K. Schiffer

High-spin yrast isomer in 211Rn and 212Rn with enhanced E3 decays

Abstract New isomeric states with Jπ = 69/2+, τm = 13(1) ns in 211Rn and Jπ = 33−, πm = 7(1) ns in 212Rn have been identified. They decay by enhanced E3 transitions with strengths of 33(3) and 43(6) single particle units to the known 63/2− and 30+ isomers in 211Rn and 212Rn, respectively. The excitation energies and transition strengths agree well with predictions of the multiparticle, octupole-vibration coupled model.

The population of superdeformed bands in the A=150 region by compound reactions

Abstract The population of superdeformed bands in the A=150 region is discussed in terms of a statistical neutron evaporation model, taking into account the two coexisting potential wells in the nucleus, and a statistical model describing the gamma decay in a superdeformed nucleus. Many systematic features, namely excitation functions, intensity patterns, relative intensities and the absence of the high energy gating mechanism can qualitatively be described and understood. A picture of the dynamics of the decay into superdeformed states is presented.

Octupole coupling and proton-neutron interactions in 214Fr

Abstract Excited states in the odd-odd nucleus 214 Fr have been studied using γ-ray and electron spectroscopy following 208 Pb( 11 B, 5n) and 205 Tl( 13 C, 4n) reactions. Levels were identified to spins of around 36 ħ and excitation energies of ∼ 8.6 MeV. A number of isomeric states have been measured and g -factors obtained using the TDPAD method. At low spin, semi-empirical shell-model calculations appear to provide a good description of the states observed. An understanding of the structure of higher spin states in terms of the probable yrast configurations requires the addition of two units of spin at an energy of around 2 MeV. States with spins around 30 ħ are formed by core-excited configurations, with double core-excitation suggested for the highest states observed. The properties of many of the isomeric states can be understood in terms of multiparticle octupole coupling, with the properties of these states well reproduced by multiparticle octupole-coupled shell-model calculations.

Contrasting behaviour of proton h92 and h11/NU>2 bands in 175,177,179,181Ir interpreted in an intruder model

Abstract Rotational bands in the odd-proton isotopes 175Ir, 177Ir, 179Ir and 181Ir based on the h 9 2 , h 11/NU> 2 , i 13 2 and d 11/NU> 2 orbitals have been identified, the first three to high spin. In all cases the h 9 2 band shows backbending with a crossing frequency and alignment gain consistent with that expected from the neutron i 2 13 2 alignment. In contrast the h 11/NU> 2 bands (and the fragments of d 11/NU> 2 bands observed) show complex alignment curves. These alignments can be explained using a phenomenological three-band model which incorporates a deformed intruder band, analogous to that proposed in the very light Pt and Os nuclei. Mixed wave functions from the model reproduce the observed B(M1)/B(E2) ratios. The presence of the intruder band in the h 11/NU> 2 and d 11/NU> 2 configurations and its absence in the h 9 2 band is compatible with its proposed association with an ( h 2 9 2 ) 0 pair excitation.

High-spin bandcrossing in 129Ba

Abstract The high-spin structure of 129Ba was investigated via in-beam γ-ray spectroscopy allowing many new transitions to be placed in the level scheme. Two isometric states with lifetimes of τ = 23 (2) ns (182 keV level) and 68 (2) ns (2463 keV level) were identified. A high-K 3-quasineutron configuration [ 7 2 + [404]⊗ 7 2 − [523]⊗ 9 2 − [514]] is proposed for the latter. A discussion of the high-spin structure and the deformation driving effects in 129Ba is presented in terms of the cranked shell model. The conclusion reached is that the alignment gains are dominated by h 11 2 proton pairs.

The population of the superdeformed continuum

Abstract The quasicontinuum ridge structures of superdeformed nuclei in the A =150 region are discussed in terms of a statistical model based on the Monte Carlo method, simulating the population and decay of superdeformed continuum and yrast states. A picture of the decay flow in the superdeformed quasicontinuum and its implications are presented. The role of rotational damping in the second minimum is discussed.

Spectroscopy of 211Rn approaching the valence limit

Abstract High-spin states in 211 Rn were populated using the reaction 198 Pt( 18 O, 5n) at 96 MeV. Their decay was studied using γ-ray and electron spectroscopy. The known level scheme is extended up to a spin of greater than 69 2 and many non-yrast states are added. Semi-empirical shell-model calculations and the properties of related states in 210 Rn and 212 Rn are used to assign configurations to some of the non-yrast states. The properties of the high-spin states observed are compared to the predictions of the multi-particle octupole-coupling model and the semi-empirical shell model. The maximum reasonable spin available from the valence particles and holes in 77 2 and states are observed to near this limit.

Gyromagnetic ratios of low-lying rotational states in156, 158, 160Gd

Transient-field precessions were measured simultaneously for levels in the ground-state bands of156, 158, 160Gd as ions of these nuclei traversed a thin polarized Fe foil. Relative g-factors of levels up to 61+ were deduced, those of the 41+ levels being determined with greatest precision. In contrast with the conclusions of the recent report by Alzner et al. [1], our results are consistent with g(41+) having the same value in all three isotopes and imply g(21+)=g(41+) in156Gd, consistent with nuclear structure models.

Interpretation of (h11/2)2 isomers in the N≈76 region of transitional nuclei

The E2 hindrance factors of high spin isomers involving (h11/2)2 excitations in the N ≈ 76 and Z ≈ 76 regions of transitional and deformed nuclei are compared. Using the correlation with the product of the valence nucléon numbers NpNn, a systematic picture of the weakly K-forbidden decays is presented.

Proton-neutron interactions in the odd-odd nucleus 214Fr

Abstract High spin states have been observed to excitation energies over 8 MeV in the odd-odd nucleus 214 Fr using in-beam γ-ray and electron spectroscopic techniques and heavy-ion induced reactions. Semi-empirical shell model calculations appear to provide a good description of the states observed, although some states expected within this model have yet to be identified.