Displacement correction factors for ionization chambers in phantoms irradiated with neutrons of different energies

Absorbed dose and kerma are quantities which are defined at points, while the ionization chambers used for absorbed dose determinations are of finite dimensions. For measurements free-in-air, the geometrical centre of the chamber is the effective point of measurement if the distance to the source is in excess of five times the diameter of the chamber. For measurements inside a phantom, the effective point of measurements can be displaced from the geometrical centre of an ionization chamber due to the replacement of phantom material by the gas filled cavity. A correction has to be applied for changes in attenuation and scattering of the radiation under these different conditions. This correction should preferably be introduced by multiplying the absorbed dose with a displacement correction factor, delta, when the geometrical centre of the chamber is taken as the measurement position. Information on effective measuring points of ion chambers in phantoms irradiated with neutrons has been given for d(35)+Be neutrons and for d+T neutrons. Here, additional results on the displacement correction factors, delta, in human phantoms for fission neutrons and for neutrons produced by the d(2.3)+D and d(50)+Be reactions will be presented. (Auth.)