| 摘要 |
PURPOSE:To detect the position of a crack in a bed on the ground surface by measuring the peak count rate of gamma rays emitted from potassium-40, thallium-208, and bismuth-214, and finding peak ratio variation rates of various nuclear species in both forward and backward directions. CONSTITUTION:Plural NaI detectors are mounted on a moving body and gamma rays are measured at a specified interval of time. The peak count rates of respective nuclear species for gamma rays emitted from three nuclear species of potassium-40, thallium-208, and bismuth-214 in the surface layer are measured and the peak ratios of the respective nuclear species are found on the basis of said measured values. Further, the forward peak variation rate at a point (q) is calculated from data extending from a point (q-n) to a point (q-1), and the backward peak variation rate at the point (q-n) is calculated from data extending from the point (q) to a point (q-n+1). The dose of gamma rays of bismuth increases at a site having a crack in the surface layer, so the position of the crack is detected from said peak variation rates. |
