O. Häusser

Gamma decay of low-lying states near the 208Pb closed shell

Abstract A number of electromagnetic matrix elements between low-lying states of several nuclei near 208Pb have been measured. Coulomb excitation of states in 204, 206, 207, 208pb and 209Bi has been studied with beams of 4He and 16O. The energy loss of 4He and 16O in Pb has been measured by a novel method and thus accurate B(E2) and B(E3) values were obtained. Gamma-ray lineshapes observed after 16O bombardment were used to derive mean lifetimes of states at 2646.5 keV (τ = 0.125±0.030 ps) in 206Pb, and at 897.7 keV (τ = 0.19±0.04 ps), at 2624.4 keV (τ = 0.13±0.05 ps), and at 2662.4 keV (τ = 0.95±0.20 ps) in 207Pb. The reactions 208pb(7Li, α2nγ)209Bi and 208Pb(7Li, 6Liγ)209Pb were used for the first time to derive several lifetimes and branching ratios in 209Bi and 209Pb. An intermediate-coupling calculation has been performed which reproduces extremely well the known B(E2) values in 207, 208Pb and 209Bi and which qualitatively explains the observed E1 matrix elements. Evidence for retardation of single-particle M1 transitions is presented. The main cause for the retardation is excitations of spin-orbit partners. Possible contributions from higher-order excitations and from mesonic exchange currents are discussed.

Magnetic moments and half-lives of isomeric states in polonium isotopes

Abstract We have observed small violations of the additivity rule for isomeric two-proton states in 202, 208–210Po. The g-factors of the 110 ns 8+ state in 202Po and of the 24 ns 13 2 − state in 209Po were measured for the first time. The accuracy of relative g-factors which were previously measured has been considerably improved. The static quadrupole moment of 209Bi g.s. is deduced from three E2 transition probabilities in 210Po. The absolute value of Q is ≈ 15% larger than obtained by optical spectroscopy and possible reasons for the discrepancy are discussed.

Quadrupole Moment of a High-Spin Yrast Trap in Gd 147

Static quadrupole interactions of three

Quadrupole moments of yrast isomers in 144, 147, 148Gd

^{147}\mathrm{Gd}

High spin yrast states in N = 126 isotones

isomers in single crystals of hexagonal gadolinium have been observed. The quadrupole moments increase with increasing spin and imply a substantial (oblate) deformation (

Reorientation measurements in even titanium isotopes

\ensuremath{\beta}\ensuremath{\sim}0.2

Large transient magnetic fields for rare-earth ions recoiling in gadolinium and g-factors of high-spin states in 156, 158, 160Gd

) for the 500-ns high-spin yrast trap.

Yrast isomers and very high spin states in 148, 149, 151, 152Dy and 147Gd

Abstract Isomeric nuclei of 144, 147, 148 Gd were produced by 120, 124 Sn ( 28 Si , x n ) fusion evaporation reactions and implanted into single crystals of Gd. The perturbed angular distribution spectra at various orientations of the crystal axis are dominated by static quadrupole interactions. The ratio of quadrupole moment Q to spin I was determined for the 10 + isomer in 144 Gd, the 13 2 + , 27 2 − and (T 1 2 = 510 ns ) isomers in 147 Gd, and the 9 − isomer in 148 Gd. In addition a tentative value of I = ( 47 2 ± 1) was obtained for the spin of the 510 ns isomer in 147 Gd. The observed quadrupole moments provide the first experimental evidence for the substantial oblate deformation ( β ∼ −0.2) predicted by the deformed independent particle model of Neergard, Dossing and Sagawa for high-spin isomers in 147 Gd. The oblate deformation is observed to increase when the number of valence nucleons (and the isomer spin) increases, and furthermore when the neutron core at N = 82 is broken. The g -factors and quadrupole moments of the 3 − and 10 + core states in 146 Gd have also been deduced.

Magnetic moments in N = 126 isotones and core polarisation blocking

Abstract A comprehensive spectroscopic investigation of yrast levels in three N = 126 isotones, 212 Rn, 213 Fr and 214 Ra, is presented. We report measurements of prompt and delayed excitation functions, γ-γ and X-γ coincidences, g -factors, linear polarizations and angular distributions of γ-rays. Yrast spectra in these nuclei extend to high spin and are rich in isomers. The isomerism and the spin dependence of yrast energies for N = 126 isotones are discussed in terms of excitations of valence protons with and without contributions from the 208 Pb core.

Calibration of the transient magnetic field for rare-earth nuclei in iron: Application to g-factors of high spin states in 152, 154Sm

Abstract The first excited 2 + states in 46,48,50 Ti were Coulomb excited using beams of 35 Cl and 32 S. The results are interpreted in terms of the reorientation effect and yield static quadrupole moments Q( 46 Ti , 889 keV ) = −0.19 ± 0.10 b , Q( 48 Ti , 983 keV ) = −0.22 ± 0.08 b and Q( 50 Ti , 1550 keV ) = −0.02 ± 0.09 b . The B ( E 2) (0 + → 2 + ) values were determined to be 0.107 ± 0.010 e 2 · b 2 , 0.069 ± 0.006 e 2 · b 2 and 0.033 ± 0.003 e 2 · b 2 , respectively. The resu compared with recent Hartree-Fock calculations. The projectile excitation of 32 S was also observed and yielded a limit for the first excited 2 + state of −0.05 Q