Baggage inspection and the like

Claim 1

An x-ray inspection apparatus comprising an x-ray tube means and associated power supply which generates an x-ray beam having a plurality of energies, means to expose to the x-ray beam an object to be inspected, means to insert into and remove from the x-ray beam a piece of reference material selected to have an absorption coefficient related to that of a substance the presence of which is to be detected, said means to insert and remove constructed to enable all regions of the object to be exposed both to the x-ray beam and to the beam obstructed by the reference material, detector means arranged on the opposite side of the object to detect x-rays and produce signals corresponding to the amount of x-rays transmitted through the object of each of a first and a second energy in the presence of said reference material and at each of said first and second energies in the absence of said reference material, and signal processing means responsive to signals from the detector means to produce an indication of the presence in the object of said substance based upon the signals produced by the exposure to the x-ray beams at each of said first and second energies in the absence of said reference material and the signals produced by the exposure to the x-ray beams at each of said first and second energies obstructed by the reference material of predetermined properties.