For a direct measurement method using a GM survey-meter, the detection efficiency and detection limit against surface contamination with nuclides emitting β-rays on a polyethylene-coated paper were examined. Three nuclides,
14C,
35S and
32P were used as a source. The detection efficiency against
14C,
35S and
32P at the place of 5.0 mm distance from the detection face of the survey-meter was approximately 1.4, 1.9 and 34.5%, respectively. Although the detection efficiency obtained for
32P was the same as the value showed in the instruction manual, that of
14C was smaller than that of the instruction manual. It is considered that such a difference in detection efficiency between
32P and
14C is ascribed to difference in source efficiency. Furthermore the detection limit against
14C,
35S and
32P at the distance of 5.0 mm was about 3.6, 2.6 and 0.2 Bq/cm
2, respectively. Hence it appears that the direct measurement method using the GM survey-meter is useful to check the surface contamination with
14C or
35S in a controlled area since the surface contamination density limit in a controlled area is 40 Bq/cm
2.
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