terror via radioactive dispersal

[Sonter Mark <sonterm@EPA.NSW.GOV.AU>]

Some people have been debating whether a stolen industrial source wrapped

with explosives could feasibly cause mischief.



It could certainly cause serious damage from the explosive, and create a

significant decontamination task, of that there is no doubt....but I thought

I might try to estimate potential radiation doses and hence health risks

from such... 



So, here's a little calculation of possible doses to emergency responders or

to members of the public:





Assume a stolen industrial Cs-137 source (e.g. from a density gauge) of

Activity 100 200 millicuries (= 3.77.4 GBq) -- i.e., a fairly big source: to

get anything much bigger, you'd probably have to knock off a radiotherapy

source. (I've seen a 500 mCi source from a molten steel density gauge that

wasn't much bigger than an earplug, but even 5x of your final calculation,

it doesn't obscure that the risk is trivial.



Assume it is exploded and all the caesium disperses as five-micron powder

into a 100m * 50m * 50m cube volume of air (e.g in a large building such as

a shopping mall) as a fine respirable powder. 



This implies an in-air concentration of (7.4 * 1094000 * 250,000) = 30,000

Bq/m3. 

Does a "100 m" cube mean 100m x 100m x 100m? (HUGE building!) If so, that

would be a concentration of 40 Bq/m3, not 4000, which would have the effect

of lowering your final result even further.  However, a building with 100 m3

of volume would yield 400,000 Bq/m3 which would have the effect of turning

your mSv amounts to mSv  It appears that you squared the 100 instead of

cubing it...



IAEA BSS Tables II-III and II-VII indicate dose per unit activity by

inhalation for Cs-137 is in the order of 5 * 10-9 Sv/Bq.



So a person breathing the contaminated air for 1 hour (without respiratory

protection) will incur about

(1 m3 * 4000 30,000 * 5 * 10-9 ) Sv or 20 150 microsieverts.  --Which is

trivial in this context!

So we can say that any injuries or deaths will be from the explosive blast

or from the panic, and not from the radiation dose.

Mark Sonter 







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