P. Schüler

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.

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.

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.

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.

Investigation of the ground state rotational bands in233U and239Pu in the (α, 3n) reactions

The ground state rotational bands in233U and239Pu were investigated in (α, 3n) reactions. Conversion electrons were measured with an iron free orange spectrometer in order to suppress the background from fission. Levels up toIπ=33/2+ of theK=5/2 band in233U andIπ=31/2+ of theK=1/2 band in239Pu were identified ine−γ coincidence measurements. The level energies of both rotational bands can be well described up to the highest observed spins by a two-parameter angular velocity expansion. The electromagnetic properties of theK=1/2 band in239Pu are discussed.

Experimental investigation of low lying excited states in201Hg

The decay of201Tl to201Hg has been investigated withγ- and conversion electron spectroscopic methods. The 26 keV level in201Hg, proposed earlier from nuclear reaction studies, was established in this decay. The half-life of this level was determined asT1/2=630(50) ps by delayedγ-e−-coincidences. TheIπ=1/2- assignment for the 1.6 and 167 keV levels was confirmed from angular correlation measurements. A Coulomb excitation experiment on201Hg was performed andB(E2) values were derived.

Isomeric transitions in203Bi and205Bi

High spin states in203, 205Bi, populated in the203, 205Tl (α,4n) reactions, have been studied using gamma-ray and conversion-electron spectroscopy. Several previously unobserved isomeric transitions were identified by electron-electron coincidence measurements in both isotopes and in205Bi a new isomer was found. The observed states can be explained as arising from couplings of the oddh9/2 proton to neutron states in the neighbouring Pb cores. Reduced transition probabilities are derived and discussed.