[en] A new accelerator mass spectrometer was successfully designed for the Cologne FN accelerator to enlarge the measurement capability of CologneAMS to medium mass radionuclides. With this AMS-system (⁵³Mn/⁵⁵Mn) isotopic ratios are measurable at a 10 MV tandem accelerator in the range of ${10}^{-9}$ to ${10}^{-10}$ for the first time, with a detection limit of $C_L=5.0\times {10}^{-12}$. A high ⁵³Cr suppression in the (⁵³Mn/⁵⁵Mn) isotopic ratio measurement was achieved by using the optimal silicon nitride degrader foil thickness in combination with an electrostatic analyzer (ESA). The new system opens the field of research for CologneAMS users to the medium mass region of cosmogenic nuclides, like ⁵³Mn for geological applications of long term erosion, exposure and burial dating and ⁶⁰Fe for nuclear astrophysical models. The presented definition of an error normalized sensitivity $S_x$ allows an inter laboratory comparison of isotopic ratio measurements.

[en] Full text: Since the first application of isotope-shift measurements a sharp shape transition in the ground states of light odd-mass mercury isotopes was observed, and shape coexistence near the Z=82 shell has been an actively studied phenomenon. In neutron-deficient even-mass mercury isotopes a weakly deformed oblate ground-state band is found to coexist with a more deformed prolate band. The prolate states are interpreted as a π(4p-6h) excitation across the Z=82 shell gap. The prolate band build upon an excited 0⁺ state can be related to similar structures in the Pb nuclei. The energy of this prolate structure is lowest in ¹⁸²Hg and shows a parabolic trend of excitation energy as a function of the neutron number. In the neighboring even-mass platinum isotopes this structure reaches even the ground state. In the Hg isotopes ¹⁸⁰Hg is the most exotic nucleus for which lifetimes of excited states are known so far. These can be used to determine model-independent B(E2)-values and absolute values of deformation employing the rotor model. A breakdown of the shape-coexistence is predicted with further decreasing neutron number. We will present lifetime measurements of excited states in ¹⁷⁸Hg using the Recoil Distance Doppler-Shift (RDDS) method. The recoil-decay tagging (RDT) technique was applied to select the ¹⁷⁸Hg nuclei and associate the prompt 𝛾-rays with the correlated characteristic ground state α-decay. (author)

[en] A dedicated setup for the in-beam measurement of absolute cross-sections of astrophysically relevant charged-particle induced reactions is presented. These, usually very low, cross-sections at energies of astrophysical interest are important to improve the modeling of the nucleosynthesis processes of heavy nuclei. Particular emphasis is put on the production of the p nuclei during the astrophysical γ process. The recently developed setup utilizes the high-efficiency γ-ray spectrometer HORUS, which is located at the 10 MV FN tandem ion accelerator of the Institute for Nuclear Physics in Cologne. The design of this setup will be presented and results of the recently measured ⁸⁹Y(p,γ)⁹⁰Zr reaction will be discussed. The excellent agreement with existing data shows that the HORUS spectrometer is a powerful tool to determine total and partial cross-sections using the in-beam method with high-purity germanium detectors

[en] Routine measurements of the last years at the 6 MV AMS system showed a good isobar suppression for all light isotopes, measured with the Degrader-Foil-Method, especially ³⁶Cl and ¹⁰Be. However, the efficiency is reduced due to the charge state distribution generated by the degrader-foil. For measurements injecting atomic ²⁶Al, the ionization efficiency becomes the bottleneck, which leads to a relatively low ion source output. In the case of AlO⁻, the output is expected about one order of magnitude higher. However, to use AlO⁻ the isobar interference of ²⁶Mg will become an issue. It has to be suppressed in several steps, e.g. by different dE/dx methods like TOF, degrader-foil or gas-filled magnet. In order to minimize the efficiency losses generated by the degrader-foil method, the 120°-magnet at the 6 MV AMS system was modified to enable a gas-filled operation, and therefore focus the beam to a mean charge state. A constraint for all modification of the detection beam line was that the operation of the degrader-foil method is not affected. In this paper, we report on the performed construction work, as well as test measurements for ²⁷Al at 40 MeV ion energy. Isobar separation for ³⁶Cl and ³⁶S was measured as a function of the gas pressure. We compare measured data with Monte Carlo simulations performed with a computer code developed by our group. In addition, we will present a new dedicated gas ionization chamber designed for particle detection directly after the gas-filled magnet.

[en] It is shown that the Blaugrund approximation could have led to some imprecise lifetime determinations in the past which used the Doppler-shift attenuation method (DSAM). Comparison with Monte Carlo simulations of the slowing-down process show that there is not an easy way to judge using them on the reliability of old data.

No abstract available

[en] AMS measurements of medium mass isotopes, e.g. of ⁵³Mn and ⁶⁰Fe, are gaining interest in various fields of operation, especially geoscience. Therefore a dedicated AMS setup has been built at the Cologne 10 MV FN tandem accelerator. This setup is designed to obtain a sufficient suppression of the stable isobars at energies around 100 MeV. In this contribution we report on the actual status of the new setup and the first in-beam tests of its individual components. The isobar suppression is done with (dE/dx) techniques using combinations of energy degrader foils with an electrostatic analyzer (ESA) and a time of flight (ToF) system, as well as a (dE/dx),E gas ionization detector. Furthermore, the upgraded ion source and its negative ion yield measurement for MnO⁻ are presented.

[en] Reduced transition strengths are sensitive signatures to describe collective excitations of atomic nuclei and the evolution of shell structures. They provide stringent tests of present shell-model interactions in the 0f1p shell along the N=Z line. Recently determined B(E2, 2${}_1^{+}$$\to <!--\; ???\; -->$ 0${}_{g.s.}^{+}$) values for ${}^{44}$Ti showed an enhanced collective behavior which was associated with core excitations from the sd-shell. However, there is a lack of information on precise values along the negative parity band in this nucleus. These states arise from a strong interplay between sd- and pf-shell orbitals and allow for refined tests of cross-shell contributions. In order to investigate the single-particle and collective characters of low-lying states, lifetime measurements employing the Recoil-Distance Doppler Shift (RDDS) and the Doppler-Shift Attenuation Method (DSAM) were performed at the FN tandem accelerator at the IKP, Cologne. Excited states in ${}^{44}$Ti were populated with a ${}^{40}$Ca(${}^6$Li,pn)${}^{44}$Ti fusion-evaporation reaction. The emitted $\mathrm{\gamma <!--\; ??\; -->}$ rays were detected by an array of 11 HPGe detectors. First lifetime results will be presented and compared to shell-model calculations including multi particle-hole cross-shell excitations.

[en] At the Cologne Tandem accelerator we are performing a systematic study of lifetimes in the ground state bands of well deformed even-even nuclei in order to increase the precision of the ns-ps lifetimes and to solve inconsistencies in the literature. The measurements are done using Orange spectrometers, LaBr_3(Ce) scintillators and Ge detectors. The data are analyzed using the slope and the generalized centroid difference method. The latter allows the measurement of lifetimes down to 5 ps. First results on Yb, Hf and W isotopes are presented.

[en] Reduced transition strengths expressed by B(E2) values are sensitive signatures to describe collective excitations of atomic nuclei and the evolution of shell structures. Along the N = Z line in the 0f1p shell they provide stringent tests of present shell-model interactions. Recently determined B(E2, 2₁⁺ → 0_g.s.⁺) values for self-conjugate nuclei in the 0f_7/2 shell showed an enhanced collective behavior. The soft shell closure at N = Z = 28 is of particular interest as it has been shown that the doubly-closed shell structure is substantially broken. In order to investigate the interplay between single-particle and collective characters of low-lying states, lifetime measurements employing the Doppler-shift attenuation method (DSAM) were performed at the FN tandem accelerator at the IKP, Cologne. Excited states in ₂₂⁴⁴Ti, ₂₄⁴⁸Cr, ₂₆⁵²Fe, and ₂₈⁵⁶Ni were populated with fusion-evaporation reactions. The emitted γ rays were detected by an array of 11 HPGe detectors. First results on lifetimes and corresponding B(E2) values are presented and discussed.