Physics:Muon capture

Short description: Capture of a negative muon by a proton

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.

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.

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 [1]'

The most precise measurement of the muon capture rate on the proton 𝛬_𝑆 =(714.9 ±5.4stat ±5.1syst)  s⁻¹ and the induced pseudoscalar coupling constant g_p⁡=8.06 ±0.55 was done by the MUCAP experiment [2,3] with a measurement performed at the Paul Scherrer Institut, Switzerland. The result is in excellent agreement with theoretical precidtions [1].

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

[1] T. Gorringe and H.W. Fearing (2004). "Induced pseudoscalar coupling of the proton weak interaction". Rev. Mod. Phys. 76 (1): 31–91. doi:10.1103/RevModPhys.76.31. Bibcode: 2003RvMP...76...31G. 

[2] V.A. Andreev (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). doi:10.1103/PhysRevLett.99.032002. PMID 17678281. Bibcode: 2007PhRvL..99c2002A. 

[3] V.A.Andreev et al, (2013) "Measurement of Muon Capture on the Proton to 1% Precision and Determination of the Pseudoscalar Coupling 𝑔𝑃" Physical Review Letters 110 (3) 012504 DOI: https://doi.org/10.1103/PhysRevLett.110.012504

[4] Nagamine, Kanetada (2016) "Nuclear Waste Disposal Method and its apparatus using muon-nuclear-absorption". (WO2016143144A1) Espacenet (Patent database).