1. A system for measuring the area density of low density materials sample comprising: means for generating x-rays having an energy in the range of three kilovolts to twenty kilovolts, said x-rays passing through the sample, means for converting said x-rays to visible light to produce a visible image corresponding to the sample and having an intensity which varies as a function of the area density across the sample, means for producing a digital signal representative of the intensity of the visible image across the sample, means responsive to said digital signal for processing the area density across the sample.