Theoretical calibration for in vivo estimation of ingestion intake of 241Am

Direct internal contamination monitoring of actinides is carried out using phoswich detector housed in a completely shielded steel room with graded Z shielding. As inhalation is the main route of intake for most radionuclides, physical phantoms like Lawrence Livermore National Laboratory (LLNL) and Japan Atomic Energy Research Institute (JAERI) which are realistic representation of human thorax with activity distributed uniformly in the lungs of these phantoms are used for calibration of these systems. In the present study, theoretical calibration of the direct monitoring system is carried out using ICRP reference male voxel phantom with activity distributed in various parts of gastrointestinal (GI) tract. The CF of organ monitoring system for 241Am distributed in the lungs of ICRP voxel phantom was estimated as 5.70E-2 counts per photon which is in good agreement with experimental value obtained for JAERI realistic thorax phantom for overlying tissue thickness of 2.69 cm. This theoretical technique was used to estimate CFs for activity distributed in various parts of GI tract in various phases of movement of ingested material. For activity distributed in the colon, intestine wall, stomach wall and GI tract the CFs were found to be 5.70E-2, 6.52E-2, 7.14E-2, 5.78E-2, 3.72E-2 counts per photon respectively. These CFs can be used to estimate the amount of activity and the dose due to ingestion of 241Am. This paper presents the details of simulation carried out using Voxel phantom and FLUKA to obtain CF for 241Am in abdomen by phoswich detector