beta-decay scheme of Te-140 to I-140: Suppression of Gamow-Teller transitions between the neutron h(9/2) and proton h(11/2) partner orbitals

Abstract

We report for the first time the beta-decay scheme of Te-140 (Z = 52) to I-140 (Z = 53), with a specific focus on the Gamow-Teller strength along N = 87 isotones. These results were obtained in an experiment performed at the Radioactive Ion Beam Factory (RIBF), RIKEN, where the parent nuclide, Te-140, was produced through the in-flight fission of a U-238 beam at 345 MeV per nucleon impinging on a Be-9 target. Based on data from the high-efficiency gamma-ray spectrometer, EUROBALL-RIKEN Cluster Array (EURICA), we constructed a decay scheme of I-140. The half-life of Te-140 has been determined to be 350(5) ms. A level at 926 keV has been assigned as a (1(+)) state based on the log ft value of 4.89(6). This (1(+)) state, commonly observed in odd-odd nuclei, can be interpreted in terms of the pi h(11/2)nu h(9/2) configuration formed by the Gamow-Teller transition between a neutron in the h(9/2) orbital and a proton in the h(11/2) orbital. We observe a sharp contrast to this type of beta-decay branching to the lower-lying 1(+) states between I-140 and I-136, where we see a large reduction as the number of neutrons increases. This is in contrast to the prediction by large-scale shell model calculations. To investigate this type of the suppression, results of the Nilsson model calculations will be discussed. Along the isotones with N = 87, we discuss a characteristic feature of the Gamow-Teller distributions at 1(+) states with respect to the isospin difference.