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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Cosmogenic neutron-capture-produced nuclides in stony meteorites

The complete neutron-flux results and production rates for Cl-36, Ni-59, and Co-60 in stony meteorites of various radii and composition are presented. The relative neutron source strengths and neutron production-versus-depth profiles were determined by using calculated H-3 production rates. The absolute source strengths were normalized to that determined for the moon by Woolum et al. (1975). The energy spectrum of the source neutrons and the neutron transport calculations, which employed the ANISN computer code, were similar to those used for the moon by Lingenfelter et al. (1972). The production rates of the three radionuclides were determined as a function of depth in various spherical meteoroids from the calculated equilibrium neutron-flux distributions and from energy-dependent neutron-capture cross sections. Rates for producing these radionuclides by spallation reactions were also calculated.

Spergel, M. S.↗
NASA NTRS1986

Status of NTD Ge bolometer material and devices

The first IR Detector Technology Workshop took place at NASA Ames Research Center on July 12 and 13, 1983. The conclusions presented at that meeting are still valid. More was learned about the physics of hopping conduction at very low temperatures which will be important for bolometer design and operation at ever decreasing temperatures. Resistivity measurements were extended down to 50 mK. At such low temperatures, precise knowledge of the neutron capture cross sections sigma (sub n) of the various Ge isotopes is critical if one is to make an accurate prediction of the dopant concentrations and compensation, and therefore resistivity, that will result from a given irradiation. An empirical approach for obtaining the desired resistivity material is described and the process of conducting a set of experiments which will improve the knowledge of the effective sigma (sub n) values for a given location in a particular reactor is discussed. A wider range of NTD Ge samples is now available. Noise measurements on bolometers with ion implanted contacts show the no 1/f noise component appears down to 1 Hz and probably lower.

Haller, E. E.↗
NASA NTRS1989

Calculation of two-neutron multiplicity in photonuclear reactions

The most important particle emission processes for electromagnetic excitations in nucleus-nucleus collisions are the ejection of single neutrons and protons and also pairs of neutrons and protons. Methods are presented for calculating two-neutron emission cross sections in photonuclear reactions. The results are in a form suitable for application to nucleus-nucleus reactions.

Norbury, John W.↗
NASA NTRS1990

Calculation of two-neutron multiplicity in photonuclear reactions

The most important particle emission processes for electromagnetic excitations in nucleus-nucleus collisions are the ejection of single neutrons and protons and also pairs of neutrons and protons. Methods are presented for calculating two-neutron emission cross sections in photonuclear reactions. The results are in a form suitable for application to nucleus-nucleus reactions.

Norbury, John W.↗
NASA NTRS1989

Prompt Gamma Activation Analysis (PGAA): Technique of choice for nondestructive bulk analysis of returned comet samples

Prompt gamma activation analysis (PGAA) is a well-developed analytical technique. The technique involves irradiation of samples in an external neutron beam from a nuclear reactor, with simultaneous counting of gamma rays produced in the sample by neutron capture. Capture of neutrons leads to excited nuclei which decay immediately with the emission of energetic gamma rays to the ground state. PGAA has several advantages over other techniques for the analysis of cometary materials: (1) It is nondestructive; (2) It can be used to determine abundances of a wide variety of elements, including most major and minor elements (Na, Mg, Al, Si, P, K, Ca, Ti, Cr, Mn, Fe, Co, Ni), volatiles (H, C, N, F, Cl, S), and some trace elements (those with high neutron capture cross sections, including B, Cd, Nd, Sm, and Gd); and (3) It is a true bulk analysis technique. Recent developments should improve the technique's sensitivity and accuracy considerably.

Lindstrom, David J.↗
NASA NTRS1993

s-process Ba isotopic compositions in presolar SiC from the Murchison meteorite

We have measured, by thermal ionization mass spectrometry, the isotopic composition of Ba in interstellar SiC-enriched samples (the KJ series) prepared from the Murchison meteorite. Ba in these samples is strongly enriched in components plausibly understood as s-process nucleosynthetic products. Inferred s-process compositions are different from the average s-process contribution to solar system materials in the sense of indicating lower effective neutron exposure. There are variations in s-process compositions which correlate with grain size, indicating lower neutron exposure for the larger grains. The inferred s-process compositions differ significantly from previous theoretical predictions, indicating the need for revision of relevant neutron capture cross sections and providing a target for more detailed modeling of s-process nucleosynthesis in specific stellar environments.

Prombo, C. A.↗
NASA NTRS1994

Aluminum 26, Be-10 and Cl-36 depth profiles in the Canyon Diablo iron meteorite

We have measured activities of the long-lived cosmogenic radionuclides Al-26, Be-10, and Cl-36 in 12 fragments of the iron meteorite Canyon Diablo and have constructed production rate-versus-depth profiles of those radionuclides. Profiles determined using differential particle fluxes calculated with the LAHET code system are in good agreement with Al-26, Be-10, and Cl-36 experimental data, but the agreement for Cl-36 was obtained only after neutron-induced cross sections were modified. Profiles calculated with lunar particle fluxes are much lower than experimental Canyon Diablo profiles. The cosmic ray exposure ages of most samples are near 540 m.y.

Michlovich, E. S.↗
NASA NTRS2001

Radiation Transmission Properties of In-Situ Materials

The development of a permanent human presence in space is a key element of NASA's strategic plan for the Human Exploration and Development of Space (HEDS). The habitation of the International Space Station (ISS) is one near-term HEDS objective; the exploration and settlement of the moon and Mars are long-term goals of that plan. Achieving these goals requires maintaining the health and safety of personnel involved in such space operations at a high level, while at the same time reducing the cost of those operations to a reasonable level. Among the limiting factors to prolonged human space operations are the health risks from exposure to the space ionizing radiation environment. In order to keep the risk of radiation induced cancer at acceptable levels, it is necessary to provide adequate shielding from the ionizing radiation environment. The research presented here is theoretical and ground-based experimental study of the neutron production from interactions of GCR-like particles in various shielding components. An emphasis is placed here on research that will aid in the development of in-situ resource utilization. The primary goal of the program is to develop an accurate neutron-production model that is relevant to the NASA HEDS program of designing technologies that will be used in the development of effective shielding countermeasures. A secondary goal of the program is the development of an experimental data base of neutron production cross sections and thick-target yields which will aid model development.

Heilbronn, L.↗
NASA NTRS2005

Lunar and Planetary Science XXXVI, Part 13

Contents include the following: A Fast, Non-Destructive Method for Classifying Ordinary Chondrite Falls Using Density and Magnetic Susceptibility. An Update on Results from the Magnetic Properties Experiments on the Mars Exploration Rovers, Spirit and Opportunity. Measurement Protocols for In Situ Analysis of Organic Compounds at Mars and Comets. Piping Structures on Earth and Possibly Mars: Astrobiological Implications. Uranium and Lead in the Early Planetary Core Formation: New Insights Given by High Pressure and Temperature Experiments. The Mast Cameras and Mars Descent Imager (MARDI) for the 2009 Mars Science Laboratory. MGS MOC: First Views of Mars at Sub-Meter Resolution from Orbit. Analysis of Candor Chasma Interior Layered Deposits from OMEGA/MEX Spectra. Analysis of Valley Networks on Valles Marineris Plateau Using HRSC/MEX Data. Solar Abundance of Elements from Neutron-Capture Cross Sections. Preliminary Evaluation of the Secondary Ion/Accelerator Mass Spectrometer, MegaSIMS. Equilibrium Landforms in the Dry Valleys of Antarctica: Implications for Landscape Evolution and Climate Change on Mars. Continued Study of Ba Isotopic Compositions of Presolar Silicon Carbide Grains from Supernovae. Paleoenviromental Evolution of the Holden-Uzboi Area. Stability of Magnesium Sulfate Minerals in Martian Environments. Tungsten Isotopic Constraints on the Formation and Evolution of Iron Meteorite Parent Bodies. Migration of Dust Particles and Volatiles Delivery to the Inner Planets. On the Sitting of Trapped Noble Gases in Insoluble Organic Matter of Primitive Meteorites. Trapping of Xenon Upon Evaporation-Condensation of Organic Matter Under UV Irradiation: Isotopic Fractionation and Electron Paramagnetic Resonance Analysis. Stability of Water on Mars. A Didactic Activity. Analysis of Coronae in the Parga Chasma Region, Venus. Photometric and Compositional Surface Properties of the Gusev Crater Region, Mars, as Derived from Multi-Angle, Multi-Spectral Investigation of Mars Express HRSC Data. Mapping Compositional Diversity on Mars: Spatial Distribution and Geological Implications. A New Simulation Chamber for Studying Planetary Environments. Folded Structure in Terra Sirenum. Mars. Nitrogen-Noble Gas Static Mass Spectrometry of Genesis Collector Materials. Neon Isotope Heterogeneity in the Terrestrial Mantle: Implication for the Acquisition of Volatile Elements in Terrestrial Planets. The Cosmic Clock, the Cycle of Terrestrial Mass Extinctions.

Source record↗
NASA NTRSDate not supplied

Additive Manufacture of Porous ZrC for NTP In-Core Insulators

Nuclear Thermal Propulsion (NTP) requires the use of in-core insulators to manage to thermal environment between high temperature fuel elements and lower temperature structural components. The unforgiving in-core operating conditions severely limit potential material candidates. Zirconium Carbide (ZrC) is a promising candidate due to a high melting temperature, high compressive strength, hardness, wear resistance, hydrogen compatibility, and low neutron absorption cross sections. However, fully dense ZrC is not an insulator but it has been found that the thermal conductivity of ZrC decreases by increasing porosity to approximately 60 % theoretical density (%TD). Previous methods for generating porous ZrC were difficult, expensive, and time consuming. Binder jet additive manufacture (AM) can print ceramic materials to near net shape. Binder jet AM is not utilized in many applications due to an inherently low post-sintering density on the order of 60 %TD. For this specific application the inherent lower density is leveraged as an advantage in production porous ZrC in order to control the thermal conductivity. A feasibility study was conducted to investigate binder jet AM parameter development for ZrC, heat treatment optimization (burn-out and sinter), microstructural characterization, mechanical testing, and thermal testing to generate near-net shape ZrC components with ~60 %TD with the desired thermal conductivity and mechanical strength.

Omar Mireles↗
NASA NTRSDate not supplied

Additive Manufacture of Porous Zirconium Carbide for Nuclear Thermal Propulsion In-Core Insulators

Nuclear Thermal Propulsion (NTP) requires the use of in-core insulators to manage to thermal environment between high temperature fuel elements and lower temperature structural components. The unforgiving in-core operating conditions severely limit potential material candidates. Zirconium Carbide (ZrC) is a promising candidate due to a high melting temperature, high compressive strength, hardness, wear resistance, hydrogen compatibility, and low neutron absorption cross sections. However, fully dense ZrC is not an insulator but it has been found that the thermal conductivity of ZrC decreases by increasing porosity to approximately 60 % theoretical density (%TD). Previous methods for generating porous ZrC were difficult, expensive, and time consuming. Binder jet additive manufacture (AM) can print ceramic materials to near net shape. Binder jet AM is not utilized in many applications due to an inherently low post-sintering density on the order of 60 %TD. For this specific application the inherent lower density is leveraged as an advantage in production porous ZrC in order to control the thermal conductivity. A feasibility study was conducted to investigate binder jet AM parameter development for ZrC, heat treatment optimization (burn-out and sinter), microstructural characterization, mechanical testing, and thermal testing to generate near-net shape ZrC components with ~60 %TD with the desired thermal conductivity and mechanical strength.

Zirconium Carbide Additive Manufacture↗
NASA NTRSDate not supplied

Additive Manufacture of Porous Zirconium Carbide for Nuclear Thermal Propulsion In-Core Insulators

Nuclear Thermal Propulsion (NTP) requires the use of in-core insulators to manage to thermal environment between high temperature fuel elements and lower temperature structural components. The unforgiving in-core operating conditions severely limit potential material candidates. Zirconium Carbide (ZrC) is a promising candidate due to a high melting temperature, high compressive strength, hardness, wear resistance, hydrogen compatibility, and low neutron absorption cross sections. However, fully dense ZrC is not an insulator but it has been found that the thermal conductivity of ZrC decreases by increasing porosity to approximately 60 % theoretical density (%TD). Previous methods for generating porous ZrC were difficult, expensive, and time consuming. Binder jet additive manufacture (AM) can print ceramic materials to near net shape. Binder jet AM is not utilized in many applications due to an inherently low post-sintering density on the order of 60 %TD. For this specific application the inherent lower density is leveraged as an advantage in production porous ZrC in order to control the thermal conductivity. A feasibility study was conducted to investigate binder jet AM parameter development for ZrC, heat treatment optimization (burn-out and sinter), microstructural characterization, mechanical testing, and thermal testing to generate near-net shape ZrC components with ~60 %TD with the desired thermal conductivity and mechanical strength.

Zirconium Carbide Additive Manufacture↗
NASA NTRS1995

Fission foil detector calibrations with high energy protons

Fission foil detectors (FFD's) are passive devices composed of heavy metal foils in contact with muscovite mica films. The heavy metal nuclei have significant cross sections for fission when irradiated with neutrons and protons. Each isotope is characterized by threshold energies for the fission reactions and particular energy-dependent cross sections. In the FFD's, fission fragments produced by the reactions are emitted from the foils and create latent particle tracks in the adjacent mica films. When the films are processed surface tracks are formed which can be optically counted. The track densities are indications of the fluences and spectra of neutrons and/or protons. In the past, detection efficiencies have been calculated using the low energy neutron calibrated dosimeters and published fission cross sections for neutrons and protons. The problem is that the addition of a large kinetic energy to the (n,nucleus) or (p,nucleus) reaction could increase the energies and ranges of emitted fission fragments and increase the detector sensitivity as compared with lower energy neutron calibrations. High energy calibrations are the only method of resolving the uncertainties in detector efficiencies. At high energies, either proton or neutron calibrations are sufficient since the cross section data show that the proton and neutron fission cross sections are approximately equal. High energy proton beams have been utilized (1.8 and 4.9 GeV, 80 and 140 MeV) for measuring the tracks of fission fragments emitted backward and forward.

Benton, E. V.↗
NASA NTRS2018

Light Ion Double-Differential Cross Sections for Space Radiation

Neutrons and light ions have been shown to make large contributions to space radiation dose equivalent for realistic shielding scenarios. However, there are considerable uncertainties in the calculation of light ion production. Efficient and accurate calculation of light ion double-differential cross sections are required for input into space radiation transport codes. A thermal proton cross section model is developed which includes proton production from the 3 sources of projectile, central fireball, and target. It is shown that this 3-source model is able to explain the low-momentum, small-angle shoulder seen in proton spectra. Using the coalescence model, the thermal proton model is used to calculate light ion double-differential cross sections for use in space radiation transport codes. The 3-source model is also seen to be essential to explain the light ion shoulders, which are even more pronounced than the proton shoulders. Extensive comparisons between models and experimental measurements are shown and necessary future work is discussed.

Norbury, John W.↗
NASA NTRS1972

An integral test of the inelastic cross sections of Pb and Mo using measured neutron spectra

Comparison of measurements and calculations of fast neutron spectra from a radioactive neutron source inside spheres of Mo or Pb and from a cylindrical reactor containing a thick Pb or Mo reflector are used as a test of ENDF cross sections. The sphere leakage spectra were measured at a sphere-to-spectrometer distance of 2 meters using a 54 Ci spherical Am-Be neutron source. Reactor leakage spectrum measurements were made at the surface of the ZP-1 reactor when bare, with a Pb radial reflector 21 cm thick, and with a metallic Mo radial reflector 10 cm thick. In the case of the thin Mo sphere there is agreement between the calculation and measurement. The Pb calculation is much lower than the measurement except at the highest neutron energy. Two-dimensional calculations of reactor spectra result indicate that the reactor source is reasonably well known. Significant differences in leakage spectrum shape for both Mo and Pb reflectors suggest that there are large uncertainties in the inelastic cross sections for Pb and some for Mo.

Shook, D. F.↗
NASA NTRS1986

Neutron capture production rates of cosmogenic 60Co, 59Ni and 36Cl in stony meteorites

Results for neutron flux calculations in stony meteoroids (of various radii and compositions) and production rates for Cl-36, Ni-59, and Co-60 are reported. The Ni-59/Co-60 ratio is nearly constant with depth in most meteorites: this effect is consistent with the neutron flux and capture cross section properties. The shape of the neutron flux energy spectrum, varies little with depth in a meteorite. The size of the parent meteorite can be determined from one of its fragments, using the Ni-59/Co-60 ratios, if the parent meteorite was less than 75 g/cm(2) in radius. If the parent meteorite was larger, a lower limit on the size of the parent meteorite can be determined from a fragment. In C3 chondrites this is not possible. In stony meteorites with R less than 50 g/cm(2) the calculated Co-60 production rates (mass less than 4 kg), are below 1 atom/min g-Co. The highest Co-60 production rates occur in stony meteorites with radius about 250 g/cm(2) (1.4 m across). In meteorites with radii greater than 400 g/cm(2), the maximum Co-60 production rate occurs at a depth of about 175 g/cm(2) in L-chondrite, 125 g/cm(2) in C3 chrondrite, and 190 g/cm(2) in aubrites.

Spergel, M. S.↗