Background measurement methods for opacity experiments conducted at the Z facility

Laboratory experiments typically test opacity models by volumetrically heating a sample with x-rays and measuring spectrally-resolved transmission by viewing a bright backlighter through the sample with a spectrometer. A potential problem is that any background signal contaminating the spectrum will cause the inferred opacity to be too low. Backgrounds can arise from many sources, including sample self-emission, emission from nearby unresolved plasmas, high-order crystal reflections, high energy x-rays, or instrument fluorescence. Methods developed to measure background signals in opacity experiments a the the Sandia Z facility are discussed.