Interface with Nuclear Physics

Abstract

For an atom with a small to moderately large atomic number Z, the typical length scale a0 ∕ Z of the innermost core orbitals is so much larger than typical nuclear length scales that the corrections to the energy levels and wave functions arising from the nonzero electric charge radius of the nucleus can accurately be computed using first-order perturbation theory, as is described in Sect. 91.2. Nonetheless, these relatively small shifts can sometimes have a profound effect on processes in atomic and/or nuclear physics, particularly if two or more energy levels are very close. For example, as is discussed in Sect. 91.3, the presence of the electron cloud makes energetically possible the β-decay of 187Re to 187Os and significantly modifies the energy distribution of products in the β-decay of tritium in various chemical environments. Also, electronic screening can greatly enhance the cross sections of low-energy nuclear reactions relative to what they would be for bare nuclei. In isotopes of hydrogen, the replacement of an electron by a muon, with mμ ≈ 207me, results in a tiny neutral atom that can closely approach another nucleus, thereby catalyzing nuclear fusion. For example, the rate of deuterium–tritium fusion is enhanced by 77 orders of magnitude if a single electron is replaced by a muon. A rich variety of bound-state properties and scattering processes for these exotic atoms and molecules has been extensively investigated, as is reviewed in Sect. 91.4.