K.H. Maier

Energy-level systematics of odd-mass lanthanum isotopes a new coupling scheme

Abstract Heavy-ion reactions have been used to populate states in the odd-A La nuclei (A = 125 → 137). The γ-ray spectra indicate strong population of a band based on the 11 2 − state of each isotope. The character of this band indicates a new type of coupling, and can only be explained if the state has a prolate deformation. This is in contrast to earlier suggestions of oblate shapes for these nuclei.

Prolate deformation in neutron-dificient lanthanum isotopes☆

Abstract The odd-A La isotopes from A = 125 to 137 have been studied by in-beam γ-ray spectroscopy of Sn ( 14 N , x n ) La reactions and from A = 131 to 139 by particle spectroscopy of the Ba(α, t) La and Ba(τ, d) La single-proton transfer reactions. In the latter experiments a low-lying 11 2 − level was systematically identified, and the rotational bands built on these levels were observed in the γ-ray work. The strong resemblance of the transition energies in these bands to the ground-band transitions in the neighbouring even Ba isotopes is very striking. These results can be understood as a decoupling of an h 11 2 single proton from the Ba core. This interpretation of the observed bands requires a prolate deformation for these nuclei, which is in contrast to previous conclusions.

Effective single-particle magnetic moments around 208Pb

Abstract An effective magnetic-moment operator is empirically derived for shell-model states around 208Pb. It reproduces thirteen measured moments to a few tenths of a nuclear magneton, but predicts too high a hindrance for M1 transitions.

A high-spin isomer in 211At☆

A 4 νs isomer has been observed in 211At at an excitation energy 4.816 MeV. The multi-polarities of the de-excitation γ-rays suggest a very high spin. The excitation energy, g-factor and the strongly enhanced E3 decay may be described by a 4p-1h configuration with Jπ = 392−.

Measurement of the magnetic moment and lifetime of the 132+ level in 205Pb

Abstract The g -factor, half-life, and branching ratios of the 13 2 + , 1014 keV isomer in 205 Pb have been measured using pulsed-beam excitation through the 204 Hg(α, 3n) 205 Pb reaction ( g = −0.150±0.006, T 1 2 = 5.55±0.2 ms ). It is shown that this is the g -factor of the i 13 2 neutron orbit within 10 %.

Stroboscopic measurement of the g-factors of the 7− isomer in 206Pb and the 212+ isomer in 207Bi

Abstract The g-factors of the 206 Pb 7 − (2200 keV , T 1 2 = 123 μ s ) and 207 Bi 21 2 + (2101.5 keV , T 1 2 =182 μ s ) isomers have been measured by the stroboscopic method using the 204Hg(α, 2n)206Pb and 204Hg(7Li, 4n)207Bi reactions to excite them. The results are g( 206 Pb 7 − ) = −0.0217 ± 0.0004 n.m. and g( 207 Bi 21 2 + ) = +0.325 ± 0.006 n.m . The implications of these values on the wave functions of the states and on the magnetic polarization of the 208Pb core are discussed.

Loss of collectivity along the yrast line in 158Er

Abstract Lifetimes of yrast states from spin 14 through 40 have been measured in 158Er. The Doppler-shift recoil-distance method was used in conjunction with the multi-Ge detector array HERA, and γγ coincidences were analyzed. The collectivity of the nucleus drops from 200 W.u. to 110 W.u. in the region of the second backbend. By spin 38 it has decreased further to 25 W.u., consistent with a band termination.

Time differential g-factor measurement of the 7+ isomer in 204Tl

Abstract The g-factor of the 1.118 MeV 7+level in 204Tl T 1 2 = 63 μ s was measured as g = +0.1696±0.0010n.m. by time-differential observation of the perturbed angular distribution of the de-exciting α-rays. The isomer was excited by a pulsed deuteron beam through the 204Hg(d, 2n)204Tl reaction. The meaning of the result for the structure of the level is discussed.

Lifetimes of ground-band states in 154Sm

Abstract The lifetimes of the 8 → 6, 6 → 4 and 4 → 2 ground-band transitions in 154 Sm have been measured by a recoil-distance Doppler-shift technique following Coulomb excitation by back-scattered 40 Ar projectiles. Within experimental error, the measured B (E2) values are those of a rigid rotor. These results and those of a previous experiment on 152 Sm are compared with current models.

Lifetimes of ground-band states in 154 Sm

Abstract The lifetimes of the 8 → 6, 6 → 4 and 4 → 2 ground-band transitions in 154 Sm have been measured by a recoil-distance Doppler-shift technique following Coulomb excitation by back-scattered 40 Ar projectiles. Within experimental error, the measured B (E2) values are those of a rigid rotor. These results and those of a previous experiment on 152 Sm are compared with current models.