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: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.

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.

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.

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