Neutron detection alternatives to 3 He for national security applications Richard T.Kouzes n , James H.Ely, Luke E.Erikson,Warnick J. Kernan,Azaree T.Lintereur, Edward R.Siciliano,Daniel L.Stephens,David C.Stromswold,Renee M.Van Ginhoven, Mitchell L. Woodring Pacific Northwest National Laboratory, MS K7-36,P.O.Box 999,Richland,WA 99352,USA a r t i c l e i n f o Article history: Received 5 May 2010 Received in revised form 11 August 2010 Accepted 12 August 2010 Available online 25 August 2010 Keywords: Neutron detection Helium-3 Radiation detection Homeland security National security MCNP a b s t r a c t One of the main uses for 3 He is in gas proportional counters for neutron detection.Large radiation detection systems deployed for homeland security and proliferation detection applications use such systems.Due to the large increase in use of 3 He for homeland security and basic research, the supply has dwindled, and can no longer meet the demand. This has led to the search for an alternative technology to replace the use of 3 He-based neutron detectors. In this paper,we review the testing of currently commercially available alternative technologies for neutron detection in large systems used in various national security applications. & 2010 Elsevier B.V. All rights reserved. 1. Introduction Neutron detection is an essential aspect of interdiction of radiologicalthreats for national security purposes,since pluto- nium, a material used for nuclear weapons, is a significant source of fission neutrons.The current demand for 3 He in commonly deployed neutron detectors and other systems has created an imminent shortage of 3 He. Therefore,a replacement technology for neutron detection is required in the very near future [1]. In this paper,we provide background information about the production and use of 3 He in detectors and various alternative technologies, while focusing on potential alternative neutron detection tech- nologies for application in large systems, especially radiation portal monitor (RPM) systems [2], of which there are thousands currently deployed for homeland security and proliferation detection purposes. We then discuss our results from experiments with four selected alternative technologies, concluding with a discussion of those that appear to be best suited for use as a replacement for 3 He-based detectors in RPMs. 1.1. Use and production of 3 He Proportionalcounters filled with 3 He are the ‘‘gold standard’’ thermal neutron detector. The great advantage that 3 He has over other neutron detector material is that 3 He has a large capture cross-section for thermal neutrons, while its sensitivity to gamma rays is negligible (pileup effects only become a problem in radiation fields of 1 R/h). Proportional counter tubes containing 3 He are very simple in design, are mechanically stable over a wide range of environmental conditions, and do not degrade over years of operation.In addition to homeland security applications, there are uses for 3 He in industry, such as well logging in the oil and gas industry,medical applications (MRI lung imaging), basic research projects in nuclear and condensed matter physics (e.g., the Spallation Neutron Source [3]), and in helium dilution refrigerators. Helium-3 is a byproduct from the beta decay of tritium (t 1/2 ¼ 12.3 y),and it is separated from tritium as part of the tritium purification process.Stores of tritium, which come from the refurbishment and dismantlement of the nuclear stockpile, must occasionally be processed to remove the ingrown 3 He and maintain the desired tritium concentration [4]. The resulting 3 He in the U.S. has been made available to commercial entities through an auction conducted by the U.S.Departmentof Energy.This is the main source of 3 He for most detector applications. Russia has been the only other significant supplier of 3 He. Tritium is also produced in the CANDU heavy water reactors used in Canada and elsewhere, and is regularly extracted by Ontario Power Generation (Toronto, Canada).However,a substantial investment would be required to extract the 3 He from this stored tritium. The production of 3 He from tritium decay has declined with the reduction in the nuclear weapons stockpile,resulting in a reduced need for tritium to maintain the stockpile. Before the Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A 0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.08.021 n Corresponding author. Tel.: +1 509 372 4858. E-mail address: rkouzes@pnl.gov (R.T. Kouzes). Nuclear Instruments and Methods in Physics Research A 623 (2010) 1035–1045