Re: Decay-In-Storage

[Franz Schoenhofer <schoenho@via.at>]

At 09:30 19.04.2000 -0500, you wrote:
>          A related question I have asked before and not had answered is why 
>          is it 10 half-lives?  Why not 8 or 12?
>          
>          Does anyone know how this "standard" decay time was determined?

After 10 half-lives, the activity will have decayed to 1/1024th of the
original activity, which is very close to 1/1000th. This is probably a
magic number.... But there is a difference whether you let decay 1 Bq or 1
TBq! The rest from the TBq will still be considerably high, but one mBq is
not so much. For radiation safety purposes I would recommend to use
absolute numbers and not relative ones like "1 permille".

We used the principle of decay after the Chernobyl accident in Austria.
Milk, containing I-131 above the limit was diverted and used to manufacture
cheese. Cheese must ripen for a long time, depending on the type of cheese
it might be up to six months and more. Since I-131 has a half life of 3.8
days you can imagine that in the cheese no I-131 was detectable. Applied
Decay-In-Storage!

Franz


Franz Schoenhofer
Habicherg. 31/7
A-1160 Vienna
Austria
Tel.: +43-1-495 53 08
Fax.: same number
mobile phone: +43-664-338 0 333
e-mail: schoenho@via.at


Office:
Hofrat Dr. Franz Schoenhofer
Federal Ministry of Agriculture, Forestry, Environment and Water Management
Radiation Protection Department (BMLUW I/8 U)
Radetzkystr. 2
A-1031 Vienna
AUSTRIA

phone: -43-1-71172-4458
fax: -43-1-7122331

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