Nuclei of low to medium mass

rECENT PROGRESS IN the physics of nuclear structure is marked by a rapid increase in the amount of new data on excited states of low‐to‐medium‐mass nuclei—those nuclei with masses roughly in the range $\text{16⩽A⩽56.}$ Concurrent with this worldwide experimental activity a significant increase in theoretical effort is perceptible. The attraction to this area of nuclear‐structure physics can possibly be related to the impressive array of physical phenomena that these nuclei exhibit. Very recent phenomenological developments include, for example, the frequent observation of unusual mixtures such as that of magnetic‐quadrupole and electric‐dipole multipolarities in radiative transitions between excited states and the discovery of very pure single‐particle isobaric analog states at high excitation energies. In addition, electric‐octupole transitions in direct competition with electric‐dipole and magnetic‐quadrupole transitions are becoming a persistent feature of these nuclei.