M. Chen, “Validation of a Dose Assessment Method to be Used in Loose Contamination Exercises”, M.S. Thesis, Nuclear Engineering, Texas A&M University, College Station, TX (2019).
Emergency responders could be exposed to loose radioactive material during a mission. As part of a research project at Texas A&M University, 18F was sprayed in a small area where an Exercise Participant (in protective gear) conducted simulated search activities. A dose assessment tool developed by the researchers was used to estimate doses to the Radiation Worker (mixer and sprayer) and Exercise Participant. The current project aimed to validate the assessment methodology by comparing actual and estimated doses of the two personnel.
In the scenario, the Radiation Worker injected and mixed 200 MBq Fludeoxyglucose 18F (FDG) with 470 ml H2O in a commercial weed sprayer. The solution was distributed evenly over a 3 m x 3 m region in 5 min. After 36 min of evaporation, the Exercise Participant entered the area for a total of 22 min. Actual whole body (WB) doses from optically stimulated luminescence (OSL) were 10 ± 2 μSv for both the Radiation Worker and Exercise Participant. WB digital personal dosimeter readings were 4.3 ± 0.4 μSv and 3.3 ± 1.0 μSv for the Radiation Worker and Exercise Participant, respectively. Actual extremity doses to Radiation Worker’s finger dosimeters were < 100 μSv (minimum detectable limit), and to exercise participant’s leg OSL was < 10 μSv. Preliminary dose assessment method was conservative for the Radiation Worker and conservatively accurate for the Exercise Participant. The predicted Radiation Worker doses were 90 μSv to the whole body (WB) and 744 μSv to the hand, both ≫2𝜎 above the actual exposures. The Exercise Participant’s estimated doses were 7 μSv to the WB and 15 μSv to the knee area, which were in the same order of magnitude as the actual. Refined dose assessment aimed to predict personnel exposure more exactly and was shown to be accurate. The predicted Radiation Worker doses were 2.8 ± 0.8 μSv to the WB and 21.8 ± 7.5 μSv to the hand. The Exercise Participant’s estimated doses were 5.2 ± 0.5 μSv to the WB and 13.4 ± 1.2 μSv to the knee area. Estimated whole body doses were in the same order of magnitude as the actual doses for both the Radiation Worker and the Exercise Participant. Comparing estimated extremity dose to the actual value was difficult, due to exposures having been below detectable limits, however, there were no obvious inconsistencies.