Replacement correction factors for plane-parallel ion chambers in electron beams
Collecting volume and guard ring for plane-parallel chambers. The collecting volume is defined by the two vertical dashed lines.
(a) values of plane-parallel chambers as a function of depth in a 6 MeV electron beam. The front face of the cavity is at the point of measurement. The value for the Markus chamber at is off scale at 1.069. (b) The corresponding values for Markus and NACP02 chambers as a function of depth in the 6 MeV electron beam when the point of measurement is shifted toward the center of the cavity by 0.45 and 0.25 mm, respectively (Ref. 17).
Beam quality dependence of values at for the five plane-parallel chambers in electron beams.
Calculated values as a function of guard width for plane-parallel chambers with the front of the cavity at in a 6 MeV electron beam. The diameter of the collecting volumes for these chambers is 10 mm. Chambers with two different collecting volume diameter to thickness ratios (5 and 10, 2 mm, and 1 mm cavity thickness, respectively) are studied. A guard width of 3 mm means a cavity diameter of 16 mm.
The calculated ratio of the perturbation factors for Markus and NACP02 chambers in electron beams, i.e., the left side of Eq. (1) (open symbols, uncertainties statistical only) compared to an experimental determination by Ding and Cygler (Ref. 5) of the right side of Eq. (1) (closed symbols, precision about 0.5%). The IAEA and TG-51 data for values for the Markus chamber of and , respectively, are also shown. They are recast from many experimental determinations of the value of the Markus chamber.
The air cavities of several plane-parallel chambers with different guard ring widths (distances in mm).
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