Energy levels of A = 21−44 nuclei (V)

A description of high-spin phenomena in atomic nuclei is presented from both the experimental and theoretical points of view. The characteristic features of collective nuclear motion, such as rotational bands, band crossings, and backbending, as well as noncollective aspects, like high-spin isomers and irregular decay patterns, are discussed in detail. Recent achievements of the cranking model including the independent quasiparticle and the shell correction methods are reviewed. Changes in the structure of nuclei excited up to the highest possible angular momenta are analyzed; in particular, angular momentum alignment effects, shape changes, possible phase transitions, and sudden rearrangements in the single-particle structure are discussed. Phenomena related to the nuclear quasicontinuum spectra are also examined.

High-spin phenomena in atomic-nuclei

A shell-model description of 0+ intruder states in even-even nuclei

Nuclear Data Sheets for A = 208

The level structures of146Gd and147Gd have been investigated by in-beamγ-ray ande− spectroscopy with (α, xn) reactions on enriched Sm targets. Detailed level schemes up to ∼4 MeV, which differ radically from earlier schemes, are reported. The energy levels are characterized as particle-hole excitations using empirical single particle energies and two nucleon interactions. Analysis of pure 1p 1h proton excitations demonstrates that theZ=64 andN=82 energy gaps are about equally large.

Particle hole yrast states in146Gd and147Gd and the Z=64 shell closure

Effective quadrupole charges in the lead region

Using the 204Hg(α,2n) reaction and the pulsed beam of our 225 cm cyclotron, we have been able to localize the 12+ and 10+ states of the (i13/2)-2 configuration in 206Pb at the energies 4 027.2 and 3 957.6 keV, respectively. It has been possible to determine the partial E2 transition probability for the 12+ → 10+ transition and to derive an effective charge for the i13/2 neutron, which is 0.94±0.04. It is concluded that the quadrupole polarization charge for the i13/2 neutron is about 50% larger than for the h9/2 proton.

E2 CORE POLARIZATION BY NEUTRONS IN THE (i/sub 13/2/)$sup -2$ CONFIGURATION IN $sup 206$Pb.

A 70 ns isomeric state at 2 641 keV has been produced in the 209Bi(α,2n)211 At reaction and interpreted as the 29/2+ state of the h9/22 i13/2 proton configuration. It decays to the states (h9/22 f7/2)23/2, (h9/23)21/2, (h9/23)17/2, (h9/23)13/2 and (h9/23)9/2 by a straight cascade of transitions with energies (multipolarities) 713.3 keV (E3), 511.6 keV (M1), 96.0 keV (E2), 253.4 keV (E2), and 1 066.9 keV (E2). There is also indirect evidence for a 24.4 keV (E2) branch to a (h9/22 i13/2)25/2 state followed by a 688.9 keV (E1) transition to the 21/2- state. The reduced transition rate B(E3, 29/2+ → 23/2-) = 51 000 e2 fm6 can be reproduced by taking the value 0.9 MeV for the particle-phonon coupling matrix element i13/2, 3-; 7/2|Hcoupl|f7/2.

Evidence for an Isomeric 29/2+ Level in 211At

B (E3) values in the trans-lead region lie in a region of about 1-50 Weisskopf units. Of particular interest are those cases which with a relatively small scattering are grouped around effective B (E3) values of 22 and 35 W.u. The former cases are due to fast single particle transitions of the type πi13/2 → πf7/2 or νj15/2 → νg9/2 Where the initial states are mixed with the final state plus the 3- octupole excitation of the core of 208Pb. Transitions with very high B (E3) values are likely to be associated with mixed configurations both in the initial and final states allowing fast proton as well as neutron transitions. The proton transitions are taken care of by the valence protons and the neutron transitions by core deexcitations. The quantitative relation between different groups of B (E3) values are illustrated by analyzing the E3 decay of the core excited 16+ and 39/2- isomeric states 210Po and 211At, respectively.

B. Fant

Papers

Effective quadrupole charges in the lead region

E2 CORE POLARIZATION BY NEUTRONS IN THE (i/sub 13/2/)$sup -2$ CONFIGURATION IN $sup 206$Pb.

Evidence for an Isomeric 29/2+ Level in 211At

Systematics of B(E3) Values in the Trans-Lead Region

Signature inversion in 120Cs: Evidence for a residual pn interaction