Engineering topics

Murty, S. V. S.

Publications and source records attributed to Murty, S. V. S..

7 records

NASA NTRS2002

Silicon in Mars' Core: A Prediction Based on Mars Model Using Nitrogen and Oxygen Isotopes in SNC Meteorites

Chemical and (oxygen) isotopic compositions of SNC meteorites have been used by a number of workers to infer the nature of precursor materials for the accretion of Mars. The idea that chondritic materials played a key role in the formation of Mars has been the central assumption in these works. Wanke and Dreibus have proposed a mixture of two types of chondritic materials, differing in oxygen fugacity but having CI type bulk chemical composition for the nonvolatile elements, for Mars' precursor. But a number of studies based on high pressure and temperature melting experiments do not favor a CI type bulk planet composition for Mars, as it predicts a bulk planet Fe/Si ratio much higher than that reported from the recent Pathfinder data. Oxygen forms the bulk of Mars (approximately 40% by wt.) and might provide clues to the type of materials that formed Mars. But models based on the oxygen isotopic compositions of SNC meteorites predict three different mixtures of precursor materials for Mars: 90% H + 10% CM, 85% H + 11% CV + 4% CI and 45% EH + 55% H. As each of these models has been shown to be consistent with the bulk geophysical properties (such as mean density, and moment of inertia factor) of Mars, the nature of the material that accreted to form Mars remains ambiguous.

Mohapatra, R. K.↗

NASA NTRS1993

Nitrogen and light noble gases in Parsa enstatite chondrite

Solar gases have been recently reported in Parsa, an EH3 chondrite. In an effort to check whether solar gases are uniformly distributed throughout Parsa or they are located in specific phases, we analyzed two additional samples of bulk Parsa and one aubritic nodule for N and noble gases. Nitrogen studies are intended for the understanding of the nitrogen components distribution in E-chondrites. The N-systematics of the nodule are entirely different from the bulk samples. The higher N contents in this nodule, as well as its complex delta(sup 15)N structure, as compared to the normal aubrites, is suggestive that the nodule is not a genuine aubrite.

Murty, S. V. S.↗

NASA NTRS1990

Search for solar-type nitrogen in the gas-rich Pesyanoe meteorite

An initial study carried out to isolate and characterize solar wind N in the dark portion of the enstatite achondrite Pesyanoe is presented. Nitrogen isotopic data obtained from a stepwise gas release of two grain-size fractions of the gas-rich meteorite are given. It is determined that more than one trapped N component is present and that indigenous N is released above 1000 C with an isotopic signature of delta N-15 = -33 per mil. A heavy N component is detected at 700-800 C, and coincides with a major release of solar-type noble gases. A lower limit of delta N-15 = -6 per mil is defined by the isotopic shifts at this range of temperature for the second element of a two-component mixture, whereas the delta N-15 signature depends on the adopted elemental abundances for a solar-type component. It is pointed out that the timing of solar wind loading of Pesyanoe is only constrained to correspond to the cosmic ray exposure age (less than 60 Ma), although it is generally assumed that this irradiation took place during an early stage.

Murty, S. V. S.↗

NASA NTRS1987

Nucleogenic noble gas components in the Cape York iron meteorite

The paper reports data on neutron capture products of the secondary cosmic ray component, the inferred proton and neutron fluences, and the identification of double beta decay of Se-82 in heavily shielded samples of the Cape York iron meteorite. One purpose of this study is to develop a new chronometer for cosmic ray exposure, based on the nuclides I-129 (16 My half-life) and Xe-129 from low energy cosmic ray reactions on Te. The abundance ratio of these two nuclides permits the determination of an (effective) exposure age of 93 + or - 16 My, which represents the first exposure age datum of Cape York. The very small concentrations of spallogenic Ar-38 = 6.5 x 10 to the -10th cu cm STP/g in the metal and troilite (per g Fe) document the heavily shielded locations of the sample. An excess of Xe-129 in the troilite is shown to be entirely due to the decay of cosmic-ray-produced I-129. On the other hand, an inclusion in the troilite reveals the presence of Xe-129 from extinct I-129 and documents its about 4.5 Gy formation age. Mono-isotopic excess of Kr-82 is identified as due to beta-beta-decay of Se-82 with an inferred half-life of 1.0 x 10 to the 20th y. This represents the first beta-beta-decay product observed in a meteorite.

Murty, S. V. S.↗

NASA NTRS1985

When did the average cosmic ray flux increase?

A new 129 to 129 Xe method to obtain cosmic ray exposure ages and to study the average cosmic ray flux on a 10 to the 7th power to 10 to the 8th power year time-scale was developed. The method is based on secondary neutron reactions on Te in troilite and the subsequent decay of 129I, the reaction product to stable 129 Xe. The first measurements of 129 I and 129 Xe in aliquot samples of a Cape York troilite sample are reported.

Nishiizumi, K.↗

NASA NTRS1985

Some chemical and isotopic observations in chondrules

Chemical, nitrogen and noble gas isotopic observations in individual chondrules of the Bjurbole (L4) and Dhajala (H3,4) chondrites are reported. The delta N-15 is +9.4 for the Bjurbole 'matrix,' ranges from +6.4 to -20.0 in chondrules, and appears to be related to the chemical composition. Nitrogen isotope systematics seem to require the presence of more than one component of distinct signatures. Although we cannot rule out complex processes of chondrule and matrix formation involving element and isotope fractionations, the oxygen isotope systematics also seem to require distinct reservoirs. The results in terms of the lack of equilibrations among chondrule minerals are discussed, as well as with the host meteorite matter, and also the paradox of the constant Fe/Mg ratio of olivines in Bjurbole and of the majority of ordinary chondrites.

Fredriksson, K.↗

NASA NTRS1984

The low-energy secondary cosmic ray flux: Detectors in iron meteorites

The cosmic ray-produced nuclides in the interiors of very large bodies are mainly due to secondary particle reactions. The records of low-energy products, specifically the neutron capture products in meteorites, may provide new information regarding multi-stage irradiation and parent body break-ups. Noble gas nuclides, in general, are the best candidates for these investigations. The troilite nodules of iron meteorites contain very low amounts of trapped gas and, because of their elemental abundance systematics of suitable target elements for low energy production of noble gas nuclides, they are ideal candidates for this purposes. Results of a study of noble gases and nitrogen in a troilite nodule of the Cape York iron are presented.

Murty, S. V. S.↗