Development and investigation of a neutron radiography imaging system with a low-pressure multistep chamber

An imaging system of thermal neutrons for an investigation of digital neutron radiography has been developed and tested. Some characteristics obtained on a neutron radiography beam of an experimental reactor are reported. The coordinates of each event are determined in this system. After processing in a LSI 1123 computer, a radiograph, accumulated in a histogramming memory of 64 K 16-bit words, is presented on a colour display. A 230 × 180 mm2 low-pressure multistep chamber is used as a detector. Neutron conversion takes place in a 6 μm boron layer enriched to 86% in 10B. The detection efficiency of thermal neutrons is no less than 3%. The count rate of the system reaches up to 2 × 105 events per second. A radiograph can be obtained within 10 minutes. The sensitivity of this system to gamma-background is low. One event/s is detected for a background of 1 R/h. The spatial resolution is found to be 0.7 mm (FWHM) using a cadmium knife edge. The integral nonlinearity is less than 0.4%. The possibility of using a hydrogeneous converter in this system for neutron radiography is discussed.