Free neutron decay

When embedded in an atomic nucleus, neutrons are (usually) stable particles. Outside the nucleus, free neutrons are unstable and have a mean lifetime of 879.6s (about 14minutes, 39.6seconds). Therefore, the half-life for this process (which differs from the mean lifetime by a factor of ln(2) ≈ 0.693) is 611s (about 10minutes, 11seconds). (An article published in October 2021, arrives at 877.75s for the mean lifetime). The beta decay of the neutron described in this article can be notated at four slightly different levels of detail, as shown in four layers of Feynman diagrams in a section below. _Neutron0 → _Proton+ + _Electron + _Electron antineutrino The hard-to-observe _W boson- quickly decays into an electron and its matching antineutrino. The subatomic reaction shown immediately above depicts the process as it was first understood, in the first half of the 20th century. The boson ( _W boson- ) vanished so quickly that it was not detected until much later. Later, beta decay was understood to occur by the emission of a weak boson ( _W boson+- ), sometimes called a charged weak current. Beta decay specifically involves the emission of a _W boson- boson from one of the down quarks hidden within the neutron, thereby converting the down quark into an up quark and consequently the neutron into a proton. The following diagram gives a summary sketch of the beta decay process according to the present level of understanding. For diagrams at several levels of detail, see § Decay process, below. For the free neutron, the decay energy for this process (based on the rest masses of the neutron, proton and electron) is 0.782343MeV. That is the difference between the rest mass of the neutron and the sum of the rest masses of the products. That difference has to be carried away as kinetic energy. The maximal energy of the beta decay electron (in the process wherein the neutrino receives a vanishingly small amount of kinetic energy) has been measured at 0.782MeV.