Apparatus for the inspection of cargo containers for nuclear materials
comprising one or more arrays of modules comprising grounded, closed
conductive tubes filled with an ionizing gas mixture such as, but not
limited to, Argon:CO.sub.2. A wire is suspended along each tube axis and
electrically connected at both ends of the tube. A positive, dc high
voltage is supplied to one end of the wire and an amplifier is attached
to the other end through a capacitance to decouple the amplifier from the
high voltage. X-rays, gamma rays or neutrons produced by nuclear material
and passing through the tube ionize the gas. The electrons from the gas
ionization process are accelerated toward the wire surface due to the
wire's electrical potential. The acceleration of the electrons near the
wire's surface is sufficient to ionize more gas and produce an
amplification of electrons/ions that create a surge of current large
enough to be detectable by the amplifier. Means are also provided for a
warning device coupled to the amplifier.