Exploitation of the Timing Capabilities of Metallic Magnetic Calorimeters for a Coincidence Measurement Scheme

In this report, we compare two filter algorithms for extracting timing information using novel metallic magnetic calorimeter detectors, applied to the precision X-ray spectroscopy of highly charged ions in a storage ring. Accurate timing information is crucial when exploiting coincidence conditions for background suppression to obtain clean spectra. For X-rays emitted by charge-changing interactions between ions and a target, this is a well-established technique when relying on conventional semiconductor detectors that offer a good temporal resolution. However, until recently, such a coincidence scheme had never been realized with metallic magnetic calorimeters, which typically feature much longer signal rise times. In this report, we present optimized timing filter algorithms for this type of detector. Their application to experimental data recently obtained at the electron cooler of CRYRING@ESR at GSI, Darmstadt is discussed

Towards an Intrinsic Doppler Correction for X-ray Spectroscopy of Stored Ions at CRYRING@ESR

We report on a new experimental approach for the Doppler correction of X-rays emitted by heavy ions, using novel metallic magnetic calorimeter detectors which uniquely combine a high spectral resolution with a broad bandwidth acceptance. The measurement was carried out at the electron cooler of CRYRING@ESR at GSI, Darmstadt, Germany. The X-ray emission associated with the radiative recombination of cooler electrons and stored hydrogen-like uranium ions was investigated using two novel microcalorimeter detectors positioned under 0∘ and 180∘ with respect to the ion beam axis. This new experimental setup allowed the investigation of the region of the N, M → L transitions in helium-like uranium with a spectral resolution unmatched by previous studies using conventional semiconductor X-ray detectors. When assuming that the rest-frame energy of at least a few of the recorded transitions is well-known from theory or experiments, a precise measurement of the Doppler shifted line positions in the laboratory system can be used to determine the ion beam velocity using only spectral information. The spectral resolution achievable with microcalorimeter detectors should, for the first time, allow intrinsic Doppler correction to be performed for the precision X-ray spectroscopy of stored heavy ions. A comparison with data from a previous experiment at the ESR electron cooler, as well as the conventional method of conducting Doppler correction using electron cooler parameters, will be discussed

The decay pattern of the Pygmy Dipole Resonance of ¹⁴⁰Ce

The decay properties of the Pygmy Dipole Resonance (PDR) have been investigated in the semi-magic N=82 nucleus ¹⁴⁰Ce using a novel combination of nuclear resonance fluorescence and γ–γcoincidence techniques. Branching ratios for transitions to low-lying excited states are determined in a direct and model-independent way both for individual excited states and for excitation energy intervals. Comparison of the experimental results to microscopic calculations in the quasi-particle phonon model exhibits an excellent agreement, supporting the observation that the Pygmy Dipole Resonance couples to the ground state as well as to low-lying excited states. A 10% mixing of the PDR and the [2+1×PDR]is extracted

Coulomb dissociation of 16O into 4He and 12C

We measured the Coulomb dissociation of 16O into 4He and 12C at the R3B setup in a first campaign within FAIR Phase 0 at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. The goal was to improve the accuracy of the experimental data for the 12C(a,?)16O fusion reaction and to reach lower center-ofmass energies than measured so far. The experiment required beam intensities of 109 16O ions per second at an energy of 500 MeV/nucleon. The rare case of Coulomb breakup into 12C and 4He posed another challenge: The magnetic rigidities of the particles are so close because of the same mass-To-charge-number ratio A/Z = 2 for 16O, 12C and 4He. Hence, radical changes of the R3B setup were necessary. All detectors had slits to allow the passage of the unreacted 16O ions, while 4He and 12C would hit the detectors' active areas depending on the scattering angle and their relative energies. We developed and built detectors based on organic scintillators to track and identify the reaction products with sufficient precision

Probing the decay characteristics of the Pygmy Dipole Resonance in the semi-magic nucleus 140Ce^{140}Ce with γ\gamma-γ\gamma coincidence measurements

This work presents the design and installation of a novel experimental setup -- the $\gamma^3$ setup -- for measuring photon-induced nuclear dipole excitations in stable isotopes at the High Intensity $\gamma$-ray Source (HIγS) at the Duke University. The high energy resolution and high detection efficiency of the detector array, consisting of a combination of LaBr and HPGe detectors, allows for the first time the efficient measurement of $\gamma$³-$\gamma$³-coincidences in combination with the method of nuclear resonance fluorescence. This technique provides access to the decay pattern of dipole excited states as an additional observable, which allows a deeper insight into the underlying structure of these excitations. The experimental setup has already been used successfully for two experimental campaigns in 2012 and 2013 in the investigation of 13 different target isotopes. Within the scope of this thesis the Pygmy Dipole Resonance (PDR) of 140Ce was studied in the excitation energy range from 5.2 MeV to 8.3 MeV based on data obtained with the $\gamma$3 setup. In particular the decay pattern of the states participating in the PDR was investigated. The experimental setup, the details of the analysis and the experimental results are presented in this thesis. A comparison of the results to theoretical quasi-particle phonon model (QPM) calculations allows for an interpretation of the observed decay behaviour

Probing the E2 properties of the scissors mode with real photons

The E2/M1 multipole mixing ratio δ1→2 of the 1+ sc → 2+ 1 γ-ray transition of 156Gd and 164Dy has been measured using the linearly polarized photon beams of the HIγS facility. The employed method of photonscattering experiments in combination with polarized, quasi-monochromatic beams and a dedicated detector setup is highly sensitive to the electric quadrupole-decay properties of the scissors mode

Probing the

The E2/M1 multipole mixing ratio δ1→2 of the 1+ sc → 2+ 1 γ-ray transition of 156Gd and 164Dy has been measured using the linearly polarized photon beams of the HIγS facility. The employed method of photonscattering experiments in combination with polarized, quasi-monochromatic beams and a dedicated detector setup is highly sensitive to the electric quadrupole-decay properties of the scissors mode

Probing the E2 properties of the scissors mode with real photons

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Study of photon strength functions via (γ→, γ′, γ″) reactions at the γ3-setup

One of the basic ingredients for the modelling of the nucleosynthesis of heavy elements are so-called photon strength functions and the assumption of the Brink-Axel hypothesis. This hypothesis has been studied for many years by numerous experiments using different and complementary reactions. The present manuscript aims to introduce a model-independent approach to study photon strength functions via γ-γ coincidence spectroscopy of photoexcited states in 128Te. The experimental results provide evidence that the photon strength function extracted from photoabsorption cross sections is not in an overall agreement with the one determined from direct transitions to low-lying excited states