Jong-Il Lee

Dosimetry calculations for internal electron sources using a Korean reference adult stylised phantom

Absorbed fractions (AFs) and specific absorbed fractions (SAFs) for internally deposited electron were calculated using a Korean reference adult stylised phantom, where a total of 15 internal organ volumes and external body dimension were designed to match average Korean adult male. The walls of oesophagus, stomach, colon and urinary bladder were additionally divided into the mucosal layer and residual wall to accommodate dose calculation for weakly penetrating electron. The mucosal wall thicknesses were determined by the data reported in the International Commission on Radiological Protection Publication 89 and other literature resources and by direct measurements. The Monte Carlo transport code MCNPX (version 2.5.0) was employed to calculate the electron energy deposited. The SAFs and AFs for monoenergetic electrons with the energies ranging from 10 keV to 2 MeV were calculated. The results were compared with those of the revised Oak Ridge National Laboratory phantoms and showed considerable differences up to 150% in SAFs, whereas no substantial differences were observed in the AFs.

Uncertainty in Committed Effective Doses Caused by Assuming a Single Intake Pathway in the Interpretation of Bioassay Results

Intakes of radionuclides through both inhalation and ingestion pathways may occur during an incident involving unsealed radionuclides. If one assumes only one intake pathway in this case, which is usual in a routine monitoring, a significant error in the evaluated committed effective dose (E50) may result. In order to quantify this potential error, variations of resultant committed effective doses were analyzed for different fractions of the inhaled activities to the total intake of some selected radionuclides: 57, 58, 60Co, 134, 137Cs, 89, 90Sr and 32P. Simulated bioassay measurements for the whole body, urine and feces at 1 day after the intakes were generated based on the biokinetic models and data of the radionuclides. For the inhalation intake, AMAD of 5 urn was assumed and the different absorption Types were considered. Given that the intake happened via both pathways, the ratios of E50 with assumption of a single intake pathway to the true E50 were in the range of 0.01~ 72.59 for 90Sr (Type S) and of 0.06 ~ 16.70 for 60Co (Type S), which are unacceptably wide ranges. Generally larger errors are expected when the feces assay and Type S are applied. A strategy which employs two methods of bioassay or two successive measurements is proposed to reduce the potential error caused by a misjudgment of the intake pathway.