K. P. Blume

High-spin states in 163–166Hf

Abstract High-spin states in 163–166 Hf, populated in 148,150 Sm ( 20,22 Ne , x n ) reactions, have been studied by in-beam γ-ray spectroscopy using the first four to six Compton-suppressed Ge detectors from the OSIRIS set-up. Levels up to I > 30 kh are identified. The results are interpreted within the framework of the cranked shell model. Good agreement is obtained between experiment and calculation for the two and three quasi-neutron alignments in all four isotopes. The nature of the second band crossing in the even- A isotopes is discussed.

High-spin structure in 169W and 170W

Abstract High-spin states in 169, 170 W have been populated in 154 Gd ( 20 Ne , x n ) reactions. In-beam γ-ray spectroscopic techniques with multi-detector set-ups, multiplicity filters and an anti-Compton shield have been used. Levels up to about spin 30 (tentatively up to 36) in 170 W and up to 57 2 (tentatively up to 61 2 ) in 169 W have been identified. The data are interpreted within the framework of a pairing-selfconsistent cranking model. The nuclear shape evolution with increasing spin is studied theoretically within a configuration-controlled shell correction approach and also pairing effects are studied. The behaviour of the yrast states around 28 + in 170 W can be related in a model-dependent way to a reduction of the neutron-pairing correlations.

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.

Decay of the ground state and the 292+ isomer in 217Ac and g-factor measurements from perturbed α-particle angular distributions

Abstract The nucleus 217 Ac was studied using the 205 Tl( 16 O, 4n), 206 Pb( 15 N, 4n) and 209 Bi( 12 C, 4n) reactions. The mesurements included αγ, γγ, α-ce and ce-ce coincidence experiments as well as γ-ray and α-particle perturbed angular distribution studies. Results are g( 217g Ac ) = + 0.85(1) and T 1 2 ( 217 g Ac ) = 69(4) ns , the shortest known α-decay of a ground state. 217m Ac decays mainly by a γ-cascade, but also by α-emission to the single-particle states π h 9 2 , f 7 2 , i f 13 2 of 213 Fr. Spins and parities of levels to the 29 2 + isomer at 2013 keV with T 1 2 = 740(40) ns and g = + 0.347(5) are determined. The level scheme of 217 Ac and the α-decay of N = 128 isotones 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.

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.

Spectroscopy of195Hg and196Hg

High-spin states in the oblate-deformed nuclei195Hg and196Hg were populated in the198Pt(α, xn) reaction and investigated by in-beamγ-ray spectroscopy using six Compton-suppressed Ge detectors. The level schemes of both nuclei are extended considerably. The level structure is interpreted within the framework of the cranked shell model. Good agreement is obtained between model predictions and experimental results.

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.

Spectroscopy of 160Hf

Excited states in 160Hf were investigated up to spins I≈20h using the OSIRIS array of 12 Compton-suppressed Ge detectors and a calorimeter of 48 BGO detectors. The results are interpreted within the framework of the cranked shell model. The systematics of the band crossing frequencies in the Hf isotopes are discussed. An analysis of the high-spin states in terms of double routhians shows the reduction of pair correlations with increasing rotational frequencies. NUCLEAR REACTIONS 144Sm(20Ne, xn), E= 105−120 MeV; 144Sm(19F,xn), E=

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.