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Neutronium

Neuronium

Neutronium is a real term for something that does not exist. This term was invented by Andreas von Antropoff in 1926 (before the neutron was officially discovered). The key concept is beta equilibrium. A neutron is more massive than a proton by 0.78 MeV. At low pressure, neutrons turn spontaneously into protons + electrons (+ antineutrinos): n ---> p + e- + a-nu. At high pressures, things change. At high pressure, fitting enough electrons into a volume to cancel proton charge means most of those electrons must have small wavepackets - which is equivalent to saying high-energy ones. The actual equilib-rium between neutrons, protons, and electrons is

p + e- + QC(e) <---> n + nu

in which QC(e) is energy required to compress the electron's wavepacket to the size it has. If QC(e) > 0.78 MeV, protons and neutrons can spontaneously turn into neutrons and neutrinos. That's more compression energy than white dwarfs can produce - but much less than neutron stars can. Going down into the crust of a neutron star, matter becomes more and more neutron rich as beta equilibrium favors neutrons over electrons. At about 30% of the way through a neutron star's crust, beta equilibrium requires more neutrons than can be bound into nuclei, so a free-neutron phase appears.

The other phase - charged nuclear particles and free electrons - does not disappear. Nuclear binding between protons and neutrons is stronger than nuclear binding between like pairs. Even through electrons cost energy at high pressure, nuclear matter will remain 5% to 10% protons regardless of depth within the star. The two phases of a neutron star's inner crust are not like water and sand. The phases interpenetrate so matter's composition remains at equilibrium even at the nuclear scale.

The two phases differ in an important way. The free neutron phase is fluid. Free electrons in the charged-nuclear-matter / electrons phase are also fluid; but charged nuclear particles are not. Due to high pressure, they assume fixed positions with respect to each other. This phase of a star's crust is solid, crystalline. While the two phases in a neutron star's crust cannot be separated, the free neutron phase can move with respect to the crust. This is important if a star is rapidly accreting matter or if it is disintegrating.

Matter made entirely of free neutrons cannot exist. However, from the macroscopic perspective of neutron star dynamics, it is convenient to think of the free-neutron phase of a neutron star's crust as a separate fluid composed entirely of neutrons. The term "neutronium" could be applied to this convenient macroscopic approximation - but there is so much confusion about neutronium that it would be unwise to use the term. A better choice would be "nilium ocean".

Since neutronium can't exist, it may seem a minor point; but it would not be an element even if it did exist. It has no charge, so it can't bind electrons. No electrons, no atoms; no atoms, no element. Period, end of file.

(11-14-22)

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