A RADIATION ACCIDENT AT AN INDUSTRIAL ACCELERATOR FACILITY

On 11 December 1991, a radiation overexposure occurred at an industria l radiation facility in Maryland. The radiation source was a 3-MV pote ntial drop accelerator designed to produce high electron beam currents for materials-processing applications. This accelerator is capable of producing a 25 milliampere swept electron beam that is scanned over a width of 112.5 cm and which emerges from the accelerator vacuum syste m through a titanium double window assembly. During maintenance on the lower window pressure plate, an operator placed his hands, head, and feet in the beam. This was done with the filament voltage of the elect ron source turned ''off,'' but with the full accelerating potential on the high voltage terminal. The operator's body, especially his extrem ities and head, were exposed to electron dark current. In an attempt t o reconstruct the accident, radiochromic film and alanine measurements were made with the accelerator operated at two beam currents. Measure d dose rates ranged from approximately 40 cGy s-1 inside the victim's shoe to 1,300 cGy s-1 at the hand position. Approximately 3 mo after t he accident, it was necessary to amputate the four digits of the victi m's right hand and most of the four digits of his left hand. Electron paramagnetic resonance spectrometry, which measures the concentration of radiation-induced paramagnetic centers in calcified tissues, was us ed to estimate the dose to the victim's extremities. A mean dose estim ate of 55.0 +/- 3.5 Gy (95% confidence level) averaged over the mass o f the bone was obtained for the victim's left middle ringer (middle ph alanx).