Atomic-Beam Investigations of Electronic and Nuclear Ground States in the Rare-Earth Region

A number of radioactive isotopes in the rare-earth region have been investigated by using the atomic-beam magnetic-resonance technique. The total electronic angular momentum (J) and the atomic g value (gJ) have been determined for some low-lying levels in, Pm, Dy, Ho, and Er. These observations are consistent with the following ground-state assignments: Pmi---(4f)⁵(6s)², ⁶H5/2; Dyi---(4f)¹⁰(6s)², ⁵I₈; Hoi---(4f)¹¹(6s)², ⁴I15/2; and Eri---(4f)¹²(6s)², ³H₆. The ground-level assignments agree with the Hund's-rule predictions, and the g values approximate the Land\'e values well. Our present experimental knowledge concerning electronic ground states in the rare-earth region is summarized. The following nuclear spin values have been obtained: Pm¹⁴⁹, I=7/2; Pm¹⁵¹, I=5/2; Gd¹⁵⁹, I=3/2; Tb¹⁶⁰, $I=3$; Dy¹⁶⁵, I=7/2; Dy¹⁶⁶, $I=0$; 27-hr Ho¹⁶⁶, $I=0$; Er¹⁶⁹, I=1/2; Er¹⁷¹, I=5/2; and Tm¹⁷¹, I=1/2. These values are compared with available beta-decay results. Most of these isotopes have large nuclear deformations, and the spin values are discussed in relation to the single-particle energy-level diagrams given by Nilsson. A few results are explained with the shell model.