Cosmogenic effects in Mbale, L5/6 chondrite

Murty, S. V. S.; Bhandari, N.; Suthar, K. M.; Clement, C. J.; Bonino, G.; Castagnoli, G. Cini

doi:10.1111/j.1945-5100.1998.tb01315.x

Cited by 21 publications

(18 citation statements)

References 27 publications

(22 reference statements)

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“…Production rate calculations carried out by several groups suggest that production rates attain maximum values for spherical objects about the size of Knyahinya (i.e., for bodies with radii close to 45 cm; Graf et al, 1990b;Leya et al, 2000). We therefore conclude that St-Robert had a radius close to 45 cm, comparable to Knyahinya and a bit bigger than Mbale (Murty et al, 1998). For a radius of 45 2 5 cm and with the density of 3.50 g/cm3 that we assumed for the model calculations we calculate a pre-atmospheric mass of (1.3 2 0.4) x 103 kg, in good agreement with the various estimates presented by Brown et al (1996).…”

Section: Pre-atmospheric Size Of St-robertmentioning

confidence: 63%

Exposure history of the St‐Robert (H5) fall

Leya

Wieler

Aggrey

et al. 2001

Meteorit & Planetary Scien

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— The compositionally typical H5 chondrite St‐Robert has an exposure age, 7.8 Ma, indistinguishable from that of the main cluster of H chondrites. Small values of the cosmogenic 22Ne/21Ne ratio in interior samples imply a pre‐atmospheric radius on the order of 40 cm. Sample depths based on tracks and the production rates of Bhattacharya et al. (1973) range from 6 to ∼40 cm and are generally larger than depths estimated from published 60Co activities, perhaps because the track production rates adopted are too high. Depth profiles of the production rates of 14C, 36Cl, 26Al, 10Be, and 21Ne in stony material show increases with depth and reach levels 5% to 15% higher than expected from modeling calculations. The maximum concentrations in St‐Robert are, however, generally comparable to those measured for the L5 chondrite, Knyahinya, whose pre‐atmospheric radius of ∼45 cm is thought to lead to the maximum possible production rates in chondrites. We infer that the pre‐atmospheric radius of St‐Robert was within 5 cm of the value that supports maximum production rates (i.e., 45 ± 5 cm). This radius corresponds to a pre‐atmospheric mass of (1.3 ± 0.4) × 103 kg. The agreement of exposure ages for St‐Robert obtained in several different ways and the similarity of the depth profiles for 14C, 26Al, 10Be, and 21Ne argue against a lengthy pre‐exposure of St‐Robert on the parent body and against a two‐stage exposure after launch from the parent body. Following Morbidelli and Gladman (1998), we suggest that St‐Robert was chipped from deep in its parent body, spent the next 7–8 Ma without undergoing a major collision, was nudged gradually into an orbital resonance with Jupiter, and then traveled quickly to Earth.

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Section: Pre-atmospheric Size Of St-robertmentioning

confidence: 63%

Exposure history of the St‐Robert (H5) fall

Leya

Wieler

Aggrey

et al. 2001

Meteorit & Planetary Scien

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“…The procedure has been described in detail earlier (Murty 1997;Murty et al 1998). Briefly, the samples were wrapped in Al foils and loaded into the extraction system of a noble gas mass spectrometer (VG 1200).…”

Section: Noble Gasesmentioning

confidence: 99%

Spectacular fall of the Kendrapara H5 chondrite

Dhingra

Bhandari

Shukla

et al. 2004

Meteorit & Planetary Scien

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Abstract-An extremely bright fireball was seen for over 250 km near the eastern coast of India in the evening sky on September 27, 2003. In a rare observation, the fireball was seen by two airline pilots, providing direction of the trail with reasonable accuracy, consistent with ground-based observations. A few fragments of the meteorite were subsequently recovered along the end of the trail in different parts of Kendrapara district (20°30′ N; 86°26′ E) of Orissa. Based on petrography and chemical composition, the meteorite is classified as H5 chondrite. The cosmogenic radionuclides 54 Mn, 22 Na, 60 Co, and 26 Al and tracks have been studied in this stony meteorite. Two of the fragments show an unusually high activity of 60 Co (~160 dpm/kg) indicating a meteoroid radius of 50-150 cm. Assuming that less than 10% (by weight) of the fragments could be recovered because of difficult terrain, an atmospheric mass ablation of >95% is estimated. Based on the observations of the trail and the estimated mass ablation, orbital parameters of the meteoroid have been calculated. The aphelion is found to lie in the asteroidal belt (1.8-2.4 AU), but the inclination of the orbit is large (22°-26°) with respect to the ecliptic. Noble gases have been analysed in two samples of this meteorite. He and Ne are dominantly cosmogenic. Using production rates based on the sample depth derived from 60 Co content, 21 Ne-based exposure age of 4.50 ± 0.45 Ma is derived for Kendrapara. One of the samples, known to be more deeply shielded based on high 60 Co activity, shows the presence of 80 Kr, 82 Kr, and 128 Xe produced by (n, γ) reaction on 79 Br, 81 Br, and 127 I, respectively. The ( 80 Kr/ 82 Kr) n ratio of 3.5 ± 0.9 is consistent with neutrons being mostly thermal. Trapped 84 Kr and 132 Xe are in the expected range for metamorphic grade H5.

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“…The low activity of 60 Co of fragment-A is not inconsistent with this result. Depth profiles of some cosmogenic nuclides, e.g., 22 Na, 10 Be, 53 Mn, 26 Al as a function of preatmospheric size and shielding depth (e.g., Bhandari et al, 1993;Murty et al, 1998) have been extensively studied. The low activities of other spallation products (Table 1) could also be partly due to small preatmospheric size of the Kobe meteorite.…”

Section: Shielding Effects (Preatmospheric Size and Depth)mentioning

confidence: 99%

Cosmogenic radionuclides in the recently fallen Kobe (CK4) meteorite.

2002

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Cosmogenic radionuclides in the Kobe chondrite (CK4) fell on September 26th, 1999, have been measured immediately after the fall (21 hours) using a ultra low-background Ge-detector. Nineteen cosmogenic nuclides including the very short-lived 24 Na were detected and their activities place constrains on the exposure history of the meteorite and reflect effect of solar modulation of galactic cosmic rays during solar maximum. Two nuclides, 28 Mg and 43 K were possibly detected for the first time and signals probably due to 56 Ni and 57 Ni were present although statistical uncertainties were very large. On the other hand, low activities of 60 Co (~1 dpm/kg) and 26 Al (~38 dpm/kg) mainly suggest a small preatmospheric size (≤10 cm) of the Kobe meteorite.

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Cosmogenic effects in Mbale, L5/6 chondrite

Cited by 21 publications

References 27 publications

Exposure history of the St‐Robert (H5) fall

Exposure history of the St‐Robert (H5) fall

Spectacular fall of the Kendrapara H5 chondrite

Cosmogenic radionuclides in the recently fallen Kobe (CK4) meteorite.

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