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

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Publication date: 
16 December 2011

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.