What I have found about neutronium.

[Admiral Piett]

I have done a research with google about neutronium.Apparently there are not many sources.The main I have found,an online encyclopedia states:

"Neutronium is the informal term for an extremely dense phase of the matter,which occurs only in the intense pressure found in the core of neutron stars.For reasons that will be explained below,it si not often used in the scientific literature of Astronomy and Astrophysic.
When a massive star creates an iron core whose mass exceeds the Chandrasekhar limit,it will collapse and create a type II supernova.The core of the collapsing star is initially composed of iron supported by electron degeneracy pressure,since the nuclear fusion of iron does not release enrgy.When the core collapse,the densities and pressures in the core overcome even the electron degeneracy pressure and the iron atom's electrons are compressed into their nuclei where they combine with protons to form neutrons.

electron+proton to neutron+neutrino

The neutrino is emitted from the core,lea ving the neutron behind.The material that remains has a density of approximately 10 raised to14-10 raised to 15 grams per cubic centimeter.A teaspoon full of this matter would have a massof 100 million metric tons.This material has often been termed neutronium.However,because the physics of material at these high densities is unknown,it is far from clear if the interior of a neutron star is best described as a sea of neutrons.It is possible that rather than that a sea of neutrons,the interior of a neutron star would be best modelled as asea of free quarks or of heavy hyperions (what are hyperions?).It is also possible that neutron star material undergoes a number of phase transitions,in which the material has radically different properties depending on the density and temperature of the material.It is also unknown how neutron star material would behave if the pressures on the star were suddenly reduced.Because of these uncertainties,the term neutronium is rarely found in the scientific literature.
All of these uncertaintiesa can be summarized in an equation of state which describes the pressure of neutron star material given a certain temperature and density.Calculating equations of state is an active and uncertain area of physics.Frequently in the literature,scientists will refer to a "stiff" equation of state or a "soft" equation of state.A "stiff" equation of state has an higher pressure than a soft equation at a given temperature and pressure.
There is a limit beyond which a neutron star can no longer support itself via nuclear degeneracy pressure and would collapse all the way into a black hole.The exact limit depends on the equation of state which is used but
estimates range varies from 1.4 to 3 solar masses.Current equations of state are considerably "softer" the guesses for equation of states used in the 1970's whcih had a limit of 7-8 solar masses.Some theories predict an intermediate form of matter between neutronium and black holes,dubbed strange matter."

And this is basically nearly all that you can find on internet.

[SPOOFE]

Well, there's a bit more info to be had:

This brief article mentions that newly-born neutron stars can attract neutrinos.

This provides a short explanation of "degenerate neutron pressure', which is the force that balances out the pull of gravity in neutron stars (and, assumedly, in neutronium) that essentially just keeps matter from compressing and compressing... until enough gravitational pressure is applied (something like three solar masses, if I recall correctly), in which case the matter becomes a black hole.

This page lists another name for neutronium... "baryon degenerate matter". Follow the links from there and you hear about all sorts of nifty things like Pauli's exclusion principle and such.