The beta decay of a neutron is the spontaneous conversion of a free neutron into a proton with the emission of a β-particle (electron) and an electron antineutrino :
The kinetic energy spectrum of the emitted electron lies in the range from 0 to 782.318 keV . The free neutron lifetime is 880.1 ± 1.1 seconds [1] (which corresponds to a half-life of 611 ± 0.8 s ). Precision measurements of neutron beta decay parameters (lifetime, angular correlations between particle momenta and neutron spin ) are important for determining the properties of weak interaction .
The neutron beta decay was predicted by Frederick Joliot-Curie in 1934 and independently discovered in 1948 - 1950 by A. Snell, J. Robson and P.E. Spivak.
Content
Rare decay channels
In addition to the decay of a neutron with the formation of a proton, an electron and an electron antineutrino, there should also be a more rare process with the emission of an additional gamma quantum - radiative (that is, accompanied by electromagnetic radiation) beta decay of the neutron:
The theory predicts that the spectrum of gamma rays emitted during radiative decay of a neutron should lie in the range from 0 to 782 keV and depend on energy (in a first approximation) as E −1 . From a physical point of view, this process is the bremsstrahlung of the resulting electron (and to a lesser extent - the proton) [2] .
In 2005, this previously predicted process was discovered experimentally [3] . Measurements in this work showed that the radiative decay channel is realized with a probability of 0.32 ± 0.16% at a gamma-ray energy E γ > 35 keV . This result was subsequently confirmed and significantly refined by a number of other experimental groups; in particular, the RDK II collaboration established [2] that the probability of decay with the release of the gamma ray is (0.335 ± 0.005 stat ± 0.015 syst )% at E γ > 14 keV and (0.582 ± 0.023 stat ± 0.062 syst )% at 0, 4 keV < E γ <14 keV . This coincides within the limits of error with theoretical predictions (0.308% and 0.515%, respectively).
There must also exist a channel for the decay of a free neutron into a bound state - a hydrogen atom
However, it is only known from experiments that the probability of such a decay is less than 3% (the partial lifetime on this channel exceeds 3 · 10 4 s ) [4] . The theoretically expected probability of decay into a bound state with respect to the total probability of decay is 3.92 × 10 −6 [5] . To fulfill the law of conservation of angular momentum, a bound electron must arise in the S- state (with zero orbital momentum), including with a probability of ≈84% in the ground state, and 16% in one of the excited S- states of the hydrogen atom [6] . In the decay into a hydrogen atom, almost all the decay energy, 782.33305 keV (with the exception of the very low kinetic energy of the recoil atom) is carried away by the electron antineutrino.
See also
- Beta decay
- Proton decay
Notes
- ↑ J. Beringer et al. (Particle Data Group), Phys. Rev. D86, 010001 (2012) http://pdg.lbl.gov/2012/tables/rpp2012-sum-baryons.pdf
- ↑ 1 2 Bales M. J. et al. (RDK II Collaboration). Precision Measurement of the Radiative β Decay of the Free Neutron ( Physical ) // Physical Review Letters . - 2016 .-- 14 June ( vol. 116 , no. 24 ). - P. 242501 . - ISSN 0031-9007 . - DOI : 10.1103 / PhysRevLett.116.242501 . - arXiv : 1603.00243 .
- ↑ Khafizov RU, Severijns N., Zimmer O., Wirth H.-F., Rich D., Tolokonnikov SV, Solovei VA, Kolhidashvili MR Observation of the neutron radioactive decay // Journal of Experimental and Theoretical Physics Letters . - 2006. - Vol. 83. - P. 366. - ISSN 0021-3640 . - DOI : 10.1134 / S0021364006080145 . - arXiv : nucl-ex / 0512001 .
- ↑ Green K., Thompson D. The decay of the neutron to a hydrogen atom // Journal of Physics G: Nuclear and Particle Physics. - 1990. - T. 16 , no. 4 . - S. L75 — L76 . - DOI : 10.1088 / 0954-3899 / 16/4/001 .
- ↑ Faber M. , Ivanov AN , Ivanova VA , Marton J. , Pitschmann M. , Serebrov AP , Troitskaya NI , Wellenzohn M. Continuum-state and bound-state β - -decay rates of the neutron (Eng.) // Physical Review C. - 2009 .-- 9 September ( vol. 80 , no. 3 ). - P. 035503 . - ISSN 0556-2813 . - DOI : 10.1103 / PhysRevC.80.035503 . - arXiv : 0906.0959 .
- ↑ Dubbers D., Schmidt MG The neutron and its role in cosmology and particle physics (Eng.) // Reviews of Modern Physics. - 2011. - Vol. 83 . - P. 1111-1171 . - DOI : 10.1103 / RevModPhys.83.1111 . - arXiv : 1105.3694 .
Literature
- Malyarov VV Fundamentals of the theory of the atomic nucleus. - M: Fizmatlit, 1959.- 471 p. - 18,000 copies.
- B. G. Erosolimsky. Neutron beta decay (Eng.) // Uspekhi Fizicheskikh Nauk : journal. - Russian Academy of Sciences , 1975. - Vol. 116 , no. 1 . - P. 145-164 .
- Neutron beta decay (article in the Physical Encyclopedia) .
- Compilation of Neutron Properties Particle Data Group