Neon reaction

Which reaction dominates depends on the ambient temperature in the interaction region Below about 100 million K, the carbon process dominates, whereas above that temperature the neon process tends to produce the slow neutrons. Since temperatures are typically higher in stars with more mass—as higher gravitational force accelerates and heats the stellar material—the neon reaction is more likely to proceed in stars much heavier than the Sun. The temperature of a distant star cannot, however, be measured directly. Rubidium production happens to be sensitive to neutron density—which is determined by the neutron production process—and can therefore be a good indicator of which reaction prevails in particular stars, especially when viewed as a ratio with other available s-process elements like yttrium or strontium. 

In 1964, workers at the Joint Nuclear Research Institute at Dubna (U.S.S.R.) bombarded plutonium with accelerated 113 to 115 MeV neon ions. By measuring fission tracks in a special glass with a microscope, they detected an isotope that decays by spontaneous fission. They suggested that this isotope, which had a half-life of 0.3 +/- 0.1 s might be 260-104, produced by the following reaction 242Pu + 22Ne —> 104 +4n. 

It is often convenient to speak of the valence electrons of an atom. These are the outermost electrons, the ones most likely to be involved in chemical bonding and reactions. For second-row elements these are the 2s and 2p electrons. Because four orbitals (2s, 2p, 2py, 2p0 are involved, the maximum number of electrons in the valence shell of any second-row element is 8. Neon, with all its 2s and 2p orbitals doubly occupied, has eight valence electrons and completes the second row of the periodic table. 

The evolution of a. star after it leaves the red-giant phase depends to some extent on its mass. If it is not more than about 1.4 M it may contract appreciably again and then enter an oscillatory phase of its life before becoming a white dwarf (p. 7). When core contraction following helium and carbon depletion raises the temperature above I0 K the y-ray.s in the stellar assembly become sufficiently energetic to promote the (endothermic) reaction Ne(y,a) 0. The a-paiticle released can penetrate the coulomb barrier of other neon nuclei to form " Mg in a strongly exothermic reaction ... 

Further capture of a-particles leads to the formation of oxygen and neon. 160 itself forms the basis for the synthesis of sulphur. The only biogenic element missing in Table 2.2 is phosphorus, which is an exception in that it is formed by a complex nuclear synthesis (Macia et al., 1997). In large stars, the reactions listed in the table take place in the following series, without stopping but over long periods of time. 

These reactions take place in the inner zone of stars heavier than 15 solar masses. Hydrostatic carbon burning is followed by explosive neon burning at temperatures of around 2.5 x 109K. Under these conditions, phosphorus (31P) can be formed, although complex side reactions also occur. In comparison with the formation of... 

The surface of Venus is hidden under an unbroken layer of clouds 45-60 km above it. Recently, the planet has been subjected to a complete cartography by radar satellites. Its atmosphere contains 96% CO2 by volume, the remainder consisting of N2, SO2, sulphur particles, H2SO4 droplets, various reaction products and a trace of water vapour. The water is probably subject to photolytic decomposition. Noble gases are more abundant than on Earth 36Ar by a factor of 500, neon by a factor of 2,700, and D (deuterium) by a factor of 400. 

Sodium loses its valence electron and its electron configuration becomes identical to that of neon Is2 2s2 2p6. Likewise, the valence shell of chlorine becomes completely filled and its electron configuration resembles that of argon. As a result, during the reaction... 

The chemical and physical properties of Unq (or rutherfordium) are homologous with the element hafnium ( jHf), located just above it in group 4 (fVB) in the periodic table. It was first claimed to be produced artificially by the Joint Institute for Nuclear Research (JINR) located in Dubna, Russia. The Russian scientists used a cyclotron that smashed a target of plutonium-242 with very heavy ions of neon-22, resulting in the following reaction Pu-242 + jjjNe-22 —> jj, Unq-260 + 4 n-1 (alpha radiation). The Russians named Unq-260 kurcha-tovium (Ku-260) for the head of their center, Ivan Kurchatov. (See details in the next section, History. )... 

The Lawrence Berkeley Laboratory and other groups were unable to confirm the spontaneous-fission reaction of Ku-260, so the Dubna groups discovery was disputed. The Berkeley equipment was unable to accelerate neon ions to the speeds required to produce Ku-260, and thus they tried a different reaction in a new automated rapid chemistry apparatus that identified and confirmed new isotopes of heavy metals. The procedure involved bombarding the element californium-239 with a mixture of the isotopes carbon-12 and carbon-13 ions, as follows ... 

In 1967 the scientists of the Joint Institute of Nuclear Research in Dubna, Russia, bombarded americium-243 with neon-22 to produce two isotopes of unnilpentium, then known as hahnium. The reaction is as follows jAm-243 + Ne-22 —> jjjjHahnium-260 and 261 (Unp-260 and 261). In 1970 Albert Ghiorso and his team at Berkeley bombarded califor-nium-249 with heavy nitrogen (N-15) in their Heavy Ion Linear Accelerator (HILAC). The reaction is as follows gCf-249 + -15 —> j jHa-260 (Unp-260). 

Carbon fusion produces neon, sodium and magnesium via reactions of the following type ... 

In the case of silicon fusion, which begins at around 2 billion K, the reactions proceed in a slightly different manner and we return to a fusion scheme similar to that of neon. At this temperature, silicon nuclei are gradually gnawed down by thermal photons which detach helium nuclei, protons and neutrons from them. These light nuclei combine with intact silicon to give nuclei in the region of iron. Schematically,... 

These reactions, which are extremely fast, are often balanced by the reverse reactions, so that an approximation known as nnclear statistical equilibrium can be applied. In this case, the most stable species, i.e. those possessing the highest binding energy, are favoured. The result depends on only three parameters, viz. temperature, density and neutron/proton ratio. The latter in its turn results from the previous nuclear reactions and the composition of the star at birth, through neon-22 (see above). 

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