ENERGIES AND HALF-LIVES OF ISOMERIC LEVELS IN THE NUCLEI 139Ce, 141Nd, 161Ho, AND 163Ho

Abstract

A search has been made for delayed γ rays with 1 second [Formula: see text] minutes following 10.5-MeV proton bombardment of 18 natural metallic targets. The five activities observed are: (1) 139Ce, Eγ = 754.5 ± 1.3 keV, [Formula: see text] second; (2) 141Nd, Eγ = 756.8 ± 1.3 keV, [Formula: see text] second; (3) 161Ho, Eγ = 211 ± 2 keV, [Formula: see text] second; (4) 163Ho, Eγ = 299 ± 2 keV, [Formula: see text] second; and (5) a γ ray of 122 ± 2 keV, [Formula: see text] second which is tentatively assigned to 179Ta. All transitions have been measured using a Ge(Li) γ-ray detector. The internal conversion electrons of the transitions in 139Ce and 141Nd were also studied using an orange β-ray spectrometer. Rotational transition energies in 158Dy, 164Er, 168Yb, and 174Hf were measured in conjunction with the internal conversion studies and are reported in an Appendix.