Search

Abstract:: High-spin states in 142Gd have been populated by means of the 99Ru(48Ti, 2p3n) reaction at 240 MeV and investigated with the γ-spectrometer EUROBALL III and the charged-particle detector array ISIS. The features of four dipole bands have been determined and compared with tilted-axis cranking model calculations indicating that they are magnetic rotational bands. A transition from regular to irregular bands has been found approaching N = 82 demonstrating that this is a general phenomenon in nuclei near a double-shell closure.

Abstract:: The band structures built on the 5- isomeric state ( T 1/2 = 3.46 m) in the doubly odd 130Cs nucleus have been established up to I = 24? via the 124Sn(11B, 5n)130Cs reaction. The previously observed bands based on the πh 11/2⊗νh 11/2, πg 7/2⊗νh 11/2 and πd 5/2⊗νh 11/2 configurations and a positive-parity side band with multiple connections to the α = 0 signature partner of the yrast πh 11/2⊗νh 11/2 band have been extended to higher spins. A new band based on the πh 11/2⊗νg 7/2 configuration is observed. The yrast πh 11/2⊗νh 11/2 band exhibits anomalous signature splitting whose magnitude decreases up to spin 15 and then increases without restoring the normal signature splitting.

Abstract:: Lifetimes for low-lying members of the irregular ΔI = 1 band in 196Pb have been measured by means of the EUROBALL spectrometer using the coincidence recoil distance technique. The 164Dy(36S,4n)196Pb reaction at a beam energy of 168 MeV was used. The data were analyzed with the differential decay-curve method (DDCM). A characteristic drop in the reduced transition probabilities with increasing angular momentum was observed in agreement with predictions by the semiclassical model for the shears mechanism.

High-spin states in 197Pb and 198Pb were populated in the 186W(18O,xn) reactions. In-beam γ-ray coincidences were measured in two experiments using the Gammasphereand the EurogamII spectrometer arrays, respectively. In both nuclei new bands of enhanced magnetic dipole transitions were found and the known cascades were partly reordered and extended to higher spins. In most cases, γ-ray transitions connecting the magnetic rotational bands to lower-lying states have been identified. Configuration assignments are suggested for the bands. The systematic behavior confirms the shears mechanism. An effective interaction between the main high-spin proton and neutron orbitals is derived.

Abstract:: High-spin states in 202Pb and 203Pb have been investigated by in-beam γ-ray spectroscopy following the reaction 198Pt(9Be,xn). A search for magnetic rotational bands in these isotopes confirmed one of the two bands previously assigned to 202Pb and revealed a new band in this isotope. No evidence for magnetic rotation has been found in 203Pb.

Magnetic-rotational bands in the nearly spherical nuclei ¹⁹⁷Pb and ¹⁹⁹Pb and their decay to the normal states have been investigated by in-beam conversion electron spectroscopy following (heavy ion,xn) reactions. The expected M1 multipolarity of the in-band transitions has been confirmed for the strongest bands and the multipolarity of several transitions in the decay of the bands has been determined.

Abstract: High-spin states in ²⁰⁰Hg have been investigated by in-beam γ-ray spectroscopy following the reaction ¹⁹⁸Pt(⁹Be,α3n). The α-emission channel leading to ²⁰⁰Hg is strongly enhanced which may be explained by an incomplete fusion reaction with pre-equilibrium emission of the α particle. The level scheme is extended to higher spins and new band crossings are observed. The band structures are compared to the lighter Hg isotopes with even mass number.

Abstract:: Excited states have been identified for the first time in 184Pb, the first even-even Pb isotope beyond the 82 < N < 126 mid-shell, using the recoil-decay tagging (RDT) technique. A collective band built on the first-excited 2+ state has been observed. This resembles those seen in 186,188Pb and the Hg isotones, and can thus be associated with a prolate-deformed shape. Variable moment of inertia (VMI) fits of the prolate 0+ level energies in 184,186,188Pb indicate that the minimum appears at N= 103, the same neutron number at which the corresponding minimum in Hg isotopes is observed.

Abstract:: Three mini-orange conversion–electron spectrometers and four Euroball Ge Cluster detectors have been used for γ–e- coincidence spectroscopy of superdeformed 135Nd. Transitions within the superdeformed band are shown to have the expected E2 multipolarity. The 766.5–keV transition which links the band to a positive-parity state has a conversion coefficient consistent with M1 multipolarity. Consequently, positive parity is deduced for the superdeformed band. No evidence for E0 transitions was found.

We have investigated the structure of the superdeformed band in 135Nd using conversion-electron spectroscopy. The transitions within the superdeformed band show conversion coefficients which are consistent with an E2 multipolarity. From the conversion coefficients of transitions linking this band with known low-lying states its positive parity was established. Hence, a direct determination of the parity of a high-spin superdeformed band could be performed for the first time.