Computing the effective dose rate conversion coefficients using the monte carlo method

In radiation applications, one needs to know the radiation dose exposed in order to protect the individuals from detrimental effects of radiation. These dose estimates are assessed from on the spot measurements or calculations and are essential in deciding whether the individuals are working within safe dose limits. However, because measurements can not be made on the basis of organ dose, the process is usually carried out through calculations, Within the scope of this thesis study, a voxel-based whole body model defined in MCNP, which is a Monte Carlo radiation transport code, and radiation interactions inside human body were simulated and absorbed doses deposited in each organ or tissue originated from photons emitted from a radioactive point source placed 1 m away from the phantom were determined. As a result of the simulations which used adult reference male and female phantoms as body models, the absorbed organ doses from both phantoms were subsequently multiplied by the radiation and tissue weight factors, in accordance with the ICRP Publication 103 methodology, and then converted to equivalent organ doses and then added to obtain effective dose. Later, the calculated effective dose was converted to the effective dose rate conversion coefficient by dividing by the unit source activity and unit exposure time and also was made independent of the distance between the source and the phantom. Simulations were performed for 8 different orientations of the source and for 1179 different radionuclide sources emitting photons, and as a result effective dose rate conversion coefficients were derived for each radionuclide source and orientation investigated. When all the orientation and the radioisotopes were examined, it was observed that Cf-254 isotope under AP orientation caused the maximum dose while Sm-251 isotope under RP orientation caused the minimum dose. When the obtained results are compared with the air kerma rate constant in the literature, it is seen that the effective dose rate conversion coefficients developed for different source orientations using whole body models will represent the radiation risk more realistically in practical applications for an individual in a radiation field.