Every year, more than 16 million vehicles and shipping containers enter the United States through its ports of entry. Suppose a nuclear bomb, a dirty bomb, or enough radioactive material to make a bomb is hidden in one them—how do we prevent nuclear terrorism?
Scientists at Los Alamos have responded to what President Barack Obama calls “the single biggest threat to national security” by proposing a new technology—muon vision—that is specifically designed to detect nuclear materials hidden inside vehicles and containers (see “What is Muon Vision?” page 39). In 2006, Los Alamos partnered with Decision Sciences International Corporation (DSIC) and granted DSIC an exclusive contract to develop and commercialize the Lab’s muon vision system.
Currently, passive radiation monitors, much like giant Geiger counters, are the main screening tools looking for nuclear contraband. These monitors detect the gamma-ray and neutron radiation given off by uranium, plutonium, or other nuclear materials.
However, not all ports have these monitors, and those that do can experience false positives from unexpected sources. For example, crates of bananas or sacks of water-softening chemicals can set off these monitors because both contain trace amounts of potassium-40, a radioactive isotope of potassium. The glazes of certain ceramics contain radioactive uranium isotopes that also set off the monitors. Tracking down those false positives wastes valuable time and resources.
Furthermore, these radiation monitors are not capable of finding radioactive materials that are shielded—for example, hidden inside lead containers. The walls of a thick lead box, for instance, will stop (absorb) uranium’s gamma rays before they escape, thereby removing the telltale radiation signal that the current radiation monitors need for effective detection. A 50-pound “cube of terror” (about the size of a half-loaf of bread) of highly enriched uranium, which is enough to make a nuclear weapon, can pass through a port without detection.
One defense is to use a very powerful x-ray machine, which would definitely “see” the lead box but could not look inside or identify the contents as nuclear material. In addition, powerful x-ray machines are massive and need lots of electrical power, which means they are very expensive to build and operate. The high voltage and lethal x-rays these machines produce also make them dangerous for port-of-entry security staff to operate. And what if an interrogated truck is smuggling human cargo?
Muon vision offers a different approach that is potentially less expensive to build and operate and uses no dangerous radiation. DSIC’s Multi-Mode Passive Detection System (MMPDS), which has been operating in Freeport, Bahamas, since 2012, safely scans cargo containers, often in about a minute or less.
In April 2015, the Department of Homeland Security’s Domestic Nuclear Detection Office successfully completed the final testing phase of its five-part system characterization of the MMPDS at Freeport, bringing muon vision much closer to possible widespread deployment in U.S. border security.