Figure 16: The effect of thickness of surrounding water on the beam hardening-related gradient of attenuation with depth from the outer surface of an aluminium tube (wall thickness 0.69mm, outer diameter 3mm), under the influence of different values of software beam hardening correction (BHC). Data are shown for (a) no filter, (b) 0.5mm Al filter, (c) 1mm Al filter and (d) 2mm (equivalent) Al filter.