Einsteinium 15 neutrons by uranium-238 nuclei followed by seven beta-decays, and had a half-life of 20.5 days. Such multiple neutron absorption was made possible by the high neutron flux density during the detonation, so that newly generated heavy isotopes had plenty of available neutrons to absorb before they could disintegrate into lighter elements. Neutron capture initially raised the mass number without changing the atomic number of the nuclide, and the concomitant beta-decays resulted in a gradual increase in the atomic number: ^{238}_{92}U ->[\ce{+15n}][6 \beta^-] ^{253}_{98}Cf ->[\beta^-] ^{253}_{99}Es </chem> Some U atoms, however, could absorb two additional neutrons (for a total of
Atomic number charge and a physical characteristic of atoms, did the word (and its English equivalent "atomic number") come into common use in this context. Loosely speaking, the existence or construction of a periodic table of elements creates an ordering of the elements, and so they can be numbered in order. Dmitri Mendeleev claimed that he arranged his first periodic tables (first published on March 6th, 1869) in order of atomic weight ("Atomgewicht"). However, in consideration of the elements' observed chemical properties, he changed the order slightly and placed tellurium (atomic weight 127.6) ahead of iodine (atomic weight 126.9). This placement is