Scatter radiation influences in nuclide calibration fields

The goal of this study is to characterize the 137Cs and 60Co nuclide calibration fields of the reference irradiation facility with collimated beam geometry as part of the Dosimetry Laboratory Seibersdorf. Air kerma along the main beam axis with source–detector distances up to 19 m and additionally lateral field profiles are investigated by comparing mainly ionization chamber measurements with MCNP Monte Carlo computer simulations. The scatter radiation contributions from various facility components including simulations with and without air environment are studied by detailed modeling of the facility. Relative differences between measured and simulated results are currently within about 1–2%, i.e., roughly two to three times of the total measurement uncertainties, but reasons due to scattering influences and further improvements in the model are discussed.