Physics:Radiohalo
Radiohalos or pleochroic halos are microscopic, spherical shells of discolouration (pleochroism) within minerals such as biotite that occur in granite and other igneous rocks. The shells are zones of radiation damage caused by the inclusion of minute radioactive crystals within the host crystal structure. The inclusions are typically zircon, apatite, or titanite which can accommodate uranium or thorium within their crystal structures (Faure 1986). One explanation is that the discolouration is caused by alpha particles emitted by the nuclei; the radius of the concentric shells are proportional to the particle's energy (Henderson Bateson).
Production
Uranium-238 follows a sequence of decay through thorium, radium, radon, polonium, and lead. These are the alpha-emitting isotopes in the sequence. (Because of their continuous energy distribution and greater range, beta particles cannot form distinct rings.)
| Isotope | Half-life | Energy in MeV |
|---|---|---|
| U-238 | 4.47×109 years | 4.196 |
| U-234 | 2.455×105 years | 4.776 |
| Th-230 | 75400 years | 4.6876 |
| Ra-226 | 1599 years | 4.784 |
| Rn-222 | 3.823 days | 5.4897 |
| Po-218 | 3.04 minutes | 5.181 |
| Po-214 | 163.7 microseconds | 7.686 |
| Po-210 | 138.4 days | 5.304 |
| Pb-206 | stable | 0 |
The final characteristics of the radiohalo depends upon the initial isotope, and the size of each ring of a radiohalo is dependent upon the alpha decay energy. A radiohalo formed from U-238 has theoretically eight concentric rings, with five actually distinguishable under a lighted microscope, while a radiohalo formed from polonium has only one, two, or three rings depending on which isotope is the starting material (Weber 2010). In U-238 haloes, U-234, and Ra-226 rings coincide with the Th-230 to form one ring; Rn-222 and Po-210 rings also coincide to form one ring. These rings are indistinguishable from one another under a lighted microscope (Pal 2004).
Creationism
Young Earth creationist Robert V. Gentry believes that radiohalos could not have been formed from molten rock which took many millennia to cool. He instead claims that solid rock must have been created instantaneously containing polonium inclusions and that the halos arose from Po-218 (rather than U-238) decaying with a half-life of 3 minutes.(Gentry 1992) However, Gentry's polonium halos are found along microscopic cracks in rocks that also contain uranium halos (Wakefield 1988)(Collins 1997) and Po-218 is also a decay product of radon which as a gas can be given off by a grain of uranium in one part of the rock and migrate to another part of the rock to form a uraniumless halo.(Baillieul 2005)(Brawley 1992)
Citations
- Baillieul, T.A. (2001–2005), "Polonium Haloes" Refuted: A Review of "Radioactive Halos in a Radio-Chronological and Cosmological Perspective" by Robert V. Gentry, TalkOrigins Archive, http://www.talkorigins.org/faqs/po-halos/gentry.html
- Brawley, J. (1992), Evolution's Tiny Violences: The Po-Halo Mystery, TalkOrigins Archive, http://www.talkorigins.org/faqs/po-halos/violences.html
- Collins, L.G. (1997), "Polonium Halos and Myrmekite in Pegmatite and Granite", in Hunt, C. W.; Collins, L. G.; Skobelin, E. A., Expanding Geospheres, Energy And Mass Transfers From Earth’s Interior, Calgary: Polar Publishing Company, pp. 128–140, http://www.csun.edu/~vcgeo005/revised8.htm.
- Durrani, S.A.; Fremlin, J.H.; Durrani, S. A. (1979), "Polonium Haloes in Mica", Nature 278 (5702): 333–335, October 1979, doi:10.1038/278333a0, Bibcode: 1979Natur.278..333H.
- Ellenberger, C.L., with reply by Gentry, R.V. 1984. "Polonium Halos Redux," Physics Today. December 1984. pp. 91–92
- Ellenberger, C.L. 1986. "Absolute Dating," unanswered surrebuttal to Gentry, Physics Today. March 1986. pp. 152, 156
- Faure, Gunter (1986), Principles of Isotope Geology, Wiley, pp. 354–355.
- Gentry, R.V. (1970), "Giant Radioactive Halos: Indicators of Unknown Alpha-Radioactivity?", Science 169 (3946): 670–673, August 1970, doi:10.1126/science.169.3946.670, PMID 17791843, Bibcode: 1970Sci...169..670G, http://www.halos.com/reports/science-1970-giant-halos.pdf.
- Gentry, R.V. (1975), "Spectacle Haloes", Nature 258 (5532): 269–270, October 1975, doi:10.1038/258269c0, Bibcode: 1975Natur.258..269G.
- Gentry, R.V. (1973), "Radioactive Halos", Annual Review of Nuclear Science 23 (1): 347–362, October 1973, doi:10.1146/annurev.ns.23.120173.002023, Bibcode: 1973ARNPS..23..347G.
- Gentry, R.V. (1974), "Radiohalos in a Radiochronological and Cosmological Perspective", Science 184 (4132): 62–66, October 1974, doi:10.1126/science.184.4132.62, PMID 17734632, Bibcode: 1974Sci...184...62G, http://www.halos.com/reports/science-1974-radiohalos.pdf.
- Gentry, R.V. (1992), Creation's Tiny Mystery, Earth Science Associates (published 2004), http://www.halos.com/book/ctm-toc.htm.
- Henderson, G.H.; Bateson, S. (1934), "A Quantitative Study of Pleochroic Haloes, I", Proceedings of the Royal Society of London A 145 (855): 563–581, doi:10.1098/rspa.1934.0120, Bibcode: 1934RSPSA.145..563H.
- Henderson, G. H., "A quantitative study of pleochroic halos: V, The genesis of halos", Proc. Roy. Soc. A, 173:250–264, 1939.
- Henderson, G. H., and F. W. Sparks, "A quantitative study of pleochroic halos, IV, New types of halos", Proc. Roy. Soc. A, 173:238–249, 1939.
- Lide, David R. (Ed.) (2001), CRC Handbook of Chemistry and Physics, 82nd Ed., London: CRC Press, ISBN 0-8493-0482-2
- Moazed, Cyrus; Richard M. Spector; Richard F. Ward, 1973, Polonium Radiohalos: An Alternate Interpretation, Science, Vol. 180, pp. 1272–1274.
- Odom, L.A., and Rink, W.J., 1989, "Giant Radiation-Induced Color Halos in Quartz: Solution to a Riddle", Science, v. 246, pp. 107–109.
- Osmon, P., 1986, "Gentry’s pleochroic halos: Creation/Evolution," Newsletter, Feser, Karl D., Editor, v. 6, no. 1, Concord College, Athens, West Virginia
- Pal, Dipak C. (2004), "Concentric rings of radioactive halo in chlorite, Turamdih uranium deposit, Singhbhum Shear Zone, Eastern India: a possible result of 238U chain decay" (PDF), Current Science, 87 n5: 662–667, 10 September 2004, http://www.ias.ac.in/currsci/sep102004/662.pdf.
- Schadewald, R., 1987. "Gentry’s tiny mystery, Creation/Evolution" Newsletter, Fezer, Karl D, Editor, v. 4, no. 2 & 3. Concord College. Athens. West Virginia, p 20.
- Schnier, C (2002), "Indications for the existence of superheavy elements in radioactive halos", Journal of Radioanalytical and Nuclear Chemistry 253 (2): 209–216, August 2002, doi:10.1023/A:1019633305770.
- Wakefield, J. R. (1988), "The geology of 'Gentry’s Tiny Mystery'", Journal of Geological Education 36: 161–175, http://www.csun.edu/~vcgeo005/gentry/tiny.htm.
- Wakefield, J. R., 1987–88, "Gentry’s Tiny Mystery - unsupported by geology," Creation/Evolution, v. 22, p. 13–33.
- York, D., 1979, Pleochroic Halos and Geochronology, EOS, v. 60, no. 33, pp. 617–618, Aug. 14, 1979 (publication of the American Geophysical Union).
External links
- Geology of Gentry's "Tiny Mystery", J. Richard Wakefield, Journal of Geological Education, May 1988.
- Polonium Halo FAQs, TalkOrigins Archive
- Thousands ... Not Billions book review, Answers in Creation
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