serious error (re. radiation shielding) in 1975 Summer Study?

On 6/26/14 8:59 AM, GARY ANSORGE dead_naked_drummer@... [ssi_list]

> ,,,and we also need to compare the penetration energy of those particles
> with the realization that the greater the energy (ev) the fewer the
> particles involved. Earth gets hit about once a year by protons with an
> energy of 10^21 ev (a baseball thrown at 30 mph),,,but that's about one
> particle/year...total rads are directly proportional to the number of
> particles plus their energy,.

That's true. But Earth is inside the geomagnetic shield, which reduces
GCR (galactic cosmic ray) particles from 60-80 rad/year, down to 0.36
rad/year in LEO. So we're getting a factor of 200 protection from the
magnetic field, before the atmosphere even gets a whack at it.

(Note that this *does* vary with the solar cycle, because the sun's
magnetic field is also shielding us somewhat. So GCR in free space is
about 2.5 times higher at solar minimum than at solar maximum. Since a
space colony needs to work at any time, I'm using the solar-minimum values.)

References all linked from:
https://www.assembla.com/spaces/high-frontier/wiki/Radiation

...and more useful references would be gratefully appreciated!

Best,
- Joe