-13- ( the ratio of plutonium concentration over bare soil on May 6-8 compared to in dust aerosol concentrations (Table 2) May 10-11 is caused by a 5.91 x increase and 3.23 x increase in enhancement factor (Table 4) —— for a combi-ne-d,effect. on %F63sol’~l”fitoniumconcentration (6466 aCi m-3/338 aCi m-3)-o-f~l_9J-1,. Resuspension of Radioactive Particles by Vehicular and Foot Traffic ., ,. ( The integrating nephelometer was installed with intake at 1.2 m height and 2 m leeward from the position of average tire tracks on a frequently-traveled, one-lane dirt road on Bikini Island. Even though the traditional vehicular traffic of light trucks at low speeds was increased in frequency by our experimental activity, we were interested in characterizing the resuspension of plutonium and inhalation exposure per vehicle pass. The nephelometer provided - details on magnitude, duration, and frequency of dust concentrations, while plutonium and dust aerosol concentrations (Table 2), and plutonium activity and enhancement factors (Table 4) were obtained by a co-located HV. Dust concentrations above background rose in a pulse exceeding 10 s duration where the peak was obtained in a period about 4.5 s after the passage of the vehicle (Figure 4). This characteristic time to arrival of the peak, regardless of concentration, was determined b,yX/uu where the travel distance X is 2 m and the RMS turbulent velocity Uu is about one-tenth the local wind speed of 4.5 m S-l. Hence the dust pulse was traveling by diffusion and not characterized by translation in the wake of the passing vehicle. The dust pulse example of Figure 4 represents an extreme case (more than 90% of occurrences had lower concentrations), but demonstrates the characteristic peak to mean ratio of 3.6 and the slow return to background on the tail of the pulse. The amplitude and frequency of dust pulses due to motor vehicle, bicycle, and foot traffic were recorded during May 11-15. The sixty-eight cases of motor vehicle passes observed showed an approximate log-normal frequency distribution with median peak concentration (above background) of 100 ~g m-s and geometric standard deviation of 3.4> Figure 5. Bicycle traffic could not be distinguished from foot traffic. In the seven observed cases of foot traffic, we found an approximate median peak concentration above background of 26 ug m-3. It should be emphasized that the log-normal concentration implies a fairly high chance (5%) of an exposure to a vehicular-induced peak concentration of 760 ~g m-s having a mean concentration 760/3.6 = 211 pg m-s for about 10 seconds. The plutonium enhancement factor was estimated at 2.5 in this study (Table 4). Personal Inhalation Exposure and Dosimetry .* ~. \ L / . Until now, the discussion has centered on the (combined) isotope 239+240Pu, since in fact this is the most important component of inhalation exposure. Extensive soil sampling on Bikini Island has established that a relatively homogeneous mixture of isotopes exists in the soil (Table 5). In the aerosols, some of the isotopes become significantly enhanced (2SBPU and ‘37CS) but they remain of lesser inhalation-hazard. The in situ gamma (ISG) spectroscopy system which measured 241Am in the soil at Bikin~w~ighly correlated to that measured in surface soil samples by special chemistry methods (r2 = 0.210), which gives confidence in both methods. However, ,data from the ISG system was consistently lower than the soil sampling method by a factor of 0.7 because it integrated a . -