Engineering topics
Publications and source records attributed to Trombka, J. I..
An attempt was made to obtain experimental data on proton induced activity and its effect on gamma ray spectral measurements. A NaI(T1) crystal flown in Apollo 17 command module was used for the experiment.
Gamma-ray spectrometers on the Apollo 15 and Apollo 16 missions have been used to map the moon's radioactivity over 20 percent of its surface. The highest levels of natural radioactivity are found in Mare Imbrium and Oceanus Procellarum with contrastingly lower enhancements in the eastern maria. The ratio of potassium to uranium is higher on the far side than on the near side, although it is everywhere lower than commonly found on the earth.
The gamma rays emitted from the moon or any similar body carry information on the chemical composition of the surface layer. The elements most easily measured are K, U, Th and major elements such as O, Si, Mg, and Fe. The expected fluxes of gamma ray lines were calculated for four lunar compositions and one chondritic chemistry from a consideration of the important emission mechanisms: natural radioactivity, inelastic scatter, neutron capture, and induced radioactivity. The models used for cosmic ray interactions were those of Reedy and Arnold and Lingenfelter. The areal resolution of the experiment was calculated to be around 70 to 140 km under the conditions of the Apollo 15 and 16 experiments. Finally, a method was described for recovering the chemical information from the observed scintillation spectra obtained in these experiments.
Several spectrometers carried in the Service Module of the Apollo 15 and Apollo 16 spacecraft were employed for the compositional mapping of the lunar surface. The observations involved the measurements of secondary (fluorescent) X-rays, gamma-rays and alpha particle emissions. A large scale compositional map of over 20 percent of the lunar surface was obtained for the first time. It was possible to demonstrate interesting chemical differences between the mare and the highlands, to find specific areas of high radioactivity and to learn something about the composition of the moon's hidden side.
Lunar gamma ray spectra obtained during Apollo-15 and -16 flights show a natural radioactivity due to potassium, thorium, and uranium as well as a cosmic ray induced activity in the lunar surface due to high neutron interactions produced by (p,n) reaction in the lunar surface. The radioactivity is at a low in the highlands on the backside of the moon; most of the radioactivity is confined to the Oceanus Procellarum/Mare Imbrium region and to the Van de Graff area on the lunar backside.
Examination of the data obtained by gamma-ray spectrometers on the Apollo 15 and Apollo 16 spacecraft has been carried out in part by summing up broad regions of the energy spectrum. The most instructive of these energy regions is 0.55 to 2.75 MeV, where the difference in count rates observed can be accounted for mainly by variations in the Th, U, and K content of the surface layers. The highest values are found in Mare Imbrium and Oceanus Procellarum, where a good deal of local variation is observed. By contrast, little increase is seen in the eastern maria surveyed compared with count rates in highland areas. The broad highland regions are low in radioactivity, but there is a measurable rise near the southernmost latitude on the far side. In addition to the radioactive lines, gamma-ray lines which can be ascribed to O, Si, Fe, Mg, and Al have been identified.
Conference papers on gamma ray astrophysics are summarized. Data cover the energy region from about 0.3 MeV to a few hundred GeV and theoretical models of production mechanisms that give rise to both galactic and extragalactic gamma rays.
The cosmic gamma ray background spectra measured by Apollo 15 between 0.3 and 27 MeV during transearth orbit are examined. Both discrete line spectra and diffuse sources were measured. Data are included on energy loss spectra, equivalent photon spectra, spallation corrections, and cosmic photon spectra.
A panel discussion was held on all data presented at the conference on Gamma Ray Astronomy. The present status and future directions of the science were outlined.
Preliminary results are presented of data on the extent of the cosmic ray-induced activity obtained by a sodium iodide thallium-activated crystal flown onboard the Apollo 17 command module. Qualitative identification is reported for the following: Na-24, I-123, I-124, I-125, I-126, and Xe-127.
An X-ray spectrometer carried in the Service Module of the Apollo 15 and 16 spacecraft were employed for compositional mapping of the lunar surface. The surface measurements involved observations of the intensity and characteristic energy distribution of the fluorescent X-rays produced by the interaction of the solar X-rays with the lunar surface as well as naturally occurring gamma-rays and cosmic ray produced gamma-rays. A large scale compositional map of approximately twenty percent of the lunar surface was obtained for the first time. It was possible to demonstrate differences between the highlands and the mare and to learn something about the composition of the moon's hidden side. Results obtained from the X-ray experiment and the gamma-ray experiment are consistent with those obtained from lunar sample analysis.
Except for some minor modifications the Apollo 16 X-ray fluorescence experiment was similar to that flown aboard Apollo 15. The Apollo 16 provided data for a number of features not previously covered such as Mare Cognitum, Mare Nubium, Ptolemaeus, Descartes, Mendeleev, and other areas. Many data points were obtained by the X-ray experiments, so that comparisons could be drawn between Apollo 15 and 16 flights. The agreement was generally within about 10%. Al/Si concentration ratios ranged from 0.38% in Mare Cognitum to 0.67% in the Descartes area highlands. A comparison of the Apollo 16 data Al/Si values with optical albedo values along the ground tracks showed the same positive correlation as in the Apollo 15 flight. A reexamination of the detector and collimator geometries showed that the spatial resolution was better by almost a factor of two than the initial estimates.
Observations by the Apollo 15 and 16 gamma-ray spectrometers are compared with those of a number of other experiments, both compositional and noncompositional. A general correspondence with topography is seen. The Van de Graaff area is a unique farside region with respect to observations by the laser altimeter, the subsatellite magnetometer, and the gamma-ray spectrometer. X-ray and alpha particle orbital measurements show a broad general agreement with gamma-ray data, although results from additional elements in the gamma-ray spectrum are needed to extend the comparison with X-ray data. A comparison of Th concentrations with those found at various landing sites shows generally good agreement, with the orbital values tending to be somewhat higher.
The spectrum of the total (diffuse and discrete sources) cosmic gamma-ray background over the 0.3 to 27 MeV range was measured with a 7.0 cm diameter x 7.0 cm long uncollimated NaI(Tl) scintillation counter located on a boom 7.6 m from the Apollo 15 service module. Data on cosmic gamma-rays were taken during transearth coast at various boom extensions, detector gains, and with the plastic anticoincidence scintillator enabled and disabled.
Several spectrometers carried in the Service Module of the Apollo 15 and Apollo 16 spacecraft were employed for the compositional mapping of the lunar surface. The observations involved the measurements of secondary (fluorescent) X-rays, gamma rays and alpha particle emissions. A large scale compositional map of over 20 percent of the lunar surface was obtained for the first time. It was possible to demonstrate interesting chemical differences between the mare and the highlands, to find specific areas of high radioactivity and to learn something about the composition of the moon's hidden side. Further the same devices were used to obtain useful astronomical data during the return to earth.
Apollo 15 and 16 will carry instruments for the purpose of measuring X-ray and gamma ray fluxes from the lunar surface and in cis-lunar space. The intensity levels expected are low over most of the energy range of interest, requiring that background contributions be minimized. The radiation sources on Apollo determined and their interference with these instruments evaluated. The results were used as a basis for dealing with this problem and for recommendations applicable to future manned and unmanned missions.
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 preliminary results from the Sco X-1 and Cyg X-1 obtained from the Apollo 15 X-ray detector data are presented along with preliminary results of the X-ray fluorescence spectrometric data of the lunar surface composition. The production of the characteristic X-rays following the interaction of solar X-rays with the lunar surface is described along with the X-ray spectrometer. Preliminary analyses of the astronomical X-ray observation and the X-ray fluorescence data are presented.