Low-lying excited levels in 116Te were studied by measuring level lifetimes with the recoil-distance Dopplershift method in the 112Sn(12C, 8Be) 116Te alpha-transfer reaction and angular correlations following the beta decay of 116I. Both experiments were performed at the Cologne FN Tandem accelerator. Several new levels were discovered below 3.2 MeV excitation energy, spins and multipole mixing ratios were determined via angular correlations. Lifetimes were measured for the 2+1 , 0+2 , 22+, and 4+1 and upper limits for lifetimes were determined for higher lying levels. The experimental findings are compared to calculations in the U(5) limit of the interacting boson model and are also discussed in the framework of shape coexistence which is expected in midshell Te isotopes.

An advanced radio-frequency quadrupole (RFQ) ion cooler was developed for accelerator mass spectrometry to use element-selective laser photodetachment and ion-molecule reactions for isobar suppression. The system will be installed as a central part of the new Anion Laser Isobar Separator (ALIS) at the 6 MV AMS system of CologneAMS. The new RFQ design intends to solve the technical challenge of the deceleration and trapping of heavy molecular ion beams with high emittance. Therefore, an elliptical injection electrode was developed to slow down the ions far away from the central entrance aperture. A new and easy-to-manufacture guide-field assembly was developed. For this purpose, diagonally-split cylindrical surface electrodes are capacitively coupled to a core rod that is carrying the RF signal. Consequently, only low DC voltages are needed to create a gradually changing potential in the longitudinal direction. The RFQ and the acceleration electrodes are installed in a self-aligned structure.

In this study we present the preliminary results about the lifetimes of the 22+ , 41+ states of 208Po and the upper limit of the lifetime of the 21+ state. For measuring the lifetimes of the 21+ and 41+ states the Recoil Distance Doppler Shift (RDDS) method and for the lifetime of the 22+ state the Doppler Shift Attenuation method (DSAM) were used. The resulting absolute transition strength B(M1;22+→21+)≥0.122(20)μN2 reveals the predominant isovector nature of the 22+ state of 208Po.

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 Cl-36 and Be-10. However, the efficiency is reduced due to the charge state distribution generated by the degrader-foil. For measurements injecting atomic Al-26, 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 Mg-26 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 degrees-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 Al-27 at 40 MeV ion energy. Isobar separation for Cl-36 and S-36 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.

The level lifetimes of the yrast 21+, 41+ and 61+ states and an upper limit of the lifetime of the 81+ state in 46Ti have been measured with high accuracy exploiting the recoil distance Doppler-shift method (RDDS) and using $\gamma\gamma$ coincidences. The nuclei were populated by the fusion evaporation reaction 40Ca(9Be, 2p1n)46Ti at a beam energy of $E=33$ MeV at the FN tandem accelerator of the University of Cologne, Germany. Lifetimes were extracted using the established differential decay curve method (DDCM).

Since 2015, the CologneAMS started operating a second SO-110 B ion source (Arnold et al., 2010; Klein and Mous, 2017) from High Voltage Engineering Europe (HVE) with a gas injection system (GIS) from Ionplus AG (Wacker et al., 2013) for the measurement of gaseous CO2 samples. Significant effort was spent increasing the efficiency of C- ion beam extraction as well as the operational reliability. Details are described in Stolz et al. (2017). Recent work was aimed at prolonging the cleaning intervals and allowing unattended routine (CO2)-C-14 measurements. Problems related to sparking inside the source chamber could be eliminated by electrically shielding the ceramic linear actuator that is used to move the target pieces into the source head. Furthermore, the Cs reservoir temperature was decreased from 135 degrees C to 120 degrees C. The negative ion formation efficiency has dropped only slightly to about 5% with the current settings. Additionally, the GIS sample magazine capacity was doubled to 16 ampules, which enables longer measurements without user interaction. A dedicated software (Gas Injection Control Software, GICS) was developed that controls GIS and AMS hardware for fully autonomous measurements, including the source and accelerator startup, sample cracking or combustion, sample mixing with the He carrier gas and the transfer to the source, as well as the subsequent data analysis. This tool also comprises error detection routines in order to minimize the risk of losing a sample due to hardware failures. The blank value was reduced from typically 7.10(-15) to similar to 3.10(-15). This was achieved by modifications in the cleaning and measurement procedures. Recently a EuroVector EA3000 elemental analyzer (EA) was coupled to the GIS and integrated into the GICS software. First EA test measurements with standards, blanks and tree rings were performed as well as first automated overnight measurements with ampules and EA samples.

The measurement capabilities of the new accelerator mass spectrometry (AMS) system at the 10 MV FN tandem accelerator of CologneAMS has been extended with AMS measurements of Fe-60/Fe in the range of 10(-8),10(-10) and 10(-12). The measurements were conducted combining a 135 degrees gas-filled magnet and a subsequent energy loss measurement in a 5 anode gas ionization chamber. This technique allows a good separation of the stable isobar 60 Ni resulting in a suppression by a factor of 10(7) for the high energy mass spectrometer. With this a limit for the background level of 7.10(-14) was achieved. The calculation of the error normalized sensitivity allowed a first comparison to other AMS laboratories.

In the field of nuclear waste management is the determination of difficult to measure isotopes important for the isotopic nuclide inventory in disposal material. Accelerator mass spectrometry propose a new precise and reliable way for the quantification of the radioactive material by the means of direct atom counting. For the radiological characterization of radioactive material, the reference nuclides Co-60 or Eu-152 are normally used, because they are relatively easy to measure by gamma ray spectroscopy. The disadvantages are the relatively short half-lives and in the case of reactor concrete they are produced at trace elements. In addition, the technique of projectile X-ray AMS (PXAMS) offers the opportunity to measure medium mass isotopes like Ni-63 and Sr-90, by the measurement of characteristic X-rays. We investigated the X-ray production yields for different target materials in a projectile ion energy range of 0.35 MeV/u to 1.80 MeV/u for the determination of attainable sensitivities.

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 CL=5.0×10-12. 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 Sx allows an inter laboratory comparison of isotopic ratio measurements.

AMS measurements of medium mass isotopes, e.g. of Mn-53 and Fe-60, 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. (C) 2017 Elsevier B.V. All rights reserved.