Double charge exchange
Double charge exchange of two neutrons into two protons by positive pion mesons
NEUTRON PHYSICS↗
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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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Coherent neutron proton-hole excitations in nuclei
Coherent neutron proton-hole excitations in zirconium 90 and yttrium 90
EXCITED STATE↗
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.↗
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.↗
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↗
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.↗
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↗
Pulse-Timing Studies of X Ray Pulsars
The pulse-timing projects supported by NASA Grant NAG8-695 were motivated in large part by our long-standing interest in the physics of rotating neutron stars and particularly the variations in rotation due to internal and external fluctuating torques. For accretion-powered pulsars, observed as compact galactic X-ray sources, our work has been motivated by questions regarding the physics of matter accretion, mass transfer, and mass loss in these X-ray binary systems. For rotation-powered pulsars using X-ray, optical, and radio observations, we have examined the internal structure of neutron stars and mechanisms for secular spin-down. These issues are still central to the continuing process of understanding the complex behavior of these fascinating systems. The work supported by this grant is based mainly on Ginga observations of three pulsating X-ray sources. We observed two of these sources (Her X-1 and SMC X-1) within the framework of a NASA-ISAS program for U.S.-Japan collaborations to obtain and analyze Ginga observations. In addition, we joined with members of the Ginga team to apply our pulse-timing methods to PSR 0540-69 data obtained as a collateral benefit of the regular monitoring by Ginga of SN 1987A. In addition to these Ginga observations, there exist other relevant data on all three of these sources. The direction of our investigations has been affected by the necessity of including these supporting data in our analyses, and setting up the necessary collaborations has sometimes entailed extra work that was not anticipated in our proposals. Indeed, we have often taken the initiative in establishing these joint projects.
Deeter, John E.↗
Evidence for Harmonic Content and Frequency Evolution of Oscillations During the Rising Phase of X-ray Bursts From 4U 1636-536
We report on a study of the evolution of burst oscillation properties during the rising phase of X-ray bursts from 4U 1636-536 observed with the proportional counter array (PCA) on board the Rossi X-Ray Timing Explorer (RXTE) . We present evidence for significant harmonic structure of burst oscillation pulses during the early rising phases of bursts. This is the first such detection in burst rise oscillations, and is very important for constraining neutron star structure parameters and the equation of state models of matter at the core of a neutron star. The detection of harmonic content only during the initial portions of the burst rise is consistent with the theoretical expectation that with time the thermonuclear burning region becomes larger, and hence the fundamental and harmonic amplitudes both diminish. We also find, for the first time from this source, strong evidence of oscillation frequency increase during the burst rise. The timing behavior of harmonic content, amplitude, and frequency of burst rise oscillations may be important in understanding the spreading of thermonuclear flames under the extreme physical conditions on neutron star surfaces.
Bgattacharyya, Sudip↗