Detectors for multi-energy radiography

摘要

For multi-energy digital radiography, a sandwich structure is proposed, comprising "scintillato -photodiode" (S-PD) type detectors. This will allow obtaining information on an object simultaneously for two or three energies in the 20-400 keV X-ray range. Criteria have been formulated and a procedure proposed that determine requirements to detector characteristics for distinction of specified substances. Under this procedure, the following characteristics have been determined for two-and three-energy detecting systems. For a two-energy detector system used for organic substances (Z_(eff)=6-8) and iron/steel (Z_(eff)=26), the X-ray tube anode voltage V_A=140 kV, sensitivity range of the low-energy detector (LED) and the high-energy detector (HED) 20-60 keV and 100-140 keV, respectively. The average detector sensitivity of LED should be closer to 40 keV, and that of HED ― to 140 keV. There is a limitation that is imposed upon the detector sensitivity by sensitivity of the radiographic system. For such variant, LED are made on the basis of a photodiode and a ZnSe(Te) scintillator, ensuring good sensitivity in this range and transparence in the HED range. HED can be made on the S-PD base using CsI(Tl), CdWO_4 or Cd_2O_2S. In a three-energy system, where elements wit Z_(eff)=6, 7 and 8 should also be determined detector sensitivity ranges should be as follows: LED ― 10-35 keV, medium-range energy detector (MED) ― 40-80 keV, HED ― 100-140 keV. Such subdivision into ranges is ensured by the use of a semiconductor senso r (e.g., silicon) as LED, S -PD with ZnSe(Te) as MED, and CsI(Tl), CdWO_4 or Cd_2O_2S ― as HED.