Radioactive decay rates vary during the year

[silverpig]

Article at /.

The paper on arxiv is linked in the article. Basically the gist is the researchers measured the decay rate of several radioactive isotopes over a long period of time and found that the decay rates varied with a period of 1 year. There's a plot showing the sine dependence of the decay rates measured and the 1/(sun-earth distance)^2 sine curve. There's a phase difference which an astute slashdotter commented:

If that red line is accurate, then the graph looks less like an out of phase correlation with earth sun/distance, and more like an in phase correlation with earth/sun relative velocity.

Maybe it could be a relativistic effect? It's an interesting observation.

 

[Rubycon]

Originally posted by: silverpig


It's an interesting observation.

Absolutely. Nothing is really constant.

 

[silverpig]

Well my wife works for the MOST project (space telescope that looks for periodic variability in stars), and they get all sorts of signals in their fourier transforms that they have to throw out. Typically any signal with a period that's an integer multiple of a year, a day, or 1.whatever hours (the orbital period of the telescope) are just thrown out. Having an observation where you measure a period of 1 year for something means you have to do a LOT of work to make sure it's not something in your equipment.

 

[Eeezee]

I was reading about this just the other day. It's a very cool observation.

I remember reading awhile ago about a scientist who was ridiculed by some people on slashdot because he was experimenting with methods to increase/decrease radioactive decay rates. It's a very cool idea, that decay rates can vary (but since they vary depending on time of year, his experiments may have been worthless or at least would have huge error bars)

 

[Gibsons]

Anyone read the whole article?

The abstract:

Unexplained periodic fluctuations in the decay rates of Si-32 and Ra-226 have been reported by groups at Brookhaven National Laboratory (Si-32), and at the Physikalisch-Technische-Bundesandstalt in Germany (Ra-226). We show from an analysis of the raw data in these experiments that the observed fluctuations are strongly correlated in time, not only with each other, but also with the distance between the Earth and the Sun. Some implications of these results are also discussed, including the suggestion that discrepancies in published half-life determinations for these and other nuclides may be attributable in part to differences in solar activity during the course of the various experiments, or to seasonal variations in fundamental constants.

I'm wondering what their speculations are and how much of a variation they're seeing. (?)

edit: scanned through it, they're guessing that it might be neutrino flux. hm.

 

[PowerEngineer]

It might be interesting to look at the decay rate of the plutonium used in the power supplies for the Voyager, Galileo, and Cassinni spacecraft.

 

[Mark R]

Is it proposed that it's is only these particular isotopes that show this variability, or is it only these where it has been detected?

It may a bit like radioactive decay rates that are affected by electron/chemical states, there are only a relatively few isotopes where the effect is detectable (e.g. Tc-99m decay rates vary by up to about 0.15% depending on the chemical compund containing the Tc).

 

[PlasmaBomb]

Do they know why the Tc-99m decay rate varies?

 

[Mark R]

Originally posted by: PlasmaBomb
Do they know why the Tc-99m decay rate varies?

Tc-99m is classically described as a gamma emitter, but the actual decay is slightly more complex. The main decay pathway is a 2 step process:
1. Internal conversion of an M or N shell electron, to yield an unstable intermediate nucleus.
2. Near instantaneous decay of the intermediate by gamma emission.

As the nuclear decay process involves the orbital electrons, the energy barrier to decay is dependent upon the energies of the electrons (and as the energy of the internal conversion is relatively low, the effect of chemical bonds represents a significant proportion of the decay energy at this step).

 

[GarionGoh]

Would that also means that carbon dating is not as accurate as many think it is, kind of like DNA has been found to be not so indisputable?

 

[DrPizza]

Originally posted by: GarionGoh
Would that also means that carbon dating is not as accurate as many think it is, kind of like DNA has been found to be not so indisputable?

No.
First of all, I don't believe the effect is really that large.
Secondly, even with a slight variation, carbon dating can still be calibrated by comparing it to items of a known age.