Cosmogenic radionuclides in L5 and LL5 chondrites from Queen Alexandra Range, Antarctica: Identification of a large L/LL5 chondrite shower with a preatmospheric mass of approximately 50,000 kg

Self Cite

Section: Resultsmentioning

confidence: 99%

Calibration of cosmogenic noble gas production in ordinary chondrites based on ³⁶Cl‐³⁶Ar ages. Part 1: Refined produced rates for cosmogenic ²¹Ne and ³⁸Ar

Dalcher

Caffee

Nishiizumi

et al. 2013

Self Cite

“…Welten et al. () gave an equation relating the activities of 10 Be and 36 Cl in meteoritic metal:

{(][, ^{36} Cl)}_{T_{Fall}} = 6.01 {(][, ^{10} Be)}_{T_{Fall}} - 0.28 {(][, ^{10} Be)}_{T_{normalFall}}^{2} - 0.009 {(][, ^{10} Be)}_{T_{normalFall}}^{3}

…”

Section: Discussionmentioning

confidence: 99%

Cosmic‐ray exposure ages of pallasites

Herzog

Cook

Cosarinsky

et al. 2015

We analyzed cosmogenic nuclides in metal and/or silicate (primarily olivine) separated from the main‐group pallasites Admire, Ahumada, Albin, Brahin, Brenham, Esquel, Finmarken, Glorieta Mountain, Huckitta, Imilac, Krasnojarsk, Marjalahti, Molong, Seymchan, South Bend, Springwater, and Thiel Mountains and from Eagle Station. The metal separates contained an olivine fraction which although small, <1 wt% in most cases, nonetheless contributes significantly to the budgets of some nuclides (e.g., up to 35% for 21Ne and 26Al). A correction for olivine is therefore essential and was made using model calculations and/or empirical relations for the production rates of cosmogenic nuclides in iron meteoroids and/or measured elemental concentrations. Cosmic‐ray exposure (CRE) ages for the metal phases of the main‐group pallasites range from 7 to 180 Ma, but many of the ages cluster around a central peak near 100 Ma. These CRE ages suggest that the parent body of the main‐group pallasites underwent a major break‐up that produced most of the meteorites analyzed. The CRE age distribution for the pallasites overlaps only a small fraction of the distribution for the IIIAB iron meteorites. Most pallasites and IIIAB irons originated in different collisions, probably on different parent bodies; a few IIIABs and pallasites may have come out of the same collision but a firm conclusion requires further study. CRE ages calculated from noble gas and radionuclide data of the metal fraction are higher on average than the 21Ne exposure ages obtained for the olivine samples. As the metal and olivine fractions were taken in most cases from different specimens, the depth‐dependency of the production rate ratio 10Be/21Ne in metal, not accounted for in our calculations, may explain the difference.

“…; Welten et al. ). When cosmic‐ray particles interact with cosmic objects, they leave tracks in their minerals and produce cascades of particles, which lead to the production of radioactive and stable nuclides in the target material.…”

Section: Introductionmentioning

confidence: 98%

Cosmogenic radionuclides and mineralogical properties of the Chelyabinsk (LL5) meteorite: What do we learn about the meteoroid?

Povinec

Laubenstein

Jull

et al. 2015

On February 15, 2013, after the observation of a brilliant fireball and a spectacular airburst over the southern Ural region (Russia), thousands of stones fell and were rapidly recovered, bringing some extremely fresh material for scientific investigations. We undertook a multidisciplinary study of a dozen stones of the Chelyabinsk meteorite, including petrographic and microprobe investigations to unravel intrinsic characteristics of this meteorite. We also study the short and long‐lived cosmogenic radionuclides to characterize the initial meteoroid size and exposure age. Petrographic observations, as well as the mineral compositions obtained by electron microprobe analyses, allow us to confirm the classification of the Chelyabinsk meteorite as an LL5 chondrite. The fragments studied, a few of which are impact melt rocks, contain abundant shock melt veins and melt pockets. It is likely that the catastrophic explosion and fragmentation of the Chelyabinsk meteoroid into thousands of stones was in part determined by the initial state of the meteoroid. The radionuclide results obtained show a wide range of concentrations of 14C, 22Na, 26Al, 54Mn, 57Co, 58Co, and 60Co, which indicate that the pre‐atmospheric object had a radius >5 m, consistent with other size estimates based on the magnitude of the airburst caused by the atmospheric entry and breakup of the Chelyabinsk meteoroid. Considering the observed 26Al activities of the investigated samples, Monte Carlo simulations, and taking into account the 26Al half‐life (0.717 Myr), the cosmic‐ray exposure age of the Chelyabinsk meteorite is estimated to be 1.2 ± 0.2 Myr. In contrast to the other radionuclides, 14C showed a very large range only consistent with most samples having been exposed to anthropogenic sources of 14C, which we associate with radioactive contamination of the Chelyabinsk region by past nuclear accidents and waste disposal, which has also been confirmed by elevated levels of anthropogenic 137Cs and primordial 40K in some of the Chelyabinsk fragments.