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Keith, J. E.

Publications and source records attributed to Keith, J. E..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Neutron measurements onboard the space shuttle

The radiation environment inside a shielded volume is highly complex, consisting of both charged and neutral particles. Since the inception of human space flights, the charged particle component has received virtually all of the attention. There is however, a significant production of secondary neutrons, particularly from the aluminum structure in low earth orbiting spacecrafts. The interactions of galactic cosmic rays (GCR), and solar energetic particles with the earth's atmosphere produce a non-isotropic distribution of albedo neutrons. Inside any reasonable habitable module, the average radiation quality factor of neutrons is about 4-5 times larger than the corresponding average quality factor of charged particles. The measurement of neutrons and their energy spectra is a difficult problem due the intense sources of charged particles. This paper reviews the results of Shuttle flight experiments (made during both solar maximum and solar minimum) to measure the contribution of neutrons to the dose equivalent, as well as theoretical calculations to estimate the appropriate range of neutron energies that contribute most to the dose equivalent. Published by Elsevier Science Ltd.

short duration↗
NASA NTRS1978

From Serenity to Langemak - A regional chemical setting for Mare Crisium

The chemistry of the region surrounding Mare Crisium is described using improved Al/Si and Mg/Si intensity ratios derived from Apollo 15 X-ray fluorescence measurements. Mg/Si ratios are shown to increase from 0.6 in the region east of Mare Smythii to 1.0 in western Mare Serenitatis, while Al/Si ratios show sharp decreases in all mare areas. It is concluded that the terra (nonmare) material has a uniform Al/Si ratio, hence plagioclase content, and increases in the Mg/Si ratio in terra material imply similar increases of Mg in the pyroxenes and olivines of this material. The observed diversity of terra soils can be explained by an originally chemically diverse region not homogenized by heavy bombardment, or by volcanism subsequent to bombardment. Maria Crisium, Serenitatis and Smythii are found to be filled with low albedo materials which have a wide range of Mg/Si values, with small and apparently consistent differences in Al/Si ratio.

Hubbard, N. J.↗
NASA NTRS1978

A declaration of independence for Mg/Si

The weak covariation that exists between Al/Si and Mg/Si for large areas of the lunar surface is little, if any, stronger than that forced on a random set of numbers that are subject to closure. The Mg and Al variations implied by the Mg/Si and Al/Si intensity ratio data are qualitatively like those seen in lunar soil sample data. Two petrogenetic provinces are suggested for terra materials; one appears to have 50% higher Mg values than the other. Using the improved data, Mg/Si variations can be studied at a signal-to-noise ratio greater than 5/1.

Hubbard, N.↗
NASA NTRS1977

Reevaluation of the Apollo orbital X-ray fluorescence data

A combination of Al/Mg ratios and Al/Si ratios has provided high-quality geochemical and geological information from the Apollo orbital X-ray fluorescence data. The high sensitivity of the characteristic Si X-rays to alterations in the energy spectra of the solar X-ray flux limits the analytical usefulness of the ratios involving Si. A photometric study indicates that the Si concentration in lunar materials varies by less than about + or - 15% of the Si present. In addition, particle size and surface roughness are shown to have small effects on the characteristic fluorescent X-ray radiation of Si.

Hubbard, N. J.↗
NASA NTRS1975

The saturated activities of Na-22, Mn-54, and Co-56 and the depth of sampling of soils

A multivariate linear regression study shows that the saturated activities of Na-22, Co-56, and Mn-54 are functions of the chemical composition and the reciprocal of the cube root of the sample weight. A procedure for taking the temporal variation in these short-lived radionuclides into account is described. The regression results are used to estimate the average depths of sampling of soil material. The data indicate that all 28 samples were in the same conditions of exposure when recovered as they had been for the last approximately 10 years. The saturation activity of Mn-54 is a very weak function of time.

Keith, J. E.↗
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 NTRS1973

RALPH: An online computer program for acquisition and reduction of pulse height data

A background/foreground data acquisition and analysis system incorporating a high level control language was developed for acquiring both singles and dual parameter coincidence data from scintillation detectors at the Radiation Counting Laboratory at the NASA Manned Spacecraft Center in Houston, Texas. The system supports acquisition of gamma ray spectra in a 256 x 256 coincidence matrix (utilizing disk storage) and simultaneous operation of any of several background support and data analysis functions. In addition to special instruments and interfaces, the hardware consists of a PDP-9 with 24K core memory, 256K words of disk storage, and Dectape and Magtape bulk storage.

Davies, R. C.↗