| 摘要 |
PURPOSE:To simplify the constitution of a driving mechanism and to reduce the size and weight of a device and also facilitate its installation and adjusting operation by arranging a beta-ray detector above a measurement gap and fixing it to a frame, and arranging a source head below the frame and scanning and driving it. CONSTITUTION:The source head 4 is supported on one side of the frame 12 where the measurement gap 9 is formed and driven reciprocally along the gap 9. The linear type beta-ray detector 13 is supported on the other side of the frame 12 and arranged along the gap 9 to the overall length of the scanning range of the head 4. Further, the detector 13 includes a plastic scintillator 14 for beta rays and a photomultiplier tube 16 which converts scintillation light generated by the scintillator photoelectrically. Then, the drift of the detector 13 is corrected with its output in calibration mode wherein the head 4 is off a body to be measured in the gap 9 and the thickness of each breadthwise section is calculated from the output of the detector 13 in measurement mode wherein the head 4 is within the width range of the body to be measured.
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