K. Hardt

On the rotation-aligned coupling of the h112 proton-hole states in 191, 193Au

The rotational bands built on the excited 112− levels in 191Au and 193Au were investigated in (α,4n) reactions with in-beam γ-ray and conversion electron spectroscopy. Half-lives of the rotation-aligned levels in these bands were determined from e−e− time spectra, which were measured with a new double-orange spectrometer. In addition, some information on the magnetic moments of the rotation-aligned levels was obtained from integral perturbed angular distribution measurements. Finally, the previously unknown low-energy 312− → 272− transition in 191Au was identified from conversion electron measurements. From these data it is concluded that the rotation-aligned Hg cores have predominantly νvi1322 structure, contrary to the earlier suggestion of a πh1122 core structure.

g-Factors of high-spin isomers in 194Hg and 196Hg

Abstract The g -factors of the 10 + isomeric states in 194 Hg and 196 Hg have been measured using the in beam IPAD method. The results g( 194 Hg ) = −0.24(4) and g( 196 Hg ) = −0.18(9) are in agreement with the value expected for an ( i 1 3 2 −2 ) neutron satructure and clearly contradict the previous assignment as ( h 1 1 2 −2 ) proton configurations. Cranking model calculations show that the neutron excitation energies in the rotating frame agree satisfactorily with the experimental energies and that the proton excitations are expected ≈2 MeV above the experimental yrast line

In-beam investigation of high-spin states in actinides with (α, xn) compound reactions

Abstract The ground-state rotational bands in 230, 232 U and 236, 238, 240 pu were investigated in ( α , x n) reactions. Conversion electrons were measured with an iron-free orange spectrometer in order to suppress the background from fission. Levels up to I π ≈ 16 + were identified in e − γ coincidence measurements. The systematics of the ground-state rotational bands in the even actinides is discussed.

The (vi2132)8+, 10+, 12+ triplets in 190–196Hg

Abstract Decays of isomeric states in the even 190–196 Hg isotopes are studied by in-beam conversion electron spectroscopy using the 181 Ta( 14 N, 5n) and 192, 194, 196 Pt(α, 4n) reactions. A superconducting solenoid was used to transport conversion electrons emitted by the recoiling excited nuclei to cooled Si(Li) detectors and singles e − as well as e − e − coincidence spectra were measured. The missing 12 + → 10 + transitions in 190, 192, 194 Hg were observed with transition energies of 24 keV, 28 keV and 52 keV. The B (E2) rates of the 12 + → 10 + and the 10 + → 8 + transitions are discussed.

Identification of the missing rotation-aligned (νi132−2) 12+ state in 196Hg

Abstract The ν i 13 2 −2 rotation-aligned structure has been verified for 196Hg by the identification of the (ν i 13 2 −2 ) 12 + state. Form half-life measurements we find B(E2) values for the 12+ → 10+ and 10+ → 8+ transitions close to those in 198Hg. Evidence is also presented for the existence of this state in 194Hg.

Investigation of196,198Pt and202,204Hg with the (d, pnγ) reaction

Gamma-ray and conversion electron spectra were measured in the reaction of 25 MeV deuterons on174Yb,196,198Pt,202,204Hg, and232Th. The (d,pxn) deuteron break-up reactions were studied by the measurement ofpγ- andγγ-coincidences. Levels with spins up to approximately 10ħ are observed in the (d,pn) reactions, with a strong preference of the population of yrast states. In the Pt and Hg nuclei the ground bands are seen up to the 6+ states and in196,198pt the semi-decoupled 5−, 7−, and 9− yrast levels are populated most strongly. In202,204Hg we observe fairly strongly new levels with tentative assignments of 5− and 7−. In addition a number of previously unknown levels are identified in the Pt and Hg nuclei, for which no spin-parity assignments could be obtained. A discussion of the level structure in terms of the interacting boson model (196,198Pt) and the shell model (202,204Hg) is given.

Multiple coulomb excitation of202Hg and204Hg

Multiple Coulomb excitation measurements on202, 204Hg have been performed with 5 MeV/u208Pb projectiles. The ground bands are excited up to the newly discovered 6+ states and B(E2) values are derived for the 4+→2+ and 6+→4+ transitions. Whereas the 2+ and 4+ levels in the Hg isotopes with 196≦A≦204 have an almost constant energy, the 6+ levels increase in202Hg and204Hg, compared to the lighter isotopes, by approximately 100 and 300 keV, respectively. The relative B(E2) values in both nuclei show that the collectivity in the neutron rich Hg nuclei is of more complex origin than expected from the few proton and neutron holes with respect to the 82 and 126 major shells.

Observation of the weakly deformedvi 13 2/2 band in188Hg

High-Spin states in188Hg have been investigated using the168Er(24Mg,4n) reaction. The rotation aligned vi132/2 band, which intersects the weakly oblate ground state band atI≈10, is observed up toIπ=20+ with an isomeric 12+ level with T1/2=134(15)ns. The coexisting strongly deformed band, built on the 825 keV 0+ level, is observed up to the 14+ state. The systematics of the vi132/2 rotation aligned bands is discussed.

Rotation aligned bands and configuration dependent interaction in189Hg

High spin states in189Hg have been studied using the181Ta(14N, 6n) reaction. The various one- and three-quasiparticle rotational bands were interpreted within the cranked shell model. The band-crossing frequencies are found to depend on the number of spectator particles. The effect can be accounted for by a residual two-body interaction of appr. −0.11 MeV.

Band crossings in weakly deformed 190Hg

Abstract High-spin states in 190 Hg have been investigated using the 181 Ta( 14 N, 5n) reaction. Back-bendings were found in the 5 − and 8 (−) side-bands and a second backbending was observed in the yrast band around I π = 20 + . Experimental band crossing frequencies and gain in alignment were deduced and compared with cranking model calculations. The comparison suggests that the band crossings are due to the rotation alignment of i 13 2 neutron pairs.