Editing Helium-3 (section)

===Neutron detection===
Helium-3 is an important isotope in instrumentation for [[neutron detection]]. It has a high absorption cross section for thermal [[neutron radiation|neutron]] beams and is used as a converter gas in neutron detectors. The neutron is converted through the nuclear reaction
:n + <sup>3</sup>He → <sup>3</sup>H + <sup>1</sup>H + 0.764 MeV
into charged particles [[tritium]] ions (T, <sup>3</sup>H) and [[Hydrogen ions]], or protons (p, <sup>1</sup>H) which then are detected by creating a charge cloud in the stopping gas of a [[proportional counter]] or a [[Geiger–Müller tube]].<ref>[http://www.lanl.gov/quarterly/q_sum03/neutron_detect.shtml A Modular Neutron Detector | Summer 2003| Los Alamos National Laboratory] {{Webarchive|url=https://web.archive.org/web/20080503051236/http://www.lanl.gov/quarterly/q_sum03/neutron_detect.shtml |date=2008-05-03 }}. Lanl.gov. Retrieved on 2011-11-08.</ref>

Furthermore, the absorption process is strongly [[Spin (physics)|spin]]-dependent, which allows a [[Spin polarization|spin-polarized]] helium-3 volume to transmit neutrons with one spin component while absorbing the other. This effect is employed in [[Polarized neutron scattering|neutron polarization analysis]], a technique which probes for magnetic properties of matter.<ref>[http://www.ncnr.nist.gov/AnnualReport/FY2002_html/pages/neutron_spin.htm NCNR Neutron Spin Filters] {{Webarchive|url=https://web.archive.org/web/20070520100431/http://www.ncnr.nist.gov/AnnualReport/FY2002_html/pages/neutron_spin.htm |date=2007-05-20 }}. Ncnr.nist.gov (2004-04-28). Retrieved on 2011-11-08.</ref><ref>[http://www.ill.eu/science-technology/neutron-technology-at-ill/optics/<sup>3</sup>He-spin-filters/ ILL <sup>3</sup>He spin filters]{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }}. Ill.eu (2010-10-22). Retrieved on 2011-11-08.</ref><ref>{{cite journal|url= http://www.ncnr.nist.gov/staff/hammouda/publications/2000_gentile_j_appl_cryst.pdf|title= SANS polarization analysis with nuclear spin-polarized <sup>3</sup>He|doi= 10.1107/S0021889800099817|journal= J. Appl. Crystallogr.|date= 2000|volume= 33|issue= 3|pages= 771–774|last1= Gentile|first1= T.R.|last2= Jones|first2= G.L.|last3= Thompson|first3= A.K.|last4= Barker|first4= J.|last5= Glinka|first5= C.J.|last6= Hammouda|first6= B.|last7= Lynn|first7= J.W.|bibcode= 2000JApCr..33..771G|access-date= 2011-11-08|archive-date= 2012-04-02|archive-url= https://web.archive.org/web/20120402004050/http://www.ncnr.nist.gov/staff/hammouda/publications/2000_gentile_j_appl_cryst.pdf|url-status= live}}</ref><ref>[http://www.ncnr.nist.gov/equipment/he3nsf/index.html Neutron Spin Filters: Polarized <sup>3</sup>He] {{Webarchive|url=https://web.archive.org/web/20111016142515/http://ncnr.nist.gov/equipment/he3nsf/index.html |date=2011-10-16 }}. NIST.gov</ref>

The United States [[Department of Homeland Security]] had hoped to deploy detectors to spot smuggled plutonium in shipping containers by their neutron emissions, but the worldwide shortage of helium-3 following the drawdown in nuclear weapons production since the [[Cold War]] has to some extent prevented this.<ref>{{Cite news |last=Wald |first=Matthew L. |date=2009-11-22 |title=Shortage Slows a Program to Detect Nuclear Bombs |url=https://www.nytimes.com/2009/11/23/us/23helium.html |access-date=2025-05-11 |work=The New York Times |language=en-US |issn=0362-4331}}</ref>  As of 2012, DHS determined the commercial supply of [[boron-10]] would support converting its neutron detection infrastructure to that technology.<ref>{{Cite web |url=http://science.energy.gov/~/media/np/pdf/research/idpra/workshop-on-isotope-federal-supply-and-demand/presentations/Slovik_He3_Alternative_Isotopes_DOE_IP_Workshop_Jan_11_2012.pdf |title=Office of Science |access-date=2014-07-18 |archive-url=https://web.archive.org/web/20140726214826/http://science.energy.gov/~/media/np/pdf/research/idpra/workshop-on-isotope-federal-supply-and-demand/presentations/Slovik_He3_Alternative_Isotopes_DOE_IP_Workshop_Jan_11_2012.pdf |archive-date=2014-07-26 |url-status=dead }}</ref>