Muon capture

Muon capture is the capture of a negative muon by a proton, usually resulting in production of a neutron and a neutrino, and sometimes a gamma photon.

Feynman diagram of the muon capture. A negatively charged muon is captured by a proton. The proton is transformed into a neutron and a muon-neutrino is emitted. The interaction is mediated by a W-boson.

Except for the flavor of neutrino, it has exactly the same result as electron capture, except that the great mass-energy of the muon makes it allowed for all nuclei and there is so much excess energy that a nucleus can disintegrate; for heavy nuclei this leads to emission of nuclear particles; most often neutrons, but charged particles can be emitted as well.

Ordinary muon capture (OMC) involves capture of a negative muon from the atomic orbital without emission of a gamma photon:

μ⁻
 + p⁺
 → ν_μ + n⁰

Radiative muon capture (RMC) is a radiative version of OMC, where a gamma photon is emitted:

μ⁻
 + p⁺
 → ν_μ + n⁰
 + γ

Theoretical motivation for the study of muon capture on the proton is its connection to the proton's induced pseudoscalar form factor g_p.

Nuclear waste disposal

Muon capture is being investigated for practical application in radioactive waste disposal, for example in the artificial transmutation of large quantities of long-lived radioactive waste that have been produced globally by fission reactors. Radioactive waste can be transmuted to stable isotopes following irradiation by an incident muon (μ⁻
) beam from a compact proton accelerator source.

References

• T. Gorringe and H.W. Fearing (2004). "Induced pseudoscalar coupling of the proton weak interaction". Rev. Mod. Phys. 76 (1): 31–91. arXiv:nucl-th/0206039. Bibcode:2003RvMP...76...31G. doi:10.1103/RevModPhys.76.31.
• V.A. Andreev; et al. (2007). "Measurement of the Rate of Muon Capture in Hydrogen Gas and Determination of the Proton's Pseudoscalar Coupling g_P". Physical Review Letters. 99 (3): 032002. arXiv:0704.2072. Bibcode:2007PhRvL..99c2002A. doi:10.1103/PhysRevLett.99.032002. PMID 17678281.
• Nagamine, Kanetada (2016) "Nuclear Waste Disposal Method and its apparatus using muon-nuclear-absorption". (WO2016143144A1) Espacenet (Patent database).