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D. COUNTING GEOMETRIC CORRECTIONS IN GAMMA-RADIATION MEASUREMENTS
Pages 245-250

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From page 245...
... If this is not practical, appropriate corrections must be determined and applied. The preparation of standard sources for various geometric calibration, and the methods of determining geometric correction factors are described in this procedure.
From page 246...
... The geometric correction factors (relative to the point source) can be obtained for the gamma rays in various sample sizes counted at various positions.
From page 247...
... The activity content in the disc source is calibrated by counting the source at a position 30 cm away from detector where the effect of size variation is negligible. The measured activity is compared with a certified standard point source counted at the same position.
From page 248...
... in air, mixed gently, and transferred to the sample container. Effort should be made to have the Vermiculite containing activity homogeneously mixed and tightly packed in the container.
From page 249...
... An appropriate correction may be empirically obtained by the following method: Obtain a number of actual samples with various sample flow rates and sampling duration. it is expected that the penetration of airborne activity in a cartridge may be different at different flow rates and sampling duration.
From page 250...
... (4) Count the sample again at the same position, and compare the count rate with the previously obtained average count rate.


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