Applying nuclear science and technology to the benefit of Canada
2013 April 22 — A number of times over the past few years, we have run stories relating to muon tomography and the use of this technology in border security as cosmic rays can be used to image and find hidden nuclear material and security threats. With three million shipping containers entering Canadian ports annually, this technology has important applications. However, prior to this year, much of the work being done in Canada was theoretical in nature. Although muon imaging tomography and detection has been in practice for many years, the techniques and technology are still very much in the early stages of development and application. In fact, there are really only a handful of countries in the world that have actual, physical facilities to conduct advanced work in muon imaging tomography. And now, we can proudly state, Canada is one of them! On 2012 October 16, the first Canadian image using muon scattering tomography was created. Known as CRIPT (Cosmic Ray Inspection and Passive Tomography), this accomplishment was a collaborative effort with private and public sector involvement. Funded by the Canadian Safety & Security Program (CSSP), this work was supported by Defence Research and Development Canada Centre for Security Science Chemical, Biological, Radiological/Nuclear, and Explosives Research and Technology Initiative (CRTI 08-0241RD) with project partnership from DRDC Ottawa, AECL, Advanced Applied Physics Solutions, Canada Border Services Agency, Carleton University, Health Canada, International Safety Research Inc. The team has been working hard over the past year to design, construct, assemble and install Canada’s first full scale detection system. Muons are very heavy, charged particles created by cosmic rays hitting the upper atmosphere. They shower the ground at the rate of about one or two per square centimetre per minute, and because of their tremendous energies, muons are able to penetrate material. When muons pass through material (such as uranium or plutonium) they deflect, changing their trajectories. By examining these changes, it becomes possible to determine the material through which they pass. Located at the Carleton University campus in Ottawa Ontario, the detector facility stands roughly 5.5 metres tall and was designed to accommodate a “ULD” or unit load device, a set of standard-sized shipping containers for aircraft. With over three kilometres of thin, wave-length shifting fibre optic cabling embedded in scintillators, the assembly and commissioning of the device was a time-consuming and detailed exercise, but with the first set of images becoming available, the hard work becomes an afterthought. As muons pass through the cables they produce just a few photons. This light is amplified with a photo-multiplier tube and converted to a digital signal. CRIPT is able to gather data points as the muon passes through the detector, providing important information about the angle at which the muon enters. With trackers located above and below the material being monitored, researchers can determine the entry angle of the muon into the material and the exit angle. One will literally then “connect the dots’ to create the image. CRIPT is uniquely Canadian. While there are other detector technologies around the world, CRIPT will provide more detailed information about the “hidden” materials than ever before. Detection of the exit energy of the muons via two layers of 10 cm of iron (a known material) in the spectrometer will, in time, allow researchers to accurately characterize the material being imaged. Again, this technology is in its infancy, and exploratory work is still underway, however it does hold great possibilities, as it will reveal more detailed information which can be used to determine the specific type of material being imaged as well as produce an image in three dimensions. Once the device has been fully commissioned, it will move from Carleton University to its new home in Building 145 at the Chalk River Laboratories. By locating CRIPT here, Canada will have the ability to work with nuclear materials similar to those it was designed to detect.