No abstract available

[en] Using the U_ν(6/12) x U_π(6/4) extended supersymmetry, we constructed the energy spectrum and electromagnetic transition properties of the supermultiplet member ¹⁹⁸Hg with two proton fermions coupled to a neutron boson core. Consistency between the supersymmetric interacting boson fermion fermion approximation (IBFFA) description and the F-spin symmetric interacting boson approximation (IBA-2) description is shown for this two-fermion-N-boson multiplet member. The data of a γγ angular correlation experiment using the HORUS cube γ-ray spectrometer--determining new multipole mixing ratios, level spins, γ transitions, and energy states--shows quite a good agreement, also for the low-energy part of the spectrum, when comparing theoretical predictions and experimental data. This is contrary to the usual assumption that a two-fermion-N-boson constellation should describe just the excited two-quasiparticle states.

[en] In recent years collectivity in the mass region around A = 100 has become the focus of increased interest. The N = 52 isotones were investigated in detail and phonon excitations -especially one- and two-phonon mixed-symmetry states--were identified. In order to investigate how vibrator-like behavior and states with mixed-symmetry character evolve with increasing neutron number it is interesting to study the N = 54 isotones. Therefore an experiment to measure the low-spin excitations of ¹⁰⁰Pd was performed at the FN-Tandem accelerator with the HORUS cube spectrometer. Besides the determination of excitation and transition energies and branching ratios, spins and multipole mixing ratios resulted from the γγ angular correlation analysis. The newly gained data were compared with predictions from theory both from collective models and from shell model.

[en] An essential property of collectivity is the proton-neutron degree of freedom, that leads to the so-called states of mixed symmetry. Predictions for the electromagnetic decay of the lowest-lying mixed-symmetry state 2_MS,1⁺ in vibrator-like even-A nuclei are a strong M1 decay to the fully-symmetric 2₁⁺ state and a weak collective E2 decay to the ground state 0₁⁺. Excited states in ⁶²Zn have been studied via the ⁶¹Ni(³He,2nγ) reaction using the HORUS-cube spectrometer of the Institute for Nuclear Physics in Cologne. Two fragments of the mixed-symmetry state 2_MS,1⁺ could be identified by determining absolute M1 transition strengths to the 2₁⁺ state.

[en] In the context of the investigation of collectivity in the A=100 mass region an experiment to measure the low-spin excitations of ¹⁰⁰Pd was performed at the Cologne Tandem accelerator with the HORUS cube spectrometer. Besides the determination of excitation and transition energies and branching ratios, data on spins and multipole mixing ratios resulted from the γγ angular correlation analysis. The level scheme was extended and clarified. Nearly 70γ transitions were identified, thereof 16 for the first time. In addition 11 new energy levels were assigned and 13 multipole mixing ratios were measured for the first time. The newly gained data are compared with theoretical predictions from collective models and the shell model.

[en] We present the results of a γγ angular correlation experiment investigating the nucleus ¹⁹⁶Hg and compare these with a theoretical description of ¹⁹⁶Hg within the U_ν(6/12) x U_π(6/4) extended supersymmetry. To populate excited ¹⁹⁶Hg states, we used the Cologne FN Tandem accelerator inducing the reaction ¹⁹⁴Pt(α,2n)¹⁹⁶Hg and analyzed the γ decays of levels up to an excitation energy of 2.4 MeV with the HORUS cube spectrometer. The new results on this mercury isotope allow a comparison between the experimental data and the supersymmetrical predictions and show good agreement. This way we can add ¹⁹⁶Hg as a fifth supermultiplet member to the so-called magical quartet consisting of ^194,195Pt and ^195,196Au.

[en] Recently, an Orange spectrometer, a focusing iron-free magnetic spectrometer, has been installed at a beam line of the 10 MV Tandem accelerator of the IKP of the University of Cologne. The high efficiency of 15% of 4π for the detection of conversion electrons and the energy resolution of 1% makes the Orange spectrometer a powerful instrument. From the conversion electron spectrum, transition multipolarities can be determined using the so called K to L ratio. In combination with an array of germanium and lanthanum bromide detectors, e^--γ-coincidences can be performed to investigate the level scheme. Moreover, the very fast lanthanum bromide scintillator with an energy resolution of 3% allows e^--γ lifetime measurements down to 0.3 ns. A second Orange spectrometer can be added to build the Double Orange Spectrometer for e^--e^--coincidences. It is indispensable for lifetime measurements of low intensity or nearby lying transitions as often occur in odd-A and odd-odd nuclei. The capabilities are illustrated with several examples.

[en] Lifetimes of the yrast states up to 12⁺ and of a negative parity 5^- state in ¹⁰⁰Pd were measured by means of the recoil distance Doppler shift technique. The experiment was performed at the Cologne FN Tandem accelerator with the Cologne Plunger using the reaction ⁹²Mo(¹¹B,p2n) to populate excited states in ¹⁰⁰Pd. Lifetimes were determined by analyzing the transitions in coincidence mode employing the differential decay curve method. The obtained E2 transition strengths were compared to predictions from collective models and the shell model.

[en] Recent experimental results on the nucleus ¹⁹⁶Hg - especially newly determined level spins and multipole mixing ratios of γ-transitions between low-energy states - show a good agreement with supersymmetrical predictions, describing ¹⁹⁶Hg as the two-fermion, five-boson member of the supermultiplet around ¹⁹⁴Pt. To complete the data of a previous ¹⁹⁴Pt(α,2n) experiment and to search for further low-lying low-spin states that might not be populated by that reaction, we chose to perform a new experiment on ¹⁹⁶Hg. This time we approach ¹⁹⁶Hg via β-decay. We used a 35 MeV proton beam at the Wright Nuclear Structure Laboratory to induce the reaction ¹⁹⁸Hg(p,3n)¹⁹⁶Tl. Our target consisted of highly enriched ¹⁹⁸Hgs. One β-decay branch populates preferably the low-spin states we are interested in. The ¹⁹⁶Hg γ-transitions were detected with the highly efficient YRAST Ball γ-spectrometer. We present results of the experiment and discuss the description of the even-even mercury isotopes in the context of the nuclear structure supersymmetry.

No abstract available