The onset of the third and most productive period in the activity of the Laboratory coincided with the Institute move to a new building in the southwest district of Moscow. The Laboratory during this period was equipped with unique modern X ray apparatuses and other devices. The conditions called for the use of poisonous com pounds containing tantalum, antimony, cesium, arsenic, etc. The staff of the Laboratory was supplemented with specialists in ultrasonic diagnosis: it has become evident that prospects of X ray diagnosis are associated with engi neering progress.The first International Conference on Luminescence of Rare Earth Luminophores (REL) including X ray REL was held in Leningrad in 1972 [68].At this time the Laboratory organized the All Union Symposium on Luminescence Detectors and X Ray Transducers 2 . The Symposium on Luminescence Detectors and X Ray Transducers in collaboration with Russian Academy of Sciences was held in Moscow in 1973. Since then, similar symposia are held every three years [65].This period was devoted to the search for new luminophores for roentgenography and roentgenoscopy most promising for medical diagnosis. A new classifica tion system was required. The classification system was developed at the Laboratory.According to the classification, X ray luminophore is denoted by letter R with a numerical index correspon ding to spectral emission maximum excited by X rays with Е eff = 45 keV; X ray intensifying screens are denoted by letters IS; roentgenographic and roentgenoscopic screens are denoted by letters SXR; the screen luminophore is denoted as a letter after a hyphen.A family of screens of new type was developed during the last decade. These screens were available commercial ly [12]:1) intensifying screens based on oxysulfides and oxy halogenides REE [2,31,32,36,37,42,43,67]: a) type IS Y based on yttrium oxysulfide alloyed with terbium (Р 383); b) type IS G based on gadolinium oxysulfide alloyed with terbium (Р 545); c) type IS L based on lanthanum oxybromide alloyed with terbium and ytterbium (Р 417);2) intensifying screens based on salts of oxygen con taining acids alloyed with REE [11,35,58]: a) type IS P based on barium phosphate alloyed with europium (Р 415); b) types IS SBS 1 and IS SBS 2 based on mixed strontium and barium sulfate alloyed with europium (Р 380);3) intensifying screens type IS PC based on barium fluorochloride alloyed with europium (Р 385) [34]; 4) roentgenographic and roentgenoscopic screens of SR C type based on cesium iodide alloyed with thallium (Р 540/410) [3,51]. The roentgenographic and roentgenoscopic screens of SR C type are used in domes tic X ray apparatuses Vega 320 for medical X ray diagno sis.
