Minfang Yeh

The nature of 0+ excitations in 166Er

Abstract Lifetimes of excited 0 + states in 166 Er have been measured with the (n,n′γ) reaction. The first and second excited 0 + states have no significant collective enhancements of their decays, and their properties are suggestive of pair-type excitations rather than those of a β vibration or phonon excitation built on the γ vibration. The third excited 0 + state at 1934 keV has an enhanced decay to the ground state band with B ( E 2; 0 4 + → 2 gsb + ) = 8.8 ± 0.9 W.u., consistent with that expected for a β vibration.

On the nature of “three-phonon” excitations in 112Cd☆

Abstract The lifetimes of proposed 3-phonon states in 112 Cd have been measured using the Doppler shift attenuation method (DSAM) following the (n,n′γ) reaction. The experimental results allow the determination of relevant B ( E 2) values which are compared to different theoretical descriptions. Collective enhancements favouring the interpretation of collectivity in the phonon model are observed for 3 + and 4 + members of the 3-phonon quintuplet. However, for the proposed 2 + member, this simple model fails most likely due to the subtle interplay between intruder, mixed-symmetry, and phonon states, and the decay pattern is strongly perturbed. The best overall agreement is obtained with IBM-2 calculations.

Two-phonon octupole excitations in and the role of E1 transitions in their decays

In recent work, candidates for two-phonon octupole excitations in have been identified based on the observation of a cascade of E3 decays and on the rates of de-exciting E1 transitions. To gain greater understanding of E1 transition rates in this region, , a nucleus with a neutron hole coupled to the octupole vibrational core of , has been examined. The status of the search for the two-phonon octupole quartet in is presented, and outstanding questions are highlighted.

On the first excited state of137Ba

The first excited state of137Ba has been excited by the inelastic scattering of accelerator-produced neutrons. The energy of this state at 283.5 keV is not in agreement with the generally accepted value of 279.2 keV, but is in accord with other recent measurements. No evidence for a doublet of states near this energy is found.

Quadrupole-octupole coupled states in

Negative-parity excitations in the 2.5 MeV region in have been investigated with the reaction. Several of these states exhibit enhanced B(E2) values for decay to the octupole state, indicative of quadrupole-octupole coupled structures. The B(E1) values observed are typically in the range of 1-, irrespective of the final state.

Properties of {sup 112}Cd from the (n,n{sup '}{gamma}) reaction: Lifetimes and transition rates

Lifetimes of levels below 4 MeV in {sup 112}Cd have been measured using the Doppler shift attenuation technique following inelastic scattering of monoenergetic neutrons. Reduced transition rates are determined using the results of previous studies and the current lifetimes. The electromagnetic properties of {sup 112}Cd are outlined, and together with results from previous nucleon-transfer studies and inelastic scattering, the levels in {sup 112}Cd are interpreted in terms of single-particle configurations and collective excitations, assuming a vibrational model with intruder states. The collective states and their {gamma}-ray decays are compared with IBM-2 model calculations that allow for the mixing between the normal phonon states and intruder configurations. Levels below 1.5 MeV are reproduced reasonably well, whereas at higher excitation energy the calculations fail to reproduce the data in detail.

Particle-vibration coupling and octupole collectivity in odd-a spherical nuclei

The (n,n′γ) reaction has been used to study the properties of low-lying excited states of 207Pb. Gamma-ray excitation functions, angular distributions, and coincidences have been measured, and the lifetimes of many excited levels were determined with the Doppler-shift attenuation method (DSAM). A sextuplet of states near 3.2 MeV is interpreted as resulting from particle-vibration coupling of the f5/2 neutron hole, the first excited state of 207Pb, with the octupole phonon of the 208Pb core.