Figure 4, of approximately nine decades, soales of three decades each, Figure 5. This is divided into four Those scales ares A. 2005 = 1 mr/br Be 0.1 - 100 o/h C. 10 to 10,000 mr/hr (0,01 to 10 rfnr) De 1,000 to 1,000,000 mr/nr (1 to 1,000 r/hr) The low level detector covers the range of scales A and B, and the high level detector covers scales C and D, The three decade scale achieves a compromise between reading and telemetering accuracy with a minimum amount of scale switching. The upper limit of scale D (1000 r/hr) is extended beyond the maximum reading of the instrument (200 r/hr) to allow for the increase in reading due to the compensation of airoraft intensities to growmd level readings. This will be fully discussed in Section 2,1.,4 on alti= tude compensation, 201.2 Detector Circuit Description (Figure 6) The detector consists of two plastic phosphors, One, 3" diameter by 4" high, is mounted on a 3" photomultiplier tube. (DuMont type 6363), and measures the low radiation levels. The second, 1" in diameter by 1/4" high, is mounted on a 1£" photomultiplier tube (DuMont type 6467) for measuring high radiation levels, The phosphor sizes were experimentally determined for the range of radiation intensities to be covered, The tenth dy- node of each photomultiplier tube is connected to the grid of the amplifier, however, high voltage is applied only to the tube in use.