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Decay of Thorium-232 in Stars
[OAB 97] A conundrum was proposed in 1987 by H.R. Butcher (Nature, v.328, pp.127-131 (9 July 1987)), who announced that there were inconsistencies between his observations of the amount of Thorium-232 in certain stars, and the accepted ages of those stars. Although some young-Earth advocates cite Butcher's work as casting doubt on standard astronomical chronologies, what was really occurring was simply working the bugs out of a new dating method. Butcher's 1987 paper was part of his pioneering work in nucleocosmochronology, the science of determining the age of stars by measuring the amounts of heavy elements produced in their cores, but his anomalous results were simply due to the fact that he had not yet perfected the method. As is pointed out in a paper by J. Westin et al (see page 784 of Astrophysical Journal, v.530, pp.783-799 (20 Feb 2000)), the spectroscopic signature of Thorium-232 is difficult to isolate from that of certain other metallic species, and therefore Butcher's method can only be accurately performed on stars that are severely depleted in metals, so that the Thorium dominates the spectral signature. There are also other important factors in perfecting the method of nucleocosmochronology, and more technical discussions of Butcher's paper can be found in papers by Morell, Kallander, and Butcher (Astronomy and Astrophysics, v.259, pp.543-548 (1992)), and by Francois, Spite, and Spite (Astronomy and Astrophysics, v.274, pp.821-824 (1993)). Also, there is a less technical brief review of nucleocosmochronology by C. Sneden (Nature, v.409, pp.673-675 (8 Feb 2001)). In conclusion, the new dating method announced in Butcher's 1987 paper is a good one, and has sparked a great deal of profitable research since that time. The anomalous ages given in the 1987 paper are simply due to bugs in the method that Butcher had yet to work out. Since those difficulties have now been overcome, the original 1987 paper should not be cited as evidence against standard astronomical chronologies.

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