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At least 271 records · Page 15
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NASA NTRS1973

Nuclear gamma rays from solar flares

The theory of gamma-ray line emission from solar flares is reviewed and revised. It is shown that the line emissions at 0.5, 2.2, 4.4, and 6.1 MeV are due to positron annihilation, deuterium deexcitation following neutron capture on hydrogen, and the deexcitation of excited states in carbon and oxygen. From the observed relative line intensities it is possible to determine the spectrum of accelerated protons in the flare region. This spectrum is found to be very similar to that of charged particles from the flare observed near earth. The total number of protons at the sun is deduced from the observed absolute line intensities for various interaction models.

Ramaty, R.↗
NASA NTRS1974

Quantitative multielement analysis using high energy particle bombardment

Charged particles ranging in energy from 0.8 to 4.0 MeV are used to induce resonant nuclear reactions, Coulomb excitation (gamma X-rays), and X-ray emission in both thick and thin targets. Quantitative analysis is possible for elements from Li to Pb in complex environmental samples, although the matrix can severely reduce the sensitivity. It is necessary to use a comparator technique for the gamma-rays, while for X-rays an internal standard can be used. A USGS standard rock is analyzed for a total of 28 elements. Water samples can be analyzed either by nebulizing the sample doped with Cs or Y onto a thin formvar film or by extracting the sample (with or without an internal standard) onto ion exchange resin which is pressed into a pellet.

Clark, P. J.↗
NASA NTRS1973

Neutral-pion-decay gamma rays from the Galaxy and the interstellar gas content

Knowledge of the total gamma-ray production rate per H atom from the decay of neutral pions produced in interstellar cosmic-ray interactions is essential for determining the possible amount of interstellar H2. This production rate is recalculated here using the latest accelerator data on neutral pion production in p-p interactions up to about 1500 GeV. A simple but accurate approximation used here resolves the past disagreement over the magnitude of this rate. An upper limit is obtained of (1.51 plus or minus 0.23) times 10 to the -25th power/sec, consistent with the observed upper limit of 1.6 times 10 to the -25th power/sec.

Stecker, F. W.↗
NASA NTRS1974

Nuclear Science Symposium, 20th, and Nuclear Power Systems Symposium, 5th, San Francisco, Calif., November 14-16, 1973, Proceedings

Subjects considered are in the areas of position sensitive detectors, semiconductor detector materials, semiconductor detector technology, biomedical instrumentation, reactor instrumentation, nuclear instrumentation, and data acquisition and processing. Topics related to photon detection are discussed together with methods for environmental radiation measurement, aspects of environmental gamma-ray analysis, and nuclear techniques for elemental analysis. Attention is also given to operation and design experience with systems at nuclear power plants. Individual items are announced in this issue.

Source record↗
NASA NTRS1974

Neutral-pion decay gamma rays from the galaxy and the interstellar gas content

The total gamma-ray production rate per H atom from the decay of neutral pions produced in interstellar cosmic-ray interactions is recalculated here using the latest accelerator data on the production of neutral pions in pp interactions up to 300 GeV. A simple but accurate approximation used here resolves the past disagreement over the magnitude of this rate. An upper limit is obtained for this rate by considering a maximum galactic cosmic-ray spectrum taking modulation into account.

Stecker, F. W.↗
NASA NTRS1974

International Cosmic Ray Conference, 13th, University of Denver, Denver, Colo., August 17-30, 1973, Proceedings. Volumes 3 & 4

Volumes 3 and 4 contain papers dealing with measurements of muons and neutrinos, ultrahigh-energy interactions, extensive air showers, and details of experimental techniques and instrumentation. Attention is given to the zenith angle and underground depth dependence of cosmic ray muons, muon charge ratios and energy spectra, extraterrestrial sources of neutrinos, strong interaction data from new accelerators, searches for quarks and other new particles, hadron fluxes and propagation in the atmosphere, high-energy gamma-ray measurements, and new models and theories for high-energy strong interactions. Extensive air showers are examined in papers dealing with associated Cerenkov light, radio emission, structure, the hadron content, and primaries. The design, operation, and performance of various detectors are explained. Individual items are announced in this issue.

Source record↗
NASA NTRS1974

Line Co-57 gamma rays - New diagnostic of supernova structure

The nuclear gamma-ray lines emitted when Co-57 decays to Fe-57 should be detectable for several years following Galactic supernovae, and the time structure of their intensity relative to those emitted following the Ni-56 and Co-56 decays can reveal the structure of the exploding star. An analysis of a simplified analytic model is presented as an example.

Clayton, D. D.↗
NASA NTRS1974

Nucleosynthesis in white-dwarf atmospheres

Consideration of events by which both s- and r-process nucleosynthesis may occur on the surfaces of white-dwarf stars. The main requirement is that the accreted hydrogen be mixed with comparable numbers of C-12 (or other alpha nuclei) before a runaway capture of protons takes place. Subsequent events offer many possibilities for nucleosynthesis and stars of peculiar composition. A new mechanism for a surface s-process due to few-MeV protons is also described. Concluding comments concern cosmic gamma-ray bursts and the origin of anomalous low-energy galactic cosmic rays.

Hoyle, F.↗
NASA NTRS1974

SAS-2 observations of celestial diffuse gamma radiation above 30 MeV

The small astronomy satellite, SAS-2, used a 32-deck magnetic core digitized spark chamber to study gamma rays with energies above 30 MeV. Data for four regions of the sky away from the galactic plane were analyzed. These regions show a finite, diffuse flux of gamma rays with a steep energy spectrum, and the flux is uniform over all the regions. Represented by a power law, the differential energy spectrum shows an index of 2.5 + or - 0.4. The steep SAS-2 spectrum and the lower energy data are reasonably consistent with a neutral pion gamma-ray spectrum which was red-shifted (such as that proposed by some cosmological theories). It is concluded that the diffuse celestial gamma ray spectrum observed presents the possibility of cosmological studies and possible evidence for a residual cosmic ray density, and supports the galactic superclusters of matter and antimatter remaining from baryon-symmetric big bang.

Thompson, D. J.↗
NASA NTRS1974

Li production in alpha-alpha reactions

The cross section for Li-7 production in alpha-alpha reactions is shown to be increased by about a factor of 2 due to the excitation levels of Li-7 and Be-7 at 478 keV and 431 keV, respectively. The cross section for Li-6 production, however, remains the same as calculated on the basis of the detailed balance principle. The lines at 478 keV and 431 keV may link Li-7 production to feasible gamma-ray observations.

Kozlovsky, B.↗
NASA NTRS1974

Neutron and proton activation measurements from Skylab

Radioactivity induced by high-energy protons and secondary neutrons (from nuclear interactions) in various samples returned from different locations in Skylab was measured directly by gamma-ray spectroscopy measurements of decay gamma rays from the samples. Incident fluxes were derived from the activation measurements, using known nuclear cross-section. Neutron and proton flux values were found to range from 0.2 to 5 particles/sq cm-sec, depending on the energy range and location in Skylab. The thermal neutron flux was less than 0.07 neutrons/sq cm-sec. The results are useful for data analysis and planning of future high-energy astronomy experiments.

Fishman, G. J.↗
NASA NTRS1974

Microwave profiling of snowpack free-water content

A microwave system is proposed to measure the amount of liquid-phase water in a snowpack operating in the range of 1 to 10 GHz. Attenuation of the beam between source and receivers is produced by the water in the snow. The relationships of frequency, distance, and volume percent of water are calculated for an assumed detector sensitivity, together with the estimated cost of a representative system. A laboratory test is described that shows the attenuation for snow at maximum wetness at 9.35 GHz. A configuration is proposed that involves a vertical tube containing microwave and radioactive sources and another vertical tube containing microwave and gamma-ray detectors, so that density and wetness profiles are obtained simultaneously over essentially the same path.

Linlor, W. I.↗
NASA NTRS1974

A comment on gamma ray lines from He-4

It is pointed out that excited states of He-4 cannot produce gamma ray line emission of astrophysical significance, contrary to a recent suggestion of Reina et al. (1974). The only possible gamma-ray lines in He-4 are above 25 MeV, but their excitation cross sections appear to be so small that they are probably of little astrophysical significance.

Kozlovsky, B.↗
NASA NTRS1974

Nuclear composition of solar cosmic rays

Experimental observations of the elemental and isotopic composition of solar flare particles are discussed. Sources and characteristics of particle-emitting solar flare events are reviewed, and techniques for separating particle species are briefly described. Data are presented for the elemental composition of the solar atmosphere, and the possibility of determining the solar helium abundance from solar cosmic-ray observations is explored. The main experimental determinations of heavy element abundances at energies greater and less than 10 MeV/nucleon are summarized, and techniques for measuring the ionic charge composition of solar cosmic rays are outlined. Models explaining heavy element enhancements are described along with processes leading to gamma-ray emission during solar flare events. Observations of the rare isotopes of hydrogen and helium during solar flare events are noted, and a lower atmospheric limit is derived for nuclear reactions leading to positron decay. The possibility of investigating low-energy solar cosmic rays by measuring the relative abundances of different elements is evaluated.

Hovestadt, D.↗
NASA NTRS1974

Descartes Mountains and Cayley Plains - Composition and provenance

Trace element compositions of petrographically characterized 2-4 mm lithic fragments from Apollo 16 soil samples are used to calculate initial REE concentrations in liquids in equilibrium with lunar anorthosites and to discuss the provenance of the Cayley Formation. Lithic fragments may be subdivided into four groups: (1) ANT rocks, (2) K- and SiO2-rich mesostasis-bearing rocks, (3) poikiloblastic rocks, and (4) (spinel) troctolites. Model liquids in equilibrium with essentially monominerallic anorthosites have initial REE concentrations 5-8 times those of chondrites. The REE contents of K- and SiO2-rich mesostasis-bearing rocks and poikiloblastic rocks are dominated by the mesostasis phases. ANT rocks appear to be more abundant in the Descartes Mountains, while poikiloblastic rocks appear to be more abundant in the Cayley Plains. Poikiloblastic rocks have intermediate to high LIL-element concentrations yet the low gamma-ray activity of Mare Orientale implies low LIL-element concentrations. Consequently, it is unlikely that the Cayley Formation is Orientale ejecta. A local origin as ejecta from smaller impacts is a more plausible model for the deposition of the Cayley Formation.

Drake, M. J.↗
NASA NTRS1974

Determination of natural and cosmic ray induced radionuclides in Apollo 17 lunar samples

Natural and cosmic ray induced radionuclides have been determined in 15 rocks and 7 soils from the Apollo 17 mission by nondestructive gamma-ray spectroscopy. The Th and K contents of these rocks and soils are shown to be linear functions of the U contents. Large amounts of Co-56, Sc-46, and Mn-54 were found in these samples due to the large proton-accelerating flares which occurred between August 2 and 6, 1972. The behavior of the Co-56 activity as a function of the Mn-54 activity seems to be the result of variation in surface to volume ratios among the samples and exposure angle. It is not necessary to invoke an asymetric solar flare flux to explain this behavior.

Keith, J. E.↗
NASA NTRS1988

Supernova 1987A

Supernova 1987A (February 23, 1987) in the Large Magellanic Cloud is the brightest supernova to be observed since SN 1604 AD (Kepler). Detection of a burst of neutrinos indicates that a neutron star was formed. Radioactive decay of about 0.07 solar mass of Co-56 is responsible for the observed optical light as well as hard X-rays and gamma-ray lines. Ultraviolet, optical, and infrared 'light echoes' and soft X-rays provide information on the distribution of circumstellar matter and the evolution of the progenitor star.

Mccray, Richard↗
NASA NTRS1971

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.↗