Finding nuclear material smuggled in on of the thousands of shipping containers that arrive in the United States each day is not easy. Radiation detectors exist, but they aren't useful for mass screenings and can't distinguish between the amount and type of material in the container.
To help get a handle on the problem, researchers at Los Alamos National Laboratories have developed an X-ray laser that can detect radioactive substances, a proof of concept that could be developed into a future detection system.
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The scientists tested the laser on two closed containers - one with nuclear material inside and one without. They also placed two other materials into the shipping containers: a piece of metal and a piece of plastic, 0.3-microns thick, that had been chemically altered to have its hydrogen atoms replaced with deuterium. Deuterium is basically hydrogen that instead of having one proton in the nucleus, it has a proton and a neutron.
They fired the laser called a TRIDENT at the shipping container. The laser, which generates 200 terawatts of power, was so powerful that when it came into contact with the deuterium molecules in the plastic, it pushed the molecule's nucleus - called a deuteron - right out of the plastic, at about 10 percent the speed of light, or 18,600 miles per second. Many of those deuterons then smacked into the atoms of the metal target nearby.
When the deuterons hit the atoms in the metal target, they created a second shower of particles, this time neutrons - imagine a tennis ball hitting a larger pile of balls and scattering them everywhere. These neutrons moved fast, and were directed in a cone shape, like a flashlight beam.
When the neutrons hit the radioactive material, they caused fission, which released yet more neutrons. Those were recorded by a neutron detector. The container with no radioactive material did not release additional neutrons.
The team found that the number of neutrons and the pattern of scattering in the container with nuclear material indicated how much material was present.
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To make a workable detection system, the laser would have to be made smaller. The X-ray laser and it's associated equipment fills a room, and miniaturizing that will be challenge. Although the power of the laser beam itself is huge, it lasts for so short a time that generating the energy isn't as difficult as it sounds. Eventually the Los Alamos team hopes to make a hand-held or tabletop-size version.
Scanning technologies aren't without their critics, who have said the likelihood of any terrorist group obtaining nuclear weapons or material is pretty small. Smuggling incidents have occurred, but none has (so far) uncovered enough uranium or plutonium to make a bomb with, even if one of those two elements was present. Even so, a single attack with a "dirty bomb" would be devastating, so efforts continue to find ways to keep the stuff out of ports will probably continue.
Credit: Los Alamos National Laboratory