During a normal monthly health physics check, the radiation monitoring badge of an Australian Nuclear Science and Technology Organisation (ANSTO) worker recently registered an unusual dose of 66 millisieverts or the equivalent of five abdominal CT scans. Other workers’ badges were normal.
An additional monitor worn daily and designed to alarm if in a radiation field did not show unusual radiation exposure.
The discrepancies between the two monitors led to an investigation into the incident to see if the reading was false. False readings can occur if a monitor is put down in a radioactive area and left for a period of time.
The investigation confirmed that routine safety procedures were followed but could not verify the reasons for the dose that was recorded on the first dosimeter. In this event, ANSTO has taken the precautionary approach of assuming the staff member received the dose.
Blood tests were also carried out to ensure that the worker had not received a dose over 100 millisieverts – the maximum dose allowed for radiation workers by IAEA and ARPANSA over five years. The maximum dose per year is 50 millisieverts. The blood test showed this was not the case.
The worker’s health is not at risk and he is not concerned about the situation. He will now be assigned to duties in non-radioactive areas of ANSTO.