Pleochroic halos are the scars of radioactive decay, particularly alpha decay. Radioactive inclusions in rock often cause concentric spheres of discoloration due to the damage caused by alpha particles as they are emitted by the radioactive substance. These scars appear as spheres (rings when views in cross-section) in the rock surrounding a decaying radioactive atom. The size of the halo is a signature of the energy of the emission and therefore the element and isotope involved.
- Super sized halos have been reported which may indicate change in the decay rate.
- Halos of short lived isotopes may indicate rapid rock formation.
- The occurrence of distorted halos within undistorted halos in coalified wood indicates rapid coal formation.
Robert Gentry and polonium halos
Robert Gentry found in rocks certain halos that are caused by Polonium, whose isotopes have half lives too brief to accommodate by the slow cooling assumed by most geologists. Gentry's work on polonium pleochroic halos led him to the conclusion that the Earth's granite was never in a molten condition, because polonium halos survive only in solid rock and the half-life of polonium is much too short to survive a multimillion-year cooling time. He explains his argument more fully at his halos site, where the book on the subject is now available as well. His results seem to indicate that granite was created instantaneously, in a cool condition. If true, it is clear evidence for creation and a young earth.
Critics have suggested that the polonium diffused from a nearby Uranium deposit through fissures or cracks. They also contend that the halos may not be caused by Polonium at all. One such critique can be found here. Gentry responds to much of the criticism of his model on reports page.
Another claim by creation scientists is that there are specimens of rock in which, due the pressure caused by alpha decay, a region of rock has been cracked or fragmented. The creationist argument is that these cracks and fragmentations do not occur along cleavage lines or natural areas of weakness, showing that the nuclear decay occurred in a short period of time, confirming their beliefs for an accelerated decay.
Dwarf, X and other halos
The final observation made by creationists is that certain halos do not appear to correspond to any known nuclear reaction, suggesting that there may be something important that science is missing or misunderstanding regarding the processes involved.
At least one critic, Thomas A. Baillieul, has suggested that these types of halos actually suggest that the whole idea of halos being created by radioactive inclusions [which has been considered the standard for nearly a century] may be refuted by these abnormal halos. His paper can be found here.
Robert Gentry's research has been challenged by Thomas Baillieul, an environmental scientist and project manager for the US federal government. He writes "Gentry's polonium halo hypothesis for a young Earth fails, or is inconclusive for, all tests. Gentry's entire thesis is built on a compounded set of assumptions. He is unable to demonstrate that concentric halos in mica are caused uniquely by alpha particles resulting from the decay of polonium isotopes. His samples are not from "primordial" pieces of the Earth's original crust, but from rocks which have been extensively reworked. Finally, his hypothesis cannot accommodate the many alternative lines of evidence that demonstrate a great age for the Earth." The full article can be found at 
RATE Group's Research
The RATE Group found that most radiohalos are found in rock thought to have formed during the Flood. Therefore, given the fact that U238 and Th232 halos take hundreds of millions of years to form at today's decay rates, this requires them to have formed quickly by accelerated decay. The data shows that heat from the flood wiped out all pre-flood radiohalos. Po halos make up a large number of radiohalos. This provides evidence of a world wide heating event. This evidence fits with a global flood, providing evidence for the Flood and for accelerated decay during the Flood. This also falsifies Robert Gentry's creation hypothesis, providing an example of creation hypotheses being falsifiable.
Po isotopes have short half lives so the Po that produces the Po halos had to come from the Uranium238 day chain.
- Po210 - 138 days.
- Po214 - 164 microsecond.
- Po218 - 3.1 minutes.
The Uranium238 is found in zircons embedded in the biotite. Rn222 is the transport isotope, with a half life of 3.8 days. Its decay produces the Po210, Po214, Po218 chain that produce the Po halos. Rn222 is not chemically active. It diffuses out of zircons and dissolves in water quickly.
When a Rn222 gets out of a zircon it decays, through the Po isotopes and others, and eventually to Pb206. To form a halo the Po must encounter a sodium or lead deposit since both chemically react with Po. Under the right conditions the Po is concentrated, allowing a halo to form. The problem is that left to itself, the Rn222 will go in random directions from the zircon they came from and never reach one place where the Po can be concentrated.
Hydrothermal flows occur in cooling biotite mica as water flows between layers quickly cooling the biotite. Rn222 dissolves in the water and is carried by the flow, carrying all Rn222 produced by a zircon in one direction. This allows the Po to be picked up by a small sodium or lead deposit, concentrating the Po and allowing the halo to form.
Radiohalos can only form in biotite mica below 150 degrees C and Po halos can only continue to form as long as the hydrothermal flow is depositing more Po to the site. Because of the short half-lives of Po isotopes, the halo stops forming shortly after hydrothermal flow stops. Since hydrothermal flows cool rocks quickly it has to stop before the rock can stop cooling, and, as a result, they cannot have flowed in these rocks the 100 + million years need for these halos form at normal decay rates, thus providing additional evidence of accelerated decay.
Since accelerated half life would be related to normal half life it is likely that the longer half life isotopes would be accelerated more, thus U238’s rate could be accelerated a billion times, while Rn222 and Po isotopes would be hardly affected.
Based on Rn222's half life of 3.8 days the optimum time for Po halo formation is seven to ten days, showing that the rocks cooled from 300 to 50 degrees C in that time. The darkness of many Po halos show that conditions were near optimum for Po halo formation, when these halos were formed
Further support for this model is the lack of evidence of a-particle tracks from Rn222 between U238 and Po halos. This suggests that much of the Rn222 was transported at temperatures greater than 150 degrees C. Furthermore, the fact that the center of Po halos is not radioactive shows that their formation has stopped. Thus the evidence is consistent with hydrothermal transport and quick cooling.
- Creation's Tiny Mystery on-line book by Dr. Robert V. Gentry
- Fingerprints of Creation video by Robert Gentry
- Evidence for Earth's Instant Creation - Polonium Halos in Granite and Coal - Earth Science Associates
- The collapse of 'geologic time'! (radiohaloes in coalified wood, Creation Ministries International)
- Polonium Pleochroic Halos by Jon Covey
- What significance do radio halos hold for recent creation by Christian Answers Net
- Polonium Radiohalos: Still "A Very Tiny Mystery" by Andrew Snelling, ICR Impact #326. Aug 1, 2000
- Polonium Radiohalos: The Model for Their Formation Tested and Verified by Andrew Snelling, ICR Impact #386. Aug 1, 2005
- RATE research reveals remarkable results
- Radioisotopes and the Age of the Earth - Volume 2
- Snelling, Baumgardner, Vardiman 2003 .ABUNDANT PO RADIOHALOS IN PHANEROZOIC GRANITES AND TIMESCALE IMPLICATIONS FOR THEIR FORMATION. - Eos, Transactions of the American Geophysical Union.
- Polonium haloes indicate a young earth Response to Talk.Origins