A study of high spin states in 151Gd

Abstract

States in the transitional nucleus, 151Gd, excited by the (α,2n) reaction have been studied by gamma-ray and conversion electron measurements. Gamma-ray energies, intensities, excitation functions, and γ–γ coincidence measurements were used to establish the levels populated. Angular distributions involving measurements at seven angles from 0° to 90° and K-conversion coefficients have been used to make spin and parity assignments.The El character of the 65, 79, 340, 358, 406, and 462 keV transitions, which in the absence of K-conversion data had been tacitly assumed to be M1 by earlier workers leads to a significant revision of their parity assignments and interpretation of the level structure. The negative parity states at 1210, 1463, 1726, 2004, 2295, 2600, 2915, and 3237 keV form a well-developed rotational band based on the 11/2− [505] state at 1210 keV. The properties of this band in this nucleus are compared with those of the same band in a number of nearby nuclei. Two non-interacting negative parity bands with states at 0(7/2−), 706(11/2−), 1435(15/2−), 2078(19/2−), and 379(9/2−), 902(13/2−), 1511(17/2−), 2297(21/2−), respectively, have been found, as well as a number of other negative parity states of spin 7/2, 9/2, and 13/2. A complex positive band structure involving states at 784(11/2+), 852(13/2+), 1116(13/2+), 1346(17/2+), 1364(15/2+), 1677(17/2+), 1851(19/2+), 1853(21/2+), 2197(21/2+), 2325(23/2+), and 2405(25/2+) has been identified. By using a somewhat unusual set of parameters, we have been able to approach a description for the positive parity states in terms of the triaxial model of Meyer-ter-Vehn.