Measuring Dopant Concentration in Graded NIF Targets through Quantitative Contact \hbox{X-Radiography}*

Doping level must be known to 0.05 atomic percent and its radial distribution to one micron for graded targets used in NIF experiments. We have developed a quantitative contact x-radiography system (x-radiograph, film digitizer, and analysis software) that can meet those conditions. Traditional x-radiograph systems (either film- or scintillator-based) contain 1)~spatial distortion errors and 2)~opacity uncertainties that are unacceptable for this case. For the first, we designed a high precision digitization system with 0.5~$\mu$m optical resolution and added a customized algorithm to remove the lens pincushion distortion and the CCD pixel size effect. For the second, we have developed a detailed film model to convert gray scale information into \hbox{x-ray} absorption strength under polychromatic radiation conditions. The model is calibrated on polypropylene flats and can measure the \hbox{x-ray} absorption (and thereby dopant level) to $\sim$10\% in each sublayers. Our measurement results on Cu-doped Be shells and Ge-doped GDP shells agrees with those from destructive techniques.