Studies were carried out on the improvement of radiographic relative fault sensitivity, and attempts were made to find out a suitable penetrameter in order to establish a technique on the radiographic inspection by X-rays for solid composite propellants up to 400mm in diameter. The solid rocket propellants have small absorption coefficient for X-rays, so it is necessary to use lower energy X-rays in comparison with the thickness of the metals and to perform the testing in as low X-ray voltage as possible. The relative fault sensitivity thus obtained is 0.5 to 1.0 percent for the solid composite propellants of 400mm in diameter. It has been found that the hole type penetrameter is the most suitable for the solid composite propellants among various sorts.
