Nuclear Weapons 199 - New Cargo Container Scanning System Promises Better Security At U.S. Ports
Nuclear security has been the subject of a lot of my blogs lately. One big concern is the possibility that nuclear materials might be smuggled into the U.S. inside one of the more than sixteen thousand cargo containers that arrive at U.S. ports each day. Currently only about two percent of the containers are thoroughly inspected. Researchers have been working for years on a way to quickly inspect cargo containers for radioactive materials.
Researchers at the Georgia Institute of Technology, the University of Michigan and Pennsylvania State University have been working on a cargo container scanning system under a grant from the National Science Foundation and the U.S. Department of Homeland Security. A report on their research was just issued today in the journal Scientific Reports.
The new system begins with an ion accelerator which produces heavy isotopes of hydrogen called deuterons which have a neutron in their nucleus in addition to the proton. The particles are emitted with energies of about four and half million electron volts and sixteen million electron volts. The deuterons slam into a boron target which results in the emission of high energy neutrons and photons. The beam of high energy neutrons and photons is focused into a fan shaped beam suitable for scanning cargo containers. The neutrons and photons pass through the container and hit Cherenkov quartz detectors which are connected to photomultiplier tubes. The high energy photons are used to form an image of the contents of the container.
The neutrons in the beam excite any nuclear materials in the cargo container which causes the materials to emit gamma rays and neutrons. These emissions are detected by the sensors outside of the container. Radioactive materials will cause time delayed neutron emissions. Other heavy elements like lead and tungsten do not emit time delayed neutrons. In addition to just indicating the presence of some kind of radioactive materials, these time delayed neutrons and gamma emissions also indicate specific types of radioactive materials. Therefore these different mixtures of gamma rays and time delayed neutrons can be used to identify the types of radioactive materials in a particular cargo container.
Earlier detection systems used high levels of X-rays which could be harmful to cargos such as electronic components and other types of cargo which could be affected by radiation. The ion beam in the new system utilizes a much lower level of radiation and so is less dangerous for sensitive cargo.
So far, the system has been tested successfully in a laboratory on samples of shielded uranium plates and rods. These tests prove that the basic idea is sound. The system has not been tested on radioactive materials in real steel cargo containers but the researchers will conduct such tests in the near future. If the new system can be scaled up for use in the real world of cargo container handling , it would provide a much greater degree of security against attempts to smuggle radioactive materials into the U.S. by terrorists.
