Highly penetrating cosmic ray muons constantly shower the earth at a rate of about 1 muon per cm2 per minute We have developed a technique which exploits the multiple Coulomb scattering of these particles to perform nondestructive inspection without the use of artificial radiation In prior work , we have described heuristic methods for processing muon data to create reconstructed images In this paper, we present a maximum likelihood/expectation maximization tomographic reconstruction algorithm designed for the technique This algorithm borrows much from techniques used in medical imaging, particularly emission tomography, but the statistics of muon scattering dictates differences We describe the statistical model for multiple scattering, derive the reconstruction algorithm, and present simulated examples We also propose methods to improve the robustness of the algorithm to experimental errors and events departing from the statistical model

Statistical Reconstruction for Cosmic Ray Muon Tomography

Over 120 million vehicles enter the United States each year. Many are capable of transporting hidden nuclear weapons or nuclear material. Currently deployed X-ray radiography systems are limited because they cannot be used on occupied vehicles and the energy and dose are too low to penetrate many cargos. We present a new technique that overcomes these limitations by obtaining tomographic images using the multiple scattering of cosmic radiation as it transits each vehicle. When coupled with passive radiation detection, muon interrogation could contribute to safe and robust border protection against nuclear devices or material in occupied vehicles and containers.

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Tomographic Imaging with Cosmic Ray Muons

New applications of charged particle radiography have been developed over the past two decades that extend the range of radiographic techniques providing high-speed sequences of radiographs of thicker objects with higher effective dose than can be obtained with conventional radiographic techniques. In this paper, we review the motivation and the development of flash radiography and in particular, charged particle radiography.

https://iopscience.iop.org/article/10.1088/0034-4885/76/4/046301/pdf

Charged particle radiography.

Nuclear waste imaging and spent fuel verification by muon tomography

A study of imaging the Fukushima Daiichi reactors with cosmic-ray muons to assess the damage to the reactors is presented. Muon scattering imaging has high sensitivity for detecting uranium fuel and debris even through thick concrete walls and a reactor pressure vessel. Technical demonstrations using a reactor mockup, detector radiation test at Fukushima Daiichi, and simulation studies have been carried out. These studies establish feasibility for the reactor imaging. A few months of measurement will reveal the spatial distribution of the reactor fuel. The muon scattering technique would be the best and probably the only way for Fukushima Daiichi to make this determination in the near future.

Imaging Fukushima Daiichi reactors with muons

We have built a detector capable of locating high Z objects in the sampling (middle) region of the detector. As atomic number increases, radiation length rapidly decreases, yielding larger variance in scattering angle. Cosmic ray muon tomography works by tracking muons above the sampling region, and tracking them below the region as well. The difference between the two trajectories yield information, via the muon scattering variance, of the materials contained within the sampling region [Borozdin, K, et al., 2003]. One of most important aspects of cosmic ray tomography is minimizing exposure time. The cosmic ray flux is about 1 cm-2 min-1, and the goal is to use them for detecting high-density materials as quickly as possible. This involves using all of the information possible to reconstruct tracks with redundant detectors. Detector scattering residuals yield a low precision measurement of muon energy. Knowing the rough energy of an incoming particle will yield more precisely the expected scattering variance (currently the expectation value of ~3 GeV is used).

Optimizing the Tracking Efficiency for Cosmic Ray Muon Tomography

In this paper we describe the principles that have guided our design and the experience we have gained building multi-wire proportional chambers detectors for the ultra-cold neutron (UCN) source at the Los Alamos Neutron Science Center (LANSCE). Simple robust detectors with 50 cm2 of active area have been designed. These have been used both in ion chamber and proportional mode for the detection of UCN.

J. Gonzales

Papers

Tomographic Imaging with Cosmic Ray Muons

Optimizing the Tracking Efficiency for Cosmic Ray Muon Tomography

Multi-wire proportional chamber for ultra-cold neutron detection