Cross-sectional view of the KRISS FAC L1 for low-energy X-ray measurement. The front wall was composed of 10-mm-thick stainless steel. The diaphragm was supported by a tungsten holder. Front view (a) and side view (b). Note that the units are given in mm and the figures are not to scale. KRISS FAC, Korea Research Institute of Standards and Science free air chamber.|@|~(^,^)~|@|Field line was drawn from the center of the air gap in the width of the collector electrode (a) and the field line drawn from the air gap in the length of the collector electrode (b). The X-ray beam axis is perpendicular to the figure plane (a), whereas the beam is incident from the left and exits right (b).|@|~(^,^)~|@|Electric field line drawn along the height at the center of the air gap. The surface plane of the collector electrode was 0 mm-high, and the HV plate was 70 mm-high. The thin line indicates the air gap in the width of the collector, and the thick line indicates the air gap in the length of the collector. The ratio (∆w⁄∆l) in Eq. (6) was 2.06.|@|~(^,^)~|@|Simulation geometry for calculating the energy deposition in the air slabs. An X-ray beam with a diameter of 10 mm was incident on the center of the front face of the air box. Fourteen air slabs with a thickness of 5-mm were piled from the bottom to the top of the air box and the energy deposited portion in each slab was calculated.|@|~(^,^)~|@|Ratio of Aⁱ, the sum of the cross-sectional areas of the paired 5-mm-thick slices in the elongated volume to A₀ (=0.85 mm²) that of the cross-sectional areas of the paired 5-mm-thick slabs with the same length equal to the peak elongation of 0.085 mm. KRISS FAC, Korea Research Institute of Standards and Science free air chamber.|@|~(^,^)~|@|Cross-sectional view of the collection volume, the elongated volume, and the effective collection volume.

Progress in Medical Physics 2022;33:1~9 https://doi.org/10.14316/pmp.2022.33.1.1