Search

Through an in-beam study of the69153Tm84 nucleus we have identified the ph112/5/2?f72/2 and ph112/5?f7/2h9/2 7-valence particle configurations up to their fully aligned spins of 47/2- and 51/2-. Shell model calculations predict that in the ph112/5?f7/2h9/2 configuration, contrary to the p112/5?f72/2 case, the h11/2 proton seniority does not increase regularly with spin. This seniority inversion is verified by the data.

In an in-beam study of67151Ho84 we have established its high-spin states up to 10 MeV and have suggested spin assignments up to (49/2) at 6.2 MeV. The main decay-cascade proceeds through the yrast states of the ph311/2?f27/2 and ph311/2?f7/2h9/2 5-particle configurations, which are predicted with good accuracy in parameter-free shell-model calculations. States with one proton in d3/2, or involving ?i13/2 or ?f7/2×3- excitations were also identified.

h11/2 neutron and g9/2 proton alignments in99,100Ru deduced from comparisons of experimental Routhians and aligned angular momenta to cranking model calculations. There is indication of band termination in100Ru.

Neutron deficient nuclei close to100Snhave been investigated in-beam by γ-ray spectroscopic methods using the NORDBALL detector array. A beam of 270 MeV58Niwas used to bombard a target of54Fe.Reaction channel separation was achieved with a 4π charged particle multidetector setup together with a 1π neutron detector wall placed in the forward direction. Excited states of102Inwere identified for the first time. The level scheme constructed from γ-γ-particle-coincidence and γ-γ-angular correlation analysis is presented. The structure of102In is discussed and compared to neighboring nuclei in the framework of the nuclear shell-model.

We report on new results for the decay of the superdeformed (SD) band in194Pb. No transitions linking the SD structure with the known level scheme of194Pb could be found, but the feeding intensities into the normal-deformed states are determined and limits on the one-step decay of the SD band are given.

High spin states in104Cd have been investigated by means of heavy ion induced reactions using the Nordball detector array. The level scheme constructed from ??-coincidences is dominated by three band structures. The positive parity band shows no rotational like energy spacing. It is thus understood mostly in terms of quasiparticle excitations with vd5/2, vg7/2 andpg9/2 configurations. The collective properties of the negative parity bands are more pronounced. These bands are most likely due to v(h11/2,d5/2) and v(h11/2,g7/2) structures.

A 53.3 keV E2 transition de-exciting the 60 ns isomer in152Dy has been identified in γγ-coincidence measurements, which locates that isomer at Ex=5088 keV. The half life of the 11− level at 3161 keV was measured to be T1/2=4.3±0.9 ns.

Through (p,2n) in-beam ? and e- measurements the excitation of the 235 µs 9+ isomer in146Eu has been determined to be 666.3 keV. High spin members of the pd52/-1 ?f7/2 and pg72/-1 ?f7/2 particle hole multiplets populated in the isomeric decay were located.

Three yrast isomers in151Dy, at 6.03 MeV (I=49/2, T/=15(3) ns), 4.90 MeV (41/2-, 5.5(1.0) ns), and at 2.96 MeV(27/2-, 1.3(6) ns) have been located through152Gd(a,5n) and136Ce(18O, 3n) measurements. Shell model configurations are suggested for them.

Adedicated γ-ray measurement with mass-separated 147Dy activity gave the direct β-feeding intensities to the 147Tb πs1=2and πh11=2single proton states in decay of the 147Dyνs-11=2andνh-111=2activities.With these results the absolute transition rates for the three Gamow-Teller decay modes of 147Dy can be deduced.

Proton rich nuclei close to100Sn have been investigated inbeam using the NORDBALL detector array. A beam of 270 MeV58Ni was used to bombard a54Fe target. Reaction channel separation was achieved with a 4p charged particle multi-detector set-up together with a 1p neutron detector wall placed in the forward direction. Gamma-ray transitions belonging to the111I nucleus were identified for the first time. A level scheme constructed from ?-?-particle-coincidence analysis is proposed. The level structure is discussed within the framework of the shell model and the systematics of the heavier odd iodine nuclei.

Levels of110Cd have been investigated via the96Zr(18O,4n)110Cd reaction by employing the NORD-BALL array of 17 Compton- suppressed Ge detectors. The yrast band has been observed up to I=28 h and 14.2 MeV excitation energy with band crossing at h?c=0.35 MeV. At least three side bands have been constructed. The negative parity bands experience band crossings at h?c ˜ 0.45 MeV.

Measurements of ?-rays from mass analyzed nuclear recoils produced in the102Pd +54Fe reaction at 245MeV have allowed us to characterize the decay of a 35 µs isomer in154Lu. The rates of E2 transitions de-exciting isomeric levels in proton-rich N=82, 83 isotones are discussed.

Levels of the N=83 nucleus147Gd have been investigated by in-beam ?-ray and conversion-electron spectroscopy using the147Sm(3He,3n) and Sm(a,n) reactions. We have observed 16 new low-and medium-spin levels in147Gd. In addition to the previously known 13/2+ level we have located the 11/2+,9/2+, 7/2+, 3/2+ and (1/2)+ members of the vf7/2×3 septuplet.

The level scheme of143Eu has been extended to I=75/2 in an experiment with the NORDBALL Compton-suppressed Ge detector array and the110Pd(37Cl, 4n) reaction. Most of the scheme shows irregular structure of multiparticle excitations. A strongly populated straight cascade of more than 10 stretched E2 transitions suggests the onset of collectivity.

Gamma-ray measurements following mass analysis of102Pd+245 MeV54Fe reaction products have characterized a 15 µs isomeric decay in153Yb and elucidated the systematics of proton-rich N=83 nuclei.

In-beam studies with (α,4n) and (3He, 3n) reactions have located a second 10+ state closely above the 10+ isomers in144Gd and142Sm. The data characterize the142Sm 10+ isomer as the νh112/−2 excitation in contrast to144Gd where the 10+ isomer is of πh112/2 character.

With the96Ru(58Ni,2pn) reaction we produced151Yb81 and studied its decay after online mass separation by ?-spectroscopic techniques. The decay populates the four positive parity single proton levels in the N=82 daughter nucleus151Tm and establishes Ip=1/2+ for the so far unknown151Tm low spin isomer. Using BCS theory proton single particle energies for151Tm were extracted from the observed excitation energies.

High-spin states in 185Re have been studied using the 176Yb(13C,p3n) reaction at 65 MeV. Levels up to spin (37/2) h̄ at Ex= 4.799 MeV have been identified. Among them two levels were observed with half-lives of 6 ± 2 ns and 123 ± 23 ns.