Cosmic Radiation

On Wednesday 24 September 2003 14:39, Al Globus wrote:
(...)
> I must be missing something.

Yes, you are. :-)

> If I'm standing on the surface of the
> Earth, the cosmic radiation coming from the sky above me is not blocked
> by the Earth before it hits me, only attenuated by the atmosphere above
> me.
(...)

That was not what TangoMan was talking about. I'll try to explain in other
way: imagine that the solid/liquid bulk of Earth magically vanishes and that
(also by magic means :-) the atmosphere is miraculously kept in the same
place. So you'll have a hollow ("vacuum-filled", so to speak) sphere limited
by a spherical "membrane" of air. Now imagine that you're in an astronaut
suit inside the hollow volume (but close to the inner surface of the
"membrane") and you have a radiation detector.

The radiation level that you'll read will be basically the same as you would
measure on the surface of the "complete" Earth. Why? Because the radiation
coming "above" you will be blocked by the portion of the membrane "above"
you, while the radiation coming from "below" will be blocked by the portion
of the membrane 12,800 kilometers "below" you, in the place that was used to
be "the other side of the Earth".

The point that TangoMan is explaining is that the play of Earth's bulk in
radiation shielding is negligible, because this bulk is enveloped by a
spherical atmospheric shield that already blocks virtually all radiation
coming from every direction before they ever hit Earth's bulk.

In fact, as Arthur Smith pointed out, the bulk of Earth is *bad* when it comes
to radiation levels, because Earth is basically a giant radioisotope battery
and there is some small amounts of radiation and radioactive waste coming
from inside.

Lucio Coelho