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The observation of a gamma-ray line feature from the direction of the galactic center by Johnson, Harnden, and Haymes is interpreted as the 478-keV nuclear de-excitation of low-energy Li-7 cosmic rays as they inelastically scatter from the interstellar gas. The prediction of an associated line at 432 keV is proposed as a definitive test of this idea.
Explorer xi detection of cosmic gamma rays, analyzing data to give altitude variation, angular distribution and celestial coordinates of event
A study program of radiation shielding against the deleterious effects of nuclear radiation on man and equipment is reported. The methods used to analyze the radiation environment from bremsstrahlung photons are discussed along with the methods employed by transport code users. The theory and numerical methods used to solve transport of neutrons and gammas are described, and the neutron and cosmic fluxes that would be present on the gamma-ray telescope were analyzed.
Evaluation of calculations and experimental evidence from 600-MeV proton irradiation indicating that cosmic-ray-induced radioactivity in detectors used to measure the diffuse gamma-ray background produces a significant counting rate in the energy region around 1 MeV. It is concluded that these counts may be responsible for the observed flattening of the diffuse photon spectrum at this energy.
Gamma-ray and X-ray spectrometers carried in the service modules of the Apollo 15 and Apollo 16 spacecraft were employed for compositional mapping of the lunar surface. The measurements involved the observation of the intensity and characteristic energy distribution of gamma rays and X-rays emitted from the lunar surface. A large-scale compositional map of over 10 percent of the lunar surface was obtained from an analysis of the observed spectra. The objective of the X-ray experiment was to measure the K spectral lines from Mg, Al, and Si. Spectra were obtained and the data were reduced to Al/Si and Mg/Si intensity ratios and ultimately to chemical ratios. Analyses of the results have indicated (1) that the Al/Si ratios are highest in the lunar highlands and considerably lower in the maria, and (2) that the Mg/Si concentrations generally show the opposite relationship. The objective of the gamma-ray experiment was to measure the natural and cosmic-ray-induced activity emission spectrum. At this time, the elemental abundances for Th, U, K, Fe, Ti, Si, and O have been determined over a number of major lunar regions. Regions of relatively high natural radioactivity were found in the Mare Imbrium and Oceanus Procellarum regions.
The principal gamma-ray emitting radioisotopes, produced in the body of astronauts by cosmic-ray bombardment, which have half-lives long enough to be useful for radiation dose evaluation, are Be-7, Na-22, and Na-24. The sodium isotopes were measured in the preflight and postflight urine and feces, and those feces specimens collected during the manned Apollo missions, by analysis of the urine salts and the raw feces in large crystal multidimensional gamma-ray spectrometers. The Be-7 was chemically separated, and its concentration measured in an all NaI (TL), anticoincidence shielded, scintillation well crystal. The astronaut radiation dose in millirads, as determined for the Apollo 7, 8, 9, 10, 11, 12, and 13 missions, was 330, 160, smaller than 315, 870 plus or minus 550, 31, 110, and smaller than 250, respectively.
Phoswich scintillation counter to observe .5 mev positron annihilation line caused by cosmic-ray interactions
High altitude balloon magnetic-core digitized spark chamber detector system for determining point sources of cosmic gamma radiation
The current state of gamma-ray astronomy is reviewed in terms of the most recent experimental results that define, in either measured fluxes or upper limits, the cosmic photon spectrum in the energy range from 0.5 MeV to 10,000 TeV. Methods of research developed during the last 10 yr are discussed and specific results are cited. Cosmic gamma rays have been observed in two regions of the spectrum - from 0.5 to 6 MeV and from about 50 MeV to several hundred mega-electronvolts. Above 50 MeV, a strong concentration of intensity is observed in a band of directions around the galactic equator. In both spectral regions a diffuse background gamma ray flux, apparently isotropic and of extragalactic origin, is observed. Evidence of 50 MeV gamma-ray pulses from the Crab pulsar has been reported. No definite evidence of any other discrete gamma-ray source besides the galaxy itself has been observed at any energy.
The experiments in gamma-ray spectrometry to determine the geochemical composition of the lunar surface are reported. The theory is discussed of discrete energy lines of natural radioactivity, and the lines resulting from the bombardment of the lunar surface by high energy cosmic rays. The gamma-ray spectrometer used in lunar orbit and during transearth coast is described, and a preliminary analysis of the results is presented.
The result of a calculation of the expected number of muons in gamma ray initiated and cosmic ray initiated air showers using a realistic model of hadronic collisions in an effort to understand the available experimental results and to assess the feasibility of using the muon content of showers as a veto to reject cosmic ray initiated showers in ultra-high energy gamma ray astronomy are reported. The possibility of observing very-high energy gamma-ray sources by detecting narrow angle anisotropies in the high energy muon background radiation are considered.
Two basalts, two breccias, and two soils from Apollo 15 were analyzed by nondestructive gamma-ray spectrometry. The concentrations of potassium, thorium, and uranium in the basalts were similar to those in the Apollo 12 basalts, but the potassium:uranium ratios were somewhat higher. Primordial radioelements were enriched in the soils and breccia, consistent with a two-component mixture of mare basalt and up to 20 percent foreign component (KREEP). The abundance patterns for cosmogenic radionuclides implied surface sampling for all specimens. The galactic cosmic-ray production rate of vanadium-48 was determined as 57 (plus or minus 11) disintegrations per minute per kilogram of iron. Cobalt-56 concentrations were used to estimate the intensity of the solar flare of January 25, 1971.
An 87-gram sample of the Havero ureilite has been analyzed by nondestructive gamma-ray spectrometry. The results of the measurements, in dpm/kg at time of fall, are: Na-22, 71 plus or minus 3; Al-26, 43 plus or minus 3; Sc-46, 3.4 plus or minus 2.1; Mn-54, 35 plus or minus 6; Co-60, less than or equal to 0.7, 2 sigma limit. Havero has 77 plus or minus 14% of the Al-26 activity calculated for its chemical composition. When averaged with previously reported analyses of Goalpara and Novo Urei, ureilites as a class have 74 plus or minus 7% of their expected Al-26 activity. The depletion in Al-26 could be the coincidental result of identical 'shielding' effects in three meteorites of apparently very different preatmospheric sizes. Alternatively, ureilites may have been exposed to a lower cosmic-ray flux than that experienced by most chondrites, probably the result of characteristically different orbits.
Gamma ray astronomy in the 50 kev to 3 mev region
Gamma ray measurement and low energy gamma ray spectrum in atmosphere produced by cosmic ray
The principal gamma-ray-omitting radioisotopes produced in the body of astronauts by cosmic-ray bombardment which have half-lives long enough to be useful for radiation dose evaluation are Be-7, Na-22, and Na-24. The sodium isotopes were measured in the preflight and postflight urine and feces, and those feces specimens collected during the manned Apollo missions, by analysis of the urine salts and the raw feces in large crystal multidimensional gamma-ray spectrometers. The Be-7 was chemically separated, and its concentration measured in an all Na(T1), anticoincidence shielded, scintillation well crystal. The overall sensitivity of the experiment was reduced by almost all variables such as low concentrations of excreted cosmogenic radionuclides, high concentrations of injected radionuclides, low sample sizes, long delay periods before analysis, and uncertain excretion rates. The astronaut radiation dose in millirads, as determined by this technique, for the Apollo 7, 8, 9, 10, 11, 12, and 13 missions was 330, 160, 315, 870 ? 550, 31, 110, and 250 respectively. In view of these limitations this technique would be best applied to cases of unusually high exposures, such as that encountered from solar flares.
The discovery of soft gamma ray bursts has led to the speculation that these bursts are caused by the bremsstrahlung of electrons accelerated to high energies in a stellar flare event. If the stellar flare hypothesis is verified, it may imply a significant source of low energy cosmic rays in the solar neighborhood, depending on the frequency and intensity of the flares.
Dual-parameter gamma ray spectrometer systems with large volume Nal (Tl) crystals and low backgrounds were used for nondestructive determination of K, Th, U and cosmic ray produced radionuclides in 60 lunar samples. The total weight of samples measured with this system is 28 kg, and the individual sample weights varied from 2 to 2300 g. Samples from Apollo 11, 12, 14, 15 and 16 were measured. Operation of the spectrometers in the coincidence mode and analyzing single coincidence spectra permits the simultaneous determination of 8-10 radionuclides in each lunar sample.