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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Magnetized Target Fusion

Magnetized target fusion (MTF) is under consideration as a means of building a low mass, high specific impulse, and high thrust propulsion system for interplanetary travel. This unique combination is the result of the generation of a high temperature plasma by the nuclear fusion process. This plasma can then be deflected by magnetic fields to provide thrust. Fusion is initiated by a small traction of the energy generated in the magnetic coils due to the plasma's compression of the magnetic field. The power gain from a fusion reaction is such that inefficiencies due to thermal neutrons and coil losses can be overcome. Since the fusion reaction products are directly used for propulsion and the power to initiate the reaction is directly obtained from the thrust generation, no massive power supply for energy conversion is required. The result should be a low engine mass, high specific impulse and high thrust system. The key is to successfully initiate fusion as a proof-of-principle for this application. Currently MSFC is implementing MTF proof-of-principle experiments. This involves many technical details and ancillary investigations. Of these, selected pertinent issues include the properties, orientation and timing of the plasma guns and the convergence and interface development of the "pusher" plasma. Computer simulations of the target plasma's behavior under compression and the convergence and mixing of the gun plasma are under investigation. This work is to focus on the gun characterization and development as it relates to plasma initiation and repeatability.

Steven T. Griffin↗
NASA NTRS2011

Polymeric Materials With Additives for Durability and Radiation Shielding in Space

Polymeric materials are attractive for use in space structures because of their light weight and high strength In addition, polymers are made of elements with low atomic numbers (Z), primarily carbon (C), hydrogen (H), oxygen (0), and nitrogen (N) which provide the best shielding from galactic cosmic rays (GCR) (ref. 1). Galactic cosmic rays are composed primarily of nuclei (i.e., fully ionized atoms) plus a contribution of about 2% from electrons and positrons. There is a small but significant component of GCR particles with high charge (Z > 10) and high energy (E >100 GeV) (ref. 2). These so-called HZE particles comprise only 1 to 2% of the cosmic ray fluence but they interact with very high specific ionization and contribute 50% of the long- term dose to humans. The best shield for this radiation would be liquid hydrogen, which is not feasible. For this reason, hydrogen-containing polymers make the most effective practical shields. Moreover, neutrons are formed in the interactions of GCR particles with materials. Neutrons can only lose energy by collisions or reactions with a nucleus since they are uncharged. This is a process that is much less probable than the Coulombic interactions of charged particles. Thus, neutrons migrate far from the site of the reaction in which they were formed. This increases the probability of neutrons reaching humans or electronic equipment. Fast neutrons (> 1 MeV) can interact with silicon chips in electronic equipment resulting in the production of recoil ions which can cause single event upsets (SEU) in sensitive components (ref. 3). Neutrons lose energy most effectively by elastic collisions with light atoms, particularly hydrogen atoms. Therefore, hydrogen-containing polymers are not only effective in interacting with GCR particles; they are also effective in reducing the energy of the neutrons formed in the interactions.

Kiefer, Richard↗
NASA NTRS1992

Heavy-element abundances from a neutron burst that produces Xe-H

We examine quantitatively the suggestion that the heavy anomalous isotopes of Xe-HL found in meteoritic diamonds were produced by a short intense neutron burst and then implanted into the diamonds. Using a large nuclear reaction network we establish one (out of many) neutron irradiation hostories that successfully reproduces the heavy isotopes of Xe-HL, and then evaluate what that same history would produce in every heavy element. This has become more relevant following recent measurement of anomalous Ba and Sr in those same diamond samples. Therefore we offer these calculations as a guide to the anomalies to be expected in all elements if this scenario is correct. We also discuss several other aspects of the problem, especially the established contradictions for Ba, the observed Kr pattern, the near normalcy of Xe-129 and some related astrophysical ideas. In particular we argue from p-process theory that the observed deficit of Kr-78 in correlation with Xe-(124-126) excess implicates Type II supernovae as the diamond sources.

Howard, W. M.↗
NASA NTRSDate not supplied

LENR Products: Lattice Confinement Fusion (LCF), Fission, or Both?

Lattice Confinement Fusion (LCF) or Low Energy Nuclear Reactions (LENR) generate heat from the high energy products they produce. Conventionally, d-d fusion reactions may produce either 2.45 MeV neutrons, 3 MeV protons, or high energy gammas. Generally, fission will give 5-10x the excess energy of fusion. However, aneutronic “cold fusion” would provide 24 MeV/reaction, D(d,γ) 4 He, where the gamma is suppressed. In a series of pressurized gas cycling experiments with a palladium silver (75 wt.% Pd and 25 wt.% Ag or Pd25Ag) alloy [1], samples cycled with deuterium showed excess heat via unexplained temperature rises. Post-test analysis of the Pd25Ag samples using a Scanning Electron Microscope (SEM/EDX) showed several molten features containing anomalous elements other than Pd and Ag. Researchers such as Liu et al [2] have also observed transmutations under similar conditions. These molten areas and anomalous elements suggest Pd fission. This nuclear process has been referred to as nuclear disintegration. Either nuclear fission or disintegration may result in neutron rich fragments. The fragments would rapidly beta decay to shorter lived daughters until they reach stability. We’ve observed evidence of both fusion and fission products [3]. Figure 1 shows neutron spectroscopy showing fusion and boosted neutron energies in bremsstrahlung-initiated fusion of TiD2. Figure 2 shows possible fission products from D2 gas cycled Pd25Ag alloy. Alternatively, Oppenheimer-Phillips stripping reactions, enhanced by electron screening [4] may also occur. In this case, the 8.6 MeV binding energy per Pd or Ag minus the 2.2 MeV deuteron binding energy leaves 6.4 MeV distributed between the reaction products. The energy is shared inversely proportional to the masses of the stripped off nucleon, p or n, and the new target nucleus.

Theresa L. Benyo↗
NASA NTRSDate not supplied

LENR Products: Lattice Confinement Fusion (LCF), Fission, or Both?

Lattice Confinement Fusion (LCF) or Low Energy Nuclear Reactions (LENR) generate heat from the high energy products they produce. Conventionally, d-d fusion reactions may produce either 2.45 MeV neutrons, 3 MeV protons, or high energy gammas. Generally, fission will give 5-10x the excess energy of fusion. However, aneutronic “cold fusion” would provide 24 MeV/reaction, D(d,γ) 4 He, where the gamma is suppressed. In a series of pressurized gas cycling experiments with a palladium silver (75 wt.% Pd and 25 wt.% Ag or Pd25Ag) alloy [1], samples cycled with deuterium showed excess heat via unexplained temperature rises. Post-test analysis of the Pd25Ag samples using a Scanning Electron Microscope (SEM/EDX) showed several molten features containing anomalous elements other than Pd and Ag. Researchers such as Liu et al [2] have also observed transmutations under similar conditions. These molten areas and anomalous elements suggest Pd fission. This nuclear process has been referred to as nuclear disintegration. Either nuclear fission or disintegration may result in neutron rich fragments. The fragments would rapidly beta decay to shorter lived daughters until they reach stability. We’ve observed evidence of both fusion and fission products [3]. Figure 1 shows neutron spectroscopy showing fusion and boosted neutron energies in bremsstrahlung-initiated fusion of TiD2. Figure 2 shows possible fission products from D 2 gas cycled Pd25Ag alloy. Alternatively, Oppenheimer-Phillips stripping reactions, enhanced by electron screening [4] may also occur. In this case, the 8.6 MeV binding energy per Pd or Ag minus the 2.2 MeV deuteron binding energy leaves 6.4 MeV distributed between the reaction products. The energy is shared inversely proportional to the masses of the stripped off nucleon, p or n, and the new target nucleus.

Theresa L. Benyo↗
NASA NTRS1992

On the evolution of slowly accreting neutron stars

In the light of recent calculations of pycnonuclear reaction rates for light elements, we consider the problem of slow interstellar accretion onto old, possibly magnetized neutron stars. We argue that accretion will occur at the Hoyle-Lyttleton rate after the star has spun down in less than about 10 exp 9 yr. A deep ocean of liquid hydrogen and helium, extending down to depths about 100 m, will cover the surface of the star once it has accreted about 10 exp 25 g of gas. Beneath the ocean will be a layer of almost pure solid O-16 which undergoes two-stage electron capture to C-16 above a pressure 2.7 x 10 exp 28 dyne/sq cm, corresponding to an accreted mass of about 10 exp 27 g. Taking into account the presence of multiple layers of distinct chemical composition, we conclude that the crust will be stable to small perturbations under the conditions envisaged for instellar accretion. A thick layer of up to 10 exp 27 g of metastable C-16 will then accumulate. We discuss the implications of these results to old Galactic neutron stars as sources of gamma-ray bursts.

Blaes, O. M.↗
NASA NTRS1971

Neutron production mechanism in a plasma focus.

The neutrons emitted by a plasma focus were analyzed by using a time-of-flight method. Flight paths as large as 80 m were used to obtain better than 10% energy resolution. The energy spectrum of neutrons from d-d reactions in the plasma focus shows a sharp onset with average maximum energies of 2.8 and 3.2 MeV in the radial and the axial directions, respectively. The average half-width of the energy spectrum was 270 keV with a shot-to-shot variation between 150 and 400 keV. Simultaneous measurements in the axial and radial directions showed no appreciable difference in the half-widths and thus indicated randomly oriented ion velocities in the plasma. A converging ion model is described which is found to be in agreement with the measured quantities.

Lee, J. H.↗
NASA NTRS1974

Gamma ray lines from solar flares

The strongest line, both predicted theoretically and detected observationally at 2.2 MeV, is due to neutron capture by protons in the photosphere. The neutrons are produced in nuclear reactions of flare accelerated particles which also positrons and prompt nuclear gamma rays. From the comparison of the observed and calculated intensities of the lines at 4.4 or 6.1 MeV to that of the 2.2 MeV line, it is possible to deduce the spectrum of accelerated nuclei in the flare region; and from the absolute intensities of these lines, it is possible to obtain the total number of accelerated nuclei at the sun. The study of the 2.2 MeV line also gives information on the amount of He-3 in the photosphere. The study of the line at 0.51 MeV resulting from positron annihilation complements the data obtained from the other lines; in addition it gives information on the temperature and density in the annihilation region.

Ramaty, R.↗
NASA NTRS1974

Solar gamma rays

The theory of gamma ray production in solar flares is treated in detail. Both lines and continuum are produced. Results show that the strongest line predicted at 2.225 MeV with a width of less than 100 eV and detected at 2.24 + or - 2.02 MeV, is due to neutron capture by protons in the photosphere. Its intensity is dependent on the photospheric He-3 abundance. The neutrons are produced in nuclear reactions of flare accelerated particles which also produce positrons and prompt nuclear deexcitation lines. The strongest prompt lines are at 4.43 MeV from c-12 and at approximately 6.2 from 0-16 and N-15. The gamma ray continuum, produced by electron bremsstrahlung, allows the determination of the spectrum and number of accelerated electrons in the MeV region. From the comparison of the line and continuum intensities a proton-to-electron ratio of about 10 to 100 at the same energy for the 1972, August 4 flare. For the same flare the protons above 2.5 MeV which are responsible for the gamma ray emission produce a few percent of the heat generated by the electrons which make the hard X rays above 20 keV.

Ramaty, R.↗
NASA NTRS1975

Gamma-ray lines from solar flares

The theory of gamma-ray line production in solar flares is treated in detail. The strongest line, both predicted theoretically and detected observationally at 2.2 MeV, is due to neutron capture by protons in the photosphere. The neutrons are produced in nuclear reactions of flare-accelerated particles which also produce positrons and prompt nuclear gamma rays. From the comparison of the observed and calculated intensities of the lines at 4.4 or 6.1 MeV to that of the 2.2-MeV line, it is possible to deduce the spectrum of accelerated nuclei in the flare region; and from the absolute intensities of these lines, it is possible to obtain the total number of accelerated nuclei at the sun. The study of the 2.2-MeV line also gives information on the amount of He-3 in the photosphere. The study of the line at 0.51 MeV resulting from positron annihilation complements the data obtained from the other lines. In addition, it gives information on the temperature and density in the annihilation region and on the anisotropy of the accelerated electron beam which produces continuum gamma rays at energies greater than about 1 MeV.

Ramaty, R.↗
NASA NTRS1979

Predictions of induced background radiations at gamma/X-ray experiment envelopes in NASA spacecraft

This work seeks to predict secondary radiation levels induced in spacecraft structures by space protons. The radiations analyzed are secondary neutrons from spallation and evaporation reactions and gamma and beta rays from the decay of induced radioactivity, as sources of interfering background to spaceborne measurements of galactic and planetary gamma rays below 10 MeV. The spacecraft considered are the Multi-Mission Spacecraft (MMS) and the Space Shuttle, modeled as spherical shells. The proton environment is that of the South Atlantic Anomaly, as well as cosmic ray protons. The induced radioactivity is analyzed in terms of its interference with various gamma-ray lines of astrophysical interest, as well as its contribution to several spectral regions of the gamma-ray continuum. The buildup of the line and continuum radioactivity background is predicted for a period of nearly 9 months in orbit (approximately 4100 orbits). In addition, background contributions from cosmic ray electron bremsstrahlung and earth gamma-ray albedo are estimated.

Fischbein, W. L.↗
NASA NTRS1983

The waiting point approximation in R-process calculations

The steady flow approximation to the r-process has been used to evaluate the validity of the waiting point assumption (that, for a given charge number Z, neutron captures become balanced by neutron photodisintegrations) under a variety of conditions. The criterion for the accuracy of the approximation for any set of nuclei with the same value of Z is that the ratio of the total rate of neutron photodisintegration in those nuclei to the total rate of neutron captures should be close to unity. No set of conditions involving neutron production by helium thermonuclear reactions (at temperatures up to 10 to the 9th K) could be found for which the waiting point approximation is useful for all values of Z, and it is recommended that all such r-process calculations not use this approximation. At higher temperatures, such as those characteristic of explosive carbon burning (2 x 10 to the 9th K), the waiting point approximation is much better.

Cameron, A. G. W.↗
NASA NTRS1997

AXAF Detector Backgrounds Produced By Cosmic Ray Protons

One of the science instruments on the Advanced X-ray Astrophysics Facility (AXAF), planned for launch in 1998 into a highly elliptical (10,000 km x 140,000 km) orbit, is a microchannel plate High Resolution Camera (HRC). This detector is designed to provide imaging and spectroscopic observations of x-rays emitted by stellar sources in the 0.1 to 10 keV energy range. Described here are analyses made to determine the expected time-dependent detector background from prompt and delayed (activation) radiation initiated by galactic cosmic-ray (GCR) proton interactions in the spacecraft and payload. Numerical simulations were made using the coupled set of Monte Carlo radiation transport codes, analysis software, and data bases shown. The major codes are HETC for nucleon-meson transport, EGS for simulating electromagnetic cascades, and MORSE for low-energy (less than 15 MeV) neutron transport. The simulation follows the transport history of photons in the energy range from - 100 GeV down to approx. 0.1 keV due to gamma-ray sources from neutral pion decay, high-energy (spallation) collisions, and low-energy neutron inelastic scattering and capture reactions. Also included is radioisotope production and the tracking of gamma-rays, electrons, and positrons from induced radioactivity.

Armstrong, T. W.↗
NASA NTRS2012

The Grand Geochemistry of 4 Vesta: First Results

On 12-Dec-2011, the Dawn spacecraft commenced low altitude mapping of the giant asteroid, 4 Vesta (264-km mean radius). Dawn's roughly circular, polar, low altitude mapping orbit (LAMO) has a mean radius of 470 km, placing the spacecraft within about 210 km of Vesta's surface. At these altitudes, Dawn s Gamma Ray and Neutron Detector (GRaND) is sensitive to Vesta's elemental com-position (Fig. 1). GRaND will acquire data in LAMO for up to 16 weeks, which is sufficient to map the elemental composition of the entire surface of Vesta. The timing of LAMO enables us to report the first results of our geochemistry investigation at this conference. In this abstract, we present an overview of our initial observations, based on data acquired at high altitude and during the first weeks of LAMO. GRaND overview. A detailed description of the GRaND instrument, science objectives and prospective results is given in [1]. At low altitudes, GRaND is sensitive to gamma rays and neutrons produced by cosmogenic nuclear reactions and radioactive decay occurring within the top few decimeters of the surface and on a spatial scale of a few hundred kilometers. From these nuclear emissions, the abundance of several major- and minor-elements, such as Fe, Mg, Si, K, and Th can be determined. Assuming the howardite, eucrite, and diogenite (HED) meteorites are representative of Vesta s crustal composition [2], then GRaND will be able to map the mixing ratios of whole-rock HED end-members, enabling the determination of the relative proportions of basaltic eucrite, cumulate eucrite, and diogenite as well as the proportions of mafic and plagioclase minerals [1,3]. GRaND will also search for compositions not well-represented in the meteorite collection, such as evolved, K-rich lithologies [4], and outcrops of olivine from Vesta s mantle or igneous intrusions in major impact basins [5]. The search for a possible mesosiderite source region is described in [6]. GRaND will globally map the abundance of H, providing constraints on the delivery of H by solar wind and the infall of carbonaceous chondrite materials.

Prettyman, T. H.↗
NASA NTRS2000

Materials for Low-Energy Neutron Radiation Shielding

Various candidate aircraft and spacecraft materials were analyzed and compared in a low-energy neutron environment using the Monte Carlo N-Particle (MCNP) transport code with an energy range up to 20 MeV. Some candidate materials have been tested in particle beams, and others seemed reasonable to analyze in this manner before deciding to test them. The two metal alloys analyzed are actual materials being designed into or used in aircraft and spacecraft today. This analysis shows that hydrogen-bearing materials have the best shielding characteristics over the metal alloys. It also shows that neutrons above 1 MeV are reflected out of the face of the slab better by larger quantities of carbon in the material. If a low-energy absorber is added to the material, fewer neutrons are transmitted through the material. Future analyses should focus on combinations of scatterers and absorbers to optimize these reaction channels and on the higher energy neutron component (above 50 MeV).

Singleterry, Robert C., Jr.↗
NASA NTRS2020

Novel Nuclear Reactions Observed in Bremsstrahlung-Irradiated Deuterated Metals

d-D nuclear fusion events were observed in an electronscreened, deuterated metal lattice by reacting cold deuterons with hot deuterons (d*) produced by elastically scattered neutrons originating from bremsstrahlung photodissociation (where “d” and “D” denote 2H). Exposure of deuterated materials (ErD3 and TiD2) to photon energies in the range of 2.5 to 2.9 MeV resulted in photodissociation neutrons that were below 400 keV and also the 2.45-MeV neutrons, consistent with 2H(d, n)3He fusion. Additionally, neutron energies of approximately 4 and 5 MeV for TiD2 and ErD3 were measured, consistent with either boosted neutrons from kinetically heated deuterons or Oppenheimer-Phillips stripping reactions in the highly screened environment. Neutron spectroscopy was conducted using calibrated lead shielded liquid (EJ-309) and plastic (stilbene) scintillator detectors. The data support the theoretical analysis in a companion paper, predicting fusion reactions and subsequent reactions in the highly screened environment.

Bruce M Steinetz↗
NASA NTRS1995

Shielding materials for highly penetrating space radiations

Interplanetary travel involves the transfer from an Earth orbit to a solar orbit. Once outside the Earth's magnetosphere, the major sources of particulate radiation are solar cosmic rays (SCR's) and galactic cosmic rays (GCR's). Intense fluxes of SCR's come from solar flares and consist primarily of protons with energies up to 1 GeV. The GCR consists of a low flux of nuclei with energies up to 10(exp 10) GeV. About 70 percent of the GCR are protons, but a small amount (0.6 percent) are nuclei with atomic numbers greater than 10. High energy charged particles (HZE) interact with matter by transferring energy to atomic electrons in a Coulomb process and by reacting with an atomic nucleus. Energy transferred in the first process increases with the square of the atomic number, so particles with high atomic numbers would be expected to lose large amounts of energy by this process. Nuclear reactions produced by (HZE) particles produce high-energy secondary particles which in turn lose energy to the material. The HZE nuclei are a major concern for radiation protection of humans during interplanetary missions because of the very high specific ionization of both primary and secondary particles. Computer codes have been developed to calculate the deposition of energy by very energetic charged particles in various materials. Calculations show that there is a significant buildup of secondary particles from nuclear fragmentation and Coulomb dissociation processes. A large portion of these particles are neutrons. Since neutrons carry no charge, they only lose energy by collision or reaction with a nucleus. Neutrons with high energies transfer large amounts of energy by inelastic collisions with nuclei. However, as the neutron energy decreases, elastic collisions become much more effective for energy loss. The lighter the nucleus, the greater the fraction of the neutron's kinetic energy that can be lost in an elastic collision. Thus, hydrogen-containing materials such as polymers are most effective in reducing the energy of neutrons. Once neutrons are reduced to very low energies, the probability for undergoing a reaction with a nucleus (the cross section) becomes very high. The product of such a reaction is often radioactive and can involve the release of a significant amount of energy. Thus, it is important to provide protection from low energy neutrons during a long duration space flight. Among the light elements, lithium and boron each have an isotope with a large thermal neutron capture cross section, Li-6 and B-10. However, B-10 is more abundant in the naturally-occurring element than Li-6, has a thermal neutron capture cross section four times that of Li-6, and produces the stable products, He-4 and Li-7 in the interaction while Li-6 produces radioactive tritium (H-3). Thus, boron is the best light-weight material for thermal neutron absorption in spacecraft. The work on this project was focused in two areas: computer design where existing computer codes were used, and in some cases modified, to calculate the propagation and interactions of high energy charged particles through various media, and materials development where boron was incorporated into high performance materials.

Kiefer, Richard L.↗