H. Maser

Lifetimes of two-phonon 1− states in even N = 82 nuclei

Abstract Photon scattering experiments on the semi magic nuclei 138 Ba and 140 Ce have been performed at the bremsstrahlung facility of the Stuttgart Dynamitron. Two-phonon 1 − states were excited at 4.026 and 3.643 MeV excitation energy respectively as well as a number of 2 + states between 2 and 4 MeV. Lifetimes and upper limits for the decay to other low-lying states were extracted from the data and are compared to lifetimes given in the literature. The systematics of B (E1) values and energies of the 1 − two-phonon states is analysed using additional data from previously published (γ, γ′) experiments on the neighbouring isotones 142 Nd and 144 Sm.

Observation of the 1{sup +} scissors mode in the {gamma}-soft nucleus {sup 134}Ba

A photon scattering experiment was performed on the {gamma}-soft nucleus {sup 134}Ba with photon energies of {ital E}{sub {gamma}}{lt}4.1. Around 3 MeV excitation energy a fragmented 1{sup +} scissors mode as well as the (2{sup +}{circle_times}3{sup {minus}}){sub 1{sup {minus}}} two-phonon dipole state were identified. The dipole excitation strengths were measured. The excitation strength of the scissors mode in this {gamma}-soft nucleus is well reproduced by an empirical {ital M}1 sum rule that generalizes the {open_quote}{open_quote}{delta}{sup 2} law{close_quote}{close_quote} to nuclei without axial symmetry. The IBM-2 describes the mixed-symmetry states in {sup 134}Ba and their decay pattern. A large {ital E}2/{ital M}1 mixing ratio for the 1{sup +}{r_arrow}2{sup +}{sub 1} decay of the scissors mode to the 2{sup +}{sub 1} state is predicted by the IBM-2. The new result from {sup 134}Ba together with a similar previous observation in {sup 196}Pt corroborates the scissors mode as a typical excitation mode of {gamma}-soft nuclei. {copyright} {ital 1996 The American Physical Society.}

The scissors mode and other magnetic and electric dipole excitations in the transitional nuclei 178,180Hf

Abstract Photon scattering experiments have been performed on the heavy deformed nuclei 178,180 Hf using an E γ K quantum numbers, dipole excitation strengths, and level widths, have been extracted from the scattering cross sections. From the measured level widths lifetimes of 67 levels can be deduced. The excitation strength of the scissors mode is discussed and extends the systematics from the neighboring rare earth nuclei. Besides the ΔK = 1 excitations other dipole excitations have been observed that are distinguished from the scissors mode states by their different decay behavior.

Low-lying dipole excitations in the isotopes 113,114Cd

Abstract High-resolution nuclear resonance flourescence (NRF) experiments have been performed on the nuclei 113,114 Cd using bremsstrahlung and Ge-γ-spectrometers. Precise excitation energies, decay widths and decay branching ratios for numerous new levels (dipole excitations) in the energy range 2–4 MeV have been extracted from the measured energy spectra and angular distributions of the scattered photons. The NRF results are compared with IBA calculations and spectroscopic data from particle-induced reactions.

Search for the electric dipole excitations to the3s1/2⊗[21+⊗31−]multiplet in117Sn

The odd-mass

Strong fragmentation of low-energy electromagnetic excitation strength in Sn-117

^{117}

Systematics of low-lying E1 and M1 excitations in heavy nuclei from photon scattering experiments

Sn nucleus was investigated in nuclear resonance fluorescence experiments up to an endpoint energy of the incident photon spectrum of 4.1 MeV at the bremsstrahlung facility of the Stuttgart University. More than 50 mainly hitherto unknown levels were found. From the measurement of the scattering cross sections model independent absolute electric dipole excitation strengths were extracted. The measured angular distributions suggested the spins of 11 excited levels. Quasi-particle phonon model calculations including a complete configuration space were performed for the first time for a heavy odd-mass spherical nucleus. These calculations give a clear insight in the fragmentation and distribution of the

Systematics of Low-Lying Dipole Strength in Heavy Nuclei from Nuclear Resonance Fluorescence Experiments

E1

Systematics of the excitation energy of the 1+ scissors mode and its empirical dependence on the nuclear deformation parameter

,

Absolute level widths in 27Al below 4 MeV.

M1