NeutrinoCenter.org | Neutrino Productions

Production Processes of Neutrinos

Neutrinos are produced primarily through weak-interaction processes involving radioactive decay, nuclear reactions, particle decays, and high-energy astrophysical events. Depending on the reaction, the emitted particle may be an electron, muon, or tau neutrino—or the corresponding antineutrino.

1. Beta-minus decay

A neutron changes into a proton, producing an electron and an electron antineutrino:

n→p+e−+νˉe​

Sources:

• Radioactive isotopes

• Nuclear-reactor fission products

• Free-neutron decay

• Neutron-rich nuclei

• Earth’s radioactive elements

This process mainly produces electron antineutrinos.

2. Beta-plus decay

A proton inside a nucleus changes into a neutron, producing a positron and an electron neutrino:

p→n+e++νe​ 

Sources:

• Proton-rich radioactive nuclei

• The solar proton–proton chain

• Medical positron-emitting isotopes

• Stellar nuclear reactions

This process produces electron neutrinos.

3. Electron capture

A proton in a nucleus captures an atomic electron and becomes a neutron:

p+e−→n+νe​ 

A nuclear form is:

A​X+e−→Z−1A​Y+νe​ 

Sources:

• Radioactive nuclei

• The Sun

• Massive-star cores

• Supernova-core collapse

• Laboratory radioactive sources

This process produces electron neutrinos.

4. Positron capture

A neutron captures a positron and becomes a proton:

n+e+→p+νˉe​ 

This process can occur in:

• Hot stellar plasma

• Supernova environments

• Neutron-rich astrophysical matter

It produces electron antineutrinos.

5. Proton–proton fusion

The primary neutrino-producing reaction in the Sun is:

p+p→d+e++νe​ 

Here, two protons ultimately form a deuterium nucleus.

Sources:

• The Sun

• Main-sequence stars

These are known as pp solar neutrinos.

6. Proton–electron–proton reaction

A less common solar reaction is:

p+e−+p→d+νe​ 

This is called the pep reaction and produces monoenergetic electron neutrinos.

7. Beryllium-7 electron capture

In the solar proton–proton chain:

7Be+e−→7Li+νe​ 

This produces characteristic beryllium-7 solar neutrinos.

8. Boron-8 beta decay

Solar boron-8 undergoes beta-plus decay:

8B→8Be∗+e++νe​ 

The unstable beryllium-8 then breaks into two alpha particles.

This reaction produces relatively high-energy solar electron neutrinos.

9. Helium-3–proton reaction

A rare solar reaction called the hep reaction is:

3He+p→4He+e++νe​ 

It produces some of the highest-energy neutrinos in the standard solar spectrum.

10. CNO-cycle beta decays

In massive stars and the Sun, the carbon–nitrogen–oxygen cycle produces neutrinos through beta-plus decays such as:

• 13N→13C+e++νe​ 

• 15O→15N+e++νe​ 

• 17F→17O+e++νe 

These reactions produce CNO solar neutrinos.

Neutrinos from Particle Decay

11. Charged-pion decay

A positively charged pion decays as:

π+→μ++νμ​ 

A negatively charged pion decays as:

π−→μ−+νˉμ​ 

Sources:

• Cosmic-ray air showers

• Particle accelerators

• Gamma-ray sources

• Supernova remnants

• Active galactic nuclei

• Neutrino beams

Pion decay is a major source of muon neutrinos and antineutrinos.

12. Muon decay

Positive-muon decay:  μ+→e++νe​+νˉμ​ 

Negative-muon decay: μ−→e−+νˉe​+νμ​ 

Sources:

• Cosmic-ray air showers

• Accelerator beams

• Muon storage rings

• Pion-decay chains

Muon decay produces both electron-flavour and muon-flavour neutrinos.

13. Charged-kaon decay

Examples include: K+→μ++νμ​ ,  K−→μ−+νˉμ​ 

Kaons can also undergo three-body decays involving neutrinos.

Sources:

• High-energy cosmic-ray air showers

• Accelerator targets

• Astrophysical hadronic interactions

Kaon decay becomes especially important for higher-energy atmospheric neutrinos.

14. Tau-lepton decay

Tau decay always produces a tau neutrino or antineutrino. Examples are:

τ−→e−+νˉe​+ντ​ 

τ−→μ−+νˉμ​+ντ​ 

For the positive tau:

τ+→e++νe​+νˉτ​ 

Tau decays produce tau neutrinos, often together with electron or muon neutrinos.

15. Charmed-particle decay

Short-lived particles containing charm quarks—such as (D) mesons and charmed baryons—can decay into neutrinos:

D→ℓ+νℓ​+hadrons 

These decays produce:

• Electron neutrinos

• Muon neutrinos

• Tau neutrinos

In the atmosphere, they generate the high-energy prompt atmospheric-neutrino component.

16. Bottom-particle decay

Particles containing bottom quarks can undergo semileptonic decay:

B→X+ℓ+νℓ​ 

These processes produce neutrinos in:

• Particle colliders

• Heavy-flavour experiments

• Very-high-energy hadronic interactions

17. Neutron decay

A free neutron undergoes beta-minus decay:

n→p+e−+νˉe​ 

Possible sources include:

• Free neutrons in laboratories

• Cosmic-ray interactions

• Neutron-rich astrophysical environments

• Ultra-high-energy cosmic-ray propagation

Nuclear and Reactor Production

18. Nuclear-fission fragment decay

Nuclear fission produces neutron-rich fragments that undergo repeated beta-minus decay:

(A,Z)→(A,Z+1)+e−+νˉe​ 

Sources:

• Nuclear power reactors

• Research reactors

• Nuclear explosions

• Natural fission processes

A reactor emits enormous numbers of electron antineutrinos.

19. Neutron activation

A stable nucleus captures a neutron and becomes radioactive:

A​X+n→ZA+1​X 

The activated nucleus may subsequently undergo beta decay and emit neutrinos or antineutrinos.

This method is used to create artificial neutrino sources.

20. Nuclear fusion reactions

Fusion can produce neutrinos whenever a proton must transform into a neutron through the weak interaction.

Examples occur in:

• Proton–proton chains

• CNO cycles

• Advanced stellar burning

• Experimental fusion plasmas, in some secondary reactions

Atmospheric Neutrino Production

21. Cosmic-ray interactions with the atmosphere

Primary cosmic rays strike atmospheric nuclei:

p+N→π±,K±,other hadrons 

The secondary particles decay:

π±→μ±+νμ​(or νˉμ​) 

μ±→e±+ν+νˉ 

This cascade produces:

• Muon neutrinos

• Muon antineutrinos

• Electron neutrinos

• Electron antineutrinos

• A small tau-neutrino component

22. Prompt atmospheric-neutrino production

Very-high-energy cosmic-ray collisions produce charmed hadrons:

p+N→D,Λc​,… 

These particles decay almost immediately, generating prompt neutrinos. Unlike conventional atmospheric neutrinos, prompt neutrinos are not strongly suppressed at high energies by meson interactions.

Astrophysical Neutrino Production

23. Proton–proton hadronic interactions

High-energy protons collide with matter:

p+p→π±+π0+other particles 

Charged pions decay into neutrinos:

π+→μ++νμ​ 

μ+→e++νe​+νˉμ​ 

Possible sources include:

• Supernova remnants

• Starburst galaxies

• Galactic cosmic-ray sources

• Active galactic nuclei

• Dense astrophysical environments

24. Proton–photon interactions

High-energy protons interact with photons:

p+γ→Δ+ 

The resonance may decay through:

Δ+→n+π+ 

or

Δ+→p+π0 

The charged pion then produces neutrinos through the pion–muon decay chain.

Possible sources include:

• Gamma-ray bursts

• Active galactic nuclei

• Relativistic jets

• Tidal-disruption events

• Ultra-high-energy cosmic-ray sources

25. Photodisintegration and neutron decay

A high-energy nucleus can be broken apart by radiation:

A+γ→(A−1)+n 

The released neutron may decay:

n→p+e−+νˉe​ 

This can produce high-energy electron antineutrinos.

26. Supernova-core processes

Core-collapse supernovae produce neutrinos through several mechanisms.

Electron capture on protons

e−+p→n+νe​ 

Electron capture on nuclei

e−+(A,Z)→(A,Z−1)+νe​ 

Positron capture

e++n→p+νˉe​ 

Electron–positron annihilation

e−+e+→ν+νˉ 

Nucleon–nucleon bremsstrahlung

N+N→N+N+ν+νˉ 

Plasmon decay

γ∗→ν+νˉ 

Neutrino-pair emission from nuclei

A∗→A+ν+νˉ 

Supernovae produce neutrinos and antineutrinos of all three flavours.

27. Neutron-star mergers

Neutron-star mergers produce neutrinos through:

• Electron and positron capture

• Pair annihilation

• Nucleon bremsstrahlung

• Hot nuclear-matter reactions

• Accretion-disk interactions

• Radioactive decay of neutron-rich ejecta

They emit large fluxes of electron neutrinos and antineutrinos, along with heavy-flavour neutrinos.

28. Accretion-disk neutrino production

Hot accretion disks around black holes or compact objects produce neutrinos through:

e−+p→n+νe​ 

e++n→p+νˉe​ 

and thermal pair-production processes.

Thermal Neutrino-Pair Production

29. Electron–positron annihilation

e−+e+→νℓ​+νˉℓ​ 

where ℓ=e,μ,τ\ell=e,\mu,\tauℓ=e,μ,τ. 

This occurs in:

• Hot stellar interiors

• Supernovae

• Neutron-star mergers

• Early-universe plasma

30. Plasmon decay

A plasmon—an electromagnetic excitation in a plasma—can decay as:

γ∗→νℓ​+νˉℓ​ 

This is important in:

• Red giants

• White dwarfs

• Hot dense stars

• Stellar-cooling calculations

31. Photoneutrino process

A photon scatters from an electron and produces a neutrino pair:

γ+e−→e−+ν+νˉ 

This process occurs in hot stellar plasma.

32. Nucleon–nucleon bremsstrahlung

During a collision between nucleons:

N+N→N+N+ν+νˉ 

This is especially important in:

• Supernova cores

• Proto-neutron stars

• Neutron-star matter

33. Nuclear de-excitation

An excited nucleus can release energy by emitting a neutrino–antineutrino pair:

A∗→A+ν+νˉ 

This can contribute in hot and dense nuclear environments.

34. Cooper-pair breaking and formation

In superfluid neutron-star matter, nucleons form and break Cooper pairs:

N+N↔[NN]+ν+νˉ 

This process contributes to neutron-star cooling.

Artificial Neutrino Production

35. Accelerator neutrino beams

A proton beam strikes a target: p+target→π±+K±+⋯ 

Magnetic horns select charged mesons, which decay in flight: π+→μ++νμ​   or

π−→μ−+νˉμ​ 

This produces controlled neutrino or antineutrino beams.

36. Neutrinos from stopped pions

A positive pion stops and decays: π+→μ++νμ​ 

The muon subsequently decays: μ+→e++νe​+νˉμ​ 

This produces well-characterized neutrino spectra for experiments.

37. Beta-beam production

Radioactive ions are accelerated and allowed to beta-decay:

N→N′+e±+νe​(or νˉe​) 

Beta beams are proposed as intense, pure electron-neutrino or electron-antineutrino sources.

38. Neutrino-factory production

Stored muons decay in a storage ring:

μ−→e−+νˉe​+νμ​   or   μ+→e++νe​+νˉμ​ 

This produces precisely characterized mixed-flavour neutrino beams.

39. Radioactive-source neutrinos

Artificial radioactive isotopes produce neutrinos through electron capture or beta decay.

Examples include:

• Chromium-51

• Argon-37

• Cerium-144

• Strontium-90

• Tritium

These sources are used for detector calibration and short-baseline neutrino experiments.

Cosmological Neutrino Production

40. Early-universe thermal production

During the first seconds after the Big Bang, neutrinos were produced and maintained in equilibrium through reactions such as:

e−+e+↔ν+νˉ 

ν+e±↔ν+e± 

These neutrinos later decoupled, forming the cosmic neutrino background.

41. Big Bang nucleosynthesis reactions

Neutrinos participated in neutron–proton conversion:

n+νe​↔p+e− 

p+νˉe​↔n+e+ 

These interactions helped determine the primordial neutron-to-proton ratio and therefore the abundances of light elements.

42. Cosmogenic neutrino production

Ultra-high-energy cosmic rays interact with cosmic-background photons:

p+γCMB​→Δ+→n+π+ 

The pion and neutron decay chains produce ultra-high-energy neutrinos known as:

• Cosmogenic neutrinos

• GZK neutrinos

43. Dark-matter-related neutrino production

Hypothetical dark-matter particles may produce neutrinos through:

Dark-matter annihilation: χ+χ→ν+νˉ 

Dark-matter decay: χ→ν+other particles 

Potential production locations include:

• The Sun

• Earth

• Galactic centre

• Dwarf galaxies

• Galaxy clusters

These processes remain hypothetical.

Summary by Neutrino Flavour

Neutrino flavour, Important production processes

• νe​ : Beta-plus decay, electron capture, solar fusion, muon decay, supernova reactions

• νˉe​ : Beta-minus decay, nuclear reactors, neutron decay, positron capture

• νμ​: Pion decay, kaon decay, muon decay, accelerator beams, cosmic-ray showers

• νˉμ: Negative-pion decay, positive-muon decay, kaon decay, atmospheric showers

• ντ: Tau decay, charm decay, high-energy hadronic processes

• νˉτ: Antitau decay, charm decay, high-energy particle interactions

A crucial distinction is that neutrino oscillation does not produce new neutrinos. 

It changes the flavour of an already-produced neutrino as it propagates, for example: νμ​→ντ​ 

Thus, many tau neutrinos detected on Earth originate as electron or muon neutrinos and later transform through oscillation.