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GAO Issues Report on Alternatives to Using Helium-3 in Neutron Detectors

Aline D. McNaull
Number 147 - December 16, 2011  |  Search FYI  |   FYI Archives  |   Subscribe to FYI

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Last year, the Subcommittee on Investigations and Oversight of the House Committee on Science and Technology held a hearing on the severe shortage of helium-3, which is used in industrial, national security, and non-proliferation applications, as well as research equipment.

Two members of this subcommittee (at that time), Representatives Donna Edwards (D-MD) and Brad Miller (D-NC) asked the Government Accountability Office (GAO) to review the effectiveness and development of alternative neutron detector technologies to be used in place of neutron detectors utilizing helium-3.  GAO released its report last month, entitled “Technology Assessment: Neutron detectors – Alternatives to using helium-3.”

The applications that GAO examined for the purposes of this report were largely national and homeland security purposes.
Among the findings in the GAO report were the following:

Neutron detectors can be classified into three categories: proportional, scintillator, and semiconductor.  Each can potentially use isotopes other than helium-3 to absorb and detect neutrons.  Boron-10 and lithium-6 are common alternative isotopes; the Department of Homeland Security (DHS) considers both isotopes to be in sufficient supply for future radiation portal monitor deployments.  The stockpile of lithium-6 has been deemed sufficient to meet detector demand and the National Nuclear Security Administration (NNSA) has reserved lithium for detector use. 

Detectors containing helium-3 became the “gold standard for neutron detection” due to their high neutron detection efficiency, good gamma radiation discrimination, nontoxicity, and low cost. 

Agency officials and experts identified three alternative neutron detector technologies currently available and in use which could potentially meet the requirements for large-area detectors and radiation portal monitors: boron-10 lined proportional detectors, boron trifluoride proportional detectors, and lithium-6 scintillators. 

“The international collaboration of science facilities has identified boron layer detectors – of which boron-lined proportional counters are a type – as an alternative neutron detector technology that could be tested and used for large-area detectors by 2014.”

“The international collaboration of science facilities has identified BF3 as the ‘most direct and probably the fastest way’ to replace helium-3 in large area detectors and expressed concern about its toxicity.”

“BF3 tubes are about 30 to 50 percent as efficient at detecting neutrons as helium-3, but multiple tubes can achieve the desired detector efficiency, and BF3 detectors can provide better gamma discrimination than helium-3 detectors.”

Current tests of the BF3 detector show that positional-sensitive detectors have appropriate position resolution, gamma discrimination, and theoretical detection efficiency.

The third alternative neutron detector technology, lithium-6 scintillator detectors, is under development and evaluation for approximately the next two years.  The lithium-6 scintillators with fiber optic light guides were identified as a potentially viable replacement technology and tests are being done to determine their suitability. 

Researchers have concerns about lithium-6 scintillators including that the “gamma radiation discrimination may not be good enough, and the detector may not be able to count neutrons at a high enough rate.  Furthermore, the materials used may not be suitable for the vacuum environment experienced by large-area detectors, and the high cost of these detectors remains a concern.”

The Domestic Nuclear Detection Office (DNDO) completed field testing, in July 2011, for one radiation portal monitor design using a boron-10 lined proportional detector.  DNDO anticipates having this alternative detector available early in the 2012 fiscal year. 

According to DNDO “it appears that a boron-10 lined proportional detector will be available for use in early fiscal year 2012.  BF3 detectors are under development at national laboratories at the direction of DNDO, but no vendor has yet made a prototype available for test and evaluation.  Lithium-6 scintillator detectors may be available later in fiscal year 2012.”

Among the conclusions of the GAO report were the following statements:

“Since the helium-3 shortage was first realized in 2008, federal agencies have collaborated to mitigate its effects by identifying or developing alternative neutron detector technologies that do not use helium-3.  Based on performance test, three alternative detector technologies – boron-lined proportional detectors, boron trifluoride proportional detectors, and lithium-6 scintillators – appear to be potential replacement technologies for use in both large-area detectors and radiation portal monitors, although additional testing is under way.”

Integration of alternative technologies in large-area detectors would minimize the impact of the helium-3 shortage and would allow federal agencies to continue deployment of radiation portal monitors with minimal additional delays.  The GAO estimated that the boron-10 lined proportional detectors “could be acquired and deployed with confidence that they would perform as required.” 

The GAO provided their report to the Department of Energy (DOE), NNSA, and DHS.  DOE and NNSA mostly agreed with the report.  DOE noted that:

“BF3 is a proven, inexpensive, and reliable alternative with minimal development cost, that detectors containing BF3 use small quantities of the gas, which mitigates the impacts of leaks from such detectors, and that the Department of Transportation does not consider less than 1 gram of BF3 in portable instruments hazardous.”

The DHS was satisfied with the report and, in particular, pleased that the report recognized the active and key role that the DNDO has had in the discovery and mitigation of the shortage of Helium-3.

Rep. Miller and Rep. Edwards commented on the GAO report in a press briefing:

“I am pleased with the success in identifying alternatives to Helium-3,” said Miller.  “I understand that national security concerns complicated the task of monitoring the supply of Helium-3, but I have to think we could have done better than we did.  We need to learn from this experience and avoid unexpected shortages of critical materials in the future,” said Miller. 

“I am pleased that the technology is catching up to the demand for alternative supplies of Helium-3 gas,” said Edwards.  “These technical successes in developing He-3 replacement technologies for homeland security applications and neutron scattering research will both alleviate the He-3 supply pressures on other industries that require it and hopefully lead to successful application of these alternative technologies in other fields as well.”

Miller and Edwards have asked the GAO to investigate the DOE’s Isotope Program to monitor the supply and demand of critical isotopes effectively, including that of helium-3.   

Aline D. McNaull
Government Relations Division
American Institute of Physics