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  1. Abstract Highlights

    We present a first true three‐dimensional analysis of chondrule size.

    Our ordinary chondrite chondrule diameter data demonstrate the trend of mean chondrule diameters increasing in the order H chondrites < L chondrites < LL chondrites.

    We also present the first detailed low‐iron enstatite chondrite chondrule size‐frequency distribution.

    We examine the shapes and collective orientations of the chondrules and show that chondrite petrofabrics can be explored with our methodology.

     
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  2. Abstract

    The radiation record of extraterrestrial rocks provides important insights into their thermal and radiation history. For meteorites this relates to their orbits, thermal history, terrestrial age, preatmospheric size and shape, and possibly cosmic ray exposure age. For meteorites from the Moon and Mars, the radiation record allows insights into transit times. For Martian surface samples, the radiation record enables estimates of their sedimentary age. Despite this, there is a growing tendency to artificially expose these samples to large radiation doses by the use of X‐ray computed tomography (CT) imaging, often as part of their initial examination. In order to understand the effect of synchrotron microCTon meteorites, we placed samples of the Bruderheim L6 chondrite in theCTimaging port of the Advanced Photon Source at the Argonne National Laboratory, Argonne, Illinois. Monoenergetic X‐ray beams of 25 and 46 keV and a high flux broad spectrum beam were used. The synchrotronCTprocedure exposed the samples to radiation doses significantly higher than the natural doses observed for meteorites (1670 to ~10,000 Gyr, compared to ~1000 Gyr for natural samples). It is clear thatCTimaging, whether using a laboratory system as in our previous report or using the synchrotron source, makes measurement of the natural radiation record of the samples impossible. Samples should not be placed in aCTscanner without due consideration of the loss of unique information for these valuable extraterrestrial samples.

     
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