High-spin states in the doubly odd nucleus 160 Tm have been investigated using the 130 Te( 35 Cl,5n) reaction and the Euroball γ -ray detector array. The previously established rotational structures in 160 Tm were extended, leading to the first observation of the second (h 11/2 ) 2 proton band crossing in this nucleus. This crossing is found to occur at a higher rotational frequency in 160 Tm than in lighter Tm isotopes. This trend resembles that of the first (h 11/2 ) 2 proton band crossing found in neighboring Er nuclei and is associated with a predicted increase in deformation as a function of neutron number in these isotopes.In rotating atomic nuclei, the Coriolis force exerted on the nucleons may at high excitation energies be large enough to counteract the pairing force. The breaking of a nucleonic pair allows the nucleons to align their spins with the axis of collective rotation. This alignment can be described as a crossing between two bands corresponding to different nucleonic configurations (see for example [1] and references therein).The experimental observation of such band crossings is an important guide for making configuration assignments and provides information on the nuclear deformation and the strength of pairing correlations. The systematic properties of the second proton (h 11/2 ) 2 (B p C p ) alignment in nuclei near 160 Tm have been discussed previously [2]. This band crossing shifts toward higher rotational frequency as a function of increasing neutron number in the odd-Z 158,159 Tm, 157,158 Ho, and 155,156 Tb nuclei (see [2] and references therein). The B p C p crossing can be found in rotational bands that have an unpaired proton in the lowest lying h 11/2 intruder orbital (A p ), so that the first possibility for rotational alignment of an h 11/2 quasiproton pair (corresponding to the A p B p crossing) is blocked. The new experimental information for 160 Tm presented in this work extends these band crossing systematics and supports the suggested trend [2] for the B p C p crossing in this mass region.The present work reports on an experiment in which highspin states in 160 Tm were populated using the 130 Te( 35 Cl,5n) reaction during one day of irradiation time. The beam, which was provided by the Vivitron accelerator of IReS, Strasbourg, had an energy of 170 MeV and an average intensity of 3 pnA. A stack of two targets was used, each target consisting of a 500-µg/cm 2 -thick layer of 130 Te backed for stability purposes * karinl@nucmar.physics.fsu.edu with 500-µg/cm 2 -thick gold foil and mounted with the gold layer facing the beam. γ rays emitted in the reactions were detected by the Euroball [3,4] detector array. The setup also included an inner BGO ball, which enabled filtering of the events based on the total detected γ -ray energy and multiplicity. The event trigger required coincident signals from five or more unsuppressed Ge crystals and six or more elements of the BGO inner ball. The event data were unfolded off-line into 1 × 10 10 coincidence suppressed triplets, which were u...
