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 <[email protected]> wrote: > <SNIP> > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
