While millions of cargo containers enter the United States each year, no effective mechanism is in place to prevent the delivery of smuggled nuclear weapons or materials to our ports and internal transportation system. In this continuation of an IPRO held in Fall 2015, we will explore the use of beams of charged particles to scan cargo containers and determine whether they contain illicit nuclear materials before they reach our cities.
These materials are designated as “fissile,” i.e., able to sustain a nuclear-fission chain reaction, and the particles we propose to use in the beam are muons – heavier “cousins” of electrons – which are nearly ideal for our purpose. Muons are able to penetrate thick layers of material, and were famously used to “X-ray” the pyramids of Giza.
When muons come to rest in uranium, plutonium, or other fissile atoms, they cause characteristic gamma rays to be emitted whose wavelengths are a unique “fingerprint” of the atom in question. Demonstration projects using muons produced in the atmosphere have successfully found hidden fissile materials; however, the rate of atmospheric muon production is thousands of times too small for practical use. Recent progress in muon accelerator technologies can solve the rate problem. Thus there is an opportunity to develop an effective solution to identify suspect containers.
The principles underlying muon-based fissile-material detection systems are well understood. But there are several practical and technical questions that must be answered before deployment of such systems could be considered. For example, what beam parameters are needed – e.g., is it better to use a single muon energy or to scan over a range of energies to distinguish different materials? What energies and intensities are required in order to identify specific materials via either gamma ray emission from captured muons or (as was done for the pyramids) via muon tomography? If we use tomography to identify dense materials, how well can we distinguish tungsten from uranium from scattering data? The principle has been demonstrated, but can it be actualized in a device that will not halt the flow of commerce?
One significant concern we would like to address is the radiation safety of the device. Initial calculations from Fall 2015 indicated that some muon energies and intensities are close to regulatory limits. In order to progress, we need to determine what maximum intensity and time we can use to scan a container, given that a stowaway could conceivably be hiding in it. What are the ethical and regulatory limits to implementing this technology if there is some possibility of exposing such individuals to radiation?
Many other practical questions abound that will impact the design and feasibility of this device, and we anticipate that participants in this IPRO will identify and determine the significance of many we have not even considered.
Depending on the interests and capabilities of the students who enroll, teams will be organized to attack a selected subset of the questions above or others that are found to be important. Prof. Sullivan is expert in particle simulations. In the Fall 2015 version of this IPRO we obtained a computer simulation code called MARS which is utilized by radiation safety personnel at Fermilab in their determinations of muon safety thresholds and learned to use it for simple case studies. Prof. Kaplan is expert in muon-beam cooling and muon and radiation detection technologies. We hope to engage with the IIT Ethics Center in addressing some of the ethical questions regarding unintentionally subjecting people to a mild radiation hazard. Other resources will include publicly accessible information regarding shipping lanes, container manufacture, etc. for national ports. Students will work together in teams and provide periodic oral and written progress reports to the group as a whole.
When this IPRO project was first held, in the Fall 2015 semester, it won the People’s Choice Award. We wish to continue in Fall 2016 and beyond. As we enter a more technical stage, this IPRO would be most suitable for students in technical fields, such as physics, engineering, computer science and applied math.