Re: Drill Scenario (Air shielding)

["Dale E. Boyce" <dale@radpro.uchicago.edu>]

Several have noted that the inverse square law prevents large doses
at ten miles, but no one has pointed out the effect of shielding by
the atmosphere.  Air at STP is 1.29 mg/cm^3 -> 129 g/cm^2/km
which in turn leads to about 2,000 g / cm^2 at ten miles. It doesn't
take many miles at about ten half thickness per kilometer for 1 MeV
gamma rays to be attentuated to safe levels even without the inverse
square law (which helps alot at short distances, but once you are
a kilometer away the next km buys you a factor of four while the
extra shielding buys another factor of 1024.

Also, wrt. heavy gases.  Better check out a good thermodynamics text.
Heavy gases will sink by mass action if contained, but will mix
freely with lighter  gases if released.  Density is a bulk not an
atomic property.  Given no stirring, there will be some mass
separation of heavy gases to lower altitudes, but it is a very
small effect.

Dale Boyce
dale@radpro.uchicago.edu