shown in Fig. 4.11. Stations 540.15 and 540.09 were both located at 15 miles, but at different azimuths from ground zero(see Fig. 2.1 for location). 4.5.1 Arrival of Fall-out It is most interesting to note that the cross-wind arrival time was completely independent of distance from ground zero, At the four stations from 8 to 15 miles, the fall-out began at +40 to +45 min, This suggests a delivery mechanism independent of winds (Chap. 8). Table 4.3-—-SIZE DISTRIBUTION OF RADIOACTIVE FALL-OUT PARTICLES Size distribution, LL Distance Station cross wind, 540.20 540.18 540.18 540.17 540.16 540.15 540.15 4.5.2 Period miles of fall-out 5.0 Early 8.0 8.0 10.0 10.0 15.0 15.0 Early Middle Middle Early Middle Late 25 50 to to 4 8 100 200 300 to to to 14 5 7 4 1 3 1 50 100 200 300 400 6 1 1 9 0 13 10 4 2 23 2 13 2 7 10 1 1 «#12 3 Remarks Several particles to 5000 Several particles to 1200 u Several particles to 500 u Several particles to 1000 » Several particles to 1200 u Several particles to 1200 u Duration of Fall-out The four stations fixed the duration of fall-out at something less than 2 hr, with three of these stations experiencing exactly the same duration. Station 540.09, to the east of 540.15, shows the cessation of the fall-out to be at 0 + 95 min, a somewhat earlier time than the time of 0 + 144 min experienced by the other three stations. 4.5.3 Distribution of Activity with Time Figure 4.11 shows the randomnessof the time distribution of fall-out within the period in which it occurred. All the stationg experienced several maxima and minima. These peaks and valleys show no correlation between time and distance. Since the samples were collected over limited areas, the levels of activity shown in Fig. 4.11 are not too representative. REFERENCES 1. LG. Poppoff, Fall-out Particle Studies, Jangle Project 2.5a-2 Report, WT-395; also in Particle Studies, WT-371. 2. U. 8. Naval Radiological Defense Laboratory Report on High Explosive Model Studies (in preparation). 47