Vanishing points of particle widths of resonances: an atomic parallel of a well known nuclear phenomenon

Attention is drawn to the close correspondence which exists between different branches of physics in which the following situation is met, namely an 'intruder' state with distinctive properties occurs in a normal sequence of levels and mixes with them. The properties of the levels can be sharply modified and, in the right circumstances, their particle widths can exhibit a pronounced minimum, or even be zero, at a certain energy. It is shown analytically from K-matrix theory that this effect, well known in nuclear physics, occurs also in atomic physics when a Rydberg series is disturbed. An experimental case has recently been reported.