Results obtained from development, construction, testing, and evaluation of GaAs:Cr ionizing radiation detectors and X-ray digital imaging systems based on such detectors are presented. The technology devised is shown to make possible the development of detectors with the following parameters: electron mobility - electron lifetime product of 10<sup>-4</sup>cm<sup>2</sup>/V, hole mobility - hole lifetime product of 10<sup>-6</sup>cm<sup>2</sup>/V, gamma-radiation resistance of ≥ 51Mrad, active layer thickness as great as 800μm, and detector chip dimensions of 51×51mm<sup>2</sup>. The detectors under consideration exhibit high speed of response (≤10ns) and high X- and charged-particle radiation sensitivity. The detector output signal is linearly dependent on the X-ray irradiation dose rate up to 120mR/s and X-ray quantum energy up to 3MeV. Scanning detection units to be used in mammographs and fluorographs and in nondestructive testing devices were constructed and tested. The spatial resolution of the detection systems is 5lp/mm.