R. A. Meyer

Evidence for the coexistence of shapes in even-mass Cd nuclei

A quasi-rotational band built on the known proton four-hole, two-particle 0+ level at 1473.07-keV in114Cd has been identified, with 2+, 4+, and 6+ members at 1783.44-, 2250.53- and 2876.75-keV respectively. These levels and their properties are compared with those in other even-mass Cd nuclei to show an increasing average deformation in both the 01+ (ground-state) and 02+ bands when neutron pairs are added beyond110Cd.

Observation of a full set of coexisting intruder excitations in 98Zr: Evidence for correlated excitations?

Abstract Results from multiparameter in-beam spectroscopy studies of 98Zr58 reveal the existence of two distinct sets of levels with strong intra-set transitions. The nine levels identified in the excited set are found to correlate well with the first nine levels of 102Ru. Similar sets in Zr isotopes and isotones of 98Zr58 are shown for this mass region.1446

Decay of the134Cs isomers and the levels of134Xe,134Cs, and134Ba

A precision study of the decay of134Csg and134Csm has been made, using ordinary Ge(Li) spectrometers and ā Compton-suppression spectrometer. The logft value of the second forbidden nonuniqueβ-decay to134Xe has been measured to be 13.0±0.2. TheM4γ-ray transition in134Csm(8−) decay has been measured to haveαK= 73±7 and a hindrance of 7.0 over the Moskowski estimate. This is discussed in terms of the level configurations and the analogous transition in133Xe. A new intensity limit of 2×10−6 has been set for the zero-phonon transition between the 4+ and 2+ members of the two-phonon triplet. This leads to an upper limit forB(E2)4→2′, greater than 905. This and the more preciseγ-ray intensity values are discussed in relation to presently available nuclear models.

The nilsson-potential parameters for neutrons at A≃-100 and new deformation values for103Mo and105Mo

The half-lives of the first excited levels in odd-neutron nuclei103Mo and105Mo have been measured. From these data, values of the deformation parameter ofɛ=0.31±0.05 and 0.29±0.06 for103Mo and105Mo, respectively, have been deduced assuming prolate spheroidal shapes. The present results in combination with previously determined properties of the ground-state bands of these nuclei are used to determineμ, the magnitude of the coefficient of the 12 term, in the Nilsson Hamiltonian, for the new region of deformation atA∼-100.

Radioactive decay of 1.7-h149Nd to levels of transitional149Pm

Sources of149Nd were produced by thermal-neutron irradiation of enriched148Nd. High resolution Ge(Li) spectrometers were used to collect gamma-ray singles and coincidence spectra in the study of the decay of 1.7-h149Nd. A total of 214 gamma rays have been assigned to the decay of149Nd, and 201 of these transitions have been placed in a level scheme of149Pm involving 42 excited states. Absolute values for the beta-group intensities were determined for transitions to the149Pm levels, and spin and parity assignments were made for many of the observed states. The experimentally determined level structure of149Pm was compared with corresponding levels in other odd-mass Pm and Eu nuclides. Interpretations were made in terms of the core-coupling model.Radioactive decay148Nd(n, γ)149Nd; measuredEγ,Iγ,γ-γ coinc.149Pm deduced levels,J,π. Compton-suppression. Ge(Li) detector. Enriched targets.

Evidence for rotational bands in103Nb

The nucleus103Nb62 has been studied through the ß− decay of the fission product103Zr at LOHENGRIN and JOSEF. The energies of the lowlying levels and the γ transitions indicate rotational bands based on the Nilsson proton configurations [422 5/2+] [303 5/2−] and [301 3/2−] at 0, 164 and 248 keV, respectively. The measured half-lives of (4.7±0.5) ns and (2.0±0.6) ns of the levels at 164 and 248 keV are consistent with the Nilsson-model estimates including pairing.

The lifetime of the 376.7-keV level and shape coexistence in111Ag

The half life of the 376.7-keV level in111 Ag, populated in the decay of111 Pd isomers, has been determined to be 16±1 ns. Compton-suppressed γ-ray spectra and γγ coincidence spectra have also been taken. These data, combined with recent charged-particle transfer data establish 3/2+ as the spin and parity of the 376.7-keV111Ag level. Our observed lifetime and γ-ray branching can be interpreted as strong indications of shape isomerism in111Ag similar to that found in odd-mass In nuclides.

Two quasi-particle levels in136Ba and the decay of136Cs

The decay of 13-day136Cs has been studied using high-resolution Ge(Li) detectors. Several low-intensity gamma rays were observed for the first time. New levels have been deduced in136Ba at energies of 2356.7 and 2372.7 keV.

Electromagnetic decay of 10+ states and yrast isomers in 208Pb

Abstract Gamma decay of the four previously known 10 + states between 4.8 and 5.9 MeV of excitation in 208 Pb, and isomerism of the lowest 10 + [T 1 2 =500(50) ns ] and 8 + [T 1 2 =3.2(5) ns ] states have been established with α - γ coincidence measurements in 209 Bi(t, αγ ) 208 Pb. Wavefunctions for the 10 + states were deduced in the model space involving 1p-1h excitations only. These show that the π h 9 2 h 11 2 −1 strength is nearly evenly distributed among the 10 + states, in disagreement with results from (e, e′) data.

Quadrupole moments of low-energy isomers in 210Po

Abstract The quadrupole interaction frequencies of the 8 + , 11 − , 13 − and 16 + isomers in 210 Po have been measured in a Bi single crystal by the DPAD method with the 209 Bi(t, 2n) 210 Po reaction. The results for the quadrupole moments, normalized to Q (8 + 1 ) = −55.2 (20)fm 2 , are | Q (11 − )| = 86 (11)fm 2 , | Q (13−)| = 90(7)fm 2 and | Q (16 + )| = 129.7 (20) fm 2 . The quadrupole moment of the 0 i 13 2 proton orbital was deduced, and found to be surprisingly small. The results are compared with shell model calculations using the surface delta interaction as residual interaction.