Reconstructive dosimetry and radiation dose evaluation of workers and public due to a Brazilian radiological accident in industrial radiography.

Radiological accidents occur mainly in the practices recognized as high risk and which are classified by the International Atomic Energy Agency (IAEA) as Categories 1 and 2: radiotherapy, industrial irradiators and industrial radiography. In Brazil, five important cases in industrial gamma radiography occurred from 1985 to 2018, involving seven radiation workers and 19 members of the public. The accidents caused localized radiation lesions on the hands and fingers. One of these accidents is the focus of this paper. In this accident, a 3.28 TBq192Ir radioactive source was left unshielded for 9 h in a non-destructive testing (NDT) company parking lot, and many radiation workers, employees and public, including teachers of a primary school were exposed. The radioactive source was also directly handled by a security worker for about 1.5 min causing severe radiation injuries in the hand and fingers. This paper presents radiation dose estimates for all accidentally exposed individuals. Four scenarios were considered, and three internationally recognised and updated reconstructive dosimetry techniques were used, named, Brazilian visual Monte Carlo Dose Calculation (VMC), virtual environment for radiological and nuclear accidents simulation (AVSAR) and RADPRO Calculator®. The main radiation doses estimated by VMC were the absorbed dose of 34 Gy for the security worker's finger and his effective dose of 91 mSv; effective doses from 43 to 160 mSv for radiation workers and NDT employees; and effective doses of 9 mSv for teachers in the schoolyard.

Dose estimation to eye lens of industrial gamma radiography workers using the Monte Carlo method.

The ICRP Statement on Tissue Reactions (2011), based on epidemiological evidence, recommended a reduction for the eye lens equivalent dose limit from 150 to 20 mSv per year. This paper presents mainly the dose estimations received by industrial gamma radiography workers, during planned or accidental exposure to the eye lens, Hp(10) and effective dose. A Brazilian Visual Monte Carlo Dose Calculation program was used and two relevant scenarios were considered. For the planned exposure situation, twelve radiographic exposures per day for 250 days per year, which leads to a direct exposure of 10 h per year, were considered. The simulation was carried out using a 192Ir source with 1.0 TBq of activity; a source/operator distance between 5 and 10 m and placed at heights of 0.02 m, 1 m and 2 m, and an exposure time of 12 s. Using a standard height of 1 m, the eye lens doses were estimated as being between 16.3 and 60.3 mGy per year. For the accidental exposure situation, the same radionuclide and activity were used, but in this case the doses were calculated with and without a collimator. The heights above ground considered were 1.0 m, 1.5 m and 2.0 m; the source/operator distance was 40 cm, and the exposure time 74 s. The eye lens doses at 1.5 m were 12.3 and 0.28 mGy without and with a collimator, respectively. The conclusions were that: (1) the estimated doses show that the 20 mSv annual limit for eye lens equivalent dose can directly impact industrial gamma radiography activities, mainly in industries with high number of radiographic exposures per year; (2) the risk of lens opacity has a low probability for a single accident, but depending on the number of accidental exposures and the dose levels found in planned exposures, the threshold dose can easily be exceeded during the professional career of an industrial radiography operator, and; (3) in a first approximation, Hp(10) can be used to estimate the equivalent dose to the eye lens.