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Description
Characterization of dose responses according to source-to-detector distance and measurement direction is important for interpreting radiation measurements involving sealed radioactive sources. In this study, a portable Geiger–Müller (G-M) tube detector was evaluated using sealed ⁶⁰Co and ²²Na sources under circumferential and distance-dependent measurement configurations. Measurements were performed at various distances and directions, including the front and rear orientations of the detector. The measured dose decreased markedly with increasing distance for both radionuclides. Direction-dependent variations were also observed at identical source-to-detector distances. In particular, the front and rear measurements exhibited different dose responses, indicating that the effective distance to the sensitive volume and the detector housing geometry influenced the measured values. These findings demonstrate that both distance and detector orientation significantly affect G-M tube responses. Therefore, the detector reference point and measurement direction should be clearly defined and consistently maintained to ensure accurate and reproducible measurements.