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Author Topic:   Quick radiometric dating question- misused techniques
Coragyps
Member (Idle past 734 days)
Posts: 5553
From: Snyder, Texas, USA
Joined: 11-12-2002


Message 31 of 40 (518498)
08-06-2009 10:48 AM
Reply to: Message 30 by Kitsune
08-06-2009 10:05 AM


Re: Half-life questions
I think a good response to this would be to show that we can see isotopes decaying in ancient starlight -- I'm assuming we can, though I haven't researched this yet.
We can and have - type 1A supernovae show the same rate of decay of nickel-56 to cobalt-56 to iron as we see right here on earth, even out to a few billion years ago. Wikipedia will get you started on the details.

This message is a reply to:
 Message 30 by Kitsune, posted 08-06-2009 10:05 AM Kitsune has replied

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Kitsune
Member (Idle past 4300 days)
Posts: 788
From: Leicester, UK
Joined: 09-16-2007


Message 32 of 40 (518517)
08-06-2009 12:04 PM
Reply to: Message 31 by Coragyps
08-06-2009 10:48 AM


Re: Half-life questions
Great, thanks. I'm better with astronomy -- nuclear physics was never my strong point!
added in edit
This is from one of JonF's favourite sources I think:
Evidence About Constants Being the Same in the Distant Past
This is a good counter to the claim that decay rates changed in the past, though Joe Meert's Were Adam and Eve Toast? works well too.
Trying to find evidence of isotopes with longer half-lives elsewhere in the universe is proving more challenging at the moment.
Edited by LindaLou, : No reason given.
Edited by LindaLou, : No reason given.
Edited by LindaLou, : No reason given.

This message is a reply to:
 Message 31 by Coragyps, posted 08-06-2009 10:48 AM Coragyps has not replied

Replies to this message:
 Message 37 by RAZD, posted 08-12-2009 10:59 PM Kitsune has replied

  
JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 33 of 40 (518524)
08-06-2009 12:40 PM
Reply to: Message 30 by Kitsune
08-06-2009 10:05 AM


Re: Half-life questions
Radioactive decay rates depend on some deep-down fundamental attributes of the universe, and if they changed traces would be left in a surprising number of places. The Constancy of Constants and The Constancy of Constants, Part 2 are good resources to start with the author is a well-knonw (in some circles) physicist.
Yep, what we see in stars is a good measure. The Oklo reactor is also a great one; Oklo natural nuclear reactor and Natural nuclear fission reactor
Finally, one strong indicator that radioactive decay rates havfen't changed to anything near the extent required dby creationists is teh fact that all life was not wiped out by the radiation, nor was all life killed by the melting of the Earth due to the heat released. The RATE group, composed of those few YECs who appear to know how bad the problem is, alludes to this. In Helium Diffusion Rates Support Accelerated Nuclear Decay they write:
quote:
Samples 1 through 3 had helium retentions of 58, 27, and 17 percent. The fact that these percentages are high confirms that a large amount of nuclear decay did indeed occur in the zircons. Other evidence strongly supports much nuclear decay having occurred in the past [14, pp. 335-337]. We emphasize this point because many creationists have assumed that "old" radioisotopic ages are merely an artifact of analysis, not really indicating the occurrence of large amounts of nuclear decay. But according to the measured amount of lead physically present in the zircons, approximately 1.5 billion years worth at today’s rates of nuclear decay occurred. Supporting that, sample 1 still retains 58% of all the alpha particles (the helium) that would have been emitted during this decay of uranium and thorium to lead.
{emphasis in original}
And, in Helium Diffusion Age of 6,000 Years Supports Accelerated Nuclear Decay:
quote:
Thus our new diffusion data support the main hypothesis of the RATE research initiative: that God drastically accelerated the decay rates of long half-life nuclei during the earth's recent past. For a feasibility study of this hypothesisincluding God's possible purposes for such acceleration, Biblical passages hinting at it, disposal of excess heat, preserving life on earth, and effects on stars, see Humphreys (2000, pp. 333-379). The last three problems are not yet fully solved, but we expect to see progress on them in future papers.
Not yet fully solved, indeed. Needless to say no progress has been forthcoming in the five years since this paper appeared.
Note that they implicitly acknowledge that there is no way that a natural process would accelerater defcay in the manner that they need; it rwequires a miracle. So it ain't science.

This message is a reply to:
 Message 30 by Kitsune, posted 08-06-2009 10:05 AM Kitsune has replied

Replies to this message:
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 Message 35 by Kitsune, posted 08-12-2009 5:25 PM JonF has replied

  
Kitsune
Member (Idle past 4300 days)
Posts: 788
From: Leicester, UK
Joined: 09-16-2007


Message 34 of 40 (518527)
08-06-2009 12:51 PM
Reply to: Message 33 by JonF
08-06-2009 12:40 PM


Re: Half-life questions
My library of links is growing rapidly thanks to you.
I've found interesting articles about uranium being detected in old Milky Way stars -- not what I was after, but great stuff to learn (which is why I do this I guess).
I'm going to spend some time reading your links here but I'm still wondering how I would answer a claim that we don't know if isotopes with long half-lives really follow the entire logarithmic curve because we "weren't there" to watch it happen. Presumably they'd be trying to argue that the decay rates could be faster at some undefined point -- they certainly wouldn't be arguing that they are slower. In which case, all of this evidence about decay rates being constant would apply.

This message is a reply to:
 Message 33 by JonF, posted 08-06-2009 12:40 PM JonF has not replied

  
Kitsune
Member (Idle past 4300 days)
Posts: 788
From: Leicester, UK
Joined: 09-16-2007


Message 35 of 40 (519256)
08-12-2009 5:25 PM
Reply to: Message 33 by JonF
08-06-2009 12:40 PM


Re: Half-life questions
Jon, I'm afraid I need to ask for your, or anyone else's help, again. This is regarding the two links the creationist has been trying to discuss -- I'll post them again here:
Strontium-92 Half-life Measurement Through Accurate Y-Ray Spectrometry
He's trying to claim that new measurements had to be made because the decay rates changed. I explained that this article and the one below are about decay rates being measured more accurately, and I started to post evidence that decay rates have not actually changed, starting with SN1987a. I was accused of "misrepresenting links" and I have been banned, though it's possible that the ban will be lifted by the forum owner. Even if it isn't, I'd like to know how best to respond to the other comments here, because I'm curious. The creationist appears to admit that the above article shows that as the decay measurement is more accurate, the margin of error decreased. He's hung up on the fact that in the second article -- which is only an abstract -- the new measurement is outside the margin of error:
Half-life evaluations for 3H, 90Sr, and 90Y.
Wading through the meaningless babble in the creationist's post, here is the crux of the matter:
quote:
The authors of the 92Sr pdf report obtaining fresh new results of decay time measurements which do not match up. Table four lists the measurements, and right beneath table four, it says
Quote:
A weighted average from the three values was determined for each fuel pin. Nevertheless, as the discrepancies were sometimes beyond their reported uncertainties, the associated uncertainty is calculated from the standard deviation between
the three values, with a multiplication factor tp() = 1.32 [15] that arose from the low degree of freedom of the sample.
"Discrepancies were sometimes beyond their reported uncertainties" means they took measurements of values, and the measurements did not match, even allowing for the inaccuracy of the method. Plain as can be. It doesn't get any simpler than that.
Now as to the question of what to make of it, there are two approaches. One can look and see here's a measurement, and here's another measurement; since they disagree I conclude a change took place.
I don't understand enough about how these measurements are done, or how margins of error are calculated, to be able to comment. It's a difficulty in that I am unable to look at the full article, which no doubt explains how the old measurements were improved upon.

This message is a reply to:
 Message 33 by JonF, posted 08-06-2009 12:40 PM JonF has replied

Replies to this message:
 Message 36 by JonF, posted 08-12-2009 6:26 PM Kitsune has replied

  
JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 36 of 40 (519262)
08-12-2009 6:26 PM
Reply to: Message 35 by Kitsune
08-12-2009 5:25 PM


Re: Half-life questions
Well, I can't get at the second paper either. But measuring half-lives over a period of time much smaller than the half-life is fraught with peril. Stated uncertainties are best estimates, and are statistically based. They are not absolute boundaries. An uncertainly of ±x (2 σ ) means that their best estimate is that there is a 95% probability that the actual value lies between the quoted value + x and the quoted value - x. But there's a 5% chance it lies outside those bounds. And it's still an estimate and subject to its own errors. Again from Begemann, F., Ludwig, K. R., Lugmair, G. W., Min, K., Nyquist, L. E., Patchett, P. J., Renne, P. R. Shih, C.- Y., Villa, I. M. and Walker, R. J. (2001). Call for an improved set of decay constants for geochronological use. Geochim. Cosmochim. Acta 65, 111--21:
quote:
Accurate radioisotopic age determinations require accurate decay constants of the respective parent nuclides. Ideally, the uncertainty on the decay constants should be negligible compared to, or at least be commensurate with, the analytical uncertainties of the mass spectrometric measurements entering the calculations. Clearly, this is not the case at present. The stunning improvements in the performance of mass spectrometers during the past three decades, starting with the seminal paper by Wasserburg et al. (1969), have not been accompanied by any comparable improvement in the accuracy of the decay constants.The uncertainties associated with direct half-life determinations are, in most cases, still at the percent level at best. The recognition of an urgent need to improve the situation is not new (cf., e.g., Renne et al., 1998; Min et al., 2000a); it has presumably been mentioned, at one time or another, by every group active in geo- or cosmochronology. The present contribution is intended to be a critical guide to the existing experimental approaches. Except in a few cases, we do not evaluate the individual reports on decay constants, and we also do not make any recommendations as to which values should be considered correct and be used by the dating community at large. This must, in our opinion, be left for existing commissions to decide, following the precedent of Steiger and Jager (1977).
Three approaches have so far been followed to determine the decay constants of long-lived radioactive nuclides.
1. Direct counting. In this technique, alpha, beta or gamma activity is counted, and divided by the total number of radioactive atoms. Among the difficulties of this approach are the self-shielding of finite-thickness solid samples, the low specific activities, imprecise knowledge of the isotopic composition of the parent element, the detection of very low-energy decays, and problems with detector efficiencies and geometry factors. Judged from the fact that many of the counting experiments have yielded results that are not compatible with one another within the stated uncertainties, it would appear that not all the difficulties are always fully realized so that many of the given uncertainties are unrealistically small, and that many experiments are plagued by unrecognized systematic errors. As the nature of these errors is obscure, it is not straightforward to decide which of the, often mutually exclusive, results of such counting experiments is closest to the true value. Furthermore, the presence of systematic biases makes any averaging dangerous. Weighted averaging using weight factors based on listed uncertainties is doubly dubious. It is well possible that reliable results of careful workers, listing realistic uncertainties, will not be given the weights they deserve—this aside from the question whether it makes sense to average numbers that by far do not agree within the stated uncertainties.
2. Ingrowth. This technique relies on measuring the decay products of a well-known amount of a radioactive nuclide accumulated over a well-defined period of time. Where feasible, this is the most straightforward technique. Ingrowth overcomes the problems encountered with measuring large fractions of low-energy b-particles, as in the case of 87Rb and 187Re. It also comprises the products of radiation-less decays (which otherwise cannot be measured at all) like the bound-beta decay branch of 187Re and the possible contribution to the decay of 40K by electron capture directly into the ground state of 40Ar. Among the drawbacks of this approach is that the method is not instantaneous.The experiment must be started long before the first results can be obtained because long periods of time (typically decades) are required for sufficiently large amounts of the decay products to accumulate. Ingrowth-experiments further require an accurate determination of the ratio of two chemical elements (parent/daughter) as well as an accurate determination of the isotopic composition of parent and daughter element at the start of the accumulation (see below). Moreover, because of the hold-up in the chain of intermediaries, for uranium and thorium measuring the ingrowth of the stable decay products in the laboratory does not work at all.
3. Geological comparison. This approach entails multichronometric dating of a rock and cross-calibration of different radioisotopic age systems by adjusting the decay constant of one system so as to force agreement with the age obtained via another dating system. In essence, because the half-life of 238U is the most accurately known of all relevant radionuclides, this amounts to expressing ages in units of the half-life of 238U.
Note especially the paragraph numbered 1. Judged from the fact that many of the counting experiments have yielded results that are not compatible with one another within the stated uncertainties, it would appear that not all the difficulties are always fully realized so that many of the given uncertainties are unrealistically small, and that many experiments are plagued by unrecognized systematic errors. But such incompatibilities are not necessarily evidence of change (and if they are, the changes increase half-life as often as they decrease half-life). If there were changes, even a percent or so, there would be other far-reaching effects that we would easily detect. (I'm not enough of a physicist to specify what they would be, but look back at Steve Carlip's posts on constants and reflect of how far-reaching go those effects are). No, they are evidence that we don't understand all the difficulties and complications involved in measuring half-lives well enough to measure them to better than a few percent or so (except for uranium). But we certainly know enough to measure them to a few percent.
But the real key is not to get down in the mud and wrestle with the creo on infinitesimal details. Changes less than several orders of magnitude are insufficient to make the creationist position tenable, and changes would have to be correlated among many different and independent mechanisms (alpha decay, beta decay, and electron capture decay … and their many sub-types). Keep pounding away at consilience between wildly different radiometric methods and even with non-radiometric methods (I posted a couple of links showing the latter), and ask for a scientifically verifiable mechanism that accounts for those results. Pound on the heat and radiation and observations of stars problems acknowledged by the RATE group.

This message is a reply to:
 Message 35 by Kitsune, posted 08-12-2009 5:25 PM Kitsune has replied

Replies to this message:
 Message 38 by Kitsune, posted 08-14-2009 3:15 AM JonF has replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 37 of 40 (519288)
08-12-2009 10:59 PM
Reply to: Message 32 by Kitsune
08-06-2009 12:04 PM


Re: Half-life questions
Hi LindaLou,
Great, thanks. I'm better with astronomy -- nuclear physics was never my strong point!
Note the reference in the link to SN1987A, a rather unique nova event that allows us to measure the actual distance to the star ... and the information on cobalt decay during the nova.
You may also want to check out Are Uranium Halos the best evidence of (a) an old earth AND (b) constant physics?
Say hi to CTD for me, and remind him that half a half-life is not a quarter-life.
Edited by RAZD, : U halo

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This message is a reply to:
 Message 32 by Kitsune, posted 08-06-2009 12:04 PM Kitsune has replied

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 Message 39 by Kitsune, posted 08-14-2009 3:23 AM RAZD has seen this message but not replied

  
Kitsune
Member (Idle past 4300 days)
Posts: 788
From: Leicester, UK
Joined: 09-16-2007


Message 38 of 40 (519476)
08-14-2009 3:15 AM
Reply to: Message 36 by JonF
08-12-2009 6:26 PM


Re: Half-life questions
Hi JonF,
Thanks for the info. It clarifies things for me, but it would be tricky to think of how to phrase some of this to a YEC without them going away thinking, "They're admitting that there's a lot of uncertainty, so none of those radiometric dates are right! It's a method that can't be trusted!" I can imagine them assuming that the decay rate for potassium, for example, is in error, and so while K-Ar dates are in consilience, they're all wrong.
So, given the pitfalls described in the paper you quoted from, how is it that we can be confident that the decay rates of elements used in radiometric dating are known to within a few percent or less? How can we be sure that the decay rate of uranium is so precisely understood -- is it because, as you said a few posts back, there have simply been many studies because bombs are big business? How would they have avoided the problems with all the measuring techniques that you outlined? After all, you said,
quote:
But measuring half-lives over a period of time much smaller than the half-life is fraught with peril.
You couldn't say this in a debate with a YEC, because if your quote applies to isotopes with short half-lives, then it should certainly apply to the longer-lived ones used in radiometric dating. In the case of uranium, perhaps you could cite the unchanged diameter of halos?
The final paragraph in your post is sensible, and I did those things. Unfortunately this is a YEC who is very touchy about the subject (understandably, because it invalidates his belief system) and who is also a moderator. If I'm even allowed back onto the forum, I am going to have to take on the subject of the specific isotopes in those papers and why the new measurements are outside of the margins of error, while making sure I don't say so much about uncertainties that the creationist feels free to believe that no radiometric dating method is accurate. I can do the former thanks to you, but the latter could be challenging.
Could you tell me where I can find those posts by Steve Carlip that you mentioned? Thanks.
Edited by LindaLou, : No reason given.

This message is a reply to:
 Message 36 by JonF, posted 08-12-2009 6:26 PM JonF has replied

Replies to this message:
 Message 40 by JonF, posted 08-14-2009 9:13 AM Kitsune has not replied

  
Kitsune
Member (Idle past 4300 days)
Posts: 788
From: Leicester, UK
Joined: 09-16-2007


Message 39 of 40 (519478)
08-14-2009 3:23 AM
Reply to: Message 37 by RAZD
08-12-2009 10:59 PM


Re: Half-life questions
Hi RAZD, thanks for that. I've read information that you've posted here and at Herb Allure about uranium halos. It's particularly amusing that where you find the supposedly parentless polonium halos, there's always a source of uranium nearby, as well as rocks that radon can leach into (for lack of a better scientific term). The information about uranium decay that you linked to in your previous post is well written so that a layperson like me can gain some understanding. I'll have a more thorough read of the thread today.
It was a sad day when Russ decided to start giving moderator positions to the most irritating YECs on the forum. If you get them too wound up, they can kick you out -- as you're well aware. Russ is considering whether CTD's claims that Linear and I have misrepresented those papers are justified. I don't have a great deal of faith in Russ' ability to be objective but you never know. If I'm through there for good, I can spend more time here.
Edited by LindaLou, : No reason given.

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 Message 37 by RAZD, posted 08-12-2009 10:59 PM RAZD has seen this message but not replied

  
JonF
Member (Idle past 168 days)
Posts: 6174
Joined: 06-23-2003


Message 40 of 40 (519499)
08-14-2009 9:13 AM
Reply to: Message 38 by Kitsune
08-14-2009 3:15 AM


Re: Half-life questions
Thanks for the info. It clarifies things for me, but it would be tricky to think of how to phrase some of this to a YEC without them going away thinking, "They're admitting that there's a lot of uncertainty, so none of those radiometric dates are right! It's a method that can't be trusted!" I can imagine them assuming that the decay rate for potassium, for example, is in error, and so while K-Ar dates are in consilience, they're all wrong.
Yes, I know all that. It's a losing proposition. That's why the key is not to go down in the mud, where the can use their lack of knowledge of what statistics, what error estimates are, and how utterly infinitesimal these differences are when compared to the changes proposed by YECs. They complain about extrapolating, then extrapolate over many orders of magnitude! You can't beat them at that game.
Fundamentally they want a Biblical version of science; knowledge is graven in stone and known exactly.
But I don't know anyone who's good at getting them to address the important points like consilience. If the decay rate for K is wrong, then so are all decay rates, and all by the same factor. To anyone with any knowledge of physics, that's ludicrous. mMybe this point can be gotten across to someone ignorant of physics. I don't know how to even get them to listen.
So, given the pitfalls described in the paper you quoted from, how is it that we can be confident that the decay rates of elements used in radiometric dating are known to within a few percent or less? How can we be sure that the decay rate of uranium is so precisely understood -- is it because, as you said a few posts back, there have simply been many studies because bombs are big business? How would they have avoided the problems with all the measuring techniques that you outlined?
Much of the answer is in my previous quote from that paper:
quote:
No decay constant of any radionuclide used for geochronology has been (or, arguably, can be) more-precisely measured than those of 238U and 235Ua consequence of the mode of decay (alpha), favorably short half-lives, and the availability of large quantities of isotopically pure parent nuclides.
I'll see if I can dig up the Jaffey paper.
The reason we can be sure that they are known to a few percent of less is that all of the numerous measurements without known systematic error lie within a few percent or less. Does that prove it? No. Nothing is ever proven in science. It's established far beyond reasonable doubt ... but not beyond unreasonable doubt.
Unfortunately this is a YEC who is very touchy about the subject (understandably, because it invalidates his belief system) and who is also a moderator. If I'm even allowed back onto the forum, I am going to have to take on the subject of the specific isotopes in those papers and why the new measurements are outside of the margins of error, while making sure I don't say so much about uncertainties that the creationist feels free to believe that no radiometric dating method is accurate. I can do the former thanks to you, but the latter
could be challenging.
Well,that's a situation in which you are near-certain to lose. Facts don't help much there. And I don't know how to teach somebody something that they refuse to learn.
Could you tell me where I can find those posts by Steve Carlip that you mentioned? Thanks.
The Constancy of Constants
The Constancy of Constants, Part 2
Steve Carlip

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 Message 38 by Kitsune, posted 08-14-2009 3:15 AM Kitsune has not replied

  
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