Date:	Wed, 25 Jan 89 17:49:00 EST
From:	stiatl!john@gatech.edu
Subject: Re:  EMP (Electro-Magnetic-Pulse) Luggage scanning.

The problem with this scheme, even if it would not damage electronics is
that it's very easy to defeat.  Simply wrap the explosive in a conductive
and/or magnetic material like Mu-metal and voila!  No Boom.

In a related issue.  Much press has been given to this new Thermal Neutron
explosive detector.  Being a Nuke by training, the underlying assumptions
give me some heartburn.

The principle of operation is that nitrogen-rich explosives, when 
irradiated with a thermal neutron flux will have some nitrogen atoms
transmuted to the N-16 isotope.  N-16 has a half-life of a few second
and decays with a highly energetic and characteristic gamma ray.
This gamma ray is detected, processed and used to generate the alarm.

Here's the rub.. Thermal neutrons are easily stopped by materials with
high cross-sections like cadmium.  No neutrons in the explosives = no
N-16.  No N-16 = no detection.  Since it is likely that Californium is
the source of neutrons, the flux is not likely to be high because of 
cost (several thousand dollars per microgram).  Thus the flux could probably
be stopped by a cadmium foil.  By implication, a perfect explosive would
be some plastique or C4 shaped like a candy bar and wrapped in cadmium 
"foil".  this would look normal to visual and X-ray inspection and would
defeat the neutron detector.

So the question arises "Is this TOO easy or am I missing something".  
Considering the government's involvement, it's quite likely the 
former.  I'm wondering if there is anybody on the net familiar with 
the specific design of the detector.  If so, am I missing something?

It seems to me that a much more suitable detector would be one of the
proven nitrate sniffers.  These things have been in use at Nuclear
plants for at least 7 or 8 years.  I can testify as to their sensitivity
after setting one off with power residue from a weekend target practice
session.  The functionality test the guards used at one site was to 
try to carry one of these nitroglycerin despensing angina patches thru 
the gate.  It would detect the fumes from the few milligrams of nitro
in these patches.

For even better sensitivity, the nitro sniffer could be coupled to the
altitude chamber now in use.  The vacuum chamber would enhance the mobility
of emitted explosive molecules and the exhaust of the vacuum pump would
contain a concentrate of the chamber atmosphere.  As an added benefit,
these things cost a few thousand bux, not a million or more like the 
neutron device.

Comments?

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Date:	Fri, 27 Jan 89 21:02:00 EST
From:	felix!chuck@dhw68k.cts.com
Subject: Re: EMP (Electro-Magnetic-Pulse) Luggage scanning.

What happens when military electronics is exposed to a big EMP, like from a
nuclear blast?  You can unit test in chambers an such, but how does the design
really work in place?  The Air Force decided to find this out by building a
huge wooden trestle next to Kirtland AFB in Albuquerque in the 70's.  Really
something to look at.  This thing stuck out over the Tijeras canyon, which runs
immediately south of the airport, roughly paralleling the main E/W runway.  I
never got to see it up close, but as you fly in or out of the airport, you can
usually see it.  (Albuquerque is joint use, military/commercial.)

The plan was sort of simple:  Test how a complete unit, electronics and all,
(read that airframe) reacts to an EMP while flying in the air.  This trestle is
big enough for them to park a B-52 on the thing and have it end up 50 or 60
feet off of the ground.  They had a taxi strip from the main airport area and
would simply tow whatever the test subject was to be out there and push it out
onto the trestle.

I remember reading about the construction of this thing and about how they were
going to zap the planes, but it has been a long time.  Something about lots of
capacitors and big coils.  Normal stuff.  The trestle was almost more
interesting because of the problems they had building it.  Seems that it was
very difficult to find enough carpenters who could still build such a thing.
The design call for 100% wood.  No metal.  No nails, no bolts.  This was
required because of the strength of the pulses they were going to be using.
Urban legend had it that they would literally pull the nails from the structure
if they had been present.  I don't know if this was true, but, electrically,
they would effect the test, since a flying aircraft usually doesn't have pieces
of metal floating around it in space.

I think both Sandia Corporation and EG&G were involved in the project, the
results of which are probably classified.

Chuck V.