Gamma-ray bursts and X-ray melting of material to form chondrules and planets

Chondrules are millimeter sized objects of spherical to irregular shape that constitute the major component of chondritic meteorites that originate in the region between Mars and Jupiter and which fall to Earth. They appear to have solidified rapidly from molten or partially molten drops. The heat source that melted the chondrules remains uncertain. The intense radiation from a gamma-ray burst (GRB) is capable of melting material at distances up to 300 light years. These conditions were created in the laboratory for the first time when millimeter sized pellets were placed in a vacuum chamber in the white synchrotron beam at the European Synchrotron Radiation Facility. The pellets were rapidly heated in the X-ray and gamma-ray furnace to above 1400C melted and cooled. This process heats from the inside unlike normal furnaces. The melted spherical samples were examined with a range of techniques and found to have microstructural properties similar to the chondrules that come from meteorites. This experiment demonstrates that GRBs can melt precursor material to form chondrules that may subsequently influence the formation of planets. This work extends the field of laboratory astrophysics to include high power synchrotron sources.Comment: 4 pages, 4 figures. Full resolution figures available from A&

Effects of temperature on the crystal structure of epidote: a neutron single-crystal diffraction study at 293 and 1070K

The effects of temperature on the crystal structure of a natural epidote [Ca1.925 Fe0.745Al2.265Ti0.004Si3.037O12(OH), a = 8.890(6), b = 5.630(4), c = 10. 50(6) \uc5 and \u3b2 = 115.36(5)\ub0, Sp.Gr. P21/m] have been investigated by means of neutron single-crystal diffraction at 293 and 1,070 K. At room conditions, the structural refinement confirms the presence of Fe3+ at the M3 site [%Fe(M3) = 73.1(8)%] and all attempts to refine the amount of Fe at the M(1) site were unsuccessful. Only one independent proton site was located. Two possible hydrogen bonds, with O(2) and O(4) as acceptors [i.e. O(10)-H(1)\ub7\ub7\ub7O(2) and O(10)-H(1)\ub7\ub7\ub7O(4)], occur. However, the topological configuration of the bonds suggests that the O(10)-H(1)\ub7\ub7\ub7O(4) is energetically more favourable, as H(1)\ub7\ub7\ub7O(4) = 1.9731(28) \uc5, O(10)\ub7\ub7\ub7O(4) = 2.9318(22) \uc5 and O(10)-H(1)\ub7\ub7\ub7O4 = 166.7(2)\ub0, whereas H(1)\ub7\ub7\ub7O(2) = 2.5921(23) \uc5, O(10)\ub7\ub7\ub7O(2) = 2.8221(17)\uc5 and O(10)-H(1)\ub7\ub7\ub7O2 = 93.3(1)\ub0. The O(10)-H(1) bond distance corrected for "riding motion" is 0.9943 \uc5. The diffraction data at 1,070 K show that epidote is stable within the T-range investigated, and that its crystallinity is maintained. A positive thermal expansion is observed along all the three crystallographic axes. At 1,070 K the structural refinement again shows that Fe3+ share the M(3) site along with Al3+ [%Fe(M3)1,070K = 74(2)%]. The refined amount of Fe3+ at the M(1) is not significant [%Fe(M1)1,070K = 1(2)%]. The tetrahedral and octahedral bond distances and angles show a slight distortion of the polyhedra at high-T, but a significant increase of the bond distances compared to those at room temperature is observed, especially for bond distances corrected for "rigid body motions". The high-T conditions also affect the inter-polyhedral configurations: the bridging angle Si(2)-O(9)-Si(1) of the Si2O7 group increases significantly with T. The high-T structure refinement shows that no dehydration effect occurs at least within the T-range investigated. The configuration of the H-bonding is basically maintained with temperature. However, the hydrogen bond strength changes at 1,070 K, as the O(10)\ub7\ub7\ub7O(4) and H(1)\ub7\ub7\ub7O(4) distances are slightly longer than those at 293 K. The anisotropic displacement parameters of the proton site are significantly larger than those at room condition. Reasons for the thermal stability of epidote up to 1,070 K observed in this study, the absence of dehydration and/or non-convergent ordering of Al and Fe3+ between different octahedral sites and/or convergent ordering on M(3) are discussed

The structure of cellulose II: a revisit

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