[time-nuts] Variation in Radioactive Decay Rate with Solar Activity

[Tristan Steele]

Hi All,

I know that I'm not a regular around here - but just a few things to
consider in this discussion.

Whilst measuring the rate of decay in a single detector signal is
representative of the decay rate of an isotope, the errors associated with
doing so are non trivial.  In addition to this, carrying out a measurement
that can actually attribute the effect to something like neutrinos is also a
challenge.

Firstly, the measurement.  In order to carry this out appropriately you
really need to use a primary standard technique for measuring the activity
of the source.  This will assist in removing environmental conditions from
the equation.  This is done using multiple detectors and looking at the
ratio between count rates instead of the absoloute count rate.  The theory
is such that an external variation in background radiation will not modify
this ratio. For more information look into gamma-gamma coincidence or
beta-gamma coincidence techniques of primary standardisation.

Also, in regard to some of the earlier math - there were a few terms
forgotten.  If you have a 1kBq source, then you get 1000 decays per second.
These normally (nearly always) will fill a 4pi (spherical) geometry,
resulting in an inverse square law to the intensity.  This also means that a
standard cylindrical detector will never get more then 50% of the events
passing through it, even if it is directly on top of the source.  There is
also a detection efficiency (that is very strongly a function of energy)
that needs to be considered. It is possible to get near 100% detection, but
this requires using a detector with a hole in it that has a very high
efficiency for the radiation your trying to measure.

After this is considered  you still have potential effects of temperate on
all components in the system, as well as other atmospheric effects that will
effect the system.  If your serious about trying to measure the apparent
effect of neutrinos, all of these effects need to be compensated first.  For
example, sodium iodide detectors make really great thermometers.  This will
shift the peak location in the spectrum - this needs to be countered by
either shifting your window of allowed pulses (which changes the background)
or using a wider window (which increases background effects).

Using a radioactive source and detector as a random number generator is very
possible, but it depends on the degree of randomness that you require.  Any
measurement system will introduce a bias into results due to dead time
effects.  Even the fastest electronics can not compensate for a crystal that
has a slow dead time.  The best systems use ultra fast scintillators, PMT's
and electronics which minimise (not remove) this bias.

Finally, there was another paper(1) published by the same group of people in
October last year that have failed to prove the results, and that was using
measurements inside a reactor where the neutrino flux is much higher then
that we get from the sun.

I'm not saying it's impossible - just that it is not necessarily as simple
as data logging the clicks from a geiger counter. :)

Tristan


(1) R.M. Lindstrom, et. al. Study of the dependence of 198Au half-life on
source geometry, Nuclear Instruments and Methods in Physics Research Section
A, Volume 622, Issue 1, 1 October 2010, Pages 93-96, DOI:
10.1016/j.nima.2010.06.270. (
http://www.sciencedirect.com/science/article/pii/S0168900210014609)

On 4 August 2011 08:28, J. Forster <jfor at quikus.com> wrote:

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