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Stability and beta decay
The Feynman diagram for beta decay of a neutron into a proton, electron, and electron antineutrino via an intermediate heavy W boson

Under the Standard Model of particle physics, because the neutron consists of three quarks, the only possible decay mode without a change of baryon number is for one of the quarks to change flavour via the weak interaction. The neutron consists of two down quarks with charge −1⁄3 e and one up quark with charge +2⁄3 e, and the decay of one of the down quarks into a lighter up quark can be achieved by the emission of a W boson. By this means the neutron decays into a proton (which contains one down and two up quarks), an electron, and an electron antineutrino.

Outside the nucleus, free neutrons are unstable and have a mean lifetime of 885.7±0.8 s (about 14 minutes, 46 seconds); therefore the half-life for this process (which differs from the mean lifetime by a factor of ln(2) = 0.693) is 613.9±0.8 s (about 10 minutes, 14 seconds).[2] Free neutrons decay by emission of an electron and an electron antineutrino to become a proton, a process known as beta decay:[5]

n⁰ → p+ + e⁻ + νe

Neutrons in unstable nuclei can also decay in this manner. However, inside a nucleus, protons can also transform into a neutron via inverse beta decay. This transformation occurs by emission of a antielectron (also called positron) and a neutrino:

p+ → n⁰ + e+ + νe

The transformation of a proton to a neutron inside of a nucleus is also possible through electron capture:

p+ + e⁻ → n⁰ + νe

Positron capture by neutrons in nuclei that contain an excess of neutrons is also possible, but is hindered because positrons are repelled by the nucleus, and quickly annihilate when they encounter electrons.

When bound inside of a nucleus, the instability of a single neutron to beta decay is balanced against the instability that would be acquired by the nucleus as a whole if an additional proton were to participate in repulsive interactions with the other protons that are already present in the nucleus. As such, although free neutrons are unstable, bound neutrons are not necessarily so. The same reasoning explains why protons, which are stable in empty space, may transform into neutrons when bound inside of a nucleus.
[edit] Electric dipole moment
Main article: Neutron electric dipole moment

The Standard Model of particle physics predicts a tiny separation of positive and negative charge within the neutron leading to a permanent electric dipole moment.[6] The predicted value is, however, well below the current sensitivity of experiments. From several unsolved puzzles in particle physics, it is clear that the Standard Model is not the final and full description of all particles and their interactions. New theories going beyond the Standard Model generally lead to much larger predictions for the electric dipole moment of the neutron. Currently, there are at least four experiments trying to measure for the first time a finite neutron electric dipole moment.[which?]
[edit] Anti-neutron
Main article: Antineutron

The antineutron is the antiparticle of the neutron. It was discovered by Bruce Cork in the year 1956, a year after the antiproton was discovered. CPT-symmetry puts strong constraints on the relative properties of particles and antiparticles, so studying antineutrons yields provide stringent tests on CPT-symmetry. The fractional difference in the masses of the neutron and antineutron is 9±5×10−5. Since the difference is only about 2 standard deviations away from zero, this does not give any convincing evidence of CPT-violation.[2]
[edit] Geometry

An article published in 2007 featuring a model-independent analysis concluded that the neutron has a negatively charged exterior, a positively charged middle, and a negative core.[7] The negatively charged exterior of the neutron gives an intuitive explanation for why more neutrons are required in atoms with large numbers of protons, as the neutrons' negatively charged surfaces attract the positively charged protons to stay clumped together in the atom.