars. The outstanding spatial and spectral resolution of this great observatory have allowed for observations of unprecedented clarity and accuracy. Many of these observations have provided new insights into neutron star physics. We present a (biased) overview of six years of these observations, highlighting new discoveries made possible by the Observatory's unique capabilities.
Weisskopf, Martin↗
Advanced X-Ray Timing Array (AXTAR) Animation
The animation depicts NASA's concept for a next-generation Advanced X-ray Timing Mission. The models and their textures doe not necessarily represent the final iteration. Delivery specifications include launch with Taurus II or Falcon 9, mass of 2650 kg, with a circular low earth orbit at approximately 600 km. The inclination depends on the launch vehicle and spacecraft mass. AXTAR's prime instrument will probe the physics of neutron stars and black holes through X-ray timing and spectral measurements. The primary instrument will be the Large Area Timing Array (LATA). The Sky Monitor Clusters configuration consists of 27 Sky Monitor cameras th at are grouped in five clusters. This configuration will achieve approximately 85 percent all sky coverage. Spacecraft components include a science bus to house the LATA of supermodules; a spacecraft bus to house components such as propulsion tanks, avionics, and reaction wheels; solar arrays configured from space-qualified GaAs 3-junction cells; star trackers for attitude knowledge; a propulsion system of four pods, each containing one 100 lbf and two 5 lbf engines; a launch vehicle adaptor; and a radiation shield.
Hopkins, Randall C.↗
Artemis III Neutron Surface Science
This paper highlights lunar neutron science that can be performed in support of the Artemis 2024 mission within 6 degrees of the lunar south pole. There are two primary science goals: the characterization of the radiation environment, and secondly, inference of regolith composition including the presence of water. Characterizing the surface radiation environment is important for risk identification and mitigation during crewed lunar missions. The lunar surface radiation environment includes a unique neutron contribution. The relative contribution from neutrons is higher outside the shielding effects of Earth’s magnetic field, which the Moon experiences ~25% of its orbit. To evaluate the radiation risk to astronauts at the lunar surface, fast neutron measurements are needed. Neutrons are generated when galactic cosmic rays (GCR) collide with the lunar regolith and provide valuable elemental composition information about the near surface (< 1m). For the characterization of regolith composition, a low energy neutron spectrometer or counter can determine surface composition. This provides ground truth for orbital neutron data from the Lunar Reconnaissance Orbiter and Lunar Prospector missions.
Lunar science, Moon, geology, geophysics, neutron ↗
Neutron measurements at the Lunar surface with PRISM
Neutron measurements at the lunar surface are performed with two goals: characterization of the radiation environment and inference of regolith composition. This submission is focused on quantifying the surface radiation environment to inform mission design and risk mitigation prior to crewed lunar missions. The lunar surface radiation environment includes a unique neutron contribution. MSFC’s Advanced Neutron Spectrometer for Lunar Surface Measurements instrument covers the most biologically significant energies from thermal to ~20 MeV. The ANSLSM is based on heritage from the Fast Neutron Spectrometer that has measured the ISS crew neutron exposure for the past 3 years, and revealed the significant neutron contribution to total exposure. The relative contribution from neutrons will increase outside the shielding effects of Earth’s magnetic field. To evaluate the radiation risk to astronauts at the lunar surface, precursor fast neutron measurements are needed.
Lunar science, Moon, geology, geophysics, neutron ↗
Prediction of neutron induced activation. Volume 2 - NAP, physical models and experimental validation Final report, May 14, 1964 - Jan. 31, 1966
Mathematical models for IBM 7094 computer program prediction of neutron induced activation
Klopp, D. A.↗
Review of recent activities with MOOSE, an open-source finite element & finite volume multi-fidelity simulation framework
Modeling and simulation are an increasing part of engineering. This is undoubtedly driven by the high costs of constructing experimental facilities, but also enabled by the exponential increase in computing powers over the last decades, which allows computational models to be closer than ever to reality. One of the main drivers for the development of MOOSE is supporting advanced nuclear reactor simulations. A challenging aspect of modeling advanced nuclear reactors is the plurality of physics involved, including neutronics, thermal hydraulics and fuel performance. These physics are all coupled to some extent and are generally solved in a sequential but iterative fashion. The United States (U.S.) national laboratories have been developing MOOSE, an open source multiphysics framework since its inception at the Idaho National Laboratory (INL) in 2008. This framework enables seamless coupling of multiphysics simulations and facilitates the implementation of new physics and material governing laws. It is continuously expanded with novel numerical methods and new pre-implemented physics module. Numerous applications, developed within the Department of Energy (DOE) laboratories, academia, and industry, including outside of nuclear engineering, have been developed to study specialized physics problems. International collaborations are welcome on this open-source modeling and simulation project.
22 - GENERAL STUDIES OF NUCLEAR REACTORS↗
Physics in strong magnetic fields near neutron stars
Electromagnetic phenomena occurring in the strong magnetic fields of neutron stars are currently of great interest in high-energy astrophysics. Observations of rotation rate changes and cyclotron lines in pulsars and gamma-ray bursts indicate that surface magnetic fields of neutron stars often exceed a trillion gauss. In fields this strong, where electrons behave much as if they were in bound atomic states, familiar processes undergo profound changes, and exotic processes become important. Strong magnetic fields affect the physics in several fundamental ways: energies perpendicular to the field are quantized, transverse momentum is not conserved, and electron-positron spin is important. Neutron stars therefore provide a unique laboratory for the study of physics in extremely high fields that cannot be generated on earth.
Harding, Alice K.↗
Physical processes in the strong magnetic fields of accreting neutron stars
Analytical formulae are fitted to observational data on physical processes occurring in strong magnetic fields surrounding accreting neutron stars. The propagation of normal modes in the presence of a quantizing magnetic field is discussed in terms of a wave equation in Fourier space, quantum electrodynamic effects, polarization and mode ellipticity. The results are applied to calculating the Thomson scattering, bremsstrahlung and Compton scattering cross-sections, which are a function of the frequency, angle and polarization of the magnetic field. Numerical procedures are explored for solving the radiative transfer equations. When applied to modeling X ray pulsars, a problem arises in the necessity to couple the magnetic angle and frequency dependence of the cross-sections with the hydrodynamic equations. The use of time-dependent averaging and approximation techniques is indicated.
Meszaros, P.↗
Accreting Neutron Stars as Astrophysical Laboratories
In the last year, we have made an extremely important breakthrough in establishing the relationship between thermonuclear burst oscillations in accreting neutron stars and the stellar spin. More broadly, we have continued t o make significant scientific progress in all four of the key focus areas identified in our original proposal: (1) the disk-magnetosphere interaction in neutron stars, (2) rapid variability in accreting neutron stars, (3) physics of accretion flows, and (4) fundamental properties of neutron stars. A list of all publications that have arising from this work since the start of our program is given.
Chakrabarty, Deepto↗
Measurement of the 252 Cf (sf) prompt fission neutron spectrum utilizing 12 C (𝑛, 𝑛) and 9 Be (𝑛, 𝑛) neutron scattering reference measurements
The 252 Cf spontaneous fission (sf), prompt fission neutron spectrum (PFNS) is a fundamental quantity for nuclear physics measurements of neutron-emitting reactions. This energy distribution of neutrons emitted from fission has been considered a neutron data standard for decades and has been utilized as a reference for neutron detection efficiency, validation of Monte Carlo simulations, benchmarking of dosimetry standards, and more. A significant portion of the global collection of nuclear data on neutron-induced reactions is correlated with the 252 Cf (sf) PFNS. Despite the reliance on this quantity by the nuclear physics community, the historical collection of 252 Cf PFNS measurements display systematic disagreements that are not understood or easily explained. These experimental discrepancies could potentially bias the 252 Cf PFNS Standard evaluation. On top of this, these past experiments frequently employed correlated experimental measurement or analysis methods. The artificial intelligence (AI)/machine learning (ML)-informed californium chi-nuclear data experiment (AIACHNE) project was formed to (a) investigate these discrepancies utilizing AI/ML methods to identify outlying regions of literature data, assign these regions to features of the experiment itself, and perform an improved evaluation of the 252 Cf PFNS and (b) perform a new experimental measurement of this quantity designed to improve upon the existing literature database. Here, in this work, we report on the AIACHNE 252 Cf PFNS experiment utilizing a new analysis method uncorrelated with all previous measurements: neutron efficiency determinations based on elastic neutron scattering on 12 C and 9 Be . This new method provides an independent test of the existing literature data and evaluation of the 252 Cf (sf) PFNS. The method is described with detailed covariance quantification procedures, as well as a direct discussion of the sources of uncertainty described as requirements in the “Templates” series of papers. The 252 Cf (sf) PFNS reported in this work agrees well with the overall shape of the existing standard PFNS evaluation as well as many literature measurements, thus verifying the current evaluation utilizing new techniques. However, the results suggest that there are deficiencies in the angle-differential 12 C and 9 Be (𝑛, 𝑛) evaluated nuclear data, which produce unphysical structures in the reported result. While these structures are relatively minor, they become obvious because of the high statistical precision of the data and the expected smooth continuity of the 252 Cf (sf) PFNS.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Neutron Activation Analysis of Water - A Review
Recent developments in this field are emphasized. After a brief review of basic principles, topics discussed include sources of neutrons, pre-irradiation physical and chemical treatment of samples, neutron capture and gamma-ray analysis, and selected applications. Applications of neutron activation analysis of water have increased rapidly within the last few years and may be expected to increase in the future.
Buchanan, John D.↗
Physics-informed Estimation of the Covariance Matrix for Various Neutron Spectra
A method for estimating covariance matrices which capture the uncertainties in calculated reactor spectra has been developed. This method is based on perturbing the parameters of a physics-based analytic model fitted to a calculated spectrum. The covariance of the perturbed analytic spectra imposes energy-dependent correlations due to the physics of the neutron processes in the reactor, i.e., a fission component, a 1/E down-scatting component, and a thermal Maxwellian component. An analytic model is developed which is shown to produce good fits to several reactor environments. The covariance matrices produced via this method are then used as the prior spectrum in STAYSL least squares spectrum adjustment where it is combined with integral metrics, such as activation measurements, to produce a high-fidelity neutron spectrum characterization. It was concluded that the methodology showed agreeable results for the ACRR free-field spectrum adjustment in STAYSL resulting in a 𝜒 2 value of 2.21 (per degree of freedom), but further work is needed to describe scattering and interface regions.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Numerical Simulation of Irradiation Induced Swelling for STAR 4.1 Blanket
Here, this article presents the preliminary results of FEM implementation of irradiation-induced swelling, hardening, and creep effect using ANSYS user programmable features (UPFs) applied to material properties. The first liquid metal breeding blanket model for STAR 4.1 tokamak as a part of the virtual prototyping system is under development at Princeton Plasma Physics Laboratory (PPPL). Intense neutron irradiation produces significant changes in the physical and mechanical properties of Fe-(8%–9%)Cr-based reduced activation ferritic martensitic (RAFM) steels. An ANSYS model of the breeding blanket was built to involve these irradiation-induced material property changes with neutron fluence distribution mapped from the MCNP model. Simulation results show that significant structure deformation forms from nuclear swelling, stress, and plastic strain arising from DPA gradient through wall thickness. The material degradation effect is not negligible. This modeling feature can either assist in analyzing the structural behaviors with the influence of nuclear swelling or provide guidance to design the structure to withstand irradiation.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Burst Oscillations: A New Spin on Neutron Stars
Observations with NASA's Rossi X-ray Timing Explorer (RXTE) have shown that the X-ray flux during thermonuclear X-ray bursts fr-om accreting neutron stars is often strongly pulsed at frequencies as high as 620 Hz. We now know that these oscillations are produced by spin modulation of the thermonuclear flux from the neutron star surface. In addition to revealing the spin frequency, they provide new ways to probe the properties and physics of accreting neutron stars. I will briefly review our current observational and theoretical understanding of these oscillations and discuss what they are telling us about neutron stars.
Strohmayer, Tod↗