Date: 13 Nov 89 05:39:21 GMT
From: gem.mps.ohio-state.edu!usc!samsung!shadooby!mailrus!jarvis.csri.toronto.edu!utgpu!utzoo!henry@tut.cis.ohio-state.edu  (Henry Spencer)
Subject: Re: Radiation exposure for Apollo astronauts

In article <1989Nov9.022837.18410@everexn.uucp> mike@everexn.UUCP (Mike Higgins) writes:
>...  A naked human in space is virtually
>transparent to cosmic rays: they pass right through all these big low density
>organic molecules that we are made of most of the time...

Unfortunately, a small fraction of cosmic rays are heavy nuclei, rather
than the usual light ones... and the naked human body is *not* transparent
to those.  They are thought to be the cause of the flashes of light Apollo
astronauts reported seeing with their eyes closed; the flashes are very
tentatively explained as heavy cosmic rays destroying retinal cells.
This is a major concern and considerably complicates the shielding
problem.  The radiation dose from light-nuclei cosmic rays in an unshielded
spacecraft is actually not big enough to be a major worry.  But blocking
the heavy cosmic rays requires enough shielding to generate a lot of
secondary radiation from the light cosmic rays, and stopping that takes
still more.
-- 
A bit of tolerance is worth a  |     Henry Spencer at U of Toronto Zoology
megabyte of flaming.           | uunet!attcan!utzoo!henry henry@zoo.toronto.edu