[Phys-L] Re: Survey Meters

[betwys1 at SBCGLOBAL.NET (Brian Whatcott)]

At 11:46 AM 10/19/2005,  John M., you wrote:
> Brian writes:
>
> > I see there is a URL for a time series for a
> > radon wipe at Buda, Texas  taken 2 or 3 years ago.
> >
> >     <http://home.austin.rr.com/cthompson15/GM10.JPG>
> >
> > ... I am  missing the obvious.
> > The half life of radon is 3.8 days, and this half life
> >   is about 40 minutes.....
>
> My guess is that the meter is recording the rate of beta decay from
> an initially stable population of Po-218 created by the alpha decay
> of Rn-222 in the air.   When the replenishing Radon source is
> removed, the Po-218 quickly (3 minute half life) alpha decays to
> Pb-214.
>
> The Pb-214 beta decays to Bi-214 with a 27 minute half life and the
> Bi-214 beta decays to Po-214  with a 20 minute half life.  The Po-214
> very quickly (0.2 ms half life) alpha decays to Pb-210 which is
> relatively stable (22 year half life).
>
> 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
>
> Professor of Physics, Cal Poly Pomona
> <http://www.csupomona.edu/~ajm>
>
> and
>
> Lead Guitarist, Out-Laws of Physics
> <http://www.csupomona.edu/~hsleff/OoPs.html>


Thanks to John for confirming the Uranium series route.
Once upon a time, in Rutherford's day in fact,
218 Po was Radium A
214 Pb was Radium B
  214 Bi was Radium C
214 Po was Radium C'
210 Pb was Radium D
210 Bi was Radium E
210 Po was Radium F
206 Pb  was Radium G

I notice the sequence 214 Pb (26.8 min HL)
through   214 Bi  (19.7 min HL) provides a
composite  39.1 min HL in my estimate.

Reminds me of the banker's puzzle:
would you rather have 10 % accrued annually, or
5% accrued six-monthly?

I have HL figures for Pb 210 as 20 yr or 19.4 yr in
various old sources rather than John's 22 yr.
I see that 22.3 yr is the value presently ascribed....

This URL has an interesting survey of check sources used on
survey meters.
<http://www.orau.org/ptp/collection/civildefense/checksources.htm>


Brian Whatcott    Altus OK    Eureka!