Skeptic Friends Network

Username:
Password:
Save Password
Forgot your Password?
Home | Forums | Active Topics | Active Polls | Register | FAQ | Contact Us  
  Connect: Chat | SFN Messenger | Buddy List | Members
Personalize: Profile | My Page | Forum Bookmarks  
Home Creation/Evolution More on the Polonium 218 Controversy
Menu
Skeptic Forums
Skeptic Summary
The Kil Report
Skeptillaneous
Creation/Evolution
About Skepticism
Fan Mail
Skepticality
Rationally Speaking
Claims List
Skeptic Links
Book Reviews
Gift Shop
Staff


Server Time: 23:32:53
Your Local Time:



Creation/Evolution
Creation and Evolution, Science, Darwin, Scientific Method, Natural Selection
Printer Friendly Printer Friendly Version of this Article... Bookmark Bookmark This Article...

More on the Polonium 218 Controversy

By TFarnon
Posted on: 4/20/2002

An SFN member explains how halos came to be found in ancient rocks, without breaking any laws of physics.


The following conversation took place on a message board between “Jeff” and our own TFarnon concerning the controversy surrounding “Polonium Halos” and Robert Gentry’s work.

“Jeff” wrote:
John Brawley has done a commendable, and I would add, a seemingly herculean amount of field work. But, I’m not sure if his “mother’s microscope” has served him as well as Dr. Gentry’s scanning electron devices did at Oak Ridge. Brawley’s paper is peppered throughout with an awful lot of “could be’s” and “might be’s,” did you notice that, too? His hypothesis of radon migration in the biotites and its contribution to crystal discoloration is interesting and certainly merits further study, admittedly. But this hardly invalidates Dr. Gentry’s hypothesis of primordial origin of cambriam pegmatites. He was also honest in admitting that he was “unfamiliar with scanning electron microscopes.” The other article you cited at the Jim Merrit web page is largely aimed, it would seem, at undermining the personal credibility and integrity of Dr. Gentry. Nothing substantial in the way of scientific falsification of his theory here! In fact the Scientic American article you allude to also concludes in its abstract there with the straightforward, nonjudgmental observation that: “Indeed Polonium halos have been offered as possible evidence of an instantaneous creation.”
TFarnon replied:
1) I didn’t allude to a Scientific American article. I referenced an article in Science. Furthermore, after referring to the primary papers, I am convinced you took your quote out of context.

2) Selective quotation aside, let’s get to the heart of the matter. Gentry first published information on the discovery of Polonium Halos in 1968. (Science 160:1228). The two subsequent papers (Science 169: 670; Science 173: 727) were similar. All three of these early papers were purely descriptive. At that point, Gentry confined himself to a description of the phenomenon in question.

From 1973 to 1975 Gentry’s papers begin to speculate on the causes of Polonium halos (Nature 244: 282-283; Science 184: 62-66; Nature 252: 564-566; Nature 258: 269-70) In these papers Gentry did fairly conclusively rule out long half-life isomers of polonium as a cause of the halos. In this, other scientists concurred, notably J.H. Fremlin (1973. Nature 258: 269-70) of the University of Birmingham Department of Physics.

I will selectively quote from these papers:
“A straightforward attempt to account for the origin of these Po haloes by assuming that Po was incorporated into the halo inclusion at the time of host mineral crystallization meets with severe geological problems: the half-lives of the polonium isotopes (t 1/2 = 3 min for 218 Po) are too short to permit anything but a rapid mineral crystallization, contrary to accepted theories of magmatic cooling rates…

“It can be definitely stated that the exceptionally high 206 signal, compared with 207, occurs only in the Po halo inclusions and is not an artefact due to a molecular ion originating with the mica itself, the inclusion, or a combination of the mica and the elemental constituents of the inclusion.”
(1973. Nature 244: 282-283)

“To explain Po halos, Henderson postulated a slow accumulation of Po isotopes (or their respective-decay precursors) from U daughter product activity. I demonstrated that this secondary accumulation hypothesis was untenable and showed, using the ion microprobe, that Po halo radiocenters (or inclusions) exhibit anomalously high 206 Pb/207 Pb isotope ratios which are a necessary consequence of Po a-decay to 206 Pb.” (1974. Science 184: 62-66)

“Admittedly, compared to ordinary [Po] types, the Pb isotope ratios of Po halos are unusual, but new ion microprobe analyses have confirmed my earlier results. It is also apparent that Po halos do pose contradictions to currently held views of Earth history.

“For example, there is first the problem of how isotopic separation of several Po isotopes (or their decay precursors) could have occurred naturally. Second, a straightforward explanation of 218 Po halos implies that the 1-Ám radiocenters of very dark halos of this type initially contained as many as 5 x 10^9 atoms (a concentration of more than 50 percent) of the isotope 218 Po (half-life, 3 minutes), a problem that almost defies reason. A further necessary consequence, that such Po halos could have formed only if the host rocks underwent a rapid crystallization, renders exceedingly difficult, in my estimation, the prospect of explaining these halos by physical laws as they are presently understood. In brief, Po halos are an enigma.”
(1974. Science 184: 62-66.)

“Do Po haloes imply that unknown processes were operative during the formative period of the Earth? Is it possible that Po halos in Precambrian rocks represent extinct natural radioactivity and are therefore of cosmological significance?” (1974. Nature 252: 564-566.)
(Gentry goes on to rule that possibility out quite conclusively.)
“The isomer hypothesis is one way that polonium halos could have been explained. My present view is that experimental results have ruled out the isomer hypothesis.” (1975. Nature 258: 269-70)
Given the knowledge of semiconductors available at the time, and Gentry’s probable lack of expertise in that field, the statements above seem quite unexceptionable.

I shall take a brief detour to explain (as best I can — I haven’t messed with materials science and semiconductors myself in 20 years) a concept that will be important in what follows:

Semiconductors have a crystalline lattice structure. When an electron gets bumped out of the lattice somehow, it makes a “hole”. These holes tend to migrate, albeit slowly, as do the electrons. That’s what makes it a semiconductor, rather than a conductor, where electrons can really move around. My apologies in advance to anyone who has a much better grasp of semiconductors than I do.

To return to polonium halos, however, Gentry’s theory was supplanted in 1989. I would like to add that Gentry apparently did not rebut the findings of this paper in the scientific literature. (I looked through the Science Citation index for the years 1984 to 1996. If it was there, I would have found it.) I now turn to that paper.
“The radii of radiation-induced color halos (RICHs) surrounding radioactive mineral inclusions in mica generally correspond closely to the calculated range of common uranogenic and thorogenic alpha particles in mica. Many exceptions are known, howver, and these variants have led investigators to some rather exotic interpretations.

“Particularly controversial have been two (perhaps artificial) classes of RICHs referred to as Po halos and giant halos.

“Beginning with the assumptions that the smoky RICHs in quartz are caused by alpha particles radiating from the mineral inclusions and that these alphas are not due to some unknown nuclides or isomers, we have tried to develop an understanding of how such giant RICHs might form.

“Aluminum centers are common extrinsic defects in natural quartz. Trivalent Al can substitute for Si, which is tetrahedrally coordinated with o, up to at least several overall structural consequences… However, holes and electrons can be trapped at a variety of extrinsic and intrinsic defects in the bend gap in quartz…

“When an alpha decay in the inclusion occurs, the alpha particle starts out with a velocity that depends on its energy…”
(Odom, L.A., and Rink, W.J. 1989. “Giant Radiation-Induced Color Halos in Quartz: Solution to a Riddle” Science 246: 107-109.)

“Thus a narrow zone at the outer limits of the range of alpha particles in quartz is a zone of excess hole production. The continuous production of holes during geologic time drives the electronic equilibrium of this microregime in the direction of stabilizing the Al color centers and producing a thin smoky halo. As hole-capturing centers such as Al defects become saturated, excess holes must migrate outward down a charge potential.

“If anomalous RICHs in other silicate minerals such as micas do not develop in fundamentally different ways (albeit the nature of the color centers can involve defects other than Al), then many of the special conditions and special alpha energies invoked to account for Po and giant halos in mica seem no longer necessary. Giant RICHs can grow by hole diffusion.

“…the sizes and structure of giant and Po RICHs in mica also are artifacts of radiation-induced conductivity and that their explanation requires neither unknown radioactivity nor an abandonment of current concepts of geologic time.”
(Ibid.)
The last two paragraphs are the most important in this argument. There you have it: how the halos came to be without invoking violation of known physical laws. If you want to refute, start doing the paper search, because I’m not wasting any more time on this unless you put some effort into it.
“Jeff” replied:
Through all of this, no one has yet accepted Gentry’s challenge to attempt to synthesize this sort of lithologic artifact in the laboratory and debunk his hypothesis. I eagerly await Dr. Gentry’s replies to all of this. You might remember that it was our friends in the atheist media who muzzled their reporters and pulled their cameramen from the courtroom when he took the stand in the Arkansas Creation Science trial. Some objectivity that, huh? I wonder what they were afraid of?
And TFarnon said:
See above. Please also note that Gentry never issued that “challenge” in the scientific literature. What he chooses to publish in the non-peer-reviewed popular press is hardly worth considering.

You may be waiting a long time indeed for Dr. Gentry’s replies, at least in peer-reviewed literature. In the first of these three segments on polonium halos, I noted his silence on the subject. Please bear in mind that it is not his beliefs that will get him “censored” from these journals. The journals accepted some pretty wild speculation on his part in the first place. If he could prove that his hypothesis was indeed valid, it would be published.

As for the three-ring-circus trial in Arkansas, I have no idea what went on there. Nor do I really care who was or wasn’t given press coverage. It was, after all, the judge who would decide, and not “our dear viewers.” I’m sure the judge got to hear it all.

Before you complain that my selected quotes are insufficient, bear in mind that I wasn’t about to type in 19 pages of very fine print. The citations are there in full for you to investigate for yourself. Raise your objections to what I typed after you have read the papers in full.


Back to Creation/Evolution



The mission of the Skeptic Friends Network is to promote skepticism, critical thinking, science and logic as the best methods for evaluating all claims of fact, and we invite active participation by our members to create a skeptical community with a wide variety of viewpoints and expertise.


Home | Skeptic Forums | Skeptic Summary | The Kil Report | Creation/Evolution | Rationally Speaking | Skeptillaneous | About Skepticism | Fan Mail | Claims List | Calendar & Events | Skeptic Links | Book Reviews | Gift Shop | SFN on Facebook | Staff | Contact Us

Skeptic Friends Network
© 2008 Skeptic Friends Network Go To Top Of Page
This page was generated in 0.78 seconds.
Powered by @tomic Studio
Snitz Forums 2000