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Scientists Confirm Nuclear Decay Rate Constancy 95

Posted by timothy
from the was-just-the-one-time-I-swear dept.
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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Scientists Confirm Nuclear Decay Rate Constancy

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  • by BSAtHome (455370) on Saturday September 25, 2010 @05:23AM (#33695658)
    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 (Score:5, Informative)

    by Frequency Domain (601421) on Saturday September 25, 2010 @06:26AM (#33695784)

    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.

  • by Anonymous Coward on Saturday September 25, 2010 @08:02AM (#33695998)

    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.

  • by Anonymous Coward on Saturday September 25, 2010 @09:35AM (#33696346)

    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.

  • by John Hasler (414242) on Saturday September 25, 2010 @10:39AM (#33696646) Homepage

    Right. One must remember that the original article did not assert that solar neutrinos were cause. They merely speculated that they might be.

  • by calidoscope (312571) on Saturday September 25, 2010 @11:19AM (#33696860)

    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.

  • Untrue (Score:3, Informative)

    by Kupfernigk (1190345) on Saturday September 25, 2010 @11:27AM (#33696910)
    It seems you do not understand the nature of statistics. "significant evidence" is a statistical measure for which there are well-defined measurements. In any field of science, including social science like polling, "significant" has a precise meaning. In this case, the difference was not significant.

    Journalism, by the way, is not science. In fact, it is usually the enemy of science.

  • I agree... (Score:4, Informative)

    by Grog6 (85859) on Saturday September 25, 2010 @01:00PM (#33697420)

    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.

    .

  • by Richard Kirk (535523) on Saturday September 25, 2010 @02:40PM (#33697920)

    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.

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