 Isotopes of neutronium

Neutronium is a hypothetical substance that consists almost entirely of neutrons. It is often discussed in the context of astrophysics and is theorized to be found in the cores of neutron stars, where extreme gravitational pressures force neutrons together in massive quantities. Since neutronium is made up entirely of neutrons, it doesn't have isotopes in the traditional sense as isotopes refer to variants of a chemical element that have the same number of protons but different numbers of neutrons.