Editing Neutrino (section)

==== Reactor neutrinos ====
Nuclear reactors are the major source of human-generated neutrinos. The majority of energy in a nuclear reactor is generated by fission (the four main fissile isotopes in nuclear reactors are {{SimpleNuclide|uranium|235|link=yes}}, {{SimpleNuclide|uranium|238|link=yes}}, {{SimpleNuclide|plutonium|239|link=yes}} and {{SimpleNuclide|plutonium|241|link=yes}}), the resultant neutron-rich daughter nuclides rapidly undergo additional beta decays, each converting one neutron to a proton and an electron and releasing an electron antineutrino. Including these subsequent decays, the average nuclear fission releases about {{val|200|u=MeV}} of energy, of which roughly 95.5% remains in the core as heat, and roughly 4.5% (or about {{val|9|u=MeV}})<ref>
{{cite book
 |title=Kay & Laby Tables of Physical and Chemical Constants
 |year=2008
 |chapter=Nuclear Fission and Fusion, and Nuclear Interactions
 |publisher=[[National Physical Laboratory (United Kingdom)|National Physical Laboratory]]
 |url=http://www.kayelaby.npl.co.uk/
 |chapter-url=http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_1.html
 |access-date=2009-06-25 
 |archive-url=https://web.archive.org/web/20060425181600/http://www.kayelaby.npl.co.uk/
 |archive-date=2006-04-25
}}
</ref> is radiated away as antineutrinos. For a typical nuclear reactor with a thermal power of {{val|4000|ul=MW}},{{efn|
Like all [[thermal power plant]]s, only about one third of the heat generated can be converted to electricity, so a {{val|4000|u=MW}} reactor would produce only {{val|1300|u=MW}} of electric power, with {{val|2700|u=MW}} being [[waste heat]].
}} the total power production from fissioning atoms is actually {{val|4185|u=MW}}, of which {{val|185|u=MW}} is radiated away as antineutrino radiation and never appears in the engineering. This is to say, {{val|185|u=MW}} of fission energy is ''lost'' from this reactor and does not appear as heat available to run turbines, since antineutrinos penetrate all building materials practically without interaction.

The antineutrino energy spectrum depends on the degree to which the fuel is burned (plutonium-239 fission antineutrinos on average have slightly more energy than those from uranium-235 fission), but in general, the ''detectable'' antineutrinos from fission have a peak energy between about 3.5 and {{val|4|u=MeV}}, with a maximum energy of about {{val|10|u=MeV}}.<ref>
{{cite journal
 |first1=Adam |last1=Bernstein
 |first2=Yifang |last2=Wang |author-link2=Wang Yifang
 |first3=Giorgio |last3=Gratta   
 |first4=Todd |last4=West    
 |date=2002
 |title=Nuclear reactor safeguards and monitoring with antineutrino detectors
 |journal=[[Journal of Applied Physics]]
 |volume=91 |issue=7 |page=4672
 |arxiv=nucl-ex/0108001 |bibcode=2002JAP....91.4672B
 |doi=10.1063/1.1452775 |s2cid=6569332
}}
</ref> There is no established experimental method to measure the flux of low-energy antineutrinos, though experiments to demonstrate the capacity of low-energy neutrino detection via the threshold-less [[Coherent Elastic Neutrino-Nucleus Scattering|CEνNS]] interaction are ongoing. Only antineutrinos with an energy above threshold of {{val|1.8|u=MeV}} can trigger [[inverse beta decay]] and thus be unambiguously identified (see ''{{section link||Detection}}'' below).

An estimated 3% of all antineutrinos from a nuclear reactor carry an energy above that threshold. Thus, an average nuclear power plant may generate over {{val|e=20}} antineutrinos per second above the threshold, but also a much larger number ({{nowrap|97% / 3% ≈ 30}} times this number) below the energy threshold; these lower-energy antineutrinos are invisible to present detector technology.