Decay width and the shift of a quasistationary state

We develop a two-potential approach to the decay of a quasistationary state. The method enables us to obtain a simple algebraic formula for the decay width and the energy shift of a metastable state. The quasiclassical limit of the width found leads to the well-known Gamow formula, this time with a well-defiend preexponential factor. The energy shift together with its quasiclassical limit is obtained in closed form.