Island 3 Question

victoriatangoman wrote:

>I see reference to O'Neill saying that the Island 3 won't need a
>radiation shield because of its size.
>
>Now, is it safe for me to infer from his statement that the
>thickness of the structural shell will be siz feet of solid metal,
>thus no need for additional shielding.
>
Doesn't have to be metal- rock or soil works fine. Don't forget that
atmospheric pressure is about 10 tonnes per square meter- the density of
1 meter of rock is about 5 or 6 tonnes per cubic meter. So, 1.5 meters
of rock about doubles the thickness of aluminum needed.

>I've seen reference to the Habitat's atmosphere being used as an
>effective shield, but that doesn't make sense to me. Yes, 4 miles of
>atmosphere above your head will probably stop the radiation, but how
>about the radiation that comes from the ground below you. If the
>shell isn't six feet thick, then what's to stop the radiation from
>entering there.
>
Well, most of the radiation won't go to you straight from below- it will
try to hit you from an angle- and the thickness through that angle will
be much greater or be absorbed by the atmosphere above. It's not like a
small space station where you will get irradiated from 6 sides. Straight
away going to an Island 3 you are sort of 5 times better off. Instead of
dying in 10 years from cancer, you may last 60 years... and any mass
below you will make it even slower.

> Also, how about radiation leakage from the windows.
>Any activity near those windows will have radiation leakage. How
>about the poor sap who lives very close to a window - what's to stop
>tangential radiation from striking him. Or lets say its just parks,
>of offices in that location, they'll still have the same radiation
>issues.
>
You could build a wall at the edge of the window to stop this issue of
course but it's not instant death at all. Still, it's a percentage
thing- it depends on the solid angle the window shows to you- the
windows are quite thick- they have to carry 10 tonnes per square
meter... so they are thick and that helps, and provided you don't get
too close the oblique angle will help as radiation has to go through
quite a thickness to get to you.

>The proximity to windows is still a radiation issue even if the
>shell is six feet of solid metal. How thick would the glass have to
>be in order to provide the same protection as six feet of metal?
>
I don't have the figure off hand, I trust O'Neill though. He's eminently
qualified to do the calculation as he's a physicist well qualified in
radiation.