Investigating the Effect of Force Input on the Pick-Up Factor of Loose Contamination

Dry swabbing is a common technique used in the characterisation of radioactive environments, however there is a large amount of uncertainty in quantifying the removal of contamination from dry swabbing. This uncertainty is often largely attributed to variability in the force input while swabbing, however no studies to our knowledge have yet quantified this effect. This paper demonstrates the effect that force input has on the removal of an idealised contaminant so that we can better understand the sources of uncertainty in pick-up factor. The work presented finds that pick-up factor, the fraction of contaminant removed from a surface, was dependent on the swabbing force, and that controlling the swabbing force can reduce the overall uncertainty in pick-up factor across multiple swabs. Force-controlled swabbing produced a much smaller standard deviation in pick-up factor, (σ=3.3), than for uncontrolled swabbing (σ=13.4 ). It was also found that there is reduced pick-up with higher swabbing forces. While a mean pick-up factor of >20% was achieved for a 20 N swabbing force, this figure reduced sharply to <10% for a 30 N swabbing force.