Radiation monitoring after experimental dirty bomb explosion.

This article reports on two 2021 experiments conducted by the National Institute of NBC Protection (SUJCHBO v.v.i.), Czech Republic, simulating radioactive dirty bomb explosions using the radionuclide technetium-99m (^99mTc) dispersed over an open-air urban square model. Filters placed on the model’s surfaces and walls before the explosions captured deposited radioactive aerosols, which were subsequently measured for surface contamination using laboratory high-purity germanium (HPGe) gamma spectrometers and a portable NaI(Tl) spectrometer (GT-40), alongside ambient dose equivalent rate (H*(10)) measurements. The first experiment tested measurement geometries and methods, finding that the portable GT-40 spectrometer could effectively perform in situ spectral measurements, while H*(10) measurements provided rapid contamination estimates above about 1 Bq/cm². The second experiment employed an optimized measuring geometry (ointment vessels) and confirmed higher contamination levels, with surface activities exceeding 2000 Bq/cm² on horizontal surfaces and nearly 65 Bq/cm² on vertical walls, demonstrating spatial variability in contamination distribution. These results support the feasibility of rapid, on-site radiometric assessment following a dirty bomb event using combined spectrometric and dose rate measurement techniques.