Cosmic-ray muons could be used to detect nuclear material in a new radioimaging technique developed by researchers in the US. Konstantin Borozdin and colleagues at the Los Alamos National Laboratory in New Mexico believe that the method could provide a safe and inexpensive alternative to conventional X-ray radiography (K N Borozdin et al. 2003 Nature 422 277).
Although it is widely used for imaging, X-ray radiography cannot penetrate dense objects or produce three-dimensional images easily. In contrast, muons are highly penetrating – a typical cosmic-ray muon can pass through more than 10 metres of water – and could be used to produce radiographic images of medium-to-large objects in a short exposure time.
To demonstrate the technique, Borozdin and co-workers sandwiched a small tungsten cylinder between two pairs of muon detectors and measured the direction of the muons before and after they had interacted with the object (see figure). The deflections they measured were then used to generate a 3-D image of the cylinder.
The Los Alamos team then simulated the passage of the muons through the volume on a computer. They found that the simulated images were indistinguishable from the experimental ones. Simulations of larger, more complex objects showed that a 10x10x10 cm3 uranium object could be detected inside a large metal container – for example in a truck full of sheep – in about one minute of exposure time.
The team believes that the method may be suitable for a variety of applications in which radiography of dense objects with low radiation dose is required. This includes the surveillance of nuclear materials at borders. “We now intend to improve our analysis methods, to extract all the information possible from each muon,” team member William Priedhorsky told Physics Web. The team also hopes to make the detectors more economical and effective.
