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NASA NTRS1991

Bremsstrahlung emission of the SN1987A interior

The down-scattering of gamma photons stores a significant fraction of the total energy in recoil electrons. This paper presents the bremsstrahlung emission of those recoil electrons in SN1987A. If the bolometric luminosity derives from radioactive decay, the bremsstrahlung emissivity must be present, but has not previously been treated. Initially it was our hope to account for the Ginga 16-28 keV measurement of SN1987A or to find a detectable X-ray luminosity near 1 keV for ROSAT. Although this bremsstrahlung emission fails to explain Ginga fluxes, it dominates the X-ray fluxes below 20 keV and can have detectable consequences for the X-ray lines from circumstellar matter. Results for day 175, 500, 1000, and 1500 are shown.

The, Lih-Sin↗

NASA NTRS1991

Solar-cosmic-ray fluxes during the last ten million years

The fluxes of energetic (E is greater than or approximately equal to 10 MeV) solar particles in the vicinity of the earth in the past can be determined from nuclides that they produced in the top centimeter of lunar rocks. Activity-vs-depth profiles of short-lived radioactivities measured in the top centimeter of lunar rocks agree with profiles calculated with directly measured solar-proton fluxes since about 1965 and were used with indirect observations to get solar-proton fluxes back to 1956. Lunar-rock profiles for long-lived radionuclides have been used to infer solar-proton fluxes averaged over several time periods in the past. New results are reported for solar-proton-produced Kr-81 measured in lunar rock 68815. Activities of 76,000-yr Ni-59 can be used to get fluxes of solar alpha particles averaged over the last 100,000 yr. The average solar-proton fluxes in the past are not greatly different from those observed during the last three 11-yr solar cycles. The work that needs to be done to determine more and better fluxes of energetic particles from the sun in the past is discussed.

Reedy, Robert C.↗

NASA NTRS1992

Interstellar SiC with unusual isotopic compositions - Grains from a supernova?

Results are presented from an ion microprobe mass spectrometric analyses of five SiC grains from the Murchison carbonaceous meteorite. Unlike most interstellar SiC grains from primitive meteorites, the five grains from the Murchison meteorite show large excesses of C-12 (up to 28 times solar) and N-15 (up to 22 times solar), depletion in Si-29 and Si-30 (up to 59 percent), Al-26/Al-27 ratios between 0.1 and 0.6, and Ti-49 excesses up to 95 percent; in addition, one grain has a large Ca-44 excess (300 percent). The Ca and Ti anomalies point toward explosive nucleosynthesis in supernovae and the in situ decay of the radioactive precursors Ti-44 and V-49 in SiC grains formed in supernova ejecta. However, there is no simple formation scenario that can give a consistent explanation for the isotopic compositions of these grains.

Amari, Sachiko↗

NASA NTRS1988

Measurement of C-12, O-16, and Fe-56 charge changing cross sections in helium at high energy, comparison with cross sections in hydrogen, and application to cosmic-ray propagation

We present measurements of the spallation cross sections of carbon, oxygen, and iron in helium and hydrogen, at beam energies from 540 to 1600 MeV/nucleon, performed by exposing liquid helium, CH2, and C targets. Charge changing cross sections are reported for fragments down to Ne for Fe + alpha and Fe + p reactions, and down to B for O + alpha, O + p, C + alpha, and C + p reactions. Alpha- to p-induced cross section ratios (sigma(sub alpha)/sigma(sub p)) are determined at the same energy per nucleon. From these measurements an empirical formula for the (sigma(sub alpha)/sigma(sub p)) ratios is derived and is found in good agreement with available isotopic cross sections data from radioactivity and radiochemical techniques. These results are applied to the propagation of heavy charged cosmic rays in an interstellar medium with a helium to hydrogen abundance ratio of 0.10. It is shown that the Sc-Mn/Fe ratio prediction is decreased relative to the B/C ratio when compared to propagation calculations in a pure hydrogen interstellar medium.

Ferrando, P.↗

NASA NTRS1992

Gamma ray astronomy

Miscellaneous tasks related to mission operations and data analysis for the Burst and Transient Source Experiment on the Gamma Ray Observatory, to collection, analysis, and interpretation of data from the Marshall Space Flight Center Very Low Frequency transient monitoring program, and to compilation and analysis of induced radioactivity data were performed. The results are summarized and relevant references are included.

Paciesas, William S.↗

NASA NTRS1992

Tagging insulin in microgravity

Knowing the exact subcellular sites of action of insulin in the body has the potential to give basic science investigators a basis from which a cause and cure for this disease can be approached. The goal of this project is to create a test reagent that can be used to visualize these subcellular sites. The unique microgravity environment of the Shuttle will allow the creation of a reagent that has the possibility of elucidating the subcellular sites of action of insulin. Several techniques have been used in an attempt to isolate the sites of action of items such as insulin. One of these is autoradiography in which the test item is obtained from animals fed radioactive materials. What is clearly needed is to visualize individual insulin molecules at their sites of action. The insulin tagging process to be used on G-399 involves the conjugation of insulin molecules with ferritin molecules to create a reagent that will be used back on Earth in an attempt to elucidate the sites of action of insulin.

Dobeck, Michael↗

NASA NTRS1992

Applications for special-purpose minerals at a lunar base

Maintaining a colony on the Moon will require the use of lunar resources to reduce the number of launches necessary to transport goods from the Earth. It may be possible to alter lunar materials to produce minerals or other materials that can be used for applications in life support systems at a lunar base. For example, mild hydrothermal alteration of lunar basaltic glasses can produce special-purpose minerals (e.g., zeolites, smectites, and tobermorites) that in turn may be used in life support, construction, waste renovation, and chemical processes. Zeolites, smectites, and tobermorites have a number of potential applications at a lunar base. Zeolites are hydrated aluminosilicates of alkali and alkaline earth cations that possess infinite, three-dimensional crystal structures. They are further characterized by an ability to hydrate and dehydrate reversibly and to exchange some of their constituent cations, both without major change of structure. Based on their unique absorption, cation exchange, molecular sieving, and catalytic properties, zeolites may be used as a solid support medium for the growth of plants, as an adsorption medium for separation of various gases (e.g., N2 from O2), as catalysts, as molecular sieves, and as a cation exchanger in sewage-effluent treatment, in radioactive waste disposal, and in pollution control. Smectites are crystalline, hydrated 2:1 layered aluminosilicates that also have the ability to exchange some of their constituent cations. Like zeolites, smectites may be used as an adsorption medium for waste renovation, as adsorption sites for important essential plant growth cations in solid support plant growth mediums (i.e., 'soils'), as cation exchangers, and in other important application. Tobermorites are cystalline, hydrated single-chained layered silicates that have cation-exchange and selectivity properties between those of smectites and most zeolites. Tobermorites may be used as a cement in building lunar base structures, as catalysts, as media for nuclear and hazardous waste disposal, as exchange media for waste-water treatment, and in other potential applications. Special-purpose minerals synthesized at a lunar base may also have important applications at a space station and for other planetary missions. New technologies will be required at a lunar base to develop life support systems that are self-sufficient, and the use of special-purpose minerals may help achieve this self-sufficiency.

Ming, Douglas W.↗

NASA NTRS1992

The gabbro-eclogite phase transition and the elevation of mountain belts on Venus

Among the four mountain belts surrounding Lakshmi Planum, Maxwell Montes is the highest and stands up to 11 km above the mean planetary radius and 7 km above Lakshmi Planum. The bulk composition and radioactive heat production of the crust on Venus, where measured, are similar to those of terrestrial tholeiitic basalt. Because the thickness of the low-density crust may be limited by the gabbro-garnet granulite-eclogite phase transitions, the 7-11 km maximum elevation of Maxwell Montes is difficult to understand except in the unlikely situation that the crust contains a large volume of magma. A possible explanation is that the base of the crust is not in phase equilibrium. It has been suggested that under completely dry conditions, the gabbro-eclogite phase transition takes place by solid-state diffusion and may require a geologically significant time to run to completion. Solid-state diffusion is a strongly temperature-dependent process. In this paper we solve the thermal evolution of the mountain belt to attempt to constrain the depth of the gabbro-eclogite transition and thus to assess this hypothesis quantitatively. The one-dimensional heat equation is solved numerically by a finite difference approximation. The deformation of the horizontally shortening crustal and mantle portions of the thermal boundary layer is assumed to occur by pure shear, and therefore the vertical velocity is given by the product of the horizontal strain rate and depth.

Namiki, Noriyuki↗

NASA NTRS1992

An Alpha-p-x Analytical Instrument for Lunar Resource Investigations

An instrument using alpha backscattering, alpha-proton nuclear reactions, and x-ray production by alpha particles and other auxiliary sources can be used on lunar landers to provide detailed analytical information concerning the lunar surface material. This information is important scientifically and can be the basis for utilizing efficiently lunar resources to build lunar colonies in the future. This alpha particle instrument uses radioactive isotopes, silicon detectors for the alpha and proton modes, and mercuric iodide detectors operating at room temperature for the x-ray mode. The alpha and proton modes of the instrument can provide an analysis for all elements (except hydrogen) present in amounts greater than about 1 percent by atom. These modes have excellent sensitivity and accuracy for the lighter elements, in particular, directly determining the amount of oxygen in the lunar soil. This is an element of paramount significance for the lunar resource mission. The x-ray mode makes possible a determination of Ti, Fe, and other important metals with even greater accuracy. In general, the x-ray mode provides increased sensitivity for heavier elements, in many cases achieving a sensitivity of several hundred ppm.

Economou, T. E.↗

NASA NTRS1993

NDE of PWA 1480 single crystal turbine blade material

Cantilever bending fatigue specimens were examined by fluorescent liquid penetrant and radioactive gas penetrant (Krypton) non-destructive evaluation (NDE) methods and tested. Specimens with cast, ground, or polished surface were evaluated to study the effect of surface condition on NDE and fatigue crack initiation. Fractographic and metallurgical analyses were performed to determine the nature of crack precursors. Preliminary results show that fatigue strength was lower for specimens with cast surfaces than for specimens with machined surfaces. The liquid penetrant and gas penetrant techniques both provided indications of a large population of defects on the cast surfaces. On ground or polished specimen surfaces, the gas penetrant appeared to estimate the actual number of voids more accurately than the liquid penetrant.

Klima, Stanley J.↗

NASA NTRS1993

Use of particle beams for lunar prospecting

A key issue in choosing the appropriate site for a manned lunar base is the availability of resources, particularly oxygen and hydrogen for the production of water, and ores for the production of fuels and building materials. NASA has proposed two Lunar Scout missions that would orbit the Moon and use, among other instruments, a hard X-ray spectrometer, a neutron spectrometer, and a Ge gamma ray spectrometer to map the lunar surface. This passive instrumentation will have low resolution (tens of kilometers) due to the low signal levels produced by natural radioactivity and the interaction of cosmic rays and the solar wind with the lunar surface. This paper presents the results of a concept definition effort for a neutral particle beam lunar mapper probe. The idea of using particle beam probes to survey asteroids was first proposed by Sagdeev et al., and an ion beam device was fielded on the 1988 Soviet probe to the Mars moon Phobos. During the past five years, significant advances in the technology of neutral particle beams (NPB) have led to a suborbital flight of a neutral hydrogen beam device in the SDIO-sponsored BEAR experiment. An orbital experiment, the Neutral Particle Beam Far Field Optics Experiment (NPB-FOX) is presently in the preliminary design phase. The development of NPB accelerators that are space-operable leads one to consider the utility of these devices for probing the surface of the Moon using gamma ray, X-ray, and optical/UV spectroscopy to locate various elements and compounds. We consider the utility of the NPB-FOX satellite containing a 5-MeV particle beam accelerator as a probe in lunar orbit. Irradiation of the lunar surface by the particle beam will induce secondary and back scattered radiation from the lunar surface to be detected by a sensor that may be co-orbital with or on the particle beam satellite platform, or may be in a separate orbit. The secondary radiation is characteristic of the make-up of the lunar surface. The size of the spot irradiated by the beam is less than 1 km wide along the ground track of the satellite, resulting in the potential for high resolution. The fact that the probe could be placed in polar orbit would result in global coverage of the lunar surface. The orbital particle beam probe could provide the basis for selection of sites for more detailed prospecting by surface rovers.

Toepfer, A. J.↗

NASA NTRS1993

Collection, analysis, and archival of LDEF activation data

The study of the induced radioactivity of samples intentionally placed aboard the Long Duration Exposure Facility (LDEF) and samples obtained from the LDEF structure is reviewed. The eight laboratories involved in the gamma-ray counting are listed and the scientists and the associated counting facilities are described. Presently, most of the gamma-ray counting has been completed and the spectra are being analyzed and corrected for efficiency and self absorption. The acquired spectra are being collected at Eastern Kentucky University for future reference. The results of these analyses are being compiled and reviewed for possible inconsistencies as well as for comparison with model calculations. These model calculations are being revised to include the changes in trapped-proton flux caused by the onset of the period of maximum solar activity and the rapidly decreasing spacecraft orbit. Tentative plans are given for the storage of the approximately 1000 gamma-ray spectra acquired in this study and the related experimental data.

Laird, C. E.↗

NASA NTRS1993

Future directions for LDEF ionizing radiation modeling and assessments

A calculational program utilizing data from radiation dosimetry measurements aboard the Long Duration Exposure Facility (LDEF) satellite to reduce the uncertainties in current models defining the ionizing radiation environment is in progress. Most of the effort to date has been on using LDEF radiation dose measurements to evaluate models defining the geomagnetically trapped radiation, which has provided results applicable to radiation design assessments being performed for Space Station Freedom. Plans for future data comparisons, model evaluations, and assessments using additional LDEF data sets (LET spectra, induced radioactivity, and particle spectra) are discussed.

Armstrong, T. W.↗

NASA NTRS1993

New materials: Fountainhead for new technologies and new science

The role of materials as the benchmark technologies which give epochs of human history their names continues into the present. The discovery of new materials has nearly always been the source of new materials science, and frequently of new technologies. This paper analyzes the actual processes by which new materials are synthesized, i.e. whether driven by serendipitous observations, new knowledge is pulled by the market, or integrated into a technological thrust. This analysis focuses on modern ceramic materials discoveries, since World War 2 and uses 45 years experience in materials synthesis in the author's own laboratory as case studies. A dozen different families of materials or processes are involved: hydrothermal reactions; sol-gel processing; clays and zeolites; electroceramics; zero expansion ceramics; diamond films; and radioactive waste host phases. Nanocomposite concepts introduced by the author a decade ago offer an entire, large, new class of materials which will dominate synthesis for the next period. The future of materials research for the next 25 years cannot be extrapolated from the past 25 years. We are near the asymptote for materials utilization in most metals. Likewise we are approaching saturation in improvement of many useful properties. Justifying much further 'basic' R/D for incremental improvement in civilian-oriented industries will not be easy. In materials synthesis, the near-term future is sure to emphasize not new phases, but tailored micro- and nanocomposites for chemical, electrical, optical, and magnetic uses. Unexpected new discoveries such as the Lanxide process may offer rarer chances for step function advances. The new structure of knowledge management will rely less on local research than on integration of worldwide inputs. Better scientific and technological opportunities will lie in designing knowledge intensive materials to meet the new environmental and conservation goals, and the human needs of the very large numbers at the bottom of the socio-economic structures of the world.

Rustum, Roy↗

NASA NTRS1992

Oriented Scintillation Spectrometer Experiment observations of Co-57 in SN 1987A

The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory has observed SN 1987A for two 2 week periods during the first 9 months of the mission. Evidence for gamma-ray line and continuum emission from Co-57 is observed with an intensity of about 10 exp -4 gamma/sq cm/s. This photon flux between 50 and 136 keV is demonstrated by Monte Carlo calculations to be independent of the radial distribution of Co-57 for models of low optical depth, viz., models having photoelectric absorption losses of 122 keV photons no greater than several percent. For such models the observed Co-57 flux indicates that the ratio Ni-57/Ni-56 produced in the explosion was about 1.5 times the solar system ratio of Fe-57/Fe-56. When compared with nearly contemporaneous bolometric estimates of the luminosity for SN 1987A, our observations imply that Co-57 radioactivity does not account for most of the current luminosity of the supernova remnant in low optical depth models. We suggest alternatives, including a large optical depth model that is able to provide the SN 1987A luminosity and is consistent with the OSSE flux. It requires a 57/56 production ratio about twice solar.

Kurfess, J. D.↗

NASA NTRS1992

Silicon isotopic composition in large meteoritic SiC particles and Na-22 origin of Ne-22

Large SiC particles extracted from acid-insoluble residues of carbonaceous chondrites are isotopically anomalous in both silicon and carbon and contain isotopically extreme noble gases. These particles are thought to have originated in mass outflows from red giant stars and to have existed in the interstellar medium at the time the solar system formed from an interstellar cloud. Calculations show that the silicon isotope correlations in those large SiC particles can be generated only in the most massive carbon stars. Consequently, the almost pure Ne-22 in those particles must be interpreted as the condensation of radioactive Na-22 in the particles as they flowed away from the stars. The Na-22 is produced through proton capture by Ne-21 at the base of the surface convection zone. Ne-22 does not exist abundantly in helium shells hot enough to burn magnesium, which is necessary to establish the measured silicon isotopic composition.

Brown, Lawrence E.↗

NASA NTRS1992

A distance-independent calibration of the luminosity of type Ia supernovae and the Hubble constant

The absolute magnitude of SNe Ia at maximum is calibrated here using radioactive decay models for the light curve and a minimum of assumptions. The absolute magnitude parameter space is studied using explosion models and a range of rise times, and absolute B magnitudes at maximum are used to derive a range of the H0 and the distance to the Virgo Cluster from SNe Ia. Rigorous limits for H0 of 45 and 105 km/s/Mpc are derived.

Leibundgut, Bruno↗

NASA NTRS1993

Hard X-ray and gamma-rays from supernovae

The hard electromagnetic radiation produced by and accompanying the explosion of supernovae is discussed. This radiation may have three origins: (i) the eruption of the shock wave from the surface of the star; (ii) radioactive decay of unstable isotopes produced during the explosion; and (iii) gamma-rays produced by neutrino annihilation following accretion-induced collapse. Though the latter has been proposed as a mechanism for making cosmological gamma-ray bursts, it is shown that this is unlikely.

Woosley, S. E.↗