SU-F-I-13: Correction Factor Computations for the NIST Ritz Free Air Chamber for Medium-Energy X Rays

Purpose:The National Institute of Standards and Technology (NIST) uses 3 free-air chambers to establish primary standards for radiation dosimetry at x-ray energies. For medium-energy × rays, the Ritz free-air chamber is the main measurement device. In order to convert the charge or current collected by the chamber to the radiation quantities air kerma or air kerma rate, a number of correction factors specific to the chamber must be applied.Methods:We used the Monte Carlo codes EGSnrc and PENELOPE.Results:Among these correction factors are the diaphragm correction (which accounts for interactions of photons from the x-ray source in the beam-defining diaphragm of the chamber), the scatter correction (which accounts for the effects of photons scattered out of the primary beam), the electron-loss correction (which accounts for electrons that only partially expend their energy in the collection region), the fluorescence correction (which accounts for ionization due to reabsorption ffluorescence photons and the bremsstrahlung correction (which accounts for the reabsorption of bremsstrahlung photons). We have computed monoenergetic corrections for the NIST Ritz chamber for the 1 cm, 3 cm and 7 cm collection plates.Conclusion:We find good agreement with otheru0027s results for the 7 cm plate. The data used to obtain these correction factors will be used to establish air kerma and itu0027s uncertainty in the standard NIST x-ray beams.