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Professor Timothy H. Heaton
Atmosphere of the Moon Creationism and social history Radiometric dating Starlight problem. Evidence against a recent creation: Text of creationist bills: Finally, the particle loses all of its kinetic energy and comes to rest, at which time it can capture electrons and become a neutral atom Knoll, In a uniform medium, the amount of energy loss - and thus the degree of disruption - is greatest at the end of the particle's path of travel although energy will have been given up, and ionization of surrounding atoms will have occurred, along the entire path.
For protons, with a single charge and relatively low mass, this effect is extremely pronounced, and is the basis for proton beam treatment of various tumors. Beams of high energy protons can be adjusted to have almost all of their energy loss the Bragg Peak occur within a small volume of cancerous tissue, with almost no energy deposition in the healthy tissue beyond. The effect of alpha particles in crystalline materials, whose physical properties vary depending on orientation, is less straight forward. Gentry's own attempts to duplicate alpha particle damage in minerals using a helium ion beam illustrates this problem.
An ion beam irradiates an "area" and has luminosities particles per beam cross section per unit time many orders of magnitude higher than the "spherical" volumetric emission of alpha particles from radioactive centers in mineral grains. Short exposure to an ion beam can create damage patterns equivalent to millions of years of low-level natural alpha exposure. Gentry notes the problem of beam intensity required to achieve a specific level of discoloration. In these experiments, the ion beam intensity was adjusted to produce a discoloration pattern in the irradiated mineral, with the extent or depth of the discoloration then being compared to the measured halo diameters in his thin section specimens.
The pattern produced by Gentry through ion beam bombardment was a zone of discoloration, faintest near the source, and increasing in intensity up to a relatively sharp termination. Gentry's ion-beam work, however, was not able to produce multiple bands or the sharply defined concentric ring structure of certain haloes. It is likely that intense alpha particle bombardment disrupts the crystallinity of the target mineral a well known natural radiation effect , changing its physical properties along the particle path.
"Polonium Haloes" Refuted
Gentry , , himself, notes a number of aspects about concentric haloes which cannot be explained by the alpha decay hypothesis. Dwarf and giant haloes cannot be reconciled with any known alpha decay energies. Gentry postulates that these anomalous size haloes represent new elements or new forms of alpha decay. Neither explanation seems likely given the current state of knowledge of radioactive elements ICRP, ; Parrington, et al.
Other haloes show "ghost" rings which don't correspond to any measured alpha decay energy, and which remain unexplained. Finally, there are "reversed coloration" haloes, supposed uranium haloes in which the gradation of color intensity in the circular band is opposite to, and the ring diameters offset from, those in a "normal" uranium pattern. Other exceptions to Gentry's energy vs.
Gentry speculates on the cause s of some of these anomalous features, but provides no empirical data to support any explanation. Indeed, Gentry appears to be more willing to question the evidence provided by the physical samples than to question the validity of his model.
Perhaps the most damaging challenge to Gentry's hypothesis comes not from what has been observed, but from what is missing. Of the three major, naturally occurring radioactive elements, uranium, thorium, and potassium, two - uranium and thorium - are marked by decay series involving alpha particle emissions. Gentry's polonium haloes are attributed to alpha particle decay of the polonium isotopes Po, Po, and Po, all part of the uranium decay chain.
Thorium decays to stable Lead through a series of steps which include two additional polonium isotopes, Po and Po Thorium has an elemental abundance between three and four times that of uranium in the Earth's crust.
Also, in areas of uranium enrichment, such as those from which Gentry's halo samples apparently have come, thorium is also enriched. These thorium decay series polonium isotopes have alpha decay energies well within the range documented for uranium-series polonium decay. Thus, polonium isotopes which result from the decay of naturally occurring thorium should also produce characteristic haloes. In fact, according to Gentry's model, all polonium isotopes should be represented equally.
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However as Collins points out, Gentry has identified only halos for those isotopes of polonium associated with the decay of uranium; halos attributable to polonium and polonium are not found. Additionally, haloes attributable to the two polonium isotopes in the decay series of uranium Po and Po are also missing. Uranium currently comprises 0. If concentric rings haloes aren't caused by alpha particles, what causes them?
Both Joly and Gentry discounted the possibility that beta particles may play a role in coloration changes within minerals; however, neither author gives a basis for this rejection beyond the erroneous statement that beta particle energies are too low to have any affect. High energy beta particles have the well documented ability to break molecular bonds.
Combinations of alpha and beta decay particles, beta particles alone, or some completely non-radioactive process may be the cause of the observed mineral discoloration haloes. Odom and Rink examined giant radiohaloes in mica and proposed an alternative hypothesis for their formation. They compare the circular halo structures in mica with radiation-induced color halos RICHs in quartz. In the quartz crystalline structure, aluminum can occasionally substitute for a silicon atom, creating a slight charge imbalance. Alpha particles from uranium decay create hole-trapping centers around the aluminum atoms.
This in turn creates a semi-conductive area where beta particles also resulting from uranium decay can cause diffusion and discoloration over a fairly large area. The width of the resulting halo can be correlated with migration of valence-band holes along a radiation-induced charge potential in the host crystal.
While this is an attractive hypothesis, Odom and Rink cautiously note that the crystal structures and chemical composition of quartz and mica are significantly different. Quartz is known to have natural piezoelectric properties missing in the mica group minerals. Without further investigation, haloes caused by migrating hole trapping centers is speculative for minerals other than quartz. Clearly, more work is required to resolve all of these questions. The association of ring-type haloes with any specific energy of alpha decay must be considered speculative.
Even if we assume that concentric ring haloes actually are due to alpha radiation damage, an immediate problem arises with the short half-life of the polonium isotopes themselves. In order to leave a visible radiation damage halo, the affected mica or fluorite grains would have to crystallize before the polonium decayed away to background levels - about 10 half lives. For polonium isotopes, this correlates to between a fraction of a second Po, Po, Po and Gentry's hypothesis calls for pure, concentrated polonium at the center of each ring. The model makes no distinction between which polonium isotopes should be present - thus, there should be equal likelihood for all.
He points out that there is no known geochemical process by which such concentrations can occur during crystallization of a magma, concluding therefore that polonium haloes are indicative of some non-natural or supernatural occurrence. While Gentry does not provide a conclusive argument for demonstrating the relationship between concentric haloes and Polonium decay, the contribution of alpha-decay to halo development cannot be discounted entirely either. Collins reports that concentric ring halo structures commonly line up along visible micro-fractures in the host mineral grains, implying some association of the haloes with the fractures.
An interesting argument can be developed to support the idea that concentric ring haloes are created following the migration of radon gas along mineral fractures and explain Gentry's missing haloes. Polonium isotopes are produced in the radioactive decay chain of naturally occurring uranium, thorium, and uranium Gentry's studies identify concentric ring structures correlated with each of the three polonium isotopes in the uranium decay series.
Ring haloes correlated with polonium isotopes from the uranium or the thorium decay series are not reported, although they would have to be present under Gentry's primordial origin hypothesis. The first polonium isotope in each decay series is the daughter of a different radon atom; these radon precursors have greatly different half-lives. If polonium ring structures are the result of radon migration along micro-fractures Collins' hypothesis , then the half-life of the specific radon precursor is important.
Clearly, radon can migrate much further than the other two radon species before it decays away. Also, because of its significantly longer half-life, radon can accumulate in more significant concentrations in structural traps along the micro-fracture surfaces. Under these circumstances, one would expect to see many more radiogenic ring haloes associated with uranium series polonium isotopes than those of the other two decay chains. This explanation is more consistent with what is observed than Gentry's hypothesis, and is completely consistent with the standard geological model for rock formation.
An alternative possibility is explored by Brawley and Collins They note that many concentric ring haloes line up along visible fractures within the host mica. Such fractures are very common in mica crystals. Micro-fractures could provide conduits for the rapid movement and concentration of radon, a gaseous daughter product of uranium which forms part way along the decay chain leading to polonium.
Radon, itself an alpha emitter, has a half life of 3. 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.
Assigning a halo diameter to radon is difficult as the radon alpha decay energy is very close to that of polonium ; the two ring structures commonly cannot be distinguished Moazed, et al. The development of fractures in the grains of mica after crystallization has occurred, and the migration of radon along these fractures over the course of millennia, is much more in keeping with current geologic models of rock formation.
Thus, the radon hypothesis is more attractive than Gentry's model since it fits the observed evidence and doesn't require supernatural occurrences. Gentry's hypothesis quickly runs into trouble with all of the accumulated evidence from many fields of earth science pointing conclusively to a great age for the Earth. Not the least of these evidences is radiometric age dating. To reconcile his presumed young age for the Earth with reported isotopic age dates for rocks around the world, Gentry argues that radioactive decay rates have varied over time.
- The Age of the Earth - Polonium Halos as a Creationist Clock: Scott Pfahler?
- Polonium - Wikipedia.
- "Polonium Haloes" Refuted.
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He is forced to conclude that decay rates for his chosen polonium isotopes have remained constant while those of dozens of other radioactive isotopes were many orders of magnitude greater 6, to 10, years ago. This of course gives rise to several major inconsistencies:. Gentry's hypothesis would require that all of the different decay schemes for the different radioactive isotopes must have been accelerated by just the exact - but very different - amounts to give the consistent age dates we find for rocks today. Given the large number of different radioactive isotopes and decay schemes that have been used in dating rocks, the chance of this coincidence taking place is essentially zero.
The slow radioactive decay of uranium, thorium, and potassium has been identified as a primary source of the Earth's internal heat. Speeding up the radioactive decay rates of these isotopes by many orders of magnitude to be consistent with a 6, - 10, year age for the Earth requires that the energies of decay 10, years ago would have been extreme, keeping the Earth in a molten state to the present day.
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