PHASE-AMPLITUDE METHOD FOR CALCULATING RESONANCE ENERGIES AND WIDTHS FOR ONE-DIMENSIONAL POTENTIALS Emil Y. Sidky and Itzik Ben-Itzhak J. R. Macdonald Laboratory, Physics Department, Kansas State University, Manhattan, KS 66506 USA We present a method for evaluating accurate resonance energies and widths in any one-dimensional potential. Semi-classical theory (WKB) provides a fast estimate of resonance positions, but it can be off for the lifetimes. Conversely, there is a multitude of numerical techniques, solving the one-dimensional Schrödinger equation that give precise resonance energies and widths, but they are much more difficult to apply. The phase-amplitude method presented here yields accurate resonance energies and widths and is as easy to apply as WKB theory.