STUDir.S I\ DETECTING RADIO-ACTIVE FALI.-OUT 



From Table 1 it can be seen that there is little doubt of the origin of the 

 fall-out collected. It is interesting to note that the time elapsed between 

 explosion and collection is approximately 10-20 days, even though some 



— c^kt' 

 • Cheesecloth sample 

 ° Rainwater sample 



01 



50 



150 



100 

 i - time in days 



Figure 4. Comparison of measured and theoretical decay 



explosions were actually in Australia and others were considerably further 

 away. It must be remembered, however, that only weekly collections w^ere 

 made, so there is no way of telling whether, for instance, the activity had 

 been collected 3 or 10 days after the explosion. 



There are certain limitations in this estimation. The main one is that 

 since such a large number of nuclear weapon tests have been carried out 



Table I. Estimated origins from graphs, compared with known dates of explosions 



132 



