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The following archive was created by hippie-mail 7.98617-22 on Fri Aug 21 1998 - 17:20:13 ADT
Mike Rosing (eresrch@msn.fullfeed.com)
Wed, 8 Jul 1998 09:19:58 -0500 (CDT)
On Wed, 8 Jul 1998, Chris Wedgwood wrote:
> Very high energy photons or not easy to shield, and shielding will often
> make matters worse because you'll get a cascade of particles creating by the
> photons interaction with the shield...
I think you're mixing high energy particles with high energy photons.
photon-electron cross sections are large compared to particle-nuclei
cross sections. It is "easy" to shield photons because you can get
lots of electron density with little effort. Stopping distance of
1GeV gammas is only a few feet of U238. Stopping 1GeV neutrons (or
protons) requires a few hundred feet.
> If easy to shield includes, putting the equipment 6000 feet underground, you
> are perhaps correct though.
10 meters of dirt will stop most anything, except high energy particles.
> By comparison, neutrons are probably easier to shield. A strong neutron
> absorbing isotope, several feet thick (maybe), may not be very portable, but
> it sure beats a mine shaft.
au contraire, stopping thermal neutrons is *hard*. Ask anyone who's
tried to design a fusion reactor with laser beam ports. You can slow 'em
down, but then you need several hundred feet of water, and running a
fusion reactor on the bottom of the ocean is more expensive than the rest
of it!
Patience, persistence, truth,
Dr. mike
The following archive was created by hippie-mail 7.98617-22 on Fri Aug 21 1998 - 17:20:13 ADT