Prompt and delayed spectroscopy ofTb142using recoil-isomer tagging

Abstract

Recoil-isomer tagging has been used to characterize the states built upon an I π = 8 + isomer in 142 Tb. High-spin states of the neutron-deficient nucleus 142 Tb were populated using an 54 Fe beam, accelerated onto a 92 Mo target of thickness ∼500 µg/cm 2 at energies of 245, 252, and 265 MeV using the K130 cyclotron at the University of Jyväskylä, Finland. Use of the JUROGAM target-position Ge-detector array coupled with the GREAT focal-plane spectrometer at the RITU gas-filled recoil separator has significantly increased the efficiency of the isomer-tagging technique. The rotational band built upon the I π = 8 + isomeric state was established with isomer-tagged γ -γ coincidence data and angular distributions were measured for some of the more intensely populated states. Two previously unobserved bands that bypass the isomer were also established. The new data have been interpreted within the framework of the cranked-shell model. The data show good agreement with the calculated triaxial nuclear shape with γ = −30 • for the 142m2 Tb isomeric state. The B(M1)/B(E2) branching ratios, nuclear alignment, signature splitting, and reduced transition probability, B(E1), of the isomeric state have been systematically compared with those of the neighboring nuclei. These comparisons give further evidence for the πh 11/2 ⊗ νh 11/2 configuration of the isomer.

Identification of isomeric states in theN=73neutron-deficient nuclei132Pr and130La

“…This competition results in soft nuclear shapes for nuclei in this region, which are susceptible to nonaxial deformations. Studies of 144 Ho [2,3], 142 Tb [2,4,5], 140 Eu [6], and 134,136 Pm [7,8] nuclei have unearthed isomers resulting from a change in nuclear shape linked by E1 γ -ray transitions. An interpretation of K isomerism was prohibited in these cases due to the γ softness associated with their shapes.…”