Using polychromatic X-radiography to examine realistic imitation firearms

Sections 36–41 of the Violent Crimes Reduction Act (2006), which came into force in England and Wales on 1st October 2007, have placed significant restrictions on the sale and possession of ‘realistic imitation firearms’. This legislation attempts to produce a definition of a ‘realistic imitation’ which clearly differentiates these items from other imitation firearms (which are not covered by the legislation). This paper will go a stage further by demonstrating techniques by which blank firing realistic imitation firearms which may be suitable for illegal conversion to fire live rounds may be differentiated from other less ‘suitable’ (but visually identical) realistic imitations. The article reports on the use of X-radiography, utilizing the bremsstrahlung of a commercial broad spectrum X-ray source, to identify the differences between alloys constituting the barrels of distinct replica and/or blank firing handguns. The resulting pseudo-signatures are transmission spectra over a range from 20 to 75 kV, taken at 1 kV intervals, which are extracted from stacks of registered, field flattened images. It is shown that it is possible to quantify differences between transmission spectra for components of different realistic imitation fire arms, and apply the results to determine the suitability of particular gun barrels from blank firing imitation firearms for illegal conversion to fire live rounds, or related illegal modifications.