Engineering topics

Dodd, R. T.

Publications and source records attributed to Dodd, R. T..

6 records

NASA NTRS1993

A CM chondrite cluster and CM streams

An elongate year-day concentration of CM meteoroid falls between 1921 and 1969 is inconsistent with a random flux of CM meteoroids and suggests that most or all such meteorites, and perhaps the Kaidun C-E chondrite breccia, resulted from streams of meteoroids in nearly circular, Earth-like orbits. To establish whether the post-1920 cluster might have arisen from random sampling, we determined the year-day distribution of 14 falls between 1879 and 1969 by treating each as the corner of a cell of specified dimensions (e.g. 30 years x 30 days) and calculated how many falls occurred in that cell. We then compared the CM cell distribution with random distributions over the same range of years. The results show that for 30 x 30 and 45 x 45 cells, fewer than 5 percent of random sets match the CM distribution with respect to maximum cell content and number of one-fall cells.

Dodd, R. T.↗

NASA NTRS1985

The Bloomington (LL6) chondrite and its shock melt glasses

The shock melt glasses of the Bloomington LL-group chondrite were examined using electron-beam microscopy and compared with data from studies of other shock melt glasses. Petrologic and mineralogic characterizations were also performed of the samples. The metal contents of the meteorite were almost wholly Ni-rich martensite. The glasses resembled shock melt glasses in L-group chondrites, and were indicative of isochemical melting during one melt phase, i.e., a very simple history.

Dodd, R. T.↗

NASA NTRS1981

Chemical studies of L-chondrites. I - A study of possible chemical sub-groups

Radiochemical neutron activation analysis of Ag, As, Au, Bi, Co, Cs, Ga, In, Rb, Sb, Te, Tl and Zn and major element data in 14 L4-6 and 3 LL5 chondrites indicates that the L-group is unusually variable and may represent at least 2 sub-groups differing in formation history. Chemical trends in the S/Fe-rich sub-group support textural evidence indicating late loss of a shock-formed Fe-Ni-S melt; the S/Fe-poor sub-group seemingly reflects nebular fractionation only. Highly mobile In and Zn apparently reflect shock-induced loss from L-chondrites. Data for L5 chondrites suggest higher formation temperatures and/or degrees of shock than for LL5 chondrites.

Neal, C. W.↗

NASA NTRS1980

On the chemical composition of L-chondrites

Radiochemical neutron activation analysis of Ag, As, Au, Bi, Co, Cs, Ga, In, Rb, Sb, Te, Tl, and Zn and major element data in 14 L4-6 and 3 LL5 chondrites indicates that the L group is unusually variable and may represent at least 2 subgroups differing in formation history. Chemical trends in the S/Fe rich subgroup support textural evidence indicating late loss of a shock formed Fe-Ni-S melt; the S/Fe poor subgroup seemingly reflects nebular fractionation only. Highly mobile In and Zn apparently reflect shock induced loss from L chondrites. However, contrasting chemical trends in several L chondrite sample sets indicate that these meteorites constitute a more irregular sampling of, or more heterogeneous parent material than do carbonaceous or enstatite chondrites. Data for 15 chondrites suggest higher formation temperatures and/or degrees of shock than for LL5 chondrites.

Neal, C. W.↗

NASA NTRS1972

Evidence for vapor fractionation in the origin of chondrules.

The major-element compositions of 47 individual Chainpur (LL-3) chondrules were determined. There appears to be no correlation between Na and Al, in contrast with the correlation previously found in Bjurbole chondrules in which these elements are characteristically found in equal molar proportions. The correlation in Bjurbole chondrules is considered to be the effect of metamorphism. The compositional variations among Chainpur chondrules point to a fractionation which basically involved only silica. This can best be explained as being the result of vapor fractionation which took place during or after the formation of the chondrules. The ratio of Ca to Al in the individual chondrules is generally close to the value 1.08, which has been found to be characteristic of the chondrites in general.

Walter, L. S.↗

NASA NTRS1972

Chemical constraints on the origin of chondrules in ordinary chondrites.

Chemical variations found among 61 chondrules from the Chainpur (LL-3) chondrite are compared with those predicted for various mechanisms of chondrule formation. Neither crystal-liquid nor liquid-vapor fractionation accounts for the pattern of variation in Chainpur, which appears to reflect fragmentation of a crystalline precursor rock whose crystal dimensions were about 1/10 of the median chondrule diameter.

Dodd, R. T.↗