The equipment for security checks at airports now uses X-rays and metal detectors. The opacity to X-rays depends on the material and its thickness, so that dense, thick objects such as guns, knives, shavers, toothpaste tubes, etc. are revealed on the screen. A metal detector senses the change in a high-frequency electromag-netic field when its probe is close to a metallic object.
But plastic explosives are transparent to X-rays, and they are neither conducting nor magnetic. They can be molded into any shape by hand, and put into a legitimate-looking object that has batteries (for detonation), such as a tape recorder. The owner of the luggage may not even know he is carrying a bomb, for the PLO and associated filth not only hide behind rock-throwing children, but their goons also put these things in the luggage of their loving girl friends.
What distinguishes most explosives from their environment is a high content of nitrogen, and that can be detected by making it artificially radioactive and observing the induced radiation.
Nitrogen (and other elements) can be made radioactive by shooting a neutron into its nucleus, which then becomes over-crowded and kicks out a particle (or gamma photon). And kicking out a particle from an overcrowded nucleus is a long way of saying "radioactive." Depending on the element, not only the particles, but also their energies will differ, so that each activated element has its own recognizable signature, and this is a powerful way of detecting certain elements
¾such as lead in paint.In the present case nitrogen 14 absorbs a neutron and becomes nitrogen 15, and though both isotopes are stable, the N 15 signals its birth by the emission of a gamma photon, making the resulting gamma radiation easy to detect and analyze. The presence of large numbers of nitrogen atoms then reveal the presence of an ex-plosive
¾or of a hefty salami (containing nitrites as a food pre-servative¾also a carcinogen courtesy of your friendly anti-food-irradiation nuts). Air is 4/5ths nitrogen, but it is not dense enough to compete with the number of nitrogen atoms in explosives or even salami.Other elements, particularly gold and sodium (in salty foods) may become radioactive, though only very weakly
¾giving the owners a dose below that received during the flight.The source of the neutrons is beryllium, which itself is activated by the alpha particles of plutonium or radium (the latter less safe, but cheaper as well as subject to less hysteria and superstition). The neutrons shot out by the beryllium are fast, and exactly as in a power reactor, they must first be slowed down (from "fast" to "thermal") by a moderator, in this case usually the hydrogen of a polyethylene layer, in order to be absorbed by the nitrogen or other target.
The source is at the end of a cadmium-lined tube. Cadmium is a good neutron absorber, leaving only the other end of the tube as an exit for the neutron beam.
The equipment is still massive, slow (6 sec/bag), and about 10 times as expensive as present devices for the same throughput. The two producers known to me are Scientific Applications Intnl. Inc. of San Diego, and the French Commission a l'Energie Atomique. The French claim only 1% false alarms, the US 4%-- the dis-crepancy is most likely due to differing stringencies of the tests.
|
Vol. 17, No. 1
Newsletter: Access to Energy Newsletter Archive Volume: Issues Issue/No.: Vol. 17, No. 1 Date: December 01, 2004 03:04 PM Title: Why the neutron activator won't work
Copyright © 2004 - Access to Energy Newsletter Archive
|