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."

Comments

Not a certain conclusion yet

[BSAtHome]

From the paper (emphasis mine):

In summary, the present experiment is the first direct precision test of whether the decay rate of a radioactive source depends on its shape. Our results in Table 1 indicate a 2.3 deviation of the foil/sphere ratio in experiment 1 from unity. From Table 2, based on the initial 30 spectra, the foil/sphere ratio for experiment 2 deviates from unity by 2.6. These results thus leave open the possibility that the half-life of a radioactive nuclide could in fact depend on its shape (due to the internal flux of neutrinos, photons, or electrons), and hence suggests that additional experiments are necessary.

So, there still is a chance that there is a deviation.

Re:Not a certain conclusion yet

[ceoyoyo]

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.

Semantism

[Kilrah_il]

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).

Re:Semantism

[Frequency Domain]

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.

How big?

[srussia]

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.

Re:How big?

[sFurbo]

The change in neutrino flux due to shape was bigger than the neutrino flux from the sun is, so it must be much bigger than changes in the solar neutrino flux (if I read the summary correctly). If that change in neutrino flux does not induce a measurable change in the rate of decay, then neither will the solar neutrino flux. I think it is a very elegant experiment, testing just what the hypothesis said.

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...

Only if it's neutrinos.

[Israfels]

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.

Re:Why wouldn't the scientists in this study...

[Kilrah_il]

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.

Re:Well maybe its something else coming from the s

[CarpetShark]

That's crazy talk. Everyone knows that the answer to all astrophysics problems is "11-dimensional dark matter particles".

Re:Variations in time rather than decay?

[maxwell demon]

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.

Re:Why wouldn't the scientists in this study...

[Anonymous Coward]

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.

Re:Not enough time

[ceoyoyo]

They're investigating the hypothesis that it's neutrinos that cause the variation. Did you even read the summary, or just the sensationalistic headline?

I agree...

[Grog6]

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.

.