Among the numerous effects of a nuclear explosion in the atmosphere are
X-rays and Gamma Rays. These are photons of two greatly different
wavelengths. These photons interact with the atmosphere in a very
complex manner depending on the frequency of the photons. Narratively,
these can be thought of in the following way.

The atmosphere absorbs the photons. The energy in the photons causes
ionization of the air molecules, primarily Nitrogen and Oxygen. The
ionization strips the electrons off of these molecules. This leaves the
nucleus positively charged and creates an electron shower that blasts
away from the nucleus.

So, the electrons, being much lighter than the nucleus, move further
away from the nucleus causing a electromagnetic wave. There is a time
varying electric field between the nucleus and the electrons: and, the
motion of the electrons creates a simultaneous time varying magnetic
field. The electrons 'curve' back to the nucleus to recombine and
produce no net charge in the time period of 10s of microseconds after
the nuclear event.

Now, the X-rays are absorbed by the atmosphere over the distance of
several meters from the blast source. While the Gamma rays are absorbed
over the distance of several kilometers. X-rays and Gamma rays travel at
the speed of light so the resulting waveform of the EM field has a very
fast rise time from the X-rays, a longer rise time for the Gamma rays
and a slower fall time from the Gamma rays.

The EM Pulse has a very fast rise time, typically less than 10
nanoseconds [10 MHz], and a longer fall time typically 10s of
microseconds [ 1 MHz]. A Fourier analysis of the frequency components
shows the EM energy ranges from 100 KHz to in excess of 200 MHz.

So, the resulting EM wave then can propagate in accordance with the
characteristics of the Low Frequency, Medium Frequency, High Frequency
and Very High Frequency propagation characteristics in effect when the
explosion occurs.

Unclassified data indicates the EMP Pulse has field intensities in
excess of 25,000 volts per meter in the HF portion of the spectrum!
[Hmmm ... a ten meter dipole antenna could be in an EM field in excess
of 125,000 volts!! WOW! Talk about ESD susceptibility with the new IC
746 Pro. Not much would survive this unless specifically designed to do so.]

This is a far as I'll go with the explanation.

Deacon Dave, W1MCE

PS: The Rev. Deacon spent many years designing equipment to MIL Specs
including nuclear effects.


[SNIP]
Snarf wrote:
"Without sounding like too much of a wise guy, please explain the single
pulse generated during the single electromagnetic pulse generated during
a nuclear or other type of large explosion."

[SNIP]