Nuclear tracks in the Angra dos Reis and Moore County meteorites
1976; Elsevier BV; Volume: 40; Issue: 8 Linguagem: Inglês
10.1016/0016-7037(76)90142-3
ISSN1872-9533
AutoresEugene A. Carver, Anders Edward,
Tópico(s)Gamma-ray bursts and supernovae
ResumoCharged particle tracks were studied in the Angra dos Reis and Moore County meteorites, both of which contain an unexplained excess of He4. A selective annealing method was used to resolve cosmic-ray tracks from fission tracks. It gave the following cosmic-ray and fission-track densities, in units of 106cm−2: Angra dos Reis 1.3–4.4 and 7.8; Moore Co. feldspar 1.9–3.0 and 0.51; Moore Co. pigeonite 2.0–2.9 and 0.078–0.35. The fission-track densities are 10–100 times higher than expected from U238; the excess is probably due to extinct Pu238. The Pu244/U238 ratios at the start of track retention were 0.003 for Angra dos Reis and 0.002–0.03 for Moore Co. No evidence was found for fission tracks attributable to the unknown progenitor of excess He4 in these meteorites; the fission branch of this progenitor comprises less than 10−5 the α-branch. A search for pleochroic halos also gave negative results. The preatmospheric radii of the two meteorites are ≥13 and ≥7cm. According to meteor theory, this implies geocentric velocities of ≥ 19 and ≥ 6 km/sec. The etching behavior of Angra dos Reis augite is highly anomalous, giving rise to spurious angular anisotropies and skewed length distributions. This confirms similar observation by Fleischer et al. (1970) on lunar augite.
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