From: John Woodgate
Subject: Re: eer
Date: Thu, 31 Oct 2002 06:00:57 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Thu, 31 Oct 2002 20:55:37 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that StevJensen
wrote (in <email@example.com>) about 'eer', on
Thu, 31 Oct 2002:
>>wrote (in <firstname.lastname@example.org>) about 'eer', on
>>Wed, 30 Oct 2002:
>>>For how long would it be more energetically active?
>>>You note that the energetic isotopes have short half lives.
>>The well-known 10000 years is in the right ball-park.
>At best that seems to be a grand oversimplification.
>The charts I have seen show uSec, hours and days for many isotopes.
>When you get up in the 10k year range then they seem to prevalent
>in the environment anyway. (i.e.: Natural - another buzz word)
It couldn't be anything BUT a simplification, given the large number of
radionuclides present. The times given in your chart are HALF-LIVES. To
reduce the amount present to negligible takes many half-lives. 1 kg
gets to 1 ug after 30 half-lives.
>Well, there might be an issue with getting a 10kg brick to my desk in the
>first place. But for say a 10g sized block, if I tossed a sheet of tin foil
>over it (or even if I didn't) would there be a real reason to care as long as I
>avoided direct contact?
Tinfoil doesn't stop gammas, and doesn't stop high-energy betas. Pu239
is an alpha and gamma emitter, but its decay products produce betas as
>In other words how close would a measurement
>probe have to get before it recognized a level above background?
>A 1/4 inch, an inch, a foot, 10 feet?
I don't have that information.
>I wore a radium watch for years. That would bury a probe at 1/4 inch,
>and was recognizable out to a couple inches.
>Interestingly enough my arm hasn't fallen off yet.
The metal of the watch is thick enough to stop alphas and most betas.
Ra226 (half-life 1602 years) is an alpha and weak gamma emitter.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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