Calculo relativista da vida media de estados atomicos perturbados pela interaccao hiperfina

We show that the hyperfine interaction plays a fundamental role in the lifetime of the ns"3 P_o level of ions with 4, 12 and 30 electrons as well as in the "5D_4 state in the (Ar)3d"4 ground configuration of 22 electron ions. In the first case, in the absence of nuclear magnetic moment, the "3P_o level can decay to the ground state only by a two-photon E1M1 transition with a very low probability. We show that hyperfine interaction decreases dramatically the lifetime of this level. In the case of the 22 electron ions, the interaction changes the lifetime of the J=4 level also by several orders of magnitude but, in opposition to the previous case, where only the magnetic dipole term as a sizable contribution, in these ions we must take into account both the magnetic dipole term and the electric quadrupole term. We show that the influence of this interaction in the lifetime of the J=4 level is due mainly to the electric quadrupole term. This can lead to a new method of obtaining the values of the nuclear electric quadrupole moments for some stable isotopes. The multiconfiguration Dirac-Fock method is used to compute atomic state energies in highly ionized systems, including the relativistic contribution to electron-electron correlations and radiative corrections. Transition probabilities among states are all done using exact relativistic formulas in the length gauge. The influnece of the hyperfine interaction in the lifetime of these states is obtained by a first order perturbative calculationAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga