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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Gigarad-tolerant power switches and memory elements

A new class of silicon devices operating without p-n junctions has been studied for radiation hardness. The electric field in these devices is uniform over most of the device, thus causing high-voltage breakdown to increase with electrode spacing. Deep acceptor levels are created in the silicon by diffusing gold atoms into the lattice, or by electron radiation. These acceptor levels, near the center of the band gap, trap out electrons so that the low resistivity of the n-type doped wafer can be raised to intrinsic resistivity. Switching between a high-resistivity state at low currents and a low-resistivity state at high currents occurs at a definite threshold voltage, exhibiting characteristics similar to silicon-controlled rectifiers. Compensating 0.1 ohm-meter (10 ohm-cm) silicon wafers requires electron fluxes of 10 to the 23rd electrons per square meter (10 to the 19th electrons per square centimeter). Experiments demonstrating gamma tolerance to 1 Gigarad(Si) are described. Calculations for maximum tolerable neutron fluence are shown, and a phenomenological explanation for these results is presented.

Joyner, W. T.↗
NASA NTRS1992

Neutron and gamma ray production in the 1991 June X-class flares

We present new calculations of pion radiation and neutron emission from solar flares. We fit the recently reported high energy GAMMA-1 observations with pion radiation produced in a solar flare magnetic loop. We calculate the expected neutron emission in such a loop model and make predictions of the neutron fluences expected from the 1991 June X-class flares.

Ramaty, R.↗
NASA NTRS1992

Preliminary total dose measurements on LDEF

After spending nearly six years in Earth's orbit twenty stacks consisting of radiation detectors and biological objects are now back on Earth. These Free Flyer Biostack experiments are part of the Long Duration Exposure Facility (LDEF). The major objective of the experiments are to investigate the biological effectiveness of single heavy ions of the cosmic radiation in various biological systems and to provide information about the spectral composition of the radiation field and the total dose received in the LDEF orbit. The preliminary analysis of the thermoluminescence dosimeters (TLD) yields maximum absorbed dose rates of 2.24 mGy day(exp -1) behind 0.7 g cm(exp -2) shielding and 1.17 mGy day(exp -1) behind 12 g cm(exp -2) shielding. A thermal neutron fluence of 1.7 n cm(exp -2)s(exp -1) is determined from the differences in absorbed dose for different isotopic mixtures of lithium. The results of this experiment on LDEF are especially valuable since LDEF stayed for almost six years in the prospected orbit of the Space Station Freedom.

Reitz, G.↗
NASA NTRS1994

New data supporting a Sm-146,147-Nd-142,143 formation interval for the lunar mantle

Very small variations in Nd-142 abundance in SNC meteorites lunar basalts, and a terrestrial supracrustal rock, have been attributed to the decay of 103 Ma Sm-146 initially present in basalt source regions in varying abundances as a result of planetary differentiation. We previously interpreted variations in Nd-142 abundances in two Apollo 17 high-Ti basalts, three Apollo 12 low-Ti basalts, and two KREEP basalts as defining an isochron giving a formation interval of approximately 94 Ma for the lunar mantle. Here we report new data for a third Apollo 17 high-Ti basalt, two Apollo 15 low-Ti basalts, the VLT basaltic lunar meteorite A881757 (formerly Asuka 31), basalt-like KREEP impact melt rocks 14310 and 14078, and three terrestrial rock standards. Those lunar samples which were not exposed to large lunar surface thermal neutron fluences yield a revised mantle formation interval of 237 +/- 64 Ma.

Nyquist, L. E.↗
NASA NTRS1995

Preliminary results of radiation measurements on EURECA

The eleven-month duration of the EURECA mission allows long term radiation effects to be studied similarly to those of the Long Duration Exposure Facility (LDEF). Basic data can be generated for projections of crew doses and electronic and computer reliability on spacecraft missions. A radiation experiment has been designed for EURECA which uses passive integrating detectors to measure average radiation levels. The components include a Trackoscope, which employs fourteen plastic nuclear track detector (PNTD) stacks to measure the angular dependence of LET (greater than or equal to 6 keV/microns) radiation. Also included are TLD's for total absorbed doses, thermal/resonance neutron detectors (TRND's) for low energy neutron fluences and a thick PNTD stack for depth dependence measurements. LET spectra are derived from the PNTD measurements. Preliminary TLD results from seven levels within the detector array show that integrated doses inside the flight canister varied from 18.8 plus or minus 0.6 cGy to 38.9 plus or minus 1.2 cGy. The TLD's oriented toward the least shielded direction averaged 53 percent higher in dose than those oriented away from the least shielded direction (minimum shielding toward the least shielded direction varied from 1.13 to 7.9 g/cm(exp 2), Al equivalent). The maximum dose rate on EURECA (1.16 mGy/day) was 37 percent of the maximum measured on LDEF and dose rates at all depths were less than measured on LDEF. The shielding external to the flight canister covered a greater solid angle about the canister than in the LDEF experiments.

Benton, E. V.↗
NASA NTRS1995

Preliminary results of radiation measurements on EURECA

The eleven-month duration of the EURECA mission allows long-term radiation effects to be studied similarly to those of the Long Duration Exposure Facility (LDEF). Basic data can be generated for projections to crew doses and electronic and computer reliability on spacecraft missions. A radiation experiment has been designed for EURECA which uses passive integrating detectors to measure average radiation levels. The components include a Trackoscope, which employs fourteen plastic nuclear track detector (PNTD) stacks to measure the angular dependence of high LET (greater than or equal to 6 keV/micro m) radiation. Also included are TLD's for total absorbed doses, thermal/resonance neutron detectors (TRND's) for low energy neutron fluences and a thick PNTD stack for depth dependence measurements. LET spectra are derived from the PNTD measurements. Preliminary TLD results from seven levels within the detector array show that integrated does inside the flight canister varied from 18.8 +/- 0.6 cGy to 38.9 +/- 1.2 cGy. The TLD's oriented toward the least shielded direction averaged 53% higher in dose than those oriented away from the least shielded direction (minimum shielding toward the least shielded direction varied from 1.13 to 7.9 g/cm(exp 2), Al equivalent). The maximum dose rate on EURECA (1.16 mGy/day) was 37% of the maximum measured on LDEF and dose rates at all depths were less than measured on LDEF. The shielding external to the flight canister covered a greater solid angle about the canister than the LDEF experiments.

Benton, E. V.↗
NASA NTRS1995

Improved Hermetic Feedthrough Seals For Optical Fibers

Improved inorganic sealing materials withstand widely ranging temperatures. Hermetic feedthrough seals for optical fibers withstand temperatures from as low as minus 325 degrees F (about minus 198 degrees C) to as high as 392 degrees F (about 200 degrees C) while maintaining helium leak rate of below 10 to the negative 11th power cm(3)/s. Demonstrated to perform exceptionally through salt spray, sinusoidal and random vibrations (20 to 2000 Hz), mechanical shock (40 g's) thermal shock at extreme temperatures, humidity, and radiation (neutron fluence, gamma, and ion) testing.

Fan, Robert Jui-Lin↗
NASA NTRS1997

Earth and Planetary Science Letters

Systematic measurements of the concentrations of cosmogen Ca-41 (half-life = 1.04 x 10(exp 5) yr) in the Apollo 15 long core 15001-15006 were performed by accelerator mass spectroscopy. Earlier measurements of cosmogenic Be-10, C-14, Al-26, Cl-36, and Mn-53 in the same core have provided confirmation and improvement of theoretical models for predicting production profiles of nuclides by cosmic ray induced spallation in the Moon and large meteorites. Unlike these nuclides, Ca-40 in the lunar surface is produced mainly by thermal neutron capture reactions on Ca-40. The maximum production of Ca-41, about 1 dpm/g Ca, was observed at a depth in the Moon of about 150 g/sq cm. For depths below about 300 g/sq cm, Ca-41 production falls off exponentially with an e-folding length of 175 g/sq cm. Neutron production in the Moon was modeled with the Los Alamos High Energy Transport Code System, and yields of nuclei produced by low-energy thermal and epithermal neutrons were calculated with the Monte Carlo N-Particle code. The new theoretical calculations using these codes are in good agreement with our measured Ca-41 concentrations as well as with Co-60 and direct neutron fluence measurements in the Moon.

K. Nishiizumi↗
NASA NTRS2000

An Improved Neutron Transport Algorithm for Space Radiation

A low-energy neutron transport algorithm for use in space radiation protection is developed. The algorithm is based upon a multigroup analysis of the straight-ahead Boltzmann equation by using a mean value theorem for integrals. This analysis is accomplished by solving a realistic but simplified neutron transport test problem. The test problem is analyzed by using numerical and analytical procedures to obtain an accurate solution within specified error bounds. Results from the test problem are then used for determining mean values associated with rescattering terms that are associated with a multigroup solution of the straight-ahead Boltzmann equation. The algorithm is then coupled to the Langley HZETRN code through the evaporation source term. Evaluation of the neutron fluence generated by the solar particle event of February 23, 1956, for a water and an aluminum-water shield-target configuration is then compared with LAHET and MCNPX Monte Carlo code calculations for the same shield-target configuration. The algorithm developed showed a great improvement in results over the unmodified HZETRN solution. In addition, a two-directional solution of the evaporation source showed even further improvement of the fluence near the front of the water target where diffusion from the front surface is important.

Heinbockel, John H.↗
NASA NTRS2003

Monte Carlo Methods in Materials Science Based on FLUKA and ROOT

A comprehensive understanding of mitigation measures for space radiation protection necessarily involves the relevant fields of nuclear physics and particle transport modeling. One method of modeling the interaction of radiation traversing matter is Monte Carlo analysis, a subject that has been evolving since the very advent of nuclear reactors and particle accelerators in experimental physics. Countermeasures for radiation protection from neutrons near nuclear reactors, for example, were an early application and Monte Carlo methods were quickly adapted to this general field of investigation. The project discussed here is concerned with taking the latest tools and technology in Monte Carlo analysis and adapting them to space applications such as radiation shielding design for spacecraft, as well as investigating how next-generation Monte Carlos can complement the existing analytical methods currently used by NASA. We have chosen to employ the Monte Carlo program known as FLUKA (A legacy acronym based on the German for FLUctuating KAscade) used to simulate all of the particle transport, and the CERN developed graphical-interface object-oriented analysis software called ROOT. One aspect of space radiation analysis for which the Monte Carlo s are particularly suited is the study of secondary radiation produced as albedoes in the vicinity of the structural geometry involved. This broad goal of simulating space radiation transport through the relevant materials employing the FLUKA code necessarily requires the addition of the capability to simulate all heavy-ion interactions from 10 MeV/A up to the highest conceivable energies. For all energies above 3 GeV/A the Dual Parton Model (DPM) is currently used, although the possible improvement of the DPMJET event generator for energies 3-30 GeV/A is being considered. One of the major tasks still facing us is the provision for heavy ion interactions below 3 GeV/A. The ROOT interface is being developed in conjunction with the CERN ALICE (A Large Ion Collisions Experiment) software team through an adaptation of their existing AliROOT (ALICE Using ROOT) architecture. In order to check our progress against actual data, we have chosen to simulate the ATIC14 (Advanced Thin Ionization Calorimeter) cosmic-ray astrophysics balloon payload as well as neutron fluences in the Mir spacecraft. This paper contains a summary of status of this project, and a roadmap to its successful completion.

Pinsky, Lawrence↗
NASA NTRS2009

The Lunar Regolith as a Remote Sensing Target for the Lunar Reconnaissance Orbiter (LRO)

Of the 6 instruments and one technology demonstration aboard the LRO, only CRaTER does not measure some kind of interaction of particles with the lunar regolith. LEND detects neutron fluence that contains information about the number density of protons in the upper regolith. To infer the presence of protons, the PI must assume a model that characterizes the surface as a collection of atoms. Thus, LEND does not sense the regolith as a structure. LROC, LOLA, and LAMP sense reflected photons whose wavelength is much shorter than the median particle size in the regolith. The photons interact with electrons, either in atomic shells or in chemical bonds. These interactions occur within a nanometer or so of the surface of a particle. Thus, the particles are macroscopic objects and models of the reflection process invoke ray-tracing optics. DIVINER senses photons that have been emitted by surface particles through thermal phonon processes. The wavelengths detected by the instrument are of the same order as the median particle size, and the photons contain information on particle dimensions as well as the molecular bonds in the constituent compounds. The Mini-RF synthetic aperture radar generates and detects photons of a few centimeters wavelength that interact with the regolith as a dielectric, the dielectric properties of the particulate component being described through effective medium theory. However, the interaction with rocks (macroscopic objects of interest to geologists) can be characterized using Fresnel or Mie models of electromagnetic properties.

Mendell, Wendell W.↗
NASA NTRS2010

Cosmogenic Samarium-150 and Calcium-41 in Norton County

Though brecciated, the Norton County (NC) aubrite contains little or no trapped noble gas and has been widely assumed to have a simple if unusually long cosmic ray exposure (CRE), 115 Ma. One goal of this ongoing study of NC has been to search for signs of pre-irradiation as proposed. One may test for multiple stages of CRE by comparing thermal neutron fluences inferred from Ca-41 (t(sub 1/2)=0.1 Ma) activities, which reflect irradiation conditions over the last approximately 0.3 Ma, with those inferred from (stable) Sm isotope abundances, which integrate over the entire CRE history. In the case of a one-stage exposure the fluences should agree. We focus on these particular comparisons because the properties of NC - its long CRE exposure, relatively large size, and low iron concentration - all promised high production rates and ease of measurement. Previously, we reported on several cosmogenic nuclides in NC. Here we present new Ca-41 data, Sm isotope measurements, and comparisons with model calculations of cosmic ray production.

Fink, D.↗
NASA NTRS2010

Sulfur Isotopes in Gas-rich Impact-Melt Glasses in Shergottites

Large impact melt glasses in some shergottites contain huge amounts of Martian atmospheric gases and they are known as gas-rich impact-melt (GRIM) glasses. By studying the neutron-induced isotopic deficits and excesses in Sm-149 and Sm-150 isotopes resulting from Sm-149 (n,gamma) 150Sm reaction and 80Kr excesses produced by Br-79 (n,gamma) Kr-80 reaction in the GRIM glasses using mass-spectrometric techniques, it was shown that these glasses in shergottites EET79001 and Shergotty contain regolith materials irradiated by a thermal neutron fluence of approx.10(exp 15) n/sq cm near Martian surface. Also, it was shown that these glasses contain varying amounts of sulfates and sulfides based on the release patterns of SO2 (sulfate) and H2S (sulfide) using stepwise-heating mass-spectrometric techniques. Furthermore, EMPA and FE-SEM studies in basaltic-shergottite GRIM glasses EET79001, LithB (,507& ,69), Shergotty (DBS I &II), Zagami (,992 & ,994) showed positive correlation between FeO and "SO3" (sulfide + sulfate), whereas those belonging to olivine-phyric shergottites EET79001, LithA (,506, & ,77) showed positive correlation between CaO/Al2O3 and "SO3".

Rao, M. N.↗
NASA NTRS2012

Correlated Observations of Epithermal Neutrons and Polar Illumination for Orbital Neutron Detectors

We correlate Lunar Reconnaisance Orbiter's (LRO) Lunar Exploration Neutron Detector (LEND) and the Lunar Prospector Neutron Spectrometer's (LPNS) orbital epithermal neutron maps of the Lunar high-latitudes with co-registered illumination maps derived from the Lunar Orbiter Laser Altimeter (LOLA) topography. Epithermal neutron count rate maps were derived from the LEND: 1) Collimated Sensor for Epithermal Neutrons, CSETNI-4 2) Uncollimated Sensor for Epithermal Neutrons, SETN and the Uncollimated Lunar Prospector: 3) Low-altitude and 4) High-altitude mapping phases. In this abstract we illustrate 1) and 3) and include 2) and 4) in our presentation. The correlative study provides unique perspectives on the regional epithermal neutron fluences from the Lunar polar regions under different detector and altitude configurations.

McClanahan, T. P.↗
NASA NTRS1967

Neutron detector simultaneously measures fluence and dose equivalent

Neutron detector acts as both an area monitoring instrument and a criticality dosimeter by simultaneously measuring dose equivalent and fluence. The fluence is determined by activation of six foils one inch below the surface of the moderator. Dose equivalent is determined from activation of three interlocked foils at the center of the moderator.

Dvorak, R. F.↗
DOE OSTI2025

Development of mesopores in superfine grain graphite neutron-irradiated at high fluence

Microstructural changes induced by neutron irradiation of superfine grain graphite G347A (Tokai Carbon, Japan) were examined by nitrogen adsorption at 77K and by three microscopy techniques (SEM, TEM and FIB-SEM tomography). The specimens were irradiated at doses of up to 30 dpa, covering stages before and after the turnaround fluence at three temperatures (300, 450, 750 °C) of their irradiation envelope. The initial graphite densification at low fluences did not produce any detectable effect in the pore size range (<350 nm) measured by gas adsorption. However, graphite irradiated at high fluences, after turnaround, showed severe structural changes. At all three temperatures and high irradiation fluences, gas adsorption revealed significant increase of the volume of narrow mesopores (<5–20nm) and up to five times increase of BET surface area, both in linear relationship with the relative volume expansion. Analysis of microscopy images showed multiplication of fine macropores (>50 nm) at high irradiation fluences and more structural changes on multiple scales, from nanometers to microns. This work demonstrates the unique ability of gas adsorption techniques to analyze open pores with sizes between sub-nanometer and sub-micron in bulk nuclear graphite, with supporting microscopy results.

I. Contescu, Cristian↗