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Elements 121 and 122 should be similar to actinium and thorium respectively. [7] At element 121, the superactinide series is expected to begin, when the 8s electrons and the filling 8p 1/2, 7d 3/2, 6f 5/2, and 5g 7/2 subshells determine the chemistry of these elements.
Supernova nucleosynthesis is the nucleosynthesis of chemical elements in supernova explosions.. In sufficiently massive stars, the nucleosynthesis by fusion of lighter elements into heavier ones occurs during sequential hydrostatic burning processes called helium burning, carbon burning, oxygen burning, and silicon burning, in which the byproducts of one nuclear fuel become, after ...
The process of slow neutron capture used to produce nuclides as heavy as 257 Fm is blocked by short-lived isotopes of fermium that undergo spontaneous fission (for example, 258 Fm has a half-life of 370 μs); this is known as the "fermium gap" and prevents the synthesis of heavier elements in such a reaction.
Scientists discovered a method to create element 116 using a titanium beam, paving the way for future synthesis of element 120, the "holy grail" of chemistry.
The first direct proof that nucleosynthesis occurs in stars was the astronomical observation that interstellar gas has become enriched with heavy elements as time passed. As a result, stars that were born from it late in the galaxy, formed with much higher initial heavy element abundances than those that had formed earlier.
Abundance peaks for the r-process occur near mass numbers A = 82 (elements Se, Br, and Kr), A = 130 (elements Te, I, and Xe) and A = 196 (elements Os, Ir, and Pt). The r-process entails a succession of rapid neutron captures (hence the name) by one or more heavy seed nuclei, typically beginning with nuclei in the abundance peak centered on 56 Fe.
The stable alpha elements are: C, O, Ne, Mg, Si, and S. The elements Ar and Ca are "observationally stable". They are synthesized by alpha capture prior to the silicon fusing stage, that leads to Type II supernovae. Si and Ca are purely alpha process elements. Mg can be separately consumed by proton capture reactions.
Normally, exchange interactions are very short-ranged, confined to electrons in orbitals on the same atom (intra-atomic exchange) or nearest neighbor atoms (direct exchange) but longer-ranged interactions can occur via intermediary atoms and this is termed superexchange.