J.R. Leigh

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.

Rotational bands in odd-odd holmium isotopes☆

Abstract Coriolis-mixed rotational bands have been observed in 160Ho and 162Ho with apparent moments of inertia approximately twice the rigid-body value. The combined effects of the two odd particles, occupying the unique-parity Nilsson orbitals 7 2 − [523] ( h 11 2 - proton ), and 5 2 + [642] ( i 13 2 - neutron ), are thought to be responsible.

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−.

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.

A study of the odd-A rhenium isotopes: 179Re and 177Re

Abstract Gamma-rays following 172 Yb( 11 B, 4n) 179 Re and 169 Tm( 12 C, 4n) 177 Re reactions have been studied with Ge(Li) detectors. Rotational bands based on the 1 2 − [541], 5 2 + [402] and 9 2 − [514] states have been populated. A pronounced variation in the energies of the quasiparticle levels is apparent although the quadrupole deformation of the isotopes below mass 183 is expected to be fairly constant. It is suggested that the variation is related to the changing hexadecapole moments of these nuclei.

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.