On evaluating respiratory tract intake of high specific activity alpha emitting particles for brief occupational exposure

The radiation protection approach for limiting the intake of radionuclides through use of the derived air concentration (DAC) can considerably overestimate the intake of highly radioactive, alpha emitting (αE) particles for brief accidental exposures of nuclear workers. Inhalation exposure over a few hours or less is considered brief exposure. Pure αE particles with specific activity greater than that for 239Pu (i.e. >2.26 x 103 MBq.g-1) are called high specific activity (HSA) αE particles. Pure αE particles with specific activity equal to or less than that for 239Pu are called low specific activity (LSA) αE particles. For HSA-αE 238PuO2 particles, there may only be a single particle in thousands of tidal volumes of air presented for inhalation when the air radioactivity concentration of 238PuO2 is at the DAC for inhalation Class Y 238Pu. For brief exposures at or near the DAC, respiratory tract intake evaluated, based on DAC-h of exposure, can be considerably overestimated (with high probability) or underestimated (with low probability) for 238PuO2. For such circumstances, it is beneficial to evaluate the probability distribution of possible intake of radioactivity, rather than the expected intake. Mathematical tools are provided that facilitate evaluating the distribution of possible respiratory tract intake of HSA-αE particles during brief occupational exposure. Approaches to limiting stochastic effects from inhaled HSA-αE particles are also discussed. (Author)