Spectral characteristics of the SMP diode for radiographic applications

The self-magnetic pinch (SMP) diode is an intense radiographic source fielded on the Radiographic Integrated Test Stand (RITS-6) accelerator at Sandia National Laboratories in Albuquerque, NM. The accelerator is an inductive voltage adder (IVA) that can operate from 2-10 MV with currents up to 160 kA (at 7 MV). The SMP diode produces spot sizes as small as 1 mm FWHM depending on the diode configuration. The dose and spot size of the SMP diode has been well characterized at 7 MV1, but the x-ray spectrum which, in turn, determines the penetrating power of the source is less well understood. Variations in the transfer curve which relates x-ray transmission to the areal density or thickness of the intervening material is one factor of the total uncertainty in doing quantitative radiography. Measured and calculated transfer curves of the SMP diode operating at 3.5 MV, 4.5 MV, and 7 MV are presented. So far the measurements at a given diode operating point indicate that whatever shot-to-shot spectral variation exists do not significantly affect the measured transfer curves within the noise of the radiographic chain.