Methodology at CIEMAT whole body counter for in vivo monitoring of radioiodine in the thyroid of exposed population in case of nuclear emergency.

Abstract

Iodine-131 is one of the main concerns from the point of view of radiological protection in a short term after a nuclear accident. The WBC Laboratory of CIEMAT has developed a methodology for in vivo monitoring of radioiodine in the thyroid of exposed individuals in case of emergency. Thyroid–neck phantoms of different sizes are required for calibrating the detection systems in appropriate counting geometries for the measurement of exposed population. A Low-Energy Germanium (LEGe) detector and a Fastscan Counter were calibrated using a set of thyroid phantoms fabricated by CIEMAT. Each neck phantom consists of a Lucite cylinder with a vial source of 131I. Counting efficiencies depending on age and thyroid sizes were obtained to be used to determine the activity of 131I in internally contaminated people. DL of 131I varies with the age, being in the range of 5–8 Bq for the LEGe detector and 26–42 Bq for the Fastscan. Detection of intakes resulting in Committed Effective doses far below 1 mSv are guaranteed for thyroid monitoring in a few days after the accidental exposure assuming a scenario of acute inhalation or ingestion of 131I by members of the public.