Inverse beta decay

Inverse beta decay proceeds as{{Cite journal|last1 = Bellini|first1 = G.|last2 = Benziger|first2 = J.|last3 = Bonetti|first3 = S.|last4 = Avanzini|first4 = M. Buizza|last5 = Caccianiga|first5 = B.|last6 = Cadonati|first6 = L.|author-link6=Laura Cadonati|last7 = Calaprice|first7 = F.|last8 = Carraro|first8 = C.|last9 = Chavarria|first9 = A.|date = 2010-04-19|title = Observation of geo-neutrinos|journal = Physics Letters B|volume = 687|issue = 4–5|pages = 299–304|doi = 10.1016/j.physletb.2010.03.051|arxiv = 1003.0284|bibcode=2010PhLB..687..299B}}

:{{subatomic particle|electron antineutrino}} + {{subatomic particle|proton}} → {{subatomic particle|positron}} + {{subatomic particle|neutron}},

where an electron antineutrino ({{subatomic particle|electron antineutrino}}) interacts with a proton ({{subatomic particle|proton}}) to produce a positron ({{subatomic particle|positron}}) and a neutron ({{subatomic particle|neutron}}). The IBD reaction can only be initiated when the antineutrino possesses at least 1.806 MeV of kinetic energy (called the threshold energy). This threshold energy is due to a difference in mass between the products ({{subatomic particle|positron}} and {{subatomic particle|neutron}}) and the reactants ({{subatomic particle|electron antineutrino}} and {{subatomic particle|proton}}) and also slightly due to a relativistic mass effect on the antineutrino. Most of the antineutrino energy is distributed to the positron due to its small mass relative to the neutron. The positron promptly undergoes matter–antimatter annihilation after creation and yields a flash of light with energy calculated as{{Cite journal|last1 = Bellini|first1 = G.|last2 = Benziger|first2 = J.|last3 = Bonetti|first3 = S.|last4 = Avanzini|first4 = M. Buizza|last5 = Caccianiga|first5 = B.|last6 = Cadonati|first6 = L.|last7 = Calaprice|first7 = F.|last8 = Carraro|first8 = C.|last9 = Chavarria|first9 = A.|date = 2013-04-15|title = Measurement of geo-neutrinos from 1353 days of Borexino|journal = Physics Letters B|volume = 722|issue = 4–5|pages = 295–300|doi = 10.1016/j.physletb.2013.04.030|bibcode=2013PhLB..722..295B|doi-access = free|arxiv = 1303.2571}}

$$\backslash begin\{align\}$$

E_\text{vis} &= 511 \text{ keV} + 511 \text{ keV} + E_{\rm \,\overline\nu_e} - 1806 \text{ keV} \\[2pt]

&= E_{\rm \,\overline\nu_e} - 784 \text{ keV}

\end{align}

where 511 keV is the electron and positron rest energy, {{math|E_vis}} is the visible energy from the reaction, and {{tmath|E_{\rm \,\overline\nu_e} }} is the antineutrino kinetic energy. After the prompt positron annihilation, the neutron undergoes neutron capture on an element in the detector, producing a delayed flash of 2.22 MeV if captured on a proton. The timing of the delayed capture is 200–300 microseconds after IBD initiation ({{val|p=≈|256|u=us}} in the Borexino detector). The timing and spatial coincidence between the prompt positron annihilation and delayed neutron capture provides a clear IBD signature in neutrino detectors, allowing for discrimination from background. The IBD cross section is dependent on antineutrino energy and capturing element, although is generally on the order of 10⁻⁴⁴ cm² (~ attobarns).{{Cite journal|last1=Strumia|first1=Alessandro|last2=Vissani|first2=Francesco|date=2003-07-03|title=Precise quasielastic neutrino/nucleon cross-section|journal=Physics Letters B|volume=564|issue=1|pages=42–54|doi=10.1016/S0370-2693(03)00616-6|arxiv=astro-ph/0302055|bibcode=2003PhLB..564...42S|s2cid=7915354}}

Another kind of inverse beta decay is the reaction

:{{subatomic particle|electron neutrino}} + {{subatomic particle|neutron}} → {{subatomic particle|electron}} + {{subatomic particle|proton}}

The Homestake experiment used the reaction

:$\backslash mathrm\{\backslash nu\_e\; +\; \backslash \; ^\{37\}Cl\; \backslash longrightarrow\; \backslash \; ^\{37\}Ar\; +\; e^-\}$

to detect solar neutrinos.

{{Main articles|Electron capture}}

During the formation of neutron stars, or in radioactive isotopes capable of electron capture, neutrons are created by electron capture:

:{{subatomic particle|proton}} + {{subatomic particle|electron}} → {{subatomic particle|neutron}} + {{subatomic particle|electron neutrino}}.

This is similar to the inverse beta reaction in that a proton is changed to a neutron, but is induced by the capture of an electron instead of an antineutrino.

• Kamioka Liquid Scintillator Antineutrino Detector

{{Reflist}}

Category:Radioactivity