Electrical charge characteristics of long-lived radioactive dust.

Respirable long-lived radioactive dust (LLRD), i.e., dust containing long-lived radionuclides such as 238U, 232Th, 226Ra, 224Ra and 228Th, interacts with unipolar and bipolar atmospheres through diffusion charging, electrical charge neutralization, and electrical self-charging mechanisms. Because of these interactions, and depending on the type of dust as well as its method of production, LLRD is found in electrically charged and neutral states. Electrical charge is important because it influences the deposition of particles in the human respiratory system. Particle size, electrical charge, and radioactive particle size distributions were measured in an area of an underground U mine where U ore crushing and transportation operations were conducted. In addition, concurrent measurements of 222Rn progeny and 220Rn progeny were made. A variety of instrumentation was used, such as particle counters. The electrical charge associated with dust generated in the primary crushing operation was substantially higher (3e- at 1 microns and approximately 500e- at 3 microns) than for the conveyor belt (2e- at 1 microns and approximately 50e- at 8 microns). In both cases the charge distribution was significantly higher than that predicted by Boltzmann's distribution.