Time varying radioactive decay?

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meat.paste
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Time varying radioactive decay?

Postby meat.paste » Wed Nov 26, 2008 4:51 pm UTC

I was reading my Science News, and they had a very nice article here that discussed how some experiments may show that the rate of weak force mediated radioactive decay is not time invariant. There seems to be a variation in the decay rate that is related to the Earth's position around the sun. The hypothesis is (if the data is not the result of experimental error) that the varying Earth-Sun distances change the neutrino flux, which then influences the decay rate. If this is true, then what does this do to our use of radionuclide ratios as clocks? How many other facts will be affected by a change in the assumption that half-lives are constant?

The possibility has me bothered :?
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Re: Time varying radioactive decay?

Postby thecommabandit » Wed Nov 26, 2008 5:21 pm UTC

Well if we haven't noticed until now, I can't say that it would make much difference.
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Re: Time varying radioactive decay?

Postby Izawwlgood » Wed Nov 26, 2008 5:33 pm UTC

Do they mention how significant the decay rate change is? I mean, a rate increase of a mere fraction of a fraction of percent isn't going to change our radiocarbon dating estimates.

It's like how with increased detection sensitivity you can find ANYTHING and EVERYTHING in water anywhere? Zomg, 5 ppgoogleplex of plutonium in the water!
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Re: Time varying radioactive decay?

Postby Monty40xi » Wed Nov 26, 2008 9:51 pm UTC

Possibly stupid question - is "weak force mediated radioactive decay" only a specific subset of radioactive decay?
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Re: Time varying radioactive decay?

Postby Minerva » Thu Nov 27, 2008 1:37 am UTC

Sigh. When ever something like this comes up, creationists usually sieze on it to say Oh me yarm carbon dating doesn't work!

These are still just preprint papers from ArXiV - and if they haven't been published, they really should be taken with a grain of salt, because there hasn't been any peer review.

You can find people uploading any old crazy crap onto arxiv.

both had seen seasonal variations of a few tenths of a percent in the decay rates


Monty40xi wrote:Possibly stupid question - is "weak force mediated radioactive decay" only a specific subset of radioactive decay?


Yes - beta decay. Also, for example, electron capture, and positron emission (positive beta decay), but not alpha decay, for example.

A 1990 paper by Kenneth Ellis of Baylor College of Medicine in Houston reported seasonal variations in plutonium-238 radioactivity in a calibration experiment for a radiotherapy machine.


Peter Cooper of the Fermi National Accelerator Laboratory in Batavia, Ill., recently did just that. He obtained and analyzed data from the Cassini mission to Saturn. Deep-space probes usually generate power from the heat emitted by a chunk of radioactive material—plutonium-238 for the Cassini spacecraft. Cassini journeyed as close to the sun as Venus and then far back to Saturn, spanning a much wider range of distances from the sun than Earth does during its yearly orbit. If the sun had an effect on plutonium decay, the fluctuations would have been much more substantial than those seen in Earth-bound experiments. As a result, Cooper reasoned, Cassini should have measured substantial changes in its generator’s output. It didn’t.


238Pu decays by alpha emission - so, if it's a weak-interaction process such as something involving neutrinos, why should the decay of 238Pu be effected?
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Re: Time varying radioactive decay?

Postby meat.paste » Fri Nov 28, 2008 2:43 pm UTC

Minerva wrote:Sigh. When ever something like this comes up, creationists usually sieze on it to say Oh me yarm carbon dating doesn't work!

238Pu decays by alpha emission - so, if it's a weak-interaction process such as something involving neutrinos, why should the decay of 238Pu be effected?


I figured carbon dating would be fine. I was more concerned about the long clocks for measuring in the 1-10 billion year range. If there is an effect, then I was thinking that perhaps the decay rate was higher when the universe was smaller, which would bias our measurements towards an older universe. As I type this, though, I thinking that the purported effect is ~0.1%, so it wouldn't throw off the overall ages by much.

I thought it was interesting as well that the Cassini probe did not show the effect but the Baylor machine did. This was pretty convincing evidence that Baylor had an error. However, the graphs showing the sinusoidal variations (especially of the Radium-226 variation in graph 3) were pretty convincing that there is some effect occurring. Of course, radium decays via alpha emission.

I didn't realize ArXiV's reputation. Thanks for the clarification.
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Re: Time varying radioactive decay?

Postby ks_physicist » Sat Nov 29, 2008 2:21 am UTC

ArXiv has been trying to increase their 'street cred' by requiring authors to be recommended for publication by an established ArXiv contributor. It is NOT peer-review, but it is a screening process that, as an idea, might help screen out crackpot authors.

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Re: Time varying radioactive decay?

Postby ThinkerEmeritus » Sat Nov 29, 2008 6:56 pm UTC

ks_physicist wrote:ArXiv has been trying to increase their 'street cred' by requiring authors to be recommended for publication by an established ArXiv contributor. It is NOT peer-review, but it is a screening process that, as an idea, might help screen out crackpot authors.


In particular, this paper is not crackpot, and the authors are legitimate. It is, however, quite speculative. Where I can estimate the data errors, none of the points seems to be more than 2 or maybe 2.5 sigma away from no effect, so the whole idea rests on taking variations in the rate, all of which are within reasonable statistical error, and correlating their small deviations with the calendar. Then the two experiments which "both show the effect" lag the calendar by different amounts. Don't hold your breath.

In addition, there is the Cassini data that has to be explained away.

I remember a conference where one author was presenting a result he admitted was speculative. He said that its flaw was that "you are only permitted one tooth-fairy." This paper violates the one-tooth-fairy rule massively.
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Re: Time varying radioactive decay?

Postby UmbrageOfSnow » Wed Nov 04, 2009 2:16 am UTC

Apologies for the Thread-Necromancy, but I have been reading all this year's Analog magazines and came across an article on this.

So I was wondering a couple of things from any of the physics people on these fora:

1. Is this pretty much the consensus view of Fischbach's work?

2. Do you agree with these points or is this a case of physicists being stubborn? (I agree, but I'm a math/microbiology guy, so my opinion isn't worth much)

3. Have any of these things been addressed since, or was it just a flash in the pan?

4. Is it just me, or does New Scientist and a bunch of other things that come up on google seem overly credible towards these findings?
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Re: Time varying radioactive decay?

Postby BlackSails » Wed Nov 04, 2009 2:36 am UTC

Neutrino flux changes is not a plausible explanation for this. Neutrinos do not react very much with matter. You need really, really large detectors of materials with really high neutrino capture cross sections to even have a dozen capture events per day.

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Re: Time varying radioactive decay?

Postby Minerva » Wed Nov 04, 2009 3:21 am UTC

UmbrageOfSnow wrote:4. Is it just me, or does New Scientist and a bunch of other things that come up on google seem overly credible towards these findings?


It's New Scientist we're talking about. It's more and more tabloid crap these days.
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Re: Time varying radioactive decay?

Postby UmbrageOfSnow » Wed Nov 04, 2009 3:47 am UTC

Minerva wrote:It's New Scientist we're talking about. It's more and more tabloid crap these days.


I hadn't read anything out of New Scientist in at least a year, but if this is their standard, I'll take your word for it.
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Re: Time varying radioactive decay?

Postby UmbrageOfSnow » Fri Nov 06, 2009 2:29 am UTC

So does anyone know for sure that NASA's probe data contradicted the radioactive decay time variation? Or has it not even been looked at?
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Re: Time varying radioactive decay?

Postby Mathom » Wed Aug 04, 2010 10:26 pm UTC

AS I understand it, the correlation with distance from the sun has been debunked; the seasonal variation remains unexplained.

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Re: Time varying radioactive decay?

Postby BlackSails » Thu Aug 05, 2010 12:14 pm UTC

I would be more likely to ascribe seasonal variation in the instruments I use instead of a fundamental force.


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