Japanese guidelines say the pills should be distributed when the likely absorbed dose of radioactivity is 100 milligray, a unit named after a British physicist.

Objective to monitor the dose of the radiation monitoring, to assess the safety and analyze the radioactivity exemptions of the X-ray luggage inspection system at an airport.

Thyroid radioactivity levels were measured for each participant within two months of the accident, and were used to estimate each individual's I-131 dose.