Slashdot Mirror
Scientists Confirm Nuclear Decay Rate Constancy
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."
So, there still is a chance that there is a deviation.
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).
Whenever in an argument, remember this.
From TFA:“There are always more unknowns in your measurements than you can think of,” Lindstrom says.
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.
Set your phasers on "funky"!
This, of course, is only true under the assumption that it's the neutrinos that are really causing the increase in radioactive decay. The article does mention that there were many unknowns in the measurements. It may be something else that causes this increase, or even a combination of two. It may also be the case that more neutrinos, the rate at which they're emitted, or other interacting fields alter the effect.
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.
Whenever in an argument, remember this.
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)
That's crazy talk. Everyone knows that the answer to all astrophysics problems is "11-dimensional dark matter particles".
It would seem that they started with the simple experiment. If there had been an effect here, no need to go and do the complicated experiment. Now that there weren't an effect, make the same experiment, but with an alloy of gold-198 and manganese-54, and only measure the decay of manganese. Of course, just the proximity of gold-198 should be enough, so perhaps layers of foil of gold and manganese? Anyway, these experiment are more complicated to carry out, so it makes perfect sense to start with the simple experiment.
well, he's not the life of the party...he's the HALF-life!
rewriting history since 2109
It is of huge significance in radiometric dating. If we can show that the half-life of a radioisotope is constant, then it increases confidence in these dating methods. Conversely, if it can be shown that decay rates vary significantly, then accurate dating becomes more difficult and merits further research.
Sent from my Tianhe-2 (MilkyWay-2).
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. The bleeding-edge is thin carbon foils, but that's expensive and tricky and takes a long time. If you want a sample quick, you use a gold substrate. No conspiracy here, folks.
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.
They're investigating the hypothesis that it's neutrinos that cause the variation. Did you even read the summary, or just the sensationalistic headline?
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.
A Shadeless room is a brighter room.
Journalism, by the way, is not science. In fact, it is usually the enemy of science.
From scarped cliff or quarried stone she cries "A thousand types are gone, I care for nothing, no not one."
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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Truth isn't Truth - Guliani
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 assumptions once in a while.
The trouble with original measurements were that they could not easily be repeated. You could wait for the sun to have another significant outburst, and see whether the same detectors measure the same pulse, but you could never be sure whether that burst happened to put out a 'clump' of neutrinos in a particular direction. However, they designed a much neater experiment. This used a gold isotope that emits neutrinos when it decays. Some of it was made into a foil and some was made into a ball. You could then measure the foil with one detector and the ball with another, and then you could swap the detectors around. If this experiment is done properly then this could cancel out any difference in the detectors or the measuring environment or the background neutrino flux (if that is important).
If you design experiments, you get to appreciate the forms of really good experiments: they have a canon-like symmetry to balance out all the known and unknown effects you can imagine except for the one you are trying to measure. This feels like one of them. So, in the end, science wins. Yay.