Old page wikitext, before the edit (old_wikitext) | '{{about|the [[geophysics|geophysical]] phenomenon|the [[astronomy|astronomical]] phenomenon|radio halo}}
[[File:Dark crown.JPG|thumb|Radiohalos around crystals of [[Zircon|zircons]] in a sample of [[biotite]]]]
'''Radiohalos''' or '''pleochroic halos''' are microscopic, spherical shells of discolouration 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 structure]]s {{harv|Faure|1986}}. One explanation is that the discolouration is caused by [[alpha particle]]s emitted by the nuclei; the radius of the concentric shells are proportional to the particle's energy {{harv|Henderson|Bateson|1934}}.
==Production==
[[Uranium]]-238 follows a [[decay chain|sequence of decay]] through [[thorium]], [[radium]], [[radon]], [[polonium]], and [[lead]]. These are the alpha-emitting [[isotope]]s in the sequence. (Because of their continuous energy distribution and greater range, [[beta particle]]s cannot form distinct rings.)
{|class="wikitable" style="text-align:center"
|-
! Isotope !! Half-life !! Energy in MeV
|-
|U-238||{{val|4.47|e=9}} years||4.196
|-
|U-234||{{val|2.455|e=5}} 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 {{harv|Weber|2010}}. In U-238 haloes, U-234, and Ra-226 rings coincide with the Th-230 to form one ring; Ra-222 and Po-210 rings also coincide to form one ring. These rings are indistinguishable from one another under a lighted microscope {{harv|Pal|2004}}.
==Creationism==
{{see also|Robert V. Gentry}}
Creationist Robert V. Gentry looked at halos which he said arose 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. He believes that they could not have been formed from molten rock which took many millennia to cool because polonium decays in a few minutes. As a [[creationist]], he took this as evidence that the Earth was formed instantaneously {{harv|Gentry|1992}}. However, Gentry's "polonium halos" are found along microscopic cracks in rocks that also contain uranium halos {{harv|Wakefield|1988}}{{harv|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 {{harv|Baillieul|2005}}{{harv|Brawley|1992}}.
==Citations==
{{Reflist}}
*{{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|date=2001–2005|publisher=[[TalkOrigins Archive]]}}
*{{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=[[TalkOrigins Archive]]}}
*{{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|editor=Hunt, C. W. |editor2=Collins, L. G. |editor3=Skobelin, E. A.|publisher=Polar Publishing Company|publication-place=Calgary|year=1997}}.
*{{citation|first1=S.A.|last1=Durrani|authorlink2=John H. Fremlin|first2=J.H.|last2=Fremlin|title=Polonium Haloes in Mica|journal=Nature|publication-date=October 1979|volume=278|issue=5702|pages=333–335|doi=10.1038/278333a0|year=1979|last3=Durrani|first3=S. A.|bibcode = 1979Natur.278..333H }}.
*[[C. Leroy Ellenberger|Ellenberger, C.L.]], with reply by Gentry, R.V. 1984. "Polonium Halos Redux," ''Physics Today''. December 1984. pp. 91–92
*[[C. Leroy Ellenberger|Ellenberger, C.L.]] 1986. "Absolute Dating," unanswered surrebuttal to Gentry, ''Physics Today''. March 1986. pp. 152, 156
*{{citation| last=Faure|first=Gunter |title=Principles of Isotope Geology|year=1986|publisher=Wiley|pages=354–355 }}.
*{{citation|last=Gentry|first=R.V.|title=Giant Radioactive Halos: Indicators of Unknown Alpha-Radioactivity?|journal=Science |publication-date=August 1970 |year=1970|volume=169|pages=670–673|url=http://www.halos.com/reports/science-1970-giant-halos.pdf|pmid=17791843|issue=3946|doi=10.1126/science.169.3946.670|bibcode = 1970Sci...169..670G }}.
*{{citation|last=Gentry|first=R.V.|title=Spectacle Haloes|journal=Nature|publication-date=October 1975| year=1975|volume=258|pages=269–270|bibcode = 1975Natur.258..269G |doi = 10.1038/258269c0|issue=5532}}.
*{{citation|last=Gentry|first=R.V.|title=Radioactive Halos|journal=Annual Review of Nuclear Science |publication-date=October 1973|volume=23|issue=1|pages=347–362|doi=10.1146/annurev.ns.23.120173.002023|year=1973|bibcode = 1973ARNPS..23..347G }}.
*{{citation|last=Gentry|first=R.V.|title=Radiohalos in a Radiochronological and Cosmological Perspective|journal=Science |publication-date=October 1974 |year=1974| volume=184|pages=62–66|url=http://www.halos.com/reports/science-1974-radiohalos.pdf|pmid=17734632|issue=4132|doi=10.1126/science.184.4132.62|bibcode = 1974Sci...184...62G }}.
*{{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 A|year=1934|volume=145|pages=563–581|issue=855|doi=10.1098/rspa.1934.0120|jstor=2935523|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.
*{{Citation|author=Lide, David R. (Ed.)|title=CRC Handbook of Chemistry and Physics, 82nd Ed.|location=London|publisher=CRC Press|year=2001|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
*{{citation|last=Pal|first=Dipak C.|url=http://www.ias.ac.in/currsci/sep102004/662.pdf|format=PDF|series=87| 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=n5|pages=662–667}}.
*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.
*{{citation|first=C|last=Schnier|title= Indications for the existence of superheavy elements in radioactive halos|journal=Journal of Radioanalytical and Nuclear Chemistry|publication-date=August 2002|volume=253|issue=2|pages=209–216|doi=10.1023/A:1019633305770|year=2002}}.
*{{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}}.
*Wakefield, J. R., 1987–88, "Gentry’s Tiny Mystery - unsupported by geology," Creation/Evolution, v. 22, p. 13–33.
*{{cite journal|title=Halos und weitere radioaktive Erscheinungen im Wölsendorfer Fluorit (in German)|journal=Der Aufschluss|volume=61|pages=107–118|year=2010|last=Weber|first=B.|url=http://www.vfmg.de/aufschluss_2-2010_Weber.htm|ref=harv}}{{dead link|date=January 2018 |bot=InternetArchiveBot |fix-attempted=yes }}
*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==
* [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''':32-38 (1988).
* [http://www.talkorigins.org/faqs/po-halos/default.htm Polonium Halo FAQs], [[TalkOrigins Archive]]
* [https://web.archive.org/web/20060625082326/http://www.answersincreation.org/bookreview/tnb/thousands_not_billions_chapter5.htm ''Thousands ... Not Billions'' book review], [[Answers in Creation]]
[[Category:Radiometric dating]]
[[Category:Creation science]]' |
