The Life-time Measurements of Some High-spin States in the ^138,139Ce and ^141,142Nd Nuclei

Abstract

A search for high-spin isomeric states in the 138,139 Ce anc 141,142 Nd nuclei has been made using (α, x n) reactions and the intrinsic pulsing of the 225-cm Stockholm cyclotron. In 138 Ce, besides the known 7 - isomeric state at 2 128.8 keV, another one at 3 538.5 keV, 10 + , with T 1/2 = (78 ± 5) ns has been found. In 139 Ce a new isomeric state at 2 631.5 keV, 19/2 - , with T 1/2 = (70 ± 5) ns has been identified. Also in 141 Nd a high-spin isomeric level exists probably at 3 104.9 keV with T 1/2 = (26 ± 5) ns. In 142 Nd the level at 3 453.0 keV, with spin I = 6, shows a half-life T 1/2 = (1.3 ± 0.1) ns while that at 4 718.5 keV, I = 8, decays with a half-life of about 0.8 ns. The time distributions in 142 Nd show that the 3 242.9 keV, I = 7, or the 3 456.2 keV, I = 8, level is also delayed and decays with T 1/2 = (1.6 ± 0.1) ns. The deduced transition probabilities are compared to theoretical predictions.