R-3 Repository :: Browsing by Author "Heymann, Dieter"

Browsing by Author "Heymann, Dieter"

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A theoretical study of radon diffusion in the lunar regolith
(1972) Friesen, Larry Jay; Heymann, Dieter
An investigation is made, via computer simulation, of the fate of radon gas produced in the lunar regolith by decay of uranium and thorium. The model used is that of radon atoms released and allowed to perform random walks within the lunar soil. Pressures based on results from Apollo lunar experiment packages indicate that the mean free path for such random walks will be the mean dimensions of void spaces within the soil rather than the (much longer) mean free path for collision with other gas molecules. Calculations are made, using various assumptions for mean void size, heat of adsorption of lunar material for radon, subsurface temperature profile, and depth of release, for the probability that a radon atom may escape through the regolith upper surface before it decays, to become part of the lunar "exosphere". Discussion is made of the implications such escape may have for lunar surface radioactivity and for lead/uranium dating of soil samples.
Ion microprobe measurements of an allende coarse-grained inclusion
(1980) Whitehead, Brian Leigh; Heymann, Dieter; Talbot, Raymond; Dunning, F. Barry
The presence of 26Mg excesses in inclusions of the Allende meteorite result from the decay of 26A1 (T = 7.3 x 105 yrs). Two distinct 1/2 hypotheses have been presented to account for the presence of 26A1 in this meteorite; a nearby supernova which occurre
On the thermal history of chondrites
(1968) Taylor, G. Jeffrey, 1944-; Heymann, Dieter
In order to investigate shock and reheating effects in ordinary chondrites, 71 bronzite, 26 hypersthene, and 6 amphoterite chondrites were examined by X-ray diffraction and 39 bronzite and 19 hypersthene chondrites were studied metallographically. In addition, the inert gas contents of 12 bronzite and 4 hypersthene chondrites were measured mass spectrometrically. It was found that virtually all chondrite with short gas- retention ages (< 2 by.) are shocked and reheated, whereas chondrites with ages > 3 by. are not reheated to any appreciable extent, although some are heavily shocked. It is concluded that few, if any, severe collisions took place on the chondrite parent bodies between 3 and 4.5 by. ago. Moreover, the bronzite and amphoterite parent objects apparently escaped fragmentation, such as was suggested by Anders and Heymann for the hypersthene object.
Patterns of soil maturation and mixing at the Apollo 16 landing site: surface soils
(1979) Ray, James R.; Heymann, Dieter; Clayton, Donald W.; Freeman, John W.
An analysis of the Apollo 16 surface soil samples is presented in an effort to distinguish the separate effects due to mixing of unlike fines from those attributable purely to regolithic maturation processes. In establishing a background needed to accomplish this task, aspects of large-scale stratigraphy and geologic sequence in the central highlands are reviewed. Likewise, a comprehensive discussion of the interrelated phenomena associated with a soil's residence in the upper millimeter of the regolith follows. Data for major element chemistry and trapped inert gases are assembled from the literature and used to infer the provenance of archetypical soils and kinship relationships of remaining surface samples. The hypothesis of maturation domination of inert gas variations is considered and its consequences are delineated. It is found that this assumption, while adequate in explaining the gas properties of most soils, fails to account for about one-fifth of the samples, particularly soil 61221. An alternative approach is then presented which views the distinctive soils as remnants of ancient solar wind irradiation. In this context, unambiguous maturation effects are discernible only for the evolution of absolute gas concentrations and the elemental ratio 2^Ne/36^Ar. The unique soil 61221 is found to have excess argon relative to its very low state of maturity by a factor of about ten after correction for outgassing. This anomaly is ascribed to an irradiation between 3.5 and 4. Gy ago by a solar wind with particle flux greater than present by the same factor. A similar gas-rich component occurs in less pure form in other surface samples.
Production of helium and neon in the lunar regolith by solar cosmic ray protons
(1973) Walton, James Richmond (b. 1947); Heymann, Dieter
In three sets of irradiations at Texas A and M's Variable Energy Cyclotron, stacks of thin Mg, Al, Si, Ca, Ti, and Fe foils were bombarded with 1 to 1 intermediate energy protons (15 to 45 MeV) in order to determine He, Ne, and Ar production cross sections. This energy range was selected because it represents a significant portion of the solar cosmic ray (SCR) spectrum. Certain radioactivities were measured by Dr. Rowe and coworkers, but these will be reported elsewhere. The He and Ne isotopes produced in the Mg, Al, and Si targets have been measured mass spectrometrically and cross sections calculated, using the Na activity in the Mg targets as a monitor. Six determinations of the He, He-, Ne, Ne, and Ne cross sections from Mg and five for Al and Si are reported. The He and He cross sections from the Mg, Al, and Si targets are all fairly comparable at similar proton energies. The He cross sections increase with energy up to a maximum value of about 2 mb at 4 to 45 MeV. The Ne and Ne cross sections from Mg are significantly greater than those from Al and Si at similar energies. The maximum Ne and Nel cross sections measured for Mg were 46.5 mb at 24.6 MeV and 12. mb at 15.3 MeV respectively. The Ne cross sections from all three elements up to 45 MeV are generally less than 1 mb and negligible in comparison to the Na2 cross sections. A major portion of the Ne measured is attributed to Na2 decay in the targets since the end of the irradiations. Combining these cross sections with those reported in literature, He, He, Ne, Ne, Ne, and Na cross section functions for the target elements Mg, A1 , and Si were derived up to 2 MeV. The literature cross sections from A1 and the Na2 cross sections from Na were also considered. By integrating the product of these functions and differential solar cosmic ray spectra, (for normal and isotropic incidence), He, (including H), He, Ne®, Ne, and Ne (including Na) production rates from the individual target elements, Na, Mg, Al, and Si were computed. These are reported as a function of depth for the top 1 to 15 centimeters of a model lunar regolith with Na, Mg, Al, and Si contents of 1. mass percent each. Applying these results to the known average chemical composition of the lunar soils, total production rates were computed for the Apollo 11, 12, 14 and 15 soils. The production rates reported are based on a solar cosmic ray spectrum derived from data observed in the two high years, 1959, and 196, in solar cycle 19 (1954-1964). In general, all of the production rates are at least comparable to the galactic cosmic ray (GCR) production rates down to a depth of about 1. gm/cm or approximately in the top 5 mm of the lunar regolith. With increasing depth beyond 1. gm/cm, all production rates decrease rapidly, becoming negligible compared to the galactic. The direct SCR production of Ne in the Apollo soils is generally less than 5 percent of the total Ne and Na production at any depth. The SCR-produced elemental (He/tîe)scR ratio and the isotopic (NeVNe)gcR and (Ne/NegcR ratios have also been calculated as a function of depth in the Apollo soils. These ratios appear to be at least moderately dependent not only on depth but also on chemical composition. At almost all depths down to 1. gm/cm, these ratios, especially (Ne/Ne), are significantly different from those characteristic of galactic spallation. Considering the maximum range in the SCR produced neon isotopic ratios in any of the four Apollo soils, SCR production is thus concluded to be an isotopically distinct component in the neon 3-isotope diagram. Using the absolute production rate values, example speculations on the two independent and unknown phenomena, past solar activity and the "gardening" process in the lunar regolith have been made. Also an example of how a "solar cosmic ray exposure age" may be derived is discussed. Several reported measurements of Apollo 11 and 12 samples along with the results of these calculations support the possibility that solar cosmic ray proton production may not only be present, but also detectable in lunar soil samples.
Rare gas analysis of Apollo 11 glassy fragments
(1971) Allen, Sharon Cornelius; Heymann, Dieter
The He, Ne, and. Ar contents of nineteen Apollo-11 glasses and four Apollo-12 glasses were measured massspectrometrically. The glasses were variously colored particles: amber, clear, green, and brown, and were approximately 500 microns in size. We have found that these glassy fragments contain much smaller quantities of trapped gas (solar wind) than lithic fragments the same size. The color of the glass particles is indicative of their chemical composition. The elemental and isotopic ratios are similar to those for lunar bulk soil. It has been shown that the amber and green glasses, and possibly the brown glasses, contain a cosmogenic component of Ne21 which can be attributed to solar cosmic ray interactions with Mg24 and probably with Al27. Similarly, the clear glasses contain a cosmogenic component of Ar38 which can be attributed to solar cosmic ray interactions with Ca40. The Ne21radiation ages of three green glasses and one amber glass are older than the average Ne21 radiation age for bulk soil. Three clear glasses show an38 radiation age older than the average Ar38 radiation age for the bulk soil.
Terrestrial ℗ℓNe and the accretion time of the earth
(1978) Palma, Russell L.; Heymann, Dieter
The atmospheric composition of neon is considered along the lines of the multicomponent theory for that gas. It is found that an excess amount of ^Ne is indicated if the terrestrial values of the 2^Ne/22Ne and 2^Ne/22Ne ratios are taken to be the result of mixtures of the components Ne-E and Ne-B or Ne-E and Ne$w. This excess ranges from 9-17% of the Ne presently in the earth's atmosphere. Production rates for 21Ne by galactic cosmic ray irradiation are calculated from consideration of meteorite and lunar drill core data. The Ne excess indicated by the selected component mixing lines places constraints on the mass distribution of the earth's protoplanetary bodies and their accretion times. The formulation developed by Safronov and Wetherill for the formation interval of the earth yields a result in concordance with this possible 21^Ne excess. Solar cosmic rays and the influx of meteroids are found to be of negligible importance in the production of Ne, as are all nuclear reactions in the earth after formation, excepting 18O(a ,n)21Ne. This last reaction contributes approximately 2.1% of all Ne over the lifetime of the earth. The possible contribution to terrestrial neon from the passage of the solar system through dense interstellar clouds is discussed, as is the retention of neon during the accretionary process.
The interaction of horizontal ionospheric and region one Birkeland currents
(1981) Karty, Janice Lee; Wolf, Richard A.; Cloutier, Paul A.; Heymann, Dieter
Linkage of field-aligned to horizontal ionospheric current, is a significant aspect in general coupling mechanisms between the magnetosphere and ionosphere. The magnetosphere generates field-aligned current that drives horizontal ionospheric conduction currents. This research provides a detailed, quantitative modelling of the ionospheric and field-aligned currents in the area, or band, covered by the higher latitude set of field-aligned (region-1 Birkeland) current, with the assumption that Birkeland current is uniformly distributed there. Current conservation implies that field-aligned current is balanced by the divergence of ionospheric current. Solution of the divergence equation, .with the area poleward of the band taken to be an insulator, appropriate boundary conditions (inferred from lower latitude modelling), and a local-time dependent conductivity allows horizontal ionospheric current- and electric field, and Birkeland current to be deduced. The new model combines with existing detailed models of the lower latitude region, forming an effectively global computer model. Application of the theoretical model to the 19 September 1976 substorm event yields many interesting features. Among these are a westward electrojet extending from about 19LT past midnight to about 9LT, with a maximum strength of -11x1^5 amp in post-midnight hours. TMs is in reasonable agreement with, observational data for substorm conditions. The calculated eastward electrojet is comparable to (but slightly smaller than) the eastward electrojet in the region just; equatorward of the one treated here, although the lower latitude electrojet; extends to ~23LT. Hear midnight, the westward electrojet modelled here is ~3 times larger than the westward electrojet in the sub-polar region. Theoretical calculations for the 19 September 1976 event using the present model indicate that electric field reversals fall within the studied region in four out of six satellite passes (corresponding to those passes when concentration of Birkeland current is toward the equatorward edge of the band). Although detailed agreement with data is modest, this model agrees with data on a crucial characteristic. In both the present; theory and data, the electric field reversal usually occurs poleward of most of the region-1 current, which means that most region-1 current flows into or out of regions of sunward convection. Since currents flowing in the investigated high-latitude region often have dominant effects on ground magnetic variations (even on magnetograms of low-latitude observations), agreement between theoretical and observed magnetograms for the modelled substorm event is greatly improved by inclusion of the large part of the westward electrojet that flows in the higher latitude region. Contributions of the present work to calculations of Joule heating of the upper atmosphere are significant, with Joule heating poleward of the equatorward edge of region-1 currents comprising ~3% of the total in the modelled event of 19 September 1976. Values for the strength of the electrojet and amount of Joule heating predicted from a simple Cowling conductivity band picture (with no radial current flowing into the band) agree with the present model to within ~2%.
The organic geochemistry and water-rock system across a contact metamorphic profile in the Mancos shale near Crested Butte, Colorado
(1982) Cuddihee, John Lee; Baker, Donald R.; Lallemant, Hans G. Avé; Valley, John W.; Heymann, Dieter
A Mid-Tertiary igneous intrusion into the Upper Cretaceous Mancos Shale provides an excellent natural laboratory to study the thermal effects of an intrusion on the organic geochemistry and water-rock system across a contact metamorphic profile. The intrusion, is believed to have established a high temperature gradient across a two mile long sampling profile. This study investigated the isotopic and chemical evolution of both kerogen and extractable organic material. Kerogen displayed a net weight loss of 11% due to methane generation. Kerogen showed essentially no carbon isotopic change. Bitumen contents decreased dramatically across the profile with a measurable 1.5 per mil depletion in 12C for the highest temperature samples. The relatively unique time-temperature history of the study area, and the difference in the kinetics of bitumen and kerogen degradation, is believed to be responsible for the difference in behavior of kerogen and bitumen. Oxygen isotope ratios of matrix calcite suggest that the calcite exchanged with connate water or a very small volume of meteoric water. The final oxygen isotopic ratio of calcite is a function of temperature and the water/calcite volume ratio. Finally, a thermal model involving conductive heating due to a subjacent extension of the White Rock pluton beneath the study area is shown to be capable of generating a temperature of 3°C.
The production of meteoritic anomalies via proton irradiation
(1978) Dziczkaniec, Marlene; Heymann, Dieter
Proton bombardment of the solar nebula is investigated as a means for the production of observed meteoritic anomalies in the elements neon and magnesium. Condensation of nebular gas during the irradiation provides the means for transporting 26Al and 22Na formed in the gas to the solid 26 22 phase where decay to Mg and Ne occurs. Each element is assigned an independent condensation rate, and isotopic ratios in both the gas and condensing solid are monitored. Results indicate that it is possible to specify a set of parameters that would produce the observed anomalies in both 26Mg and 22Ne without disturbing other isotopic ratios. The required condensation rates seem to agree with current models of the condensation of a cooling gas of cosmic composition. In addition, the irradiation model is capable of producing the negative 2 6Mg anomalies that have currently been deduced from the analysis of meteorite inclusions.

Browsing by Author "Heymann, Dieter"

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