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NASA NTRS1978

Cryogenic cooling for spacecraft sensors, instruments, and experiments

Several disciplines requiring in-space cryogenic cooling are identified including high-energy, gamma-ray, and IR astronomy, relativity missions, and superconducting devices. Radiant coolers are limited in terms of temperature ranges and cooling loads. Other spacecraft cryogenic systems include stored solid cryogenic coolers using materials such as hydrogen, neon, argon, and methane. Two such cooler designs are described including one for the Nimbus F limb radiance inversion radiometer and one for the Nimbus G limb infrared monitoring of the atmosphere. Suggestions for increasing the performance of solid cryogenic coolers are made, such as a multimission cooler, a mechanical refrigerator, Stirling-cycle refrigerators, and Vuilleumier mechanized coolers. Techniques for obtaining cryogenic cooling in the milli-K range are identified as dilution refrigeration and adiabatic demagnetization.

Sherman, A.↗

NASA NTRS1979

A Mars airplane

An airplane specifically designed for Mars flight is described, emphasizing its conceivable role as an aerial surveyor for visual imaging, gamma-ray and IR reflectance spectroscopy, studies of atmospheric composition and dynamics, and gravity-field, magnetic-field, and electromagnetic sounding. Possible imaging systems and surveying tasks are considered, along with a plausible mission scenario for a fleet of 12 airplanes, which would be taken to Mars in squadrons of four by three Shuttle/IUS Twin Stage/spacecraft carriers. A basic configuration closely resembling that of a competition glider is examined, and four types of airplane are discussed: hydrazine-powered cruisers and landers and electrically powered cruisers and landers. Attention is given to navigation, guidance, and control avionics, vehicle weight, the use of composite materials for the wing, and flight testing on earth.

Clarke, V. C.↗

NASA NTRS1978

Cryogenics for spacecraft

It is pointed out that cryogenic engineering has been an integral part of space research almost from the beginning of the space age because of the significant performance advantages available from cryogenically fueled rocket engines. In recent years, space-related cryogenic engineering has expanded from booster engines to include spacecraft systems because of the vastly improved performance available from cooled detectors and systems. The requirements for detector cooling in space are examined, taking into account earth observation, atmospheric measurements, infrared astronomy, X-ray astronomy, gamma-ray astronomy, radio astronomy, relativity measurements, magnetic field measurements, time measurements, and data processing. A description is presented of 1978-1981 U.S. spacecraft cryogenic detector systems.

Vorreiter, J. W.↗

NASA NTRS1979

Solar gamma rays above 8 MeV

Processes that lead to the production of gamma rays with energy greater than 8 MeV in solar flares are reviewed and evaluated. Excited states that can be produced by inelastic scattering, charge exchange, and spallation reactions in the abundant nuclear species are considered in order to identify nuclear lines that may contribute to the gamma-ray spectrum of solar flares. The flux of 15.11-MeV gamma rays relative to the flux of 4.44-MeV gamma rays from the deexcitation of the corresponding states in C-12 is calculated for a number of assumed distributions of exciting particles. This flux ratio is shown to be a sensitive diagnostic of accelerated particle spectra. Other high-energy nuclear levels are not so isolated as the 15.11-MeV state and are not expected to be so strong. The spectrum of gamma rays from the decay of neutral pions is shown to be sensitive to the energy distribution of particles accelerated to energies greater than 100 MeV.

Crannell, C. J.↗

NASA NTRS1979

Gamma rays from accretion onto rotating black holes

Ionized matter falling onto an isolated rotating black hole will be heated sufficiently that proton-proton collisions will produce mesons, including neutral pions, which decay into gamma rays. For massive (1000-solar mass) black holes, the resulting gamma-ray luminosity may exceed 10 to the 36th erg/s with a spectrum peaked near 20 MeV.

Collins, M. S.↗

NASA NTRS1978

Interconversion of biologically important carboxylic acids by radiation

The interconversion of a group of biologically important polycarboxylic acids (acetic, fumaric, malic, malonic, succinic, citric, isocitric, tricarballylic) under gamma-ray or ultraviolet radiation was investigated. The formation of high molecular weight compounds was observed in all cases. Succinic acid was formed in almost all radiolysis experiments. Citric, malonic, and succinic acids appeared to be relatively insensitive to radiation. Interconversion of the polycarboxylic acids studied may have occurred under the effect of radiation in the prebiotic earth.

Negron-Mendoza, A.↗

NASA NTRS1979

X-ray observations of AM Herculis from OSO 8

X-ray observations of the white dwarf binary system AM Herculis in the range 2 to 250 keV, taken by OSO 8, are presented and compared with balloon and Ariel 5 measurements. The composite spectrum of the 2 to 40 and 20 to 250 keV fluxes determined by the proportional counter and the high energy scintillation spectrometer, respectively, on board the satellite is shown averaged over the entire binary cycle. Variations in spectral shape and intensity between the OSO 8 results and balloon measurements taken 10 to 20 days apart are observed. Results indicate the presence of a spectral break at about 15 keV on some occasions, similar to that seen in Her X-1, however presumably caused by a different mechanism than in the neutron star. It is also considered unlikely that the gamma-ray tail observed by Ariel 5 existed during OSO 8 observations.

Coe, M. J.↗

NASA NTRS1979

A possible line feature at 73 keV from the Crab Nebula

Evidence is reported for a possible line feature at 73 keV from the Crab Nebula. The experiment was conducted with a balloon-borne high-resolution gamma-ray spectrometer on June 10, 1974, over Palestine, Texas. The intensity and the width of the line derived from the fitting of these data are approximately 0.0038 photon per (sq cm-sec) and less than 4.9 keV FWHM, respectively. The line is superposed on a power-law continuum of 11.2 E to the -2.16 photons per (sq cm-keV) in the energy range from 53 to 300 keV, which is consistent with other measurements of the Crab Nebula spectrum.

Ling, J. C.↗

NASA NTRS1979

Solar flares

The present paper deals with explosions in a magnetized solar plasma, known as flares, whose effects are seen throughout the electromagnetic spectrum, from gamma-rays through the visible and to the radio band. The diverse phenomena associated with flares are discussed, along with the physical mechanisms that have been advanced to explain them. The impact of solar flare research on the development of plasma physics and magnetohydrodynamics is noted. The rapid development of solar flare research during the past 20 years, owing to the availability of high-resolution images, detailed magnetic field measurements, and improved spectral data, is illustrated.

Rust, D. M.↗

NASA NTRS1979

The distribution of titanium on the lunar surface

Titanium concentrations derived from the lunar-orbiting gamma-ray experiment on Apollo 15 and 16 by analyzing a spectral interval in which the titanium signal is relatively enhanced are presented. Landing site soil values provide the reference for a regression curve from which Ti concentrations in 137 regions of adequate counting statistics are calculated. Mare Tranquillitatis contains the highest, and Mare Crisium the lowest Ti concentration, and regional values in the western maria range from 1.1% to 4.1%. Highland Ti concentrations suggest a north-south symmetry which is not consistent with previously reported Fe and Th results. Comparisons with telescopic spectral reflectance studies of the maria do not show complete agreement and suggest that effects due to Fe may not have been fully removed from the reflectance data.

Metzger, A. E.↗

NASA NTRS1979

Evidence for variability of hard X-rays from NGC 4151

A search for gamma-rays in the 35-keV to 8.7-MeV energy range from the Seyfert galaxy NGC 4151 was made using an actively collimated scintillation detector. Upper limits to the flux in the 100-200-keV energy range are inconsistent with previous observations. Variability on a time scale of several months is indicated. Implications in terms of current models of NGC 4151 are discussed.

Meegan, C. A.↗

NASA NTRS1979

The radioracemization of isovaline - Cosmochemical implications

The optically pure D- and L-enantiomers of isovaline, which cannot be racemized by ordinary chemical mechanisms involving alpha-hydrogen removal and which has been isolated in apparently racemic form from the Murchison meteorite, have been subjected to partial radiolysis by the ionizing radiation from a 3000-Ci Co-60 gamma-ray source. Both in the anhydrous and hydrated solid states and as solid sodium or hydrochloride salts each enantiomer suffered significant radioracemization of the undestroyed residue during its partial radiolysis. The sodium salt of isovaline in 0.1-M aqueous solution suffered extensive radiolysis with relatively small radiation doses, but showed no detectable radioracemization. The significance of these observations with respect to the primordial enantiomeric composition of the isovaline (and other amino acids) indigenous to meteorites is discussed.

Bonner, W. A.↗

NASA NTRS1979

Positron production by pulsars

Analytical calculations based on the 'polar-cap light-cylinder' (PCLC) (Sturrock, 1971a) and 'polar-cap force-balance' (PCFB) (Roberts and Sturrock, 1972,3) pulsar models show that in either case the intensity of the 511 keV gamma-ray line from the galactic center can be explained as the result of the annihilation of positrons produced by pulsars. The Crab pulsar (braking index approximately 2.5) is estimated to have a power budget of 10 to the 38th ergs/s, and to produce a total number of 10 to the 51.7th positrons. It is suggested that positron annihilation can be supplied by pulsars if the birthrate of pulsars in the galactic center is 10 to the -8.2nd/s.

Sturrock, P. A.↗

NASA NTRS1980

X-ray quasars

Observational data for the seven quasars or Seyfert-quasar transition objects identified with X-ray sources is reviewed for radio, infrared, optical, ultraviolet, X-ray and gamma-ray frequencies. The observational histories of the quasars 3C 273, MR 2251-178 and 0241+622 and the quasar-like Seyfert nuclei Fairall-9, Mk 509, IC 4329A and IIIZw 2 are discussed in detail, and it is noted that their X-ray variability and spectra do not differentiate them from Seyfert nuclei, supporting the similarity between the several types of active extragalactic nuclei. The space density of the six objects (excluding 3C 273) within 600 Mpc is found to be comparable to that of other Seyferts and quasars, suggesting that X-ray emitting objects constitute a substantial fraction of the luminous transition objects in the neighborhood of the Galaxy. It is also pointed out that observations of the X-ray variability of these objects, which indicates that the X-rays originate from compact regions, represent a promising means for the further understanding of the emission process.

Bradt, H. V.↗

NASA NTRS1979

Observations of particle acceleration in solar flares

Solar flares provide several examples of nonthermal particle acceleration. The paper reviews the information gained about these processes via X-ray and gamma-ray astronomy, which can presently distinguish among three separate particle-acceleration processes at the sun: an impulsive accelerator of more than 20 keV electrons, a gradual accelerator of more than 20 keV electrons, and a gradual accelerator of more than 10 MeV ions. The acceleration energy efficiency (total particle energy divided by total flare energy) of any of these mechanisms cannot be less than about 0.1%, although the gradual acceleration does not occur in every flare. The observational material suggests that both the impulsive and gradual accelerations take place preferentially in closed magnetic-field structures, but that the electrons decay in these traps before they can escape. The ions escape very efficiently.

Hudson, H. S.↗

NASA NTRS1979

Energetic particles in solar flares

The principal properties of energetic particles accelerated in solar flares are reviewed. Particular emphasis is placed on the high-energy flare component whose acceleration is often referred to as second-phase acceleration. Stochastic Fermi acceleration is treated analytically, and the results of the computation are compared with particle and gamma-ray data to deduce information on the timing of the acceleration, the spectrum of the particles, and the energy content of the nucleonic component. A discussion of He-3 and heavy element abundances is also presented.

Ramaty, R.↗

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.↗