From: "Paul F. Dietz" <dietz@interaccess.com>
Newsgroups: sci.space.policy,sci.space.shuttle,sci.space.history
Subject: Re: von Braun (was Re: It's that time of year again...)
Date: Mon, 25 Dec 2000 01:09:56 -0600

"Michael R. Irwin" wrote:

> That partially solves part of the problem as you noted.  Chemical and
> biological agents and 5 minute accuracy on a globe sized search area
> to go.

Global scale pinpointing in five minutes -- or even country
scale pinpointing in five minutes -- is not believable.

On a global scale, the detectors would have to be in
satellites.  But the atmosphere is (vertically) about
30 absorption lengths thick for gamma photons (attenuating
unscattered photons by a factor of e^30, or about 10^13;
a 1 watt gamma source puts out roughly 10^13
photons/second.)  So essentially nothing emitted at
the surface will make it to space.

Oh, and 30 absorption lengths of concrete would be
about 3 meters.  For lead, about 2 feet.

	Paul