Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!


Forgot your password?

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."
This discussion has been archived. No new comments can be posted.

Scientists Confirm Nuclear Decay Rate Constancy

Comments Filter:
  • 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: (Score:3, Insightful)

      Yup, that's the nature of statistics. In order to "call" the result with a reasonable level of certainty the sample size requirements increase with smaller signal/noise ratios.
    • Re: (Score:2, Interesting)

      by Anonymous Coward

      "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

    • by ceoyoyo ( 59147 ) on Saturday September 25, 2010 @11:05AM (#33696786)

      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)

        by Kupfernigk ( 1190345 )
        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.

        • Re: (Score:3, Insightful)

          by ceoyoyo ( 59147 )

          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

        • It doesn't matter anyway. This experiment does not show what the headlines of both OP and TFA claim. It does not reaffirm "constancy"; rather (if there is any significance to it at all) it only indicates that neutrinos are probably not the cause of observed fluctuations.

          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)

            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 jd ( 1658 )

              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

              • "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.

                • by jd ( 1658 )

                  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

              • by Alsee ( 515537 )

                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

                • by jd ( 1658 )

                  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

                  • by Alsee ( 515537 )

                    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

    • by MrKaos ( 858439 )

      These results thus leave open the possibility that the half-life of a radioactive nuclide could in fact depend on its shape

      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)

    by Kilrah_il ( 1692978 ) on Saturday September 25, 2010 @05:25AM (#33695660)

    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: (Score:1, Redundant)

      by TapeCutter ( 624760 ) *
      "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"

      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.
      • Re: (Score:3, Interesting)

        by Kilrah_il ( 1692978 )

        Well, but our nice editors have used the incorrect phrase "Scientists confirm nuclear decay rate consistancy". Just responding to that.

        • Re: (Score:2, Insightful)

          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.

          • > They did confirm nuclear decay rate constancy.

            No. They confirmed that nuclear decay rate is independent of shape.

      • 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.

        • 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??

    • by Demena ( 966987 )
      No. They have no conclusion on consistency. Only that (they say) it is not caused by 'neutron flux'. However their study does not seem to do even that as there has been no defined mechanic. WIthout a hypothesised mechanic then not test is of much value as it only eliminates one possible mechanism.
  • How big? (Score:4, Insightful)

    by srussia ( 884021 ) on Saturday September 25, 2010 @05:39AM (#33695690)
    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? (Score:5, Interesting)

      by sFurbo ( 1361249 ) on Saturday September 25, 2010 @05:58AM (#33695736)
      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...
  • by Israfels ( 730298 ) on Saturday September 25, 2010 @06:52AM (#33695816)
    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: (Score:3, Informative)

      by John Hasler ( 414242 )

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

  • 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)

    • Re: (Score:3, Interesting)

      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.

      • 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?

        • And furthermore, this would be an excellent conversation to have with beer.

        • 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

      • by jasticE ( 196565 )

        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?

  • A Gold-198 foil hat, to keep the neutrinos out...

  • I hate to be THAT person, but what does this mean for us normal humans? Does it mean anything at all?

    • "Normal humans"? This is Slashdot. If you don't find science intrinsically interesting you don't belong here.

      • 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.

        • by kmcarr ( 1185785 )

          Knowing whether radioactive decay rates are constant goes to our fundamental understanding of matter. How does that not have significance??

    • 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).

      • by Megaport ( 42937 )

        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.


        (PS - I love nuclear power, but I'm always a sceptic about our confidence when predicting unforeseen consequences.)

        • ...I'm always a sceptic about our confidence when predicting unforeseen consequences.

          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.

    • Re: (Score:2, Insightful)

      by axedog ( 991609 )
      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.
      • I may be wrong, but I would expect other uncertainties to play a more dominant role in radiometric dating. The initial concentration of the measured isotope, for instance, or the possibility of contamination.
    • Re: (Score:1, Interesting)

      The constancy of nuclear decay rates is a fundamental assumption for our understanding of stellar processes, big bang theory and the like. If someone can prove a deviation, it will break just about every cosmological model. If they had found a deviation, the implications could be comparable to what Copernicus did, so I believe this does mean something for the "normal human"...
  • The variation in decay rates is said to have two cycles; a yearly fluctuation, and a 33-day cycle (proposed first because that's the rotation of the sun's core, THEN found in the data). These experiments should have been run for at least 66 days, preferably for more than two years, before making claims that this has anything at all to do with the effects that have been observed so far. They can't even say that gold-198 displays evidence of the phenomenon they are trying to measure. This experiment cannot pr
  • by russotto ( 537200 ) on Saturday September 25, 2010 @10:38AM (#33696634) Journal

    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.

    • by ceoyoyo ( 59147 )

      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.

    • 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.

  • 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

    • Re: (Score:3, Informative)

      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: 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

  • ...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?

  • 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

  • All they proved is that neutrinos created by decaying gold 198 don't seem to affect the decay rate of gold 198. The variable decay rate issue is still alive and kicking.

    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

  • 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.

1 1 was a race-horse, 2 2 was 1 2. When 1 1 1 1 race, 2 2 1 1 2.