Abstract: The ash content of coal suspended in a slurry is determined by bombarding a sample of the slurry flowing past a window of a measuring chamber with radiation from an annular nucleonic source, such as Cm-244, for emitting radiation within the range of about 7 to about 30 KeV and causing the sample to emit both backscattered and iron fluorescent x-rays. These x-rays are detected by a radiation detector which produces first and second electrical signals representative of the intensity of each. The density of the sample flowing from the measuring chamber is measured, such as by a nucelonic density gauge, to produce an electrical signal representative of the density and the ash content is determined from the detected intensities of the backscattered and iron fluorescent x-rays and the sample density.