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Numerical simulation is used to study the possibility of long-term chain nuclear reactions deep inside the Earth over 4 billion years. The active layer (the natural nuclear reactor operating on fast neutrons in lakes) can form when uranium oxides or carbides precipitate from a liquid layer onto the Earth's solid interior core. A mechanism of uranium concentration in the Earth's core is studied, experiments are performed, and it is shown that a nuclear chain reaction with breeding of fissioning nuclides could have occurred in such a layer. The basic neutron-physical characteristics of such a natural nuclear reactor are calculated. It most likely operates in a pulsed mode. The critical condition for the duration of the reaction is the power level. It is found that for certain optimal power this process in the Earth's core can last for more than 4 billion years up to the present time.The Earth emits more heat (~45 TW) than it could as a result of only cooling [1]. Additional heat (~40%) is released as a result of the decay of radionuclides. A substantial quantity of radioactive elements is found not only in the Earth's crust but also in the lower mantle [2]. The heat flux from the Earth's core due to cooling and crystallization of its material ranges from 5 to 10 TW [3]. It is known that because of the differences in the half-lives of 235 U and 238 U the fraction of the former nuclide decreases with time, and billions of years ago uranium contained more 235 U [4]. It follows from the present-day concentration of uranium in pitchblende that about 2 billion years ago and earlier, when the 235 U fraction exceeded 3%, a spontaneous fission chain reaction could have occurred in rich uranium deposits. In 1972, traces of a natural nuclear reactor were discovered in West Africa in a uranium deposit at Oklo (Gabon) [5]. Later about 20 reactor zones were found in the same region. Investigations of other locations of actinide concentration and operation of natural nuclear reactors, not only in the Earth's crust but also in the Earth's core, have been started [3,6,7].The yield of fission products, which migrate from the chain reaction zone and reach the Earth's surface, is analyzed to determine the characteristics of natural nuclear reactors. The ratio 3 He/ 4 He is instructive [3]. Approximately 1 of 10,000 fissions of actinides occurs not into two but three fragments, one of which is tritium, which after undergoing β decay converts into 3 He. Thus, the ratio 3 He/ 4 He in volcanic lava in Hawaii is almost 40 times higher than its value in the Earth's atmosphere. Data confirming these facts in other locations (actually over the entire Earth) exist [8]. Other fission products of the actinides from a natural nuclear reactor, which have reached volcanic lava, are also being studied. Electron antineutrinos, which arise as a result of the β decay of the fission products from fissioning of heavy nuclei during a nuclear chain reaction [9], can be anoth-

Recent high-precision measurements of the isotopic composition of lunar rocks demonstrate that the bulk silicate Earth and the Moon show an unexpectedly high degree of similarity. This is inconsistent with one of the primary results of classic dynamical simulations of the widely accepted giant impact model for the formation of the Moon, namely that most of the mass of the Moon originates from the impactor, not Earth. Resolution of this discrepancy without changing the main premises of the giant impact model requires total isotopic homogenisation of Earth and impactor material after the impact for a wide range of elements including O, Si, K, Ti, Nd and W. Even if this process could explain the O isotope similarity, it is unlikely to work for the much heavier, refractory elements. Given the increasing uncertainty surrounding the giant impact model in light of these geochemical data, alternative hypotheses for lunar formation should be explored. In this paper, we revisit the hypothesis that the Moon was formed directly from terrestrial mantle material. We show that the dynamics of this scenario requires a large amount of energy, almost instantaneously generated additional energy. The only known source for this additional energy is nuclear fission. We show that it is feasible to form the Moon through the ejection of terrestrial silicate material triggered by a nuclear explosion at Earths core-mantle boundary (CMB), causing a shock wave propagating through the Earth. Hydrodynamic modelling of this scenario shows that a shock wave created by rapidly expanding plasma resulting from the explosion disrupts and expels overlying mantle and crust material.Comment: 26 pages, 5 figures, 1 tabl

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A method of electrical conductivity and an analysis of recovered explosion products are used to study interaction of aluminum with detonation products of condensed high explosives. The electrical conductivity of HMX/Al and RDX/Al mixtures is inhomogeneous; a region with the maximum electrical conductivity is adjacent to the detonation front, whereas the electrical conductivity decreases with distance from the front. If the wave is incident onto a wall, the electrical resistance of the composite high explosive increases, which indicates that the high-conducting zone disappears. The electrical conductivity, resistance of the conducting zone, and the time of resistance growth are found as functions of the particle size of the additive. The results obtained confirm the reaction of the metal additive with detonation products in a microsecond range of time. An analysis of condensed explosion products shows that the reaction of aluminum with detonation products proceeds on the particle surface. The amount of reacted aluminum and the oxide-layer thickness are estimated.

An analysis is performed of experimental data from isotopic tracer studies of the detonation mechanism and formation of the diamond phase of carbon in the detonation products of TNT, RDX, HMX, and their mixtures. Dependences of the relative yield and phase composition of carbon in the detonation products of components of composite explosives on the particle sizes of the explosives are given.

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