J. Blomqvist

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

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.

EFFECTIVE QUADRUPOLE CHARGES IN THE LEAD REGION.

Abstract The presently available experimental material on effective E2 charges in the lead region is surveyed. Within the experimental accuracy of about 10 % no evidence was found for a variation in the effective charge of the h 9 2 . proton orbital as a function of the number of nucleons outside the core. The state dependence of the effective charges for transitions involving different orbitals is well described by a shape-vibrational model of particle-core coupling. There is clear evidence for an isovector polarization charge of about 0.1 τ z , e .

The retarded transitions in 181Ta and 175Lu and the effective magnetic moment operator

Abstract The retarded transitions assigned as 5 2 , 5 2 + [402]→ 7 2 , 7 2 + [404] in 181Ta (482 keV) and 175Lu (343 keV) are analysed with special regard to the large hindrance of the M1 radiation in 181Ta. The E2 component is dominated by the band mixing which is thus determined by B(E2). For the analysis of B(M1), we exploit the relation between the Coriolis and M1 intrinsic matrix elements. The result shows a marked difference between 181Ta and 175Lu. Calculations with extended models for particle motion indicate possible effects of the detailed deformation structure for the two cases. Furthermore, the predicted tensor term k2[Y2, s]1 in the μ operator gives a significant contribution to B(M1), when k2 is of the order of unity. The present data are consistent with the condition k2 ⪅ 0.6, whereas k 2 ⪆ is 0 preferred because of consistency with the model calculations. The effective magnetic moment operator can be written in the form μ ≈ (g l 0 + δg l ex ) l +(g s 0 +δg s pol +δg s ex ) s +(k 2 pol +k 2 ex )[Y 2 , s ] 1 , where gl0 and gs0 are the unrenormalized nucleon g-factors. The term δgspol represents the well-known gs renormalization due to spin polarization (δgsex is small). We have estimated the pion-exchange contributions, giving τ3glex ≈ 0.1 and τ3k2ex ≈ − 1. When our preferred range for k2 from the present analysis is combined with previous data from other work, we can give the conservative semiempirical estimate 0

SPIN-ALIGNED NEUTRON-PROTON PAIR MODE IN ATOMIC NUCLEI

Shell model calculations reveal that the low-lying spectrum of the N = Z nucleus 92 Pd is generated from a correlated isoscalar spin-aligned neutron-proton pair mode, exhibiting a new form of collectivity different from vibrational and rotational excitations. Already the ground state structure of 92 Pd is mostly built from isoscalar pairs each carrying angular momentum J = 9. This structure is different from all other even-even nuclei studied so far. The energy spectrum generated by the correlated neutron-proton pairs has two distinctive features: i) it is almost equidistant for low-lying energies and ii) the transition probability I ! I − 2 is approximately constant and independent of I. This exotic coupling scheme is predicted to correspond to the yrast structures of the heaviest nuclei approaching the doubly-magic 100 Sn.

High-spin spectroscopy of the 142Eu, 143Eu and 144Eu nuclei

Abstract High-spin level schemes of the 142Eu, 143Eu and 144Eu nuclei have been investigated by in-beam γ-ray spectroscopic methods using the NORDBALL Compton-suppressed multi-detector array. The previously known schemes have been extended to considerably higher spin and excitation energy, up to I ≈ 30, Ex ⩾ 9 MeV in 142Eu, I = 75 2 , Ex = 15.6 MeV in 143Eu and I ≈ 40, Ex ⩾ 16 MeV in 144Eu. The level schemes are very complicated, characteristic of spherical or slightly oblate nuclei. Also, long cascades of stretched E2 transitions have been observed in all three nuclei. Plunger and DSAM lifetime results demonstrate high collectivity values up to ∼100 W.u. (up to ∼200 W.u. in 142Eu) in these E2 cascades and they are proposed to represent several crossing collective bands with the nucleus at triaxial shape of β2 ≈ 0.25 and γ ≈ 30°. Low parts of the level schemes have been discussed within the spherical shell model. Below 5.5 MeV excitation in 144Eu and 3.5 MeV in 143Eu practically all the observed levels are interpreted with shell model configurations of respectively two or four, and one or three quasiparticles.

An isomeric 19+ state of the\(\pi h_{{9 \mathord{\left/ {\vphantom {9 2}} \right. \kern-\nulldelimiterspace} 2}}^2 i_{1{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} vg_{{9 \mathord{\left/ {\vphantom {9 2}} \right. \kern-\nulldelimiterspace} 2}} (j^{ - 2} )_{0^ + }\) configuration in 85 210 At125 and the question of isospin dependence in the two-particle core polarization

AbstractUsingα-particles of energies 35–51 MeV and in-beam conversion electron andγ-spectroscopy techniques, a 4.0±1.7 μs core-excited 19+ isomeric state in210At with ag-factor of 0.737±0.025 has been observed at an excitation energy of 4027.7 keV. The 19+ state is suggested to have the

Collective monopole vibrations in closed-shell nuclei

\pi h_{{9 \mathord{\left/ {\vphantom {9 2}} \right. \kern-\nulldelimiterspace} 2}}^2 i_{1{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} vg_{{9 \mathord{\left/ {\vphantom {9 2}} \right. \kern-\nulldelimiterspace} 2}} (j^{ - 2} )_{0^ + }

The decay of the 560 ns Isomer at 8.6 MeV in 64 147 Gd83

configuration with maximum alignment of the angular momenta. The total two-particle core polarization due to theh9/2 andi13/2 protons and theg9/2 neutron was found to be −68±20 keV as compared to −125±18 keV for the 29/2+ isomeric state of the