No abstract available

No abstract available

[en] A proton-neutron pseudo-SU(3) model is used to study the nature of low-lying magnetic dipole excitations. Triaxiality of the parent proton and neutron distributions is shown to add a twist degree of freedom to the usual scissors mode picture and is reflected in a more complex spectrum for magnetic dipole mode (M1) transition strengths. Fragmentation of the M 1 strength distribution can be reproduced within the framework of the model by including single-particle terms and pairing in the Hamiltonian

[en] The decay of the yrast and near-yrast high-spin states in ¹⁶¹Tm has been observed following the reaction ¹²⁸Te(³⁷Cl,4n). Extension of the known level scheme reveals previously unobserved crossings in the bands built on the 7/2^-523, 7/2⁺404 and 1/2^-541 Nilsson states. The use of both gold- and terbium-backed targets has enabled the measurement by the Doppler shift attenuation method of lifetimes of states in the h_11/2 yrast band in the spin range 41/2≤I ≤67/2. The results show little evidence for change in the nuclear deformation over this interval in spin (Q_t ∼6eb). From lifetime measurements and B(M1)/B(E2) values in the h_11/2 band, absolute B(M1) values for five transitions (for states with 41/2 ≤I ≤51/2) were determined. These results provide some evidence for a reduction in the proton spin projection on the deformation axis relative to its value at low rotational frequency. The signature splitting in the Routhians and B(M1)/B(E2) values for the h_11/2 band is discussed in terms of the inclusion of non-axially-symmetric (γ-deformed) components in the nuclear wavefunction. ((orig.))

[en] Short communication

[en] Short communication

[en] Short communication

[en] The strengths of γ-ray transitions in A = 5-44 nuclei are discussed and classified according to character: Electric (E) or magnetic (M), multipolarity (L), and isospin retardation (isoscalar, IS, or isovector, IV). All transitions are listed which have strength errors below 50%, but of the very abundant E1_IV, E1_IS, and M1_IV transitions, only about the 5% strongest transitions are given. Because the total number of transitions has increased considerably from that in a previous review (4261 compared to 2419 in 1979) recommended upper limits (RUL) for γ-ray strengths could be derived with more confidence. 26 refs., 3 figs., 14 tabs

[en] It has hitherto been assumed that the charge radius of the ¹¹⁹Sn nucleus in an excited state at the 23.8-keV level is greater than in the ground state (ΔR/R>0). This deduction from data for the chemical shift of lines in the Moessbauer spectra of tin compounds was based on a very approximate conception of the structure of the electron shell of these compounds, and their interaction with the nucleus. The authors' analysis has produced a general formula for the dependence of the chemical shift on the parameters of the molecular orbits and those of the inner shells, estimation of which for tetrahalogenides of tin leads to the conclusion that ΔR/R<0. These results are important for the interpretation of many of the experimental data obtained by Moessbauer spectroscopy of tin compounds. (author). 15 refs, 1 fig

[en] High spin states in ¹⁶⁴Yb were populated via ¹²⁴Sn(⁴⁴Ca,4n)¹⁶⁴Yb reaction at the 25 MV Tandem Accelerator at the Holifield Heavy Ion Research Facility. Three new transitions were added to the previously known decay sequences of ¹⁶⁴Yb. The extracted B(E1, I → I - 1)/B(E2, I → I -2) ratios for ¹⁶⁴Yb show an enhancement compared to its neighboring isotopes, which suggests that ¹⁶⁴Yb neutron number N = 94 possess an instability with respect to the octupole degree of freedom. Lifetimes of high spin states with I^π = 20⁺ to 32⁺ in the yrast band and 23^- to 25^- in the (-,1)-band in ¹⁶⁴Yb were measured by using the Doppler shift attenuation method. A reduction of the stretched E2 transition quadrupole moments was observed at high spins in the yrast decay sequences. A systematic summary of the available experimental lifetime data and kinetic moments of inertia has been given for even-even ytterbium isotopes. The loss of collectivity implies that at high rotational frequency, nuclei undergo shape changes (mainly toward a reduced β₂ deformation for well deformed ytterbium isotopes), which can be understood as arising from the deoccupation of strongly shape-polarizing, high-j, anti aligned orbits with nucleons moving opposite to the rotation axis. The self-consistent cranking calculations, the so-called total routhian surface calculations, were performed for several ytterbium isotopes. Qualitatively the drops observed in transition quadrupole moments at high spin states in the yrast band are reproduced when the reduction of the pair correlation with increasing rotational frequency is taken into account