Y. K. Agarwal

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.

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.

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.

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.

High-spin rotational bands and pairing reduction in 166Hf

Abstract Rotational properties of the 166Hf nucleus have been studied by in-beam spectroscopic methods using the 150Sm(20Ne, 4n)166Hf reaction. The ground band was observed up to the Iπ = 18+ level, the s-band from the Iπ = 12+ up to Iπ = 22+ level; in addition two side bands were found. The results are interpreted in terms of the pairing-self-consistent Hartree-Fock-Bogolyubov cranking model. Quantitative agreement between theory and experiment is obtained for the crossing of the ground band and s-band. The calculations predict a reduction of about 50 % in the neutron pairing energy gap of yrast states in the crossing region. The kinematical ( I (1)) and dynamical ( I (2)) moments of inertia are analysed.

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.

A superconducting electron spectrometer

Abstract The set-up and tests of an electron spectrometer for in-beam conversion electron measurements are described. A superconducting solenoid is used to transport the electrons from the target to cooled Si(Li) detectors. The solenoid is designed to produce either a homogeneous axially symmetric field of up to 2 T or a variety of field profiles by powering the inner and outer set of coils of the solenoid separately. The electron trajectories resulting for various field profiles are discussed. In-beam electron spectra taken in coincidence with electrons, gammas and alpha-particles are shown.

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.

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.