Radiohalo

Radiohalos are microscopic, spherical shells of discolouration in rocks, such as granite, or biotite caused by the inclusion of radioactive grains in the rock or by deposition of radioactive material in them. One widely accepted theory 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 harv|Henderson|Bateson|1934. The phenomenon of radiohalos has been known to geologists since the early part of the 20th century, but wider interest was prompted by the claims of creationist Robert V. Gentry that radiohalos in biotite are evidence for a young earth harv|Gentry|1992. The claims are contested by the mainstream scientific community as an example of creationist pseudoscience harv|Wakefield|1988.

Production

Uranium-238 follows a sequence of decay through thorium, radium, radon, polonium, and lead. These are the alpha-emitting isotopes in the sequence. (According to the standard theory, beta particles do not discolour the rock, although harvtxt|Baillieul|2005 suggests the need to reexamine the possible role of beta emission.)

The final characteristics of the radiohalos depend upon the initial isotope. The U-234 and Ra-226 rings coincide, with the Th-230 ring merely thickening it,harv|Pal|2004 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 theoretically eight concentric rings, with five actually distinguishable, while a radiohalo formed from polonium can have only one, two, or three rings depending on which isotope is the starting material.Fact|date=May 2008 However, a halo formed from Ra-222 is not distinguishable from one formed from Po-210.harv|Wakefield|1988harv|Pal|2004

Christian Schnier harv|Schnier|2002 has suggested that anomalous radiohalos result from the decay chain of unidentified Superheavy elements in the earth's crust. He postulates the presence of two long-lived superheavy elements, one with an atomic mass of between 280 and 300, and another with an atomic mass greater than 300.

Controversy

Robert V. Gentry studied halos which appeared to have arisen from Po-218 rather than U-238 and concluded that solid rock must have been created with these polonium inclusions, which decayed with a half-life of 3 minutes.Fact|date=May 2008 They could not have been formed from molten rock which took many millennia to cool (the standard theory) because polonium decays in a few minutes. This is taken by creationists as evidence that the Earth was formed instantaneously harv|Gentry|1992.

Critics of Gentry, including Thomas A. Baillieul harv|Baillieul|2005 and John Brawley harv|Brawley|1992, have pointed out that Po-218 is 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 collected in another part of the rock to form a uraniumless halo. Apparently a large number of radon atoms are caught or adsorbed at a particular point. This has not been proved experimentally, but is supported by the fact that Gentry's "polonium halos" are found along microscopic cracks in rocks that also contain uranium halos harv|Wakefield|1988.

Gentry's work has been continued and expanded by the creationist [http://www.icr.org/rate/ "Radioactivity and the Age of the Earth"] (R.A.T.E.) project that was operating between 1997 and 2005 harv|Wieland|2003. Radiohalos were studied as part of the R.A.T.E. project by creationists such as Andrew Snelling of Answers in Genesis, Russell Humphreys, John Baumgardner and Steven A. Austin at the Institute of Creation Research as well as others at the Creation Research Society. However, harvtxt|Collins|1997, harvtxt|Wakefield|1988 and others have repeatedly and soundly rebutted the radiohalo evidence for a young Earth in peer-reviewed publications.

Citations

*citation | last=Gentry|first=R.V. | title=Spectacle Haloes | journal=Nature | publication-date=October 1975| year=1975 | volume=258 | pages=269–270.

*citation | last=Gentry|first=R.V. | title=Radioactive Halos | journal=Annual Review of Nuclear Science | year=1973|publication-date=October 1973 | volume=23 | pages=347-362.

*citation | last=Gentry|first=R.V. | title=Radiohalos in a Radiochronological and Cosmological Perspective | journal=Science | year=1974|publication-date=October 1974 | volume=184 | pages=62–66.

*citation | last=Gentry|first=R.V.|title=Creation's Tiny Mystery|year=1992|publication-date=2004|publisher=Earth Science Associates|url=http://www.halos.com/book/ctm-toc.htm.

*citation|first1=G.H.|last1=Henderson|first2=S.|last2=Bateson|title=A Quantitative Study of Pleochroic Haloes, I|journal=Proceedings of the Royal Society of London, Series A, Containing Papers of a Mathematical and Physical Character|year=1934|volume=145|number=855|pages=563-581|url=http://links.jstor.org/sici?sici=0950-1207(19340702)145%3A855%3C563%3AAQSOPH%3E2.0.CO%3B2-G.

*citation|last=Wakefield|first=J. R.|year=1988|title=The geology of 'Gentry’s Tiny Mystery'|journal=Journal of Geological Education|volume=36|pages=161-175|url=http://www.csun.edu/~vcgeo005/gentry/tiny.htm.

*citation|first=L.G.|last=Collins|url=http://www.csun.edu/~vcgeo005/revised8.htm|contribution=Polonium Halos and Myrmekite in Pegmatite and Granite|title=Expanding Geospheres, Energy And Mass Transfers From Earth’s Interior|pages=128-140|editors=Hunt, C. W., Collins, L. G., and Skobelin, E. A.|publisher=Polar Publishing Company|publication-place=Calgary|year=1997.

*citation|first=T.A.|last=Baillieul|url=http://www.talkorigins.org/faqs/po-halos/gentry.html|title="Polonium Haloes" Refuted: A Review of "Radioactive Halos in a Radio-Chronological and Cosmological Perspective" by Robert V. Gentry|publication-date=2001-2005|year=2005|publisher=talk.origins archives|

*citation | last=Pal|first=Dipak C. | url=http://www.ias.ac.in/currsci/sep102004/662.pdf| title=Concentric rings of radioactive halo in chlorite, Turamdih uranium deposit, Singhbhum Shear Zone, Eastern India: a possible result of 238U chain decay | journal=Current Science | publication-date=10 September 2004 | year=2004 | volume=87 n5 | pages=662–667.

*citation|url=http://www.talkorigins.org/faqs/po-halos/violences.html|title=Evolution's Tiny Violences: The Po-Halo Mystery|first=J.|last=Brawley|year=1992|publisher=talk.origins archives

*citation|url=http://www.answersingenesis.org/docs2003/0821rate.asp|title=RATE group reveals exciting breakthroughs!|first=C.|last=Wieland|publisher=Answers in Genesis|year=2003|publication-date=21 August 2003

Disputing a young earth interpretation

*citation | first1=S.R.|last1=Hashemi-Nezhad|authorlink2=John H. Fremlin|first2=J.H.|last2=Fremlin|first1=S.A.|last1=Durrani | title=Polonium Haloes in Mica | journal=Nature | year=1979|publication-date=October 1979 | volume=278 | pages=333-335.

*citation | first=Schnier|last=C | title= Indications for the existence of superheavy elements in radioactive halos | journal=Journal of Radioanalytical and Nuclear Chemistry, | year=2002|publication-date=August 2002 | volume=253 | pages=209-216.

*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

*Osmon, P., 1986, "Gentry’s pleochroic halos: Creation/Evolution," Newsletter, Feser, Karl D., Editor, v. 6, no. 1, Concord College, Athens, West Virginia

*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.

*Wakefield, J. R., 1987-88, "Gentry’s Tiny Mystery - unsupported by geology," Creation/Evolution, v. 22, p. 13-33.

*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.

*York, D., 1979, Pleochroic Halos and Geochronology, EOS, v. 60, no. 33, pp. 617-618, Aug. 14, 1979 (publication of the American Geophysical Union).

*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.

Other

*cite book | author=Lide, David R. (Ed.) | title=CRC Handbook of Chemistry and Physics, 82nd Ed. | location=London | publisher=CRC Press | year=2001 | id=ISBN 0-8493-0482-2

External links

Non-scientific Sites

* [http://www.icr.org/pubs/imp/imp-326.htm Polonium radiohalos: still "a very tiny mystery"] , from the Institute for Creation Research
* [http://www.halos.com/index.htm Fingerprints of Creation]

External links

* [http://www.csun.edu/~vcgeo005/gentry/tiny.htm "Geology of Gentry's "Tiny Mystery"] , J. Richard Wakefield, Journal of Geological Education, May 1988.
* [http://www.grisda.org/origins/15032.htm "Examining radiohalides"] , R. H. Brown, H. G. Coffin, L. J. Gibson, A. A. Roth, and C. L. Webster, Origins 15(1):32-38 (1988).
* [http://www.talkorigins.org/faqs/po-halos/default.htm Talkorigins FAQ on the criticisms of Gentry's interpretation]
* [http://www.answersincreation.org/bookreview/tnb/thousands_not_billions_chapter5.htm Answers In Creation expose showing that radiohalos do not support a young earth]