[Phys-L] Re: Survey Meters

[betwys1 at SBCGLOBAL.NET (Brian Whatcott)]

At 11:46 AM 10/19/2005,  John M., you wrote:

> The result of the two beta decays from initially stable populations
> of Pb-214 and Bi-214 produces radiation with an approximately 40
> minute half life.  I constructed a simple spread sheet to model the
> decay sequence and it produced a graph of beta production versus time
> that very nicely matches the Buda figure.
>
> --
> John "Slo" Mallinckrodt

If instead of using a spreadsheet, I synthesize the effect
of a double decay cascade like this,
where the first species decays at one third the rate of
  the daughter species,......

   'exponential decay of double series
     count = 1000
     for a = 1 to 1000
     count = count*0.99
     count2 = count* 0.97
     print a; " " ;count; " "; count2
     next a
     end

... a single exponential of this form:
count2 = 970* exp(-0.001005 *a)

leads to a fit with exceptionally good statistics
anovar: F = 9.6E20, SE estimate = 1.4E-7
using just a single exponential equation.

Therefore, I expect I am misunderstanding some prior comments
about the possibility of pulling details of a double decay out of an
exponential time series. I cannot do this.
Or was my synthetic dataset faulty?


Brian Whatcott    Altus OK    Eureka!