Rotational alignment in158Er and159Er

Abstract

High-spin states in ¹⁵⁸Er have been populated with the reactions ¹⁴⁵Nd(¹⁶O,3n) and ¹⁴⁶Nd(¹⁶O,4n) and high-spin states in ¹⁵⁹Er by the reaction ¹⁴⁵Nd(¹⁸O,4n). Gamma-gamma coincidence and angular correlation data were obtained using an array of five Ge(Li)-NaI(Tl) escape-suppressed spectrometers. Linear polarisation data were obtained using a sectored Ge(Li) detector and internal conversion data were obtained using a mini-orange spectrometer. In ¹⁵⁸Er the yrast band has been observed up to J^pi =26⁺ and three negative-parity side bands have been observed up to spins J^pi =23^-, 22^- and 15^- respectively. The ground-state band has been observed to continue after the first backbend in the yrast sequence to J^pi =20⁺ and the odd- and even-spin members of the gamma-vibrational band were observed up to 7⁺ and 10⁺, respectively. In ¹⁵⁹Er the yrast band has been observed up to J^pi =⁵⁷/₂⁺ and four side bands have been identified to spins J^pi =¹⁵/₂^-, ³⁹/₂⁺, ⁴⁹/₂^-, and ⁵¹/₂^- respectively. The bands observed are interpreted as configurations of quasiparticles using the cranked shell model. Residual quasiparticle interactions are calculated as a function of rotational frequency.