Re: Time needed for Rn-222 daughters to reach equilibrium withtheirparent?

[Kai Kaletsch <eic@shaw.ca>]

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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