Annual Report for 2010/11 and Forward Programme - Sellafield Ltd

SSEM/2011/4730 June 2011Figure 3.22. Probability Plot of Log of 238 Pu Particle Activity (positive data only).From the plots and statistics above all three radionuclides show a strong correlation to a lognormal distribution with p values greater than 0.1. The Anderson-Darling test is heavilyweighted at the tails which explains the lowest p value being seen for 241 Am. Figure 3.20shows that the upper end of the 241 Am activity is under represented and the lower end overrepresented. The 238 Pu and 239 Pu activity plots (Figure 3.21 and Figure 3.22) show similarunder representation at the higher activities with some indication of over representation atlower activities for 238 Pu. Of the three radionuclides 241 Am is the critical radionuclide fordetection by the Groundhog TM Synergy system. The over representation at lower 241 Amactivities would suggest that Groundhog TM Synergy is capable of detecting all members ofthis population of alpha-rich finds and the limit of detection (LOD) is not an issue. To confirmthis conclusion a probability plot (Figure 3.23) of just the particles found at the sand surfacecan be assessed.© Nuclear Decommissioning Authority 2011. 46