Atomic effects on the [ital ft] value for tritium [beta] decay

The atomic effects on the [beta]-decay [ital ft] value of tritium are discussed for three atomic systems: the tritium atom and the ions T[sup +] and T[sup [minus]]. The effect of exchange between bound and continuum electrons in the decay of the tritium atom is shown to lead to an increase in the phase-space integral [ital f] by 0.15% relative to the [ital f] value for T[sup +]. This corrects an error in earlier work which suggested that the inclusion of exchange effects led to a decrease in the [ital f] value for this decay. Differences in atomic-electron screening between the T atom and the T[sup +] ion are shown to lead to a reduction in [ital f] for the T atom by 0.41%, significantly larger than previous estimates of screening effects on [ital f]. The combined atomic effects are shown to lead to a difference in [ital f] between T[sup +] and the T atom of 0.30%. The effect of these changes in [ital f] on a recent evaluation of the ratio of the weak-interaction coupling constants, [ital G][sub [ital A]]/[ital G][sub [ital V]], is discussed.