EMP 101, was Re: galactic EMP

From: Michael M. Butler (butler@comp-lib.org)
Date: Sun Jan 14 2001 - 09:14:27 MST

EMP doesn't imply scorching the Earth, though it's not totally out of
the question. And no, EMP per se is an electromagnetic effect, not a
"heavy particles" one; heavy particles are a separate deal from EMP,
though they can indeed be a bad thing, and strong enough X-radiation can
induce them.

Off-the-cuff summary (anyone who knows more than I, please correct me if
I err):

In open literature on the subject, there are two primary types:
Atmospheric (AEMP) and System (SEMP). Nuclear EMP (NEMP) can induce
both, depending on distance and other factors.

When a nuke explodes, there is a short (perhaps 200 nanosecond duration)
very strong pulse of extremely shortwave radiation (hard X-rays or gamma
photons, whichever you choose to call them). As this ionizing radiation
encounters normal matter, the matter is strongly stimulated (ionized).
The combination of freed electrons, photons emitted as electrons falling
back to nearer their ground states, and "downshifted" photons due to
Rayleigh scattering of the original gamma constitutes EMP.

AEMP is the atmospheric effect, which takes the form of very wideband
radio from DC to well past daylight. Signal levels can reach many
kilovolts per meter. Very unpleasant for anything with an antenna or
wiring that can act like one, since typical signal levels for radio
inout stages are microvolts, and regular telephone service is designed
for a ring voltage of 98 V RMS. It's like lightning hitting all over the
place at once.

SEMP is where the gamma hits a system pretty much directly, without much
intervening atmospheric effect. Here, "bremmstrahlung" (electrons being
knocked out by fast photons) happens right inside the system, with
similar deleterious effects. Note that a conventional Faraday cage
shield might provide some protection from AEMP, but is not very
effective against SEMP.

Chuck Kuecker wrote:
> If the blast from galactic center is intense enough to scorch bodies in our
> solar system, you don't have to worry about present day military gear
> surviving. More to the point - would our atmosphere provide enough
> shielding to allow life to remain on the surface, or even in the first 100
> yards of the surface?
> I take it the "EMP" will be caused by heavy particles traveling at sublight
> speeds. If it's pure radiation, the first warning we get will also be the
> last thing we ever see...
> Chuck Kuecker

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