Scientists Confirm Nuclear Decay Rate Constancy 95
As_I_Please writes "Scientists at the US National Institute of Standards and Technology and Purdue University have ruled out neutrino flux as a cause of previously observed fluctuations in nuclear decay rates. From the article: 'Researchers ... tested this by comparing radioactive gold-198 in two shapes, spheres and thin foils, with the same mass and activity. Gold-198 releases neutrinos as it decays. The team reasoned that if neutrinos are affecting the decay rate, the atoms in the spheres should decay more slowly than the atoms in the foil because the neutrinos emitted by the atoms in the spheres would have a greater chance of interacting with their neighboring atoms. The maximum neutrino flux in the sample in their experiments was several times greater than the flux of neutrinos from the sun. The researchers followed the gamma-ray emission rate of each source for several weeks and found no difference between the decay rate of the spheres and the corresponding foils.' The paper can be found here on arXiv. Slashdot has previously covered the original announcement and followed up with the skepticism of other scientists."
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well, he's not the life of the party...he's the HALF-life!
Not a certain conclusion yet (Score:5, Informative)
So, there still is a chance that there is a deviation.
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"So, there still is a chance that there is a deviation."
Yes, of course. People have been saying that all along. And even with more experiments in the future it will always be the case that a deviation from constancy is possible. However, if there is a deviation, it's vanishingly small and what remains possible is getting smaller as the experiments are refined.
People have been testing the constancy of radiometric decay rates for many decades. Those experiments always have limits in terms of their resolut
Re:Not a certain conclusion yet (Score:4, Interesting)
Those are some pretty big deviations to go with the headline "Scientists Confirm Nuclear Decay Rate Constancy." In any field except physics they would be considered significant evidence of a difference.
Untrue (Score:3, Informative)
Journalism, by the way, is not science. In fact, it is usually the enemy of science.
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I think I have a pretty good grasp of statistics, thanks.
As I explicitly mentioned in my post, you're correct, there are different standards for "statistically significant" in different fields. Contrary to what you think, they're not particularly precise. They're basically rules of thumb and differ between fields, and even within fields, due to tradition, history, and sometimes experience. Note also that I was talking about the Slashdot headline and summary. In fact, I quoted the former. Sorry, I thoug
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It is accurate.
You can't prove that their is a change either. You CAN show that there is certain, arbitrarily small chance that there is (or is not) a change. You are correct, the latter case has to assume a certain minimum magnitude of change but that can also be made arbitrarily small.
The evidence from their four experiments is somewhat contradictory, but two of them show a a p-value of 0.02 or less (that's in the paper, if you care to go look). That's (roughly) a 2% chance that there is no change, and
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I'm not going to bother RTFAing, but this would depend on whether the test is two-tailed or one-tailed, in terms of how to interpret the p value. Because this kind of statistical test ultimately boils down to a simple measure of the observed versus a given expected, it is also only really good at testing against H0, the Null Hypothesis. There are more complex tests which allow you to measure against multiple variables in a single test (a good approach as it, in theory, allows you to examine the interactions
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All in all, however, it seems to me that this experiment used far too little mass to involve many neutrino interactions at all, and thus is very questionable.
I agree... (Score:4, Informative)
This experiment covered only the decay of Gold-198; The ones that were found to be changing were exhibiting electron capture decays, a completely different mechanism.
For such a limited experiment, the claims are grandiose, IMHO.
Neutrinos also oscillate forms; perhaps the emitted form doesn't interact the same way.
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In principle, the emission of a neutrino with some energy E and momentum M should be identical to the absorption of an anti-neutrino of identical energy and momentum. BUT, and this is important, it would have to be absorbed in such a way as to alter the angular momentum of the nucleus by the correct amount. Because ALL of the equations have to match up exactly, it's not merely a matter of a neutrino being in the general vicinity. It has to impact in a way that makes the symmetry complete.
Because the system
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"ALL invalid interactions will result in the neutrino passing by/through the nucleus. This is already known to be virtually all such interactions. Thus, the shape won't significantly alter the number of neutrinos any given gold nucleus would interact with. It might alter it a little, but if the variation in neutrino flux is smaller than the variation in decay events due to shape, your signal just got swamped."
Yes, exactly my point. It appears to me that it would be difficult to measure the differences of something that must be so near zero in the first place. They would have to use a vastly larger amount of mass (think: those massive neutrino detectors elsewhere) to get a sample of any significance.
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Yes, a larger mass would definitely help, as does the sensitivity of the measurements. You can also lengthen the time of the experiment. This is not dependent on the half-life as documented anywhere, except insofar as there has to be enough radioactive material left in all three samples that you can draw useful conclusions. Now, a larger mass only helps to a degree. Remember, after one half-life, half of that mass is gone as far as the experiment is concerned. You have to double the amount of mass to add a
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three locations that we can expect to have different neutrino fluxes. Let's have one at high altitude, say a passenger jet that's going to make a fair number of transatlantic journeys. The second can be in a laboratory. The third, let's put that in a box and have an ROV place it in some deep sea trench
It's possible I'm misunderstanding what you're trying to test, but your experiment appears to be broken. All three samples will have effectively identical neutrino flux. Being the same shape they will have the
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The reason neutrino detectors are underground is that you don't want them to detect any old neutrino. You can indeed shield from -some- neutrinos, and it is my argument that the very fact that you can shield from them makes them interesting. If they are being absorbed, they must presumably do something. The question then becomes one of what do they do. The sorts of neutrinos that affect one chlorine atom per many thousands of moles of the stuff are less interesting. Any effect they have would be too small f
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The reason neutrino detectors are underground is that you don't want them to detect any old neutrino.
Neutrino detectors are put underground to shield out noise from stuff like cosmic rays.
You can indeed shield from -some- neutrinos
A solid lead wall one trillion miles thick would provide less than 10% shielding against neutrinos.
An entire planet will shield 0.000000000% of neutrinos. An entire star will shield 0.00000000% of neutrinos. Nothing short of a black hole will noticeably shield against neutrinos, a
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Assuming the error is normally distributed, 2.3 * sigma is p = 10. They get p=0.02.
In physics I believe the custom is to wait for 3*sigma before you get excited, and 6*sigma before you announce a discovery. In most sciences it's 1.96 (for a reasonable dof) though.
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Just going with the possibility *if* it does maybe the radionuclides radiate at a certain frequency and the shape helps it achieve a resonance where the decay rate is altered.
I'm not qualified to say whether that question even makes any sense, my brother has some relevant qualifications (I'll ask him tomorrow). Surely there is some physicists here who can tell if that is feasible?
Semantism (Score:5, Insightful)
I think the proper phrasing should be "No evidence for inconsistency of nuclear decay found". It seems pedantic, but proper scientific methodology works this way. There
can still be inconsistency in nuclear decay, just not in this test scenario. You cannot prove consistency, you con only be very, very sure this is how nuclear decay works because you performed many studies that have failed to show something else. (Not that I despute their findings).
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To be uber-pedantic they are not claiming proof of consistency. They are claiming the same thing you are, ie: their test rules out nutrino flux as a possible cause for the observations.
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Well, but our nice editors have used the incorrect phrase "Scientists confirm nuclear decay rate consistancy". Just responding to that.
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They did confirm nuclear decay rate constancy. A confirmation is not a proof. It's just what the word says: A strengthening of the claim. It makes you more confident that the claim is true.
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> They did confirm nuclear decay rate constancy.
No. They confirmed that nuclear decay rate is independent of shape.
Re:Semantism (Score:5, Informative)
To be uber-pedantic they are not claiming proof of consistency. They are claiming the same thing you are, ie: their test rules out nutrino flux as a possible cause for the observations.
Not quite, it doesn't rule it out. The observed changes are not large enough to be considered inconsistent with the hypothesis that neutrino flux has no role. With a larger sample or better control of variability, it's still possible that future experiments could reject the hypothesis.
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Since we're already being pedantic... and all good science takes it to the max...
What if the decay-rate inconsistency observed in the previous results is the more sensitive measurement of neutrino flux? Then this would be like saying that a measurement of 1cm doesn't exist because you used a ruler with inches.
tl;dr - OR IS IT??
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Re:Why wouldn't the scientists in this study... (Score:5, Insightful)
You are right, they are purposely avoiding using the same isotopes to avoid observing the phenomenon that caused them to perform this research. "Truly, you have a dizzying intellect." :)
Call me naive, but maybe they had better reasons not to use the same material. I am not a physicist, so I don't know if it's correct, but here are some reasons I thought of, of the top of my head:
1) Gold may have more neutrino activity, so there was a better chance to observe said phenomenon.
2) The scientists involved have more experience working with gold, so they preferred using a material they are experienced with.
3) Gold may be easier to work with and this it is easier to construct thin foils.
4) They had a pile of unused gold and didn't know what to do with it
Again, I don't know if these are valid/correct reasons, but I'm somehow convinced there is a better reason than the one you stated.
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How can they invalidate the orginal experimenter's experiment unless they try to replicate the original experiment?
They weren't trying to invalidate the findings of the original experiment. That was just something Slashdot made up for the heading (I've no idea why). They were investigating whether a particular mechanism could account for the findings of the original experiment.
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Yes, they're not replicating the original experiment, but they are testing the proposed, more general, mechanism -- i.e. that seasonal variations in neutrino flux from the Sun cause variation in decay rates. That's what the original experimenters were wondering about -- does this affect everything? I suppose followup studies could do the same experiment for every element in the period table and every radioactive isotope, including the ones used in the prior experiment, but the fact remains that the new ex
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you may not be a physicist, but you nailed the scientific methodology exactly. Kudos.
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3) Gold may be easier to work with and this it is easier to construct thin foils.
This. Gold is a phenomenally ductile metal -- ideal for making the thin foils typically used in preparing radioactive sources. If you want a radioactive source, the easiest thing to try (broadly speaking) is electroplating your nuclide of interest on a gold substrate. Then all your measurements require you to take the shielding properties of gold into account, but that's not usually too big a deal.
I am a nuclear physicist (grad student), and one of the key issues we have to deal with is sample preparation.
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...4) They had a pile of unused gold and didn't know what to do with it :)...
You may have been trying to be funny, but perhaps it is simply the cheapest material to work with.
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How big? (Score:4, Insightful)
How big were the foil and spherical samples? Neutrinos interact very weakly, so much so that neutrino detectors need to be on the order of 1 km^3.
Heck, if I had that much gold (whatever isotope) I'd have better ways to spend my time.
Re:How big? (Score:5, Interesting)
The effect might be different for different decays, so the hypothesis isn't completely dead. Now, if they made an alloy of gold-198 and the isotopes that is claimed to change decay rate...
Re:Well maybe its something else coming from the s (Score:5, Funny)
That's crazy talk. Everyone knows that the answer to all astrophysics problems is "11-dimensional dark matter particles".
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I call bull'... It's turtles, turtles all the way down!!
Re:Well maybe its something else coming from the s (Score:2)
Only at night.
Only if it's neutrinos. (Score:5, Insightful)
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Right. One must remember that the original article did not assert that solar neutrinos were cause. They merely speculated that they might be.
Variations in time rather than decay? (Score:2, Interesting)
Could it be that there are local variations in time during the original solar flare observations rather than fluctuations in the actual decay rate, and that it is not related to neutrinos from the flare but from some other gravitational changes coupled with flares?
I know, my ignorance is showing. Sorry. IANASH (I am not a stephen hawking)
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I'd guess any variation in time so large that you can see it in decay time measurements would have created so many other clearly visible effects that it would not have gone unnoticed.
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I suppose that's true if they were observable or more importantly if they were being searched for. But if nobody was looking for them they could have been missed.
What else would one look for?
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And furthermore, this would be an excellent conversation to have with beer.
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The atomic clocks which form the base of our official time are constantly monitored, and they are far more precise than any decay time measurement can be. I doubt any major disturbance in time would have gone unnoticed.
Moreover effects in time should go with gravitational effects. Note that the earth's gravity only has an effect on time of about 1e-16 per meter, and that already gives a clearly noticeable gravitational force. I couldn't find anything about the size of the effect, but the accuracy of the exp
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I'd guess any variation in time so large that you can see it in decay time measurements would have created so many other clearly visible effects that it would not have gone unnoticed.
What would be the most striking?
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Objects mysteriously moving around due to the gravitational fields connected with such time variations.
I want one. (Score:1)
A Gold-198 foil hat, to keep the neutrinos out...
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So really... this means? (Score:1)
I hate to be THAT person, but what does this mean for us normal humans? Does it mean anything at all?
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"Normal humans"? This is Slashdot. If you don't find science intrinsically interesting you don't belong here.
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Oh i find it intrinsically interesting.
I was just wondering if it had any real world implications, which as i have read other people's comments, was noted as to the accuracy of dating methods.
Thats all. Science IS cool, i just wanted to know if this actually had any significance, or just one of those cool but non significant things science brings around ya know.
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Knowing whether radioactive decay rates are constant goes to our fundamental understanding of matter. How does that not have significance??
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It means there's no new physics at this point. So also no hope to exploit that new physics in new technology (e.g. to deal with nuclear waste).
On the positive side, it means that we don't have to expect nasty surprises from this new physics for our existing technologies (e.g. we don't have to expect that an extraordinary large solar flare suddenly makes a nuclear reactor fail, or something like that).
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On the positive side, it means that we don't have to expect nasty surprises from this new physics for our existing technologies (e.g. we don't have to expect that an extraordinary large solar flare suddenly makes a nuclear reactor fail, or something like that).
Umm, we didn't know that already? Oh dear. "New physics" had better not turn out to be an excuse for why we all suddenly glow in the dark, while it still isn't the nuclear power industry's fault.
--M
(PS - I love nuclear power, but I'm always a sceptic about our confidence when predicting unforeseen consequences.)
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I'm not. I'm quite confident of our inability to predict unforeseen consequences, because if we did predict them they would not be unforeseen. On the other hand I am also quite confident about our ability to predict that every act (or inaction) will have unforeseen consequences. Fortunately, most are not consequential.
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Not enough time (Score:2)
Re:Not enough time (Score:4, Insightful)
They're investigating the hypothesis that it's neutrinos that cause the variation. Did you even read the summary, or just the sensationalistic headline?
Radioactive decay variations (Score:3, Interesting)
This study provides strong evidence against solar neutrino flux being the reason for observed variations in radioactive decay. However, it does not provide evidence against those variations -- nor was it designed to. The measurements still need to be explained; there have been reports of changes in radioactive decay during solar flares, and also seasonal variations; most likely IMO they're some sort of systemic measurement error, but maybe not.
Also note that the idea that decay rates might be affected by particle flux or shape isn't all that farfetched. Fission rates in certain isotopes are, for instance.
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The process that produces fission is well understood, and the reasons why shape should play a role are well understood. If source shape affects decay rates it would be something very unexpected.
Neutrino oscillations? (Score:3, Informative)
The study overlooks neutrino oscillations, the neutrinos from the gold have had little chance to oscillate. While it is probable that neutrinos don't affect decay rates, the study isn't as conclusive as the summary makes it out to be.
The decay rate for electron capture is mildly affected by pressure.
How can they do such an experiment? (Score:2)
IANAphysicist, but everything I've heard about neutrinos is along the lines of "they pass through the entire Earth with a very small chance of hitting anything". This makes me wonder how you can measure any kind of effect involving neutrinos, in a sample that isn't the size of an underground cavern full of water. Certainly they don't have a chunk of gold that big, or does gold have unusually high neutrino-interacting properties? How long does the experiment have to run? How sensitive is the whole setup a
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You are right - neutrinos can pass through a lot of matter without the matter affecting the neutrino, or the neutrino affecting the matter. Or so we think. A couple of people noticed that the apparent decay rates were different during a solar flare, which could mean there may be strange circumstances where the neutrinos had more effect than we expect. Or it could have been something other than neutrinos, if our understanding is that far off. I didn't think that was likely, but it doesn't hurt to test your a
FAQ (Score:2)
FAQ: Do rates of nuclear decay depend on environmental factors?
There is one environmental effect that has been scientifically well established for a long time. In the process of electron capture, a proton in the nucleus combines with an inner-shell electron to produce a neutron and a neutrino. This effect does depend on the electronic environment, and in particular, the process cannot happen if the atom is completely ionized.
Other claims of environmental effects on decay rates are crank science, often quote
Gold 198 emits antineutrinos, (Score:1)
...while the Sun, through proton-proton fusion, emits neutrinos. If solar neutrinos do affect radioactive decay, maybe it's because of the difference between neutrinos and antineutrinos?
What it really confirms... (Score:2)
Ignoring the noted discrepancies (which may mean the experiments don't confirm anything), the experiment as designed confirms only that neutrino flux -- of the type of neutrinos emitted by Au-198 decay -- does not affect the decay rate of Au-198.
One could generalize this further to say that (Au-198) neutrino flux doesn't affect beta decay, but that's only one type of decay ... and one flavor of neutrino. (Neutrinos come in three flavors, plus their antiparticles. Beta decay actually produces electron anti
Headline is wrong (Score:1)
And with the short half life of gold 198, it's hard to believe they even proved that. I work with it on a daily basis, as an integrating neutron detector for my fusor (normal gold 197 picks up a neutron in a moderated neutron oven and becomes radioactive). It's fairly numb compared to say, Silver or Indium, but a little longer lived so
Headline is wrong (Score:2)
The experiment doesn't address the larger question of variable decay rate, nor was it designed to. Instead, it indicates that if there is a variability, it probably isn't caused by neutrino flux. That is, in itself, a useful (non)result.