This report details a comparison of the determination of lead equivalence and attenuation factor measurements carried out by Public Health England (PHE) (previously by the Health Protection Agency) and the National Physical Laboratory (NPL) on a variety of identical samples of differing thicknesses of vinyl materials. The comparison includes a joint analysis of results determined independently by each facility.
The measurements were performed over a range of x-ray excitation potentials from 60 to 120 kV as defined in BS EN 61331-1:2002. Due to physical constraints within the facilities, neither PHE nor NPL are able to reproduce the exact measurement geometry as defined in this standard and there are also differences in the geometries between each facility. As a result, additional measurements were performed to determine if these differences produced any significant variation in results obtained.
The comparison also included a detailed analysis and review of the uncertainties associated with the determination of lead equivalence and attenuation factor, for both PHE and NPL measurements.
A comparison was also made of the 2 sets of lead reference materials, of varying thicknesses, used by each of the facilities.
Crucially, an analysis was performed of the dependence of the results obtained on the techniques used for the interpolation of the measurement data.