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Self-conjugate nuclei in the A ≈ 70–80 region have attracted a great deal of attention due to phenomena such as shape coexistence and increasing collectivity along the N=Zline. We investigate the structure of nuclei in this region through lifetime measurements using the GRETINA array. The first implementation of the Differential Recoil Distance Doppler Shift technique with fast radioactive beams is demonstrated and verified through a measurement of the well-known B(E2; 2₁⁺→ 0₁⁺)transition strength in ⁷⁴Kr. The method is then applied to determine the B(E2; 2₁⁺→ 0₁⁺) transition strength in ⁷⁴Rb, the heaviest odd–odd N=Z nucleus for which this quantity has been determined. This result and extended systematics along N=Z suggest the dominance of the isoscalar part of the quadrupole transition strengths in self-conjugate nuclei, as well as the possible presence of shape coexistence in ⁷⁴Rb.

This letter reports lifetime measurements of excited states in the odd-N nucleus 163W using the recoil-distance Doppler shift method to probe the core polarising effect of the i13/2 neutron orbital on the underlying soft triaxial even-even core. The ratio B(E2:21/2⁺ → 17/2⁺)/B(E2:17/2⁺ → 13/2⁺) is consistent with the predictions of the collective rotational model. The deduced B(E2) values provide insights into the validity of collective model predictions for heavy transitional nuclei and a geometric origin for the anomalous B(E2) ratios observed in nearby even-even nuclei is proposed.

Accelerator mass spectrometry (AMS) has a great potential for various geological applications. The precision and sensitivity is directly linked to technical developments. Therefore CologneAMS, the center for accelerator mass spectrometry of the University of Cologne (Dewald et al., 2013a, 2013b), does extensive work on method developments for isotopic ratio measurement, for new applications and to improve the precision. We present two important technical developments: (1) dating of sediments with Mn-53 and (2) ultra-small (CO2)-C-14 samples. (1) The age determination of discontinuously deposited sediments by measurement of cosmogenic Mn-53 and He-3 concentration in iron-titaniumoxides (hematite, magnetite, titanomagnetite, ilmenite), where the measurement of the medium mass isotope Mn-53 is difficult because of the interfering isobar Cr-53. It can be measured at only 2 laboratories worldwide. The new AMS system at the Cologne 10 MV FN tandem accelerator is therefore designed especially for the measurement of medium mass isotopes, e.g. Mn-53. It provides the opportunity to use several detector systems in different combinations: degrader foils with an electrostatic analyzer, a 4 m time-of-flight system, a new 135 degrees gas-filled magnet, different gas ionization detectors and a projectile x-ray detector. With the implementation of the new 135 degrees gas-filled magnet to the 10 MV FN-Tandem accelerator AMS beamline the first tests have shown an increase in transmission and reduction of blank value in comparrison to the measurement with the degrader foil technique (Schiffer et al. 2018). The background level was reduced by a factor of 3.3 and the error normalized sensitivity (Schiffer et al. 2018) was increased by a factor of 1.6. (2) For the measurement of extremely low carbon from cosmogenic in-situ produced C-14 or from C-14 content of bulk sediments, with 0.01% carbon, technical developments are required to measure low concentrations in terrestrial rocks of 100,0

A new multi-isotope plutonium standard for isotopic ratio measurements with Accelerator Mass Spectrometry (AMS) was created by gravimetric mixing of different single-isotope standards provided by IRMM (Pu-239, Pu-240, Pu-242, Pu-244). This standard material has been measured at the AMS facilities at Canberra (Australia), Cologne (Germany), Caserta (Italy), Sevilla (Spain) and Zurich (Switzerland). Additionally, the material was characterized using a Neptune MC-ICPMS (multi-collector inductively coupled plasma mass spectrometry) at the joint Cologne-Bonn isotope facility. The results of this laboratory intercomparison are presented and consensus values for the isotope compositions of the standard material are proposed.

Two natural mineral separates, labeled CoCal-N and CoFsp-N, have been prepared to serve as intercomparison material (ICM) for in situ-produced cosmogenic Cl-36 and natural chlorine (Cl-nat) analysis. The sample CoCal-N is derived from calcite crystals in a Namibian lag deposit, while the sample CoFsp-N is derived from a single crystal of alkali-feldspar from a Namibian pegmatite. The sample preparation took place at the University of Cologne and a rotating splitter was used to obtain homogeneous splits of both ICMs. Forty-five measurements of CoCal-N (between 1 and 16 per facility) and forty-four measurements of CoFsp-N (between 2 and 20 per facility) have been undertaken by ten target preparation laboratories measured by seven different AMS facilities. The internal laboratory scatter of the Cl-36 concentrations indicates no overdispersion for half of the laboratories and 3.9 to 7.3% (1 sigma) overdispersion for the others. We show that the CoCal-N and CoFsp-N splits are homogeneous regarding their Cl-36 and Cl-nat concentrations. The grand average (average calculated from the average of each laboratory) yields initial consensus Cl-36 concentrations of (3.74 +/- 0.10) x 10(6) at Cl-36/g (CoCal-N) and (2.93 +/- 0.07) x 10(6) at Cl-36/g (CoFsp-N) at 95% confidence intervals. The coefficient of variation is 5.1% and 4.2% for CoCal-N and CoFsp-N, respectively. The Cl-nat concentration corresponds to the lower and intermediate range of typical rock samples with (0.73 +/- 0.18) mu/g in CoCal-N and (73.9 +/- 6.8) mu/g in CoFsp-N. We discuss the most relevant points of the sample preparation and measurement and the chlorine concentration calculation to further approach inter-laboratory comparability. We propose to use continuous measurements of the ICMs to provide a valuable quality control for future determination of Cl-36 and Cl-nat concentrations.

Increasing demands for small-scale radiocarbon (C-14) analyses required the installation of a SO-110 B type ion source (HVE Europa B.V.) at our 6 MV Tandetron AMS (HVE) dedicated for the direct injection of CO2 using either the gas injection system (GIS) from Ionplus AG or a EuroVector EA 3000 elemental analyzer (EA). We tested both systems with multiple series of C-14-free and modern standards (2.5-50 mu g C) combusted in quartz ampoules or EA containers and were able to quantify exogenous C introduced. In EA-GIS-AMS analysis exogenous C is mainly derived from the EA sample containers. Blank values for 50 mu g C combusted in solvent-cleaned tin (Sn) vessels were 0.0127 +/- 0.0012 (FC)-C-14 (boats) and 0.0090 +/- 0.0010 (FC)-C-14 (capsules), while they were much higher for thermally cleaned silver (Ag) capsules. The processing of gas samples for GIS-AMS yields similar blank values corresponding to 0.30 +/- 0.08 mu g exogenous C with 0.93 +/- 0.23 (FC)-C-14 consisting of 0.28 mu g C modern and 0.02 mu g C fossil C. The combustion of larger amounts of blank material (1 mg C) in a single quartz tube split into aliquots gives lower blanks (0.0064 +/- 0.0008 (FC)-C-14; 50 mu g C). Thus, C-14 analysis of small, gaseous samples is now possible at CologneAMS.

A new multi-isotope plutonium standard for isotopic ratio measurements with Accelerator Mass Spectrometry (AMS) was created by gravimetric mixing of different single-isotope standards provided by IRMM (Pu-239, Pu-240, Pu-242, Pu-244). This standard material has been measured at the AMS facilities at Canberra (Australia), Cologne (Germany), Caserta (Italy), Sevilla (Spain) and Zurich (Switzerland). Additionally, the material was characterized using a Neptune MC-ICPMS (multi-collector inductively coupled plasma mass spectrometry) at the joint Cologne-Bonn isotope facility. The results of this laboratory intercomparison are presented and consensus values for the isotope compositions of the standard material are proposed.

Lifetimes of excited states in Tc-107, Rh-109, Rh-111, and Rh-113 were measured at GANIL using the Recoil-Distance Doppler Shift method. The neutron-rich nuclei were produced in fission reactions in inverse kinematics with a U-238 beam impinging on a Be-9 target. Fission fragments were identified event-by-event in the ray-tracing spectrometer VAMOS++ and correlated with prompt gamma rays observed around the target position with the EXOGAM Ge detector array. Several lifetimes were obtained for states in the positiveparity yrast bands in the four nuclei and compared to triaxial particle-rotor calculations. The results clarify the configuration for the strongest positive-parity band in Tc-107 and suggest a gradual increase of triaxial deformation with atomic number Z, reaching almost maximum triaxiality for the neutron-rich Rh nuclei.

Lifetimes of excited states in Y-99, Y-101, Nb-101, Nb-103, and Nb-105 were measured in an experiment using the recoil distance Doppler shift method at GANIL (Grand Accelerateur National dIons Lourds). The neutron-rich nuclei were produced in fission reactions between a U-238 beam and a Be-9 target. Prompt gamma rays were measured with the EXOGAM array and correlated with fission fragments that were identified in mass and atomic number with the VAMOS++ spectrometer. The measured lifetimes, together with branching ratios, provide B(M1) and B(E2) values for the strongly coupled rotational bands built on the [422] 5/2(+) ground state in the Y and Nb nuclei with neutron number N GT = 60. The comparison of the experimental results with triaxial particle-rotor calculations provides information about the evolution of the nuclear shape in this mass region.

Lifetimes of short-lived excited states in a wide range of neutron-rich fission fragments were measured using the recoil distance Doppler shift (RDDS) technique, which was applied to fusion-fission reactions in inverse kinematics for the first time. The fission fragments were identified event-by-event in mass, charge, and atomic number using the VAMOS magnetic spectrometer at GANIL. Gamma rays originating from the fission fragments were measured with the EXOGAM array of Ge Clover detectors around the target position. Using a degrader, the change in the Doppler shift of the gamma ray allows the application of the RDDS method. Details of the experimental technique will be discussed and the status for the ongoing analysis for odd-mass yttrium isotopes will be presented.

The nuclear structure of the odd-mass Zn-69 and Zn-71 isotopes, with one hole or one particle outside the N = 40 subshell closure, has been investigated by measuring the lifetime of excited states using the recoil distance Doppler-shift method. The nuclei of interest were produced in a deep-inelastic reaction in inverse kinematics with a U-238 beam impinging on a Zn-70 target. Single-particle and collective states were found to coexist at low energy in Zn-69 and Zn-71.

Absolute electromagnetic transition probabilities in Po196 have been measured using the recoil distance Doppler-shift technique. The lifetimes of the three lowest yrast states in Po196 were extracted from singles γ-ray spectra by using the recoil-decay tagging method. In addition, configuration mixing calculations of angular momentum projected mean-field states have been carried out for Po196. The present study sheds light on the onset of collectivity and mixing of competing structures in neutron-deficient Po nuclei. © 2009 The American Physical Society., SCOPUS: ar.j, info:eu-repo/semantics/published

Lifetimes of prolate intruder states in 186Pb and 188Pb and oblate intruder states in 194Po have been determined through recoil distance Doppler-shift lifetime measurements. Deformation parameters of, SCOPUS: ar.j, info:eu-repo/semantics/published

Several cross-section measurements of proton as well as α-particle capture reactions in the Se-Sb region have been carried out at sub-Coulomb energies with the aim to obtain global input parameters for Hauser-Feshbach (HF) calculations. Some of the results are compared with HF calculations using various optical model potentials and nuclear level densities. © 2005 IOP Publishing Ltd., SCOPUS: cp.j, info:eu-repo/semantics/published

Several in-beam cross section measurements of proton- as well as α-capture reactions in the Se-Sb region have been carried out to obtain global input parameters for Hauser-Feshbach (HF) calculations. In total, 20 (p,γ) and 7 (α, γ) reactions were measured. We compare some of these results with Hauser-Feshbach calculations using various optical model potentials and nuclear level densities. © 2005 Elsevier B.V. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Picosecond lifetimes of medium spin states in Lu-165 were measured for the first time. The reaction used to populate the nucleus of interest was La-139(Si-30,4n)Lu-165 at a beam energy of 135 MeV. The beam was provided by the XTU-tandem accelerator of Laboratori Nazionali di Legnaro, Italy. By using the differential decay curve method, lifetimes of 19 states in four different rotational bands were obtained. Therefrom the B(E2) values and the transitional quadrupole moments were deduced. The obtained Q(t) for the different bands are compared with total Routhian surface (TRS) calculations and particle-rotor-model calculations. The TRS calculations predict different axial symmetric shapes for the bands built on the 9/2(-)[514], 9/2(+)[404], and 1/2(-)[541] configurations, with a gamma softness for the 9/2(-)[514] configuration. This band has also been studied using the particle-rotor model, the results of which, however, are consistent with a triaxial shape with a gamma value of -15(p)., QC 20100621