Effects of the Hyperfine Interaction on Orbital Electron Capture

Electron capture from an unfilled atomic s orbital is investigated theoretically. Analyses are carried out for two simple situations, a mirror transition of a nucleus with a nucleon in an outer s1/2 state and a Gamow-Teller transition decreasing the nuclear spin by one unit. It is shown that the hyperfine interaction between electron and nuclear spins has a great influence on the rate of electron capture at temperatures small compared to the hyperfine splitting. The possibility of inducing electron capture with resonant electromagnetic fields is discussed.