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RadiohaloRadiohalos are microscopic, spherical shells of discoloration in rocks, such as granite, or wood caused by the inclusion of radioactive grains in the rock or by deposition of radioactive material in them. The discoloration is caused by alpha particles emitted by the nuclei; the radius of the concentric shells are proportional to the particle's energy. Production Uranium follows a sequence of radioactive through thorium, radium, radon, polonium, and lead. These are the alpha-emitting isotopes in the sequence. (Beta particles do not discolor the rock.) | Isotope | Half-life | Energy in MeV | | U238 | 4.47e9 years | 4.196 | | U234 | 2.455e5 years | 4.776 | | Th230 | 75400 years | 4.6876 | | Ra226 | 1599. years | 4.784 | | Rn222 | 3.823 days | 5.4897 | | Po218 | 3.04 minutes | 5.181 | | Po214 | 163.7 microseconds | 7.686 | | Po210 | 138.4 days | 5.304 | | Pb206 | infinite | 0 | The final characteristics of the radiohalos occur depend upon the initial isotope. The U-234 and Ra-226 rings coincide, with the Th-230 ring merely thickening it, so it is hard to tell which one of those isotopes started the halo, but it is easy to tell a polonium halo from a uranium halo. A radiohalo formed from U-238 has eight concentric rings while a radiohalo formed from Po-210 only has one. Controversy Robert V. Gentry studied these halos and concluded that the rock must have formed within three minutes if the halo was formed by Po-218. This is taken by creationists as evidence that the earth was formed instantaneously. Critics of Gentry's theory claim that radon, given off by a grain of uranium elsewhere in the rock, collected at a point in the rock and formed a uraniumless halo. The radon ring is close to the Po-210 ring and it is a bit difficult to tell them apart. However, multiple studies have suggested that the polonium did not come from a uranium precursor. Evidence includes polonium radiohalos physically removed from available conduits, highly concentrated points of origin, and lack of discoloration due to the decay of radioactive precursors en route. Furthermore, Po-214 and Po-210 radiohalos discount the mistaken radon radiohalo theory because they are easily distinguished and yet still pose the original problem of short half-lives. References External link *Polonium radiohalos: still "a very tiny mystery", from the Institute for Creation Research
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