Cosmic Radiation

--- In spacesettlers@yahoogroups.com, Al Globus wrote:
>
> On Tuesday, September 23, 2003, at 12:07 AM, Andy Goddard wrote:
>
> > Al wrote:
> >
> >> For radiation protect similar to Earth you need twice the mass
of the
> >> atmosphere per unit surface area. You need 2x since the Earth
blocks
> >> almost all cosmic radiation coming from below so the dosage
coming
> >> from
> >> any one direction needs to be cut in half.
> >
> > Ummm...if I'm on the inside surface of a cylinder, I can presume
that
> > the
> > stuff "above" my local horizon is similar/greater in density
than that
> > which is below my feet, so surely the minimum thickness that's
> > important
> > here is the cylinder materials?
> >
> > Which, if I take a realistic atmospheric scale height (8.4km)
and
> > density
> > (1.225 kg/m3), means I only need 10 tonnes of "stuff" per square
metre
> > for
> > decent protection. Say 4m of concrete, 10m of ice...
>
> I come up with (approximately) the same number.
>

But according to the Earth Blocking maxim, shouldn't your number be
twice the above quoted numbers, as Andy points out in his following
message?

If your number is correct, then where did I go wrong in my
calculations in my previous post?

TangoMan