Progress in Medical Physics (한국의학물리학회지:의학물리)

Korean Society of Medical Physics (한국의학물리학회)
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Effective Volume of the Korea Research Institute of Standards and Science Free Air Chamber L1 for Low-Energy X-Ray Measurement

  • Received : 2022.02.24
  • Accepted : 2022.03.25
  • Published : 2022.03.31
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Abstract

Purpose: To evaluate the effective volume of the Korea Research Institute of Standards and Science free air chamber (KRISS FAC) L1 used for the primary standard device of the low-energy X-ray air kerma. Methods: The mechanical dimensions were measured using a 3-dimensional coordinate measuring machine (3-d CMM, Model UMM 500, Carl Zeiss). The diameter of the diaphragm was measured by a ring gauge calibrator (Model KRISS-DM1, KRISS). The elongation of the collector length due to electric field distortion was determined from the capacitance measurement of the KRISS FAC considering the result of the finite element method (FEM) analysis using the code QuickField v6.4. Results: The measured length of the collector was 15.8003±0.0014 mm with a 68% confidence level (k=1). The aperture diameter of the diaphragm was 10.0021±0.0002 mm (k=1). The mechanical measurement volume of the KRISS FAC L1 was 1.2415±0.0006 cm3 (k=1). The elongated length of the collector due to the electric field distortion was 0.170±0.021 mm. Considering the elongated length, the effective measurement volume of the KRISS FAC L1 was 1.2548±0.0019 cm3(k=1). Conclusions: The effective volume of the KRISS FAC L1 was determined from the mechanically measured value by adding the elongated volume due to the electric field distortion in the FAC. The effective volume will replace the existing mechanically determined volume in establishing and maintaining the primary standard of the low-energy X-ray.

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Acknowledgement

This work was supported by the Korea Research Institute of Standards and Science (KRISS) under the project "Development of Measurement Standards for Medical Radiation (2022)." The authors express gratitude to Dr. D.T. Burns in the Bureau International des Poids et Mesures (BIPM) for suggesting the introduction of (𝚫w/𝚫l) Eq. (6), which gives a 0.033-mm-reduction in the elongated length (originally, it was evaluated to be 0.203 mm, with an assumption of 𝚫l=𝚫w). We note that this study was motivated from by the discussion between the author (Yi) with Dr. D.T. Burns and Dr. C Kessler during his stay in the BIPM dosimetry laboratory for the BIPM-CCRI(I) Key Comparison measurement of the low-energy X-ray air kermas between KRISS and BIPM in 2017.

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