Patent Number: 049875825
Section: claims

1. A system for detecting the presence of elements in an object comprising: gamma ray source means for irradiating an object with gamma rays of predetermined minimum energy to produce X-ray fluorescence of elements therein;  X-ray detector means, including a first dislocation free single crystal having substantially parallel input and transmission surfaces at opposite ends thereof, positioned to intercept X-rays radiated by said elements, and disposed at an angle of incidence with respect to the X-rays to transmit only X-rays incident at predetermined Bragg angles characteristic of a known element; and  further including a second dislocation free single crystal disposed substantially parallel to the first crystal and having a predetermined offset therefrom to intercept and measure X-rays transmitted by the first crystal at a specific Bragg angle. 2. The system of claim 1 further including means for varying the angle of incidence of the transmission surface with respect to the second crystal and means for measuring the intensity of the X-rays radiated by material at each of a plurality of known materials. 3. The system of claim 2 further including a plurality of X-ray detector means disposed in a linear array. 4. The system of claim 3 further including means for scanning the object with the X-ray detector means including means in a direction generally perpendicular to array. 5. The system of claim 4 further including means for moving the object relative to the detector means to effect scanning of the object. 6. The system of claim 1 wherein the X-ray detector means include a dislocation free crystal having a dimension to pass X-rays of characteristic wavelength in accordance with the relationship .lambda.=2d sin .sigma., where .lambda. is the X-ray wavelength, d is the lattice spacing of the atoms in the crystal, and .sigma. is the Bragg angle of the specific element of interest.