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

2.52.72.93.13.33.53.73.94.14.34.54.74.95.15.35.55.75.96.16.36.52.52.72.93.13.33.53.73.94.14.34.54.74.95.15.35.55.75.96.16.36.5SSEM/2011/4730 June 2011histograms for both are given in Figure 3.24 and 3.25 respectively. The activity data used forthe histogram plots has been transformed using a log base 10 transformation to show theshape of the distribution more clearly. There are 428 data points for stones and 270 forparticles and all the analysis results are greater than the limit of detection.Log Stone Cs137 Activity Histogram45403530Frequency2520151050Log to base 10 of Cs137 ActivityFigure 3.24. 137Cs Stone Activity Histogram.A tail at higher activities is observed for stones that may be due to random outliers (~ 2% oftotal) but is more probably due to either overlapping populations of beta-rich stones (i.e. twoor more populations with overlapping activity ranges) or an unusual 90 Sr to 137 Cs ratio or apopulation that does not fit a statistical distribution type.Log Particle Cs137 Activity Histogram353025Frequency20151050Log to base 10 of Cs137 ActivityFigure 3.25. 137 Cs Particle Activity Histogram.There are fewer outliers for particles compared with stones. It is expected that the outliers inboth groups will result in a poor fit to their corresponding log normal probability plots. Theprobability plot for stones (Figure 3.26) has a probability p value of < 0.05 and hence the log© Nuclear Decommissioning Authority 2011. 50