FIRST OBSERVATION OF LOW-ENERGY LONG-LIVED ISOMERIC TRANSITIONS IN TM-166

A study of Tm-166 by the Gd-160(B-11,5n gamma) reaction was performed with the aim for searching for low-energy isomeric transitions using t he Recoil Shadow Method (RSM). gamma-rays from the production target a nd from the recoil ions stopped on an annular carbon catcher placed 16 cm downstream were observed with Ge detectors. Singles spectra follow ing bombardment at three different energies, and coincidence spectra, were measured. Six isomeric gamma-rays were observed. New levels are e stablished and their configuration assignments are proposed. One of th ese levels, at (x + 109.3) keV, is isomeric with a half-life of 340(25 ) ms. An upper limit for x was set to 25 keV. The half-life of the yra st band head was determined to be 2(1) mu s. Two alternatives for the decay path of the 340(25) ms level to the ground state are proposed. T he structure of the low-lying {p7(+)/2[404] + n5(-)/2[523]}K-pi = 6(-) band is established for the first time.