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A review of the results studies on luminescence of mainly natural diamonds under X-ray excitation is presented. Such luminescence of diamond crystals is widely used in separation of diamond-bearing ores in diamond mining industry. Diamonds contain numerous luminescence centers that can be excited by optical radiation. Photoluminescence (PL) is characterized by wide variety of properties. It is difficult to discern PL of diamonds from PL of accompanying minerals and provide sufficient extraction selectivity. The first comparative studies of the properties of X-ray excited luminescence (XL) and photoluminescence, carried out in the last century, showed the properties of XL are much less diverse. X-ray luminescence spectra of most natural diamonds contain mainly one band, so-called A-band, visually perceived as blue emission. Spectral bands and lines observed in photoluminescence appear additionally in XL spectra of some samples. Some samples do not exhibit A-band in XL. The specific properties of XL of diamonds determined the capability of usage of XL in separation of diamond-bearing ores. In the mid-sixties, an idea stating the donor-acceptor process of emission of the A-band under X-ray excitation had appeared. This idea has been disputed on the basis of detailed study of kinetics and other properties of XL, but the concept of the donor-acceptor process has been circulating in various publications for several decades. The review presents the temperature dependences of the decay time constants of individual components of X-ray excited luminescence, which as a whole should be considered as the temperature-time passport of the A-band. The article provides data on the practical use of luminescence in the separation of diamond ores, provides some information on the design of separators. [ABSTRACT FROM AUTHOR]

Railway crossing has always been a source of increased danger for vehicles and pedestrians crossing it. Every year in Russia, several hundred-road accidents occur at railway crossings, dozens of people die. To increase the safety of traffic at railway crossings, automatic systems for detection of objects in the immediate danger zone can be used. These are sensors of optical (cameras, lidars) and radio ranges. The main disadvantage of optical devices is their limited functionality in insufficient visibility conditions: snowfall, rain, fog. Note that the radar is devoid of this disadvantage and retains its specified detection characteristics under any weather conditions. The paper deals with the analysis of the approach to form the directivity characteristics of the phased antenna array for 24 GHz FMCW radar used in the system of automatic control at the railway crossings. The feature of the proposed technique is applying of two widely spaced incoherent omnidirectional in azimuthal plane transmitters that provide the interferometric structure of transmit pattern. The important requirement for radar systems of detecting objects at a railway crossing are a wide field of view (up to 90 degrees) and, at the same time, high accuracy in determining coordinates. The last requirement assumes a relatively high resolution in angular coordinates (several degrees). The proposed structure of the transmitting antenna array allows the improvement of the angular resolution in comparison with the conventional array with the same aperture. The receiving antenna array should provide a low level of the sidelobes and a given beamwidth of the radar directivity pattern. The rotation of the beam of the receiving phased antenna array is carried out in the digital signal processing (DSP) system, since separated phase shifters are also not used in receivers. Optimization was carried out on the level of the side lobes and the resulting width of the radar beam. To reduce the side lobe level, a sidelobe compensation method is used. It is known, zero is formed in DP of the compensation channel in the direction of the maximum of DP of the main channel. In the presented work, the central six channels of the receiver are used to form the main beam. In the case of a compensation beam, the first six channels have the opposite phase to the rest to form a zero of DP. Theoretical justification is presented. The results of mathematical modeling are shown. To study the features of work in a real railway crossing, a prototype of 24 GHz radar was designed. Also, transmit and receive positions of FSR were used. The work of the prototype was studied in the conditions when objects of interest, including cars and pedestrians, were moving through the crossing. The results of the prototype testing are also presented. [ABSTRACT FROM AUTHOR]