A Prototype Scintillating-Fibre Tracker for the Cosmic-ray Muon Tomography of Legacy Nuclear Waste Containers

D Mahon ,B Mckinnon,C Staines,D G Ireland,C Shearer,S Nutbeam-Tuffs,T Keri,M Hoek,J Johnstone ,R Kaiser ,M Murray ,A Clarkson ,D Hamilton ,S Lumsden ,Guang Yang ,C.h Zimmerman

doi:10.1051/epjconf/20146610005

Abstract

Cosmic-ray muons are highly penetrative charged particles observed at sea level with a flux of approximately 1 cm−2 min−1. They interact with matter primarily through Coulomb scattering which can be exploited in muon tomography to image objects within industrial nuclear waste containers. A prototype scintillating-fibre detector has been developed for this application, consisting of two tracking modules above and below the volume to be assayed. Each module comprises two orthogonal planes of 2 mm fibres. The modular configuration allows the reconstruction of the initial and scattered muon trajectories which enable the container content, with respect to atomic number Z, to be determined. Fibre signals are read out by Hamamatsu H8500 MAPMTs with two fibres coupled to each pixel via dedicated pairing schemes developed to avoid space point ambiguities and retain the high spatial resolution of the fibres. A likelihood-based image reconstruction algorithm was developed and tested using a GEANT4 simulation of the prototype system. Images reconstructed from this simulation are presented in comparison with experimental results taken with test objects. These results verify the simulation and show discrimination between the low, medium and high-Z materials imaged.

Highlights

Muons occur naturally from the decay of pions and kaons produced in cosmic ray showers in the Earth’s atmosphere
Cosmic muons are highly-penetrating particles which interact only weakly with matter via ionising interactions with atomic electrons and Coulomb scattering off nuclei. They are observed at sea level with a flux of approximately one muon per square centimetre per minute. These properties can be exploited in muon tomography (MT) to image the internal composition of shielded structures which would otherwise block more conventional forms of imaging radiation e.g. X-rays
Muon tomography is a promising technique for characterising the content of these legacy waste containers to assist in mitigating the risk inherent with the long-term storage of materials of this nature

Summary

Introduction

Muons occur naturally from the decay of pions and kaons produced in cosmic ray showers in the Earth’s atmosphere. [5] by Borozdin et al revealed, for the first time, the potential to utilise the Coulomb scattering of muons to identify high-Z materials within shielded containers.

Results

Conclusion