METHODOLOGY FOR THE ASSESSMENT OF INGESTED ACTINIDES FROM MONTE CARLO SIMULATION OF VOXEL PHANTOM

Area of Science:

• Medical Physics
• Radiation Detection and Measurement
• Nuclear Medicine

Background:

• Internal contamination with actinides poses health risks, requiring accurate monitoring.
• The alimentary tract is a primary pathway for actinide absorption following ingestion.
• Assessing ingested activity necessitates understanding detector response to distributed sources over time.

Purpose of the Study:

• To estimate counting efficiencies (CEs) for Phoswich and HPGe detectors for actinides in the human alimentary tract.
• To evaluate CEs as a function of time post-ingestion and photon energy.
• To assess the impact of detector choice and activity distribution on internal dose assessment.

Main Methods:

• Utilized the Monte Carlo code 'FLUKA' to model a voxel phantom and detector systems (Phoswich, HPGe array).
• Simulated 1 Bq ingestion intake, tracking actinide activity distribution in the alimentary tract over 0.5-5 days.
• Calculated CEs for photon energies from 18-238 keV, representing actinide decay.

Main Results:

• Phoswich detectors exhibited higher CEs than HPGe arrays due to larger size and higher effective Z.
• CEs decreased significantly (16-75%) from 0.5 days to 5 days post-ingestion.
• Liver activity contributed substantially (30-50% in chest, 75% in abdomen) to measurements.

Conclusions:

• Counting efficiencies are highly dependent on the detector type and time elapsed since ingestion.
• Accurate assessment of ingested actinides requires using time-dependent CEs tailored to activity distribution.
• Cross-contamination between organs (e.g., lungs and abdomen) must be considered in dose estimations.