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Alternatives To Employing Helium-3 As A Neutron Detector

May 31

The effectiveness of currently available alternative neutron detector technologies for use in large-area detectors and radiation portal monitors (RPM)—the two neutron detector applications that have created the greatest demand for helium-3—is being investigated by science facilities and federal agencies. Three alternative neutron detector technologies that are available and might satisfy requirements for use have been identified by an international collaboration of science facilities that plan to deploy large-area detectors for research and federal agencies that procure and deploy RPMs for security: boron-10 lined proportional detectors, boron trifluoride proportional detectors, and lithium-6 scintillators. Instead of helium-3, these devices detect neutrons using boron-10 and lithium-6. The multinational partnership has agreed on a strategy to use these technologies to create and test huge area detectors. The testing of these technologies for use in RPMs has been directed by federal agencies such as DHS, and field testing of RPMs employing boron-10 lined proportional detectors has been completed. A boron-10 lined proportional detector may be ready for domestic RPM installations in early fiscal year 2012, according to agency officials. GAO believes that this neutron detector is developed enough that it may be used in future portal monitor installations with confidence that the portals will work as expected. Our estimate is based on our evaluation of the technological readiness levels (TRL), which rate an application's maturity on a scale of one to nine. These three different neutron detector technologies presently available vary in TRL from 5 to 7.

More than 30 research and development initiatives are being funded by federal agencies, with the goal of developing more alternative neutron detector technologies. These initiatives are now focusing on security applications, but they might potentially be used to other neutron detector applications. Some of these technologies might be integrated into deployable detection systems in less than two years, thereby helping to cut helium-3 usage.

Neutron detectors are used to detect neutron radiation, a form of ionizing radiation made up of neutron particles, in research, security, and industrial applications. Helium-3 gas, a rare, nonradioactive isotope of helium that is a result of the radioactive decay of tritium, a major component of the nation's nuclear weapons that is utilized to boost their potency, is a fundamental component of many such neutron detectors (GAO 2011).

Beginning in the 1980s, helium-3 became a popular material for neutron detectors. We discovered in May 2011 that flaws in the Department of Energy's (DOE) handling of helium-3 caused a delay in the government reaction to a helium-3 shortage in 2008. According to DOE authorities, helium-3 is in high demand for largearea neutron detectors, hence the helium-3 scarcity hampered scientific study. These He3 detectors are employed at sites across the globe, including the DOE's Spallation Neutron Source, to undertake materials research in health, energy, and transportation (SNS). Future deployments of radiation detection portal monitors with neutron detectors by the Department of Homeland Security (DHS), the Department of Defense (DOD), and the Department of Energy (DOE) have also been impacted.

More than 1,400 radiation detection portal monitors have been put in the United States at ports and border crossings for security reasons to check cargo and vehicles for nuclear material that terrorists may use in a nuclear bomb (GAO 2011). More than 9 million containers were offloaded yearly at US seaports in 2009, according to DHS (CBP 2009), while 103 million trucks and personal automobiles entered the US via land border crossings in 2010. Neutron detectors are also utilized in around 2,000 radiation portal monitors deployed by the US abroad.

To mitigate the impact of the helium-3 shortage on its largest consumers—large-area detectors in research facilities and radiation detection portal monitors at ports and border crossings—federal agencies and DOE's national laboratories are collaborating to acquire or develop alternative neutron detection technologies. DHS, DOD, DOE, and the Department of Commerce funded roughly $16 million in fiscal year 2009 and nearly $20 million in fiscal year 2010 to projects in business, academia, and national labs to assist initiatives developing alternate neutron detection technology and their testing.