Muon Tomography (MT) has been shown to be a viable candidate for the assay of nuclear storage containers . By reconstructing the trajectories of muons both entering and exiting a volume of interest, a 3D gradient density map can be built from the reconstructed scattering angle distributions. This technique is particularly useful when imaging shielded nuclear waste containers where discontinuity of knowledge or loss of pointer cannot be ruled out, capable of non-destructively confirming the contents of a container whilst avoiding the cost and safety concerns involved with explicitly opening it. However, work is still needed to understand the different experimental factors that can affect the techniques ability to discriminate between different materials. In particular, a suitable Figure Of Merit (FOM) is needed for waste characterization that can be used to compare the performance of competing detector systems and algorithms for the detection and evaluation of radioactive material hidden inside large waste volume containers.
We present our work on the application of “optical” resolution tests (see ) to understand size and feature resolution in a muon tomography system. By imaging test objects with decreasing features sizes, the number of easily distinguishable objects is an indicator of the resolution of a given tomography technique when interpreting the reconstructed density matrix. This method allows comparisons to be made between significantly different algorithms by converting their qualitative outputs into discrete figures of merit.
The expected signals for these testing methods are presented from simulations of a representative muon tomography system. Three different commonly used tomography algorithms are considered for testing (binned clustering , angle statistics back-projection , and simple point-of-closest-approach ). The results highlight the importance of understanding feature resolution in muon tomography systems when imaging heterogenous nuclear waste storage containers. In the future an experimental testing apparatus for the production of these FOMs will be developed and used to further calibrate and characterize the performance of a muon tomography system being commissioned at the University of Bristol for the CHANCE Horizon-2020 project .
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 CHANCE 2020 : http://chance-h2020.eu. Future work will be funded by the European NFRP7 program, grant no. 755371 (CHANCE).