Year
2017
Abstract
Mirion Technologies In Situ Object Counting System is an established tool used for gammaspectrometry allowing a physical representation of complex geometries and mathematical calculationof the calibration function while avoiding the need for radioisotope standards. The ISOCS UncertaintyEstimator tool can be used to calculate defensible systematic calibration uncertainties. However theuncertainties depend on knowledge of the properties of the item being measured and for poorlycharacterized materials these can be large, often leading to large costs for waste sentencing.An ISOCS–based advanced in-situ gamma spectrometry services tool has been developed to reducethose uncertainties. This system is based on generating and comparing a range of candidate geometrymodels that yield figures of merit indicative of improved consistency between modelled data andavailable diverse measurement data.The approach and results of initial performance testing have previously been published, demonstratingan analysis procedure and enhanced accuracy for measurement of 200 litre waste drums withheterogeneous activity, further analysis here shows improved results for large item measurements.As it is technically difficult to experimentally measure known source combinations in shippingcontainers (Half-height ISO containers or Third Height ISO containers) under representativeconditions, modelling was conducted of various experimental conditions using the softwareMCNPX™ in order to produce simulated high resolution gamma spectra. The results of the newservices tool analysis in comparison to the input modelling scenario have been presented hereshowing great improvements to the uncertainties on quantitative radionuclide measurements.