Abstract: A method is disclosed for obtaining the density distributions of three-dimensional elements that compose objects or groups of objects, by examining the objects with beams of x-rays or gamma radiation that are transmitted through the object in a plurality of approximately parallel paths and measuring the intensity of the radiation, scattered approximately perpendicular to the parallel paths, in arrays of detectors around the object. The energy of the x-rays or gamma rays is such that dominant interaction in the object is Compton scattering. The density of each element is determined from the totality of measurements by standard mathematical tomographic or relaxation techniques of data manipulation.

Abstract: A new type of x-ray fluorescence detector is disclosed that utilizes the measured intensities of fluorescent L.sub..alpha. and L.sub..beta. x-rays, or K.sub..alpha. and K.sub..beta. x-rays of a target element, to determine the absorption of the covering layer over the target element, without a priori knowledge of the concentration of the target element. The detector uses a source of initiating photons whose energy is in a specific range, a detector of the characteristic lead L or K x-rays with sufficient energy resolution to measure the intensities of the L.sub..alpha. and L.sub..beta. rays separately. The detector will, in a rapid, non-destructive manner, provide information as to the depth that the lead paint is beneath the surface. This information is of use to those who mitigate a lead-paint infested area.

Abstract: A method is disclosed for obtaining the density distributions of three-dimensional elements that compose objects or groups of objects, by examining the objects with beams of x-rays or gamma radiation that are transmitted through the object in a plurality of approximately parallel paths and measuring the intensity of the radiation, scattered approximately perpendicular to the parallel paths, in arrays of detectors around the object. The energy of the x-rays or gamma rays is such that dominant interaction in the object is Compton scattering. The density of each element is determined from the totality of measurements by standard mathematical tomographic or relaxation techniques of data manipulation.