On to what prompts my new thread:, a recent post, Are polonium radiohalos primordial? at Paul Garner's blog The New Creationism deals with radiohalos and specifically the fundamental differences between Selling's recent work - and his hydrothermal fluid transport model - and Gentry's 'primordial radiohalo' hypothesis. A commenter (Eelco) then disputed Garner's post, citing TalkOrigins, after which Garner and Eelco began a discussion. Well, Tom Bailleul himself just jumped into the fray, making his case against Gentry's work. Garner responded and Bailleul doesn't fare too well:
Radiohalos By this I assume you mean Polonium Haloes and the now discredited work of creationist Robert Gentry who has argued that ring-shaped discoloration haloes in primordial granite rocks are the result of damage from alpha-particle emission by radioactive isotopes of the element polonium (Po). Scientest/Geologist Tom Bailleul has taken a look at look at Gentry's work arguing that there is no good evidence they are the result of polonium decay as opposed to any other radioactive isotope, or even that they are caused by radioactivity at all. Gentry is taken to task for selective use of evidence, faulty experiment design, mistakes in geology and physics, and unscientific principles of investigation and argument style.
What I said in my critique regarding the radon migration hypothesis is: Ã¢â‚¬Å“Migration of radon along fractures with hold-up points at tiny structural traps would result in exactly the same concentric ring pattern assigned by Gentry to polonium alone (because polonium is a daughter isotope of radon decay).Ã¢â‚¬Â Brawley and Collins both noted that ring type halo structures lined up on visible fractures in the host mica. This is a physical, not a chemical process. It is well known that radon is a highly mobile atom Ã¢â‚¬â€œ and hold-up of movement due to microscopic structural traps has many analogs in the geological world.
Another problem with GentryÃ¢â‚¬â„¢s work is the assignment of specific alpha decay energies to measured rings of different sizes. Assume that you have an alpha emitting source in a crystal, and the the Bragg Effect causes the emitted alpha particles to deposit most of their energy in a narrow zone at a specific radial distance from the source. Over time you will get a spherical Ã¢â‚¬Å“damageÃ¢â‚¬Â shell. Alpha particles of several different energies would be expected to form damage shells of differing diameters. When you cut through these shells, as in a thin section, you see circular structures Ã¢â‚¬â€œ GentryÃ¢â‚¬â„¢s halos. You can only assign alpha decay energies (and their associated isotopes) to a specific circular halo if you know that you were looking at a radial cross section of the spherical damage shell. A radial cross section passes through the center of the sphere and thus shows the maximum diameter for the circular section. It is possible to cut a sphere along an infinite number of planes (e.g., thin sections) that donÃ¢â‚¬â„¢t pass through the sphereÃ¢â‚¬â„¢s center, and that result in circular features of smaller diameter than the maximum.
Gentry never demonstrated that his measured halos were radial sections, and thus his assignment of alpha particle energies to any feature is hugely suspect.
Regarding the incompatibility of proposed young-Earth models and the overwhelming evidence from radiometric age-dating, Gentry notes the problem and solves it by declaring that a miraculous event occurred. That miracle kept the decay rate unchanged for those Polonium isotopes Gentry used in his study, while accelerating the decay rates for every other radioactive species by orders of magnitude Ã¢â‚¬â€œ and by widely differing amounts depending on the isotope. This acceleration would even have affected the uranium decay series of which GentryÃ¢â‚¬â„¢s polonium isotopes were a part. This scenario of course is patently absurd and has not one shred of evidence to back it up.
GentryÃ¢â‚¬â„¢s hypothesis fails on multiple grounds.
I hope Bailleul replies; I'd like to see a lively, informed debate on the subject. Thought I'd pass this along in case anyone is interested. Read the back and forth between Eelco and Garner before Bailleul jumps in also - Garner easily dispatches Eelco's objections.
This is in response to the two previous comments. We will examine, firstly, the claim that radon formed these halos, not polonium, and that it did so by accumulating in structural traps, and, secondly, the claim that the halos might not be radial sections and therefore the rings cannot be assigned with any certainty to particular steps in a decay chain.
We have already established that radon is inert and there is therefore no chemical process by which it could have accumulated in radiocentres to form radiohalos. That point is now conceded. But what about the suggestion that radon might have accumulated in structural traps instead? Think about what is being proposed here. Some kind of unspecified structural trap in the halo-bearing mineral would have to stop the radon in a single spot (approximately a micron in width) for millions of years in order for 500 million to 1 billion radon atoms to accumulate and decay to form each radiohalo. But precisely how could that happen, especially in the case of a mineral such as mica? Mica has very strong cleavage planes along which radon would inevitably migrate, particularly in the presence of hydrothermal fluids. The evidence for the movement of hydrothermal fluids along the cleavage planes of halo-bearing biotite flakes is ubiquitous, including the presence of former fluid bubbles and the alteration of biotite to chlorite. In other words, BaillieulÃ¢â‚¬â„¢s hypothesis is extremely far-fetched and really amounts to little more than Ã¢â‚¬Ëœhand-wavingÃ¢â‚¬â„¢. We certainly need more specifics (preferably from published, peer-reviewed sources) before such an idea can be seriously considered.
ItÃ¢â‚¬â„¢s also worth noting that many of those who have argued with Gentry in the past have not disputed his identification of the radiohalos. For example, G. Brent Dalrymple, former Deputy Director of the U. S. Geological Survey, famously testified in 1989 at the Arkansas creation trial that the polonium radiohalos were Ã¢â‚¬Å“a very tiny mysteryÃ¢â‚¬Â. Had Gentry misidentified the halos, here was the perfect opportunity for an expert to say so. The fact that Dalrymple did not do this, but rather conceded that Gentry had correctly identified the halos, speaks volumes. No doubt Gentry and Snelling themselves will be dismissed because they are creationists, but between them they have studied hundreds of thousands of halos and have accumulated far more expertise in this field than most of their critics.
Next we come to BaillieulÃ¢â‚¬â„¢s claim that the measured radiohalos have never been shown to be radial cross-sections, and therefore the concentric rings in the halos cannot be confidently identified with specific alpha particle energies. In fact, this criticism is easily countered by an examination of the experimental procedures involved.
Snelling (2005) describes how the sheets composing the halo-bearing biotite flakes were progressively pulled apart using adhesive Scotch tape, and mounted on microscope slides. Tens of microscope slides were prepared for each sample, each with many (at least twenty to thirty) thin biotite flakes mounted on it. A minimum of thirty (usually fifty) microscope slides was prepared for each sample (at least 1,000 biotite flakes) to ensure good representative sampling statistics.
Each slide was then carefully examined under a petrological microscope in plane polarized light and all radiohalos present were identified, noting any relationships between the different radiohalo types and any unusual features. The numbers of each type of radiohalo in each slide were counted by progressively moving the slide backwards and forwards across the field of view, and the numbers for each slide were then tallied and tabulated for each sample. Snelling notes: Ã¢â‚¬Å“Only radiohalos whose radiocentres were clearly visible were counted.Ã¢â‚¬Â (p.114)
This last point is very important for two reasons. Firstly, because it ensured that individual radiohalos were not counted more than once, and, secondly, because it ensured that the identified radiohalos were complete radial cross-sections. In other words, BaillieulÃ¢â‚¬â„¢s statement is without foundation. Ironically, it is further refuted by the very photographs of GentryÃ¢â‚¬â„¢s radiohalos that are included in BaillieulÃ¢â‚¬â„¢s own article, because in those photographs the halosÃ¢â‚¬â„¢ radiocentres can clearly be seen, demonstrating beyond any doubt that they indeed represent radial sections.
To sum up, there is no evidence that radon, rather than polonium, is the source of the observed radiohalos, because there is no viable physical or chemical mechanism by which radon could have produced them. Neither is there any substance to the claim that the measured radiohalos might have been misidentified because they do not represent radial cross-sections. Attempts to dismiss the radiohalo evidence for rapid granite formation and accelerated nuclear decay have once again failed to stand up to critical analysis and, from a uniformitarian perspective, DalrympleÃ¢â‚¬â„¢s Ã¢â‚¬Å“very tiny mysteryÃ¢â‚¬Â remains unsolved.
Snelling A. A. 2005. Radiohalos in granites: evidence for accelerated nuclear decay. In: Vardiman L., Snelling A. A. and Chaffin E. F. (editors). Radioisotopes and the Age of the Earth: Results of a Young-Earth Creationist Research Initiative, Institute for Creation Research, El Cajon, California and Creation Research Society, Chino Valley, Arizona, pp.101-207.