 More accurate calculations taking into account the effects of the finite size of the nucleus indicate that the binding energy first exceeds 2"mc"2 for "Z" > "Z"cr ≈ 173.For "Z" > "Z"cr, if the innermost orbital (1s) is not filled, the electric field of the nucleus will pull an electron out of the vacuum, resulting in the spontaneous emission of a positron.This diving of the 1s subshell into the negative continuum has often been taken to constitute an "end" to the periodic table, although more detailed treatments suggest a less bleak outcome.