High Quality Content by WIKIPEDIA articles! Naturally occurring lithium (chemical symbol Li) (standard atomic mass: 6.941(2) atomic mass units, a.m.u.) is composed of two stable isotopes, lithium-6 and lithium-7, with the latter being by far the more abundant one: about 92.5 percent of the atoms. Both of the natural isotopes have an unexpectedly low nuclear binding energy per nucleon when compared with the adjacent lighter and heavier elements, helium and beryllium. This means that solely among the stable light elements, lithium can release energy through nuclear fission. The most stable radioisotope of lithium is lithium-8, which has a half-life of just 838 milliseconds. Lithium-9 has a half-life of 178 milliseconds, and lithium-11 has a half-life of about 8.6 milliseconds. All of the remaining isotopes of lithium have half-lives that are smaller than 10 nanoseconds. The shortest-lived known isotope of lithium is lithium-4 which decays by proton emission with a half-life of about...
С нового учебного года всех первоклассников России будут принимать в учебные заведения по месту жительства. Президент РФ недавно утвердил поправки, определяющие закон «Об образовании». Данные поправки закрепляют первоочередное право на законные места в младших классах для детей, которые проживают неподалеку от школы. Нововведенные поправки будут действительны с первого января следующего года.