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RE: Time needed for Rn-222 daughters to reach equilibrium with theirparent?
Thanks, Kal. Much appreciate! Steve x3839
-----Original Message-----
From: Kai Kaletsch [mailto:eic@shaw.ca]
Sent: Wednesday, January 14, 2004 4:15 PM
To: Franz Schoenhofer; Frey, Steven R.; radsafe@list.vanderbilt.edu
Subject: Re: Time needed for Rn-222 daughters to reach equilibrium with theirparent?
Franz and Steve,
We usually let radon progeny grow in for 3 hours to reach an equilibrium factor of 0.99. Theoretically, ten half lives would bring the daughter to 99.9% of the parent activity (1-2^-10=0.999). In the case of radon progeny, we have to consider that Bi-214 follows Pb-214 and they have similar 1/2 lives, so it takes a bit longer to grow in than just a single daughter.
We have put a program on the web that, among other things, calculates the equilibrium factor as a function of time. It is at: http://members.shaw.ca/eic/Tools/RoomRadonTime.htm
Keep in mind that the calculation is done numerically in 15 second time increments, so there is an inherent error and equilibrium factors >1 are reported after long decay times. Hope this helps,
Kai
----- Original Message -----
From: "Franz Schoenhofer" <franz.schoenhofer@CHELLO.AT>
To: "Frey, Steven R." <sfreyohp@SLAC.STANFORD.EDU>; <radsafe@list.vanderbilt.edu>
Sent: Wednesday, January 14, 2004 2:32 PM
Subject: AW: Time needed for Rn-222 daughters to reach equilibrium with theirparent?
>
>
> -----Ursprüngliche Nachricht-----
> Von: owner-radsafe@list.vanderbilt.edu
> [mailto:owner-radsafe@list.vanderbilt.edu]Im Auftrag von Frey, Steven
> R.
> Gesendet: Mittwoch, 14. Jänner 2004 20:23
> An: RADSAFE (radsafe@list.vanderbilt.edu)
> Betreff: Time needed for Rn-222 daughters to reach equilibrium with
> theirparent?
>
>
> Dear Radsafers -
>
> How long does it take Radon-222 daughter products to reach equilibrium
with
> their parent,
> assuming one starts with only Radon-222 gas (no daughters yet having
> begun ingrowth)?
>
> -------------------------------------------
>
> Steve,
>
> Provided that the parent nuclide is longer-lived than the daughters as
> a rule of thumb more than 99% equilibrium will be reached after ten
> half-lifes. I suppose you are looking at the s h o r t -lived
> daughters
of
> Rn-222. The short-lived daughter with the longest half-life is Pb-214
> with 26.8 minutes half-life, so the time required will be
> approximately 270 minutes. The system has to be closed and
> undisturbed.
>
> Best regards,
>
> Franz
>
>
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