H-J Selbach et al 2008 Metrologia 45 422 doi:10.1088/0026-1394/45/4/007
H-J Selbach1, H-M Kramer1 and W S Culberson2
Show affiliationsA large air-filled parallel-plate extrapolation chamber with thin graphite front and back electrodes is used as a primary standard measuring device for low-energy interstitial brachytherapy sources from which the unit of air-kerma strength or reference air-kerma rate can be derived. The chamber is suitable for low-energy photons with energies up to 40 keV. The underlying principle is that the air-kerma rate at a given point is proportional to the increment of ionization per increment of chamber volume at chamber depths greater than the range of secondary electrons originating from the electrode. The fundamentals for evaluating the extrapolation curves are presented as well as a detailed description of the present set-up of the PTB large-volume extrapolation chamber (GROVEX). Comparisons between the GROVEX and other primary standards for air-kerma and reference air-kerma rate are presented.
87.53.Bn Dosimetry/exposure assessment
29.40.Cs Gas-filled counters: ionization chambers, proportional, and avalanche counters
Accelerators, beams and electromagnetism
Issue 4 (August 2008)
Received 9 October 2007
Published 9 July 2008
H-J Selbach et al 2008 Metrologia 45 422
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