RE: Color TV screens as radon daughter collectors

[alstonchris@netscape.net]

Sir



Everyone has access to all the messages in this string at all times.  And, no, I didn't "confirm what you just said".  What you said was that "the radon decay series is the longer lived (approx 4 days) and thoron is the shorter lived decay series.  The discussion has, since its inception, borne upon radon and thoron *daughters*, not the parents per se.  It is certainly true that "radon" (Rn-222) is a daughter of U-238, while "thoron" (Rn-220) is in the thorium (Th-232) decay chain. Hence its historical name, I would guess.  Anyway, this sort of misunderstanding is exactly why I provided the actual half-lives, i.e., so that people can make their own assessments of the rather gnarly relative proportions of the nuclides of interest.



Cheers

cja





Jeffries Cameron <jeffriesc@epa.nsw.gov.au> wrote:

>So you have just confirmed what I said. Thanks for that. 

>I have worked in a uranium mine and am very familiar with the uranium-238

>decay series. But thank you for telling those half-lifes.

>

>I see that you deleted the original message where you stated that Radon had

>the short half life and thoron the long half-life. NB Radon and Thoron were

>the terms you used and it is generally accepted that radon is part of the

>U-238 series and thoron is not.

>

>

>

>

>-----Original Message-----

>From: alstonchris@netscape.net [mailto:alstonchris@netscape.net]

>Sent: Wednesday, 20 November 2002 3:48 AM

>To: jeffriesc@epa.nsw.gov.au; radsafe@list.vanderbilt.edu

>Subject: RE: Color TV screens as radon daughter collectors

>

>

>Well, *radon's* half-life is 3.8 d.  But, here are its first four (4)

>daughters (of more than 0.1% abundance), with half-lives parenthesized:

>Po-218 (3 m), Pb-214 (27 m), Bi-214 (20 m), Po-214 (164 us). Pb-210 is next,

>but, given its 22 y half-life, there's clearly not a great deal of time for

>ingrowth, in this context.

>

>Now, *thoron's* half-life is 56 s.  So, most of the time it's not a problem,

>because it decays before it can escape the soil, to spread daughters.  But,

>the daughters', and half-lives, are: Po-216 (0.15 s), Pb-212 (10.6 h),

>Bi-212 (61 m), Po-212 (305 ns), Tl-208 (3.1 m), Pb-208 (stable).  So, you

>see some weird ingrowth curves, and counts from thoron daughters will

>actually increase, in the short term after sampling, instead of decreasing,

>like those of radon daughters.

>

>Note: all the decay data above are from the 3rd edition of the Rad Health

>Handbook.

>

>Cheers

>cja

>

>

>Jeffries Cameron <jeffriesc@epa.nsw.gov.au> wrote:

>>Actually you have it round the wrong way. The radon decay series is longer

>>lived (approx 4 days) and thoron is the shorter lived decay series.





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