Toward a RPC-based muon tomography system for cargo containers.

Abstract

A large area scanner for cosmic muon tomography is currently being developed at University of Bristol.Thanks to their abundance and penetrating power, cosmic muons have been suggested as ideal candidates to scan large containers in search of special nuclear materials, which are characterized by high-Z and high density. The feasibility of such a scanner heavily depends on the detectors used to track the muons: for a typical container, the minimum required sensitive area is of the order of 100 2. The spatial resolution required depends on the geometrical configuration of the detectors. For practical purposes, a resolution of the order of 1 mm or better is desirable. A good time resolution can be exploited to provide momentum information: a resolution of the order of nanoseconds can be used to separate sub-GeV muons from muons with higher energies.Resistive plate chambers have a low cost per unit area and good spatial and time resolution; these features make them an excellent choice as detectors for muon tomography.In order to instrument a large area demonstrator we have produced 25 new readout boards and 30 glass RPCs. The RPCs measure 1800 mm× 600 mm and are read out using 1.68 mm pitch copper strips.The chambers were tested with a standardized procedure, i.e. without optimizing the working parameters to take into account differences in the manufacturing process, and the results show that the RPCs have an efficiency between 87% and 95%. The readout electronics show a signal to noise ratio greater than 20 for minimum ionizing particles. Spatial resolution better than 500 μm can easily be achieved using commercial read out ASICs. These results are better than the original minimum requirements to pass the tests and we are now ready to install the detectors.

A generalized muon trajectory estimation algorithm with energy loss for application to muon tomography

“…Using fewer muons provides significant time savings but lower quality images, while a higher number of measured muons results in improved image contrast and resolution but increased measurement time. Existing studies on muon-CT detectors have demonstrated that muons on the order of millions (requiring minutes to days of measurement time, depending on the size and orientation of the detectors) are required for imaging large scale objects such as cargo containers [4,5,11] or dry casks [21][22][23]. Recent work based on simulations showed that several days (>10 6 muons) are needed to identify the location of spent nuclear fuel in dry casks [21][22][23].…”

“…Recently, the use of muons in nuclear nonproliferation and safeguards verification applications has received attention as a passive and penetrating way to interrogate objects. This endeavor has been assisted by the development of detectors that can measure and provide information related to the incoming and outgoing trajectories of individual muons [2][3][4][5][6]. Recently, cosmic ray muons have been investigated for volcano imaging [7][8][9] and cargo scanning applications [10][11][12].…”

A compact, high resolution tracker for cosmic ray muon scattering tomography using semiconductor sensors

“…Cosmic ray muon imaging has found many applications, some that can sacrifice high resolution imaging for short acquisition and object detection times [3,5], and some that require high resolution images with less emphasis on the acquisition time [17,18]. An example of early detection of a lead sample is given in Figure 20 for 100, 1000, 5000 and 25000 muons.…”

Passive 3D imaging of nuclear waste containers with Muon Scattering Tomography

“…For that purpose, a small-scale prototype consisting of 12 RPCs with a fiducial region of 48 x 48 cm 2 was developed, and after the successful completion of this system, a large-scale prototype consisting of 24 RPCs with a fiducial region of 178 x 54 cm 2 was built. Details and results of both systems can be found in [4,5]. The simulated detectors used in this study have been based on these detectors; in particular, the intrinsic spatial resolution was assumed to be 450 µm based on the prototype results.…”