Аннотация:The neutron matter in our time is quite concrete physical reality, which strongly demands its rightful place in the Periodic System of elements (PS) and to be studied from point of view of not
only its physical but also chemical, and possibly in the near future, technical properties. It is postulated, that the PS of elements begins (zero period) with the neutron matter, or rather with the Element it corresponds to, and finishes (supercritical atoms) by it. The paper deals with the formation of neutron matter and, in addition to the gravitational neutronization, considers other mechanisms, such as condensation of ultracold neutrons (UCN) and neutronization by critical increasing of atomic number of elements in the PS. I.E. Tamm’s "original" theory of exchangeable nuclear forces (e - exchange of nucleons), but not only its modification made by Hideki Yukawa (meson-exchange of nucleons), is still awaiting its acceptance (since except as meson cloud around a nucleon, there are certainly other particles) and "dominates" in the neutron matter of the Universe, providing its stability and a wide cosmic spreading. Another factor of additional stability of the neutron matter during the significant increase of its mass (up to a macro scale) will be the ever-increasing contribution to the gravitational interaction. The neutron matter is conferred the sustainability already at the micro-level by means of Tamm interaction, not just at the macro-level due to the gravitational interaction, as it is now considered to be in astrophysics. The possibility of neutronization is not only due to the gravitational interaction, but also due to other mechanisms (supercritical increase the atomic number of elements and UCNs condensation), so there is a principal possibility of the neutron matter obtaining in the Earth conditions. Also, the possibility of chemical interaction of UCN with molecules of substances with an odd number of electrons is considered. The possible plan of the experiment on "chemistry" of UCN is discussed. The neutron matter is necessary link connecting (inducing a bridge) the micro-, the macro- and mega-World, from the free neutron to the neutron stars and the black holes. The neutron matter consistently fits into the original concept of the Periodic Law and the System proposed by Dmitry Ivanovich Mendeleev.
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