> For space use we are looking at using devices resistant to 300k rad for
low
> earth orbit, and expect the instrument lifetime to be something like 5
> years. However the radiation does get tempered by being in an aluminium
case
> which does some shielding.

How well shielding works depends very much on particle energies. Cobalt 60
is about as bad a gamma emitter as you would normally encounter and requires
1.5cm of lead to halve the intensity whereas something like americium needs
only about 0.01mm.

A rather good but disturbing Radiation Safety Training Manual

        http://www.ehs.ucsf.edu/Manuals/RSTM/TableOfC.htm

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