| 摘要 |
PURPOSE:To measure accurate radioactive concentration by correcting the slit width of a variable slit width collimator according to the transmissivity of gamma rays, correcting an error in measurement due to the horizontal ray source state in a sample to be measured, and inputting measurement data from a gamma ray detector and calculating the radioactive concentration by nuclear species. CONSTITUTION:A container 2 to be measured is mounted on a sample mount table 9 and a sample on the table 9 is divided lengthwise into plural columnar segments for radiation evaluation; and transmitted gamma rays from an external gamma ray source 10 are measured by a gamma ray detector 11 at a position opposite to the ray source 10 across the container 2 and an arithmetic device calculates the mean concentration in a segment from the transmissivity by using a specific expression. Then, the slit width of the rectangular variable slit width collimator 12 installed in front of the detector 11 is determined on the basis of the gamma ray transmissivity. Then, the arithmetic device calculates the peak count rate of an object nuclear species from gamma ray spectrum data inputted from respective detectors and calculates the radioactive concentration by nuclear species.
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