J. Endres

Investigation of the reaction 74Ge(p,gamma)75As using the in-beam method to improve reaction network predictions for p nuclei

A measurement of 74Ge(p,gamma)75As at low proton energies, inside the astrophysically relevant energy region, is important in several respects. The reaction is directly important as it is a bottleneck in the reaction flow which produces the lightest p nucleus 74Se. It is also an important addition to the data set required to test reaction-rate predictions and to allow an improvement in the global p+nucleus optical potential required in such calculations. An in-beam experiment was performed, making it possible to measure in the energy range between 2.1 and 3.7 MeV, which is for the most part inside the astrophysically relevant energy window. Angular distributions of the gamma-ray transitions were measured with high-purity germanium detectors at eight angles relative to the beam axis. In addition to the total cross sections, partial cross sections for the direct population of twelve levels were determined. The resulting cross sections were compared to Hauser-Feshbach calculations using the code SMARAGD. Only a constant renormalization factor of the calculated proton widths allowed a good reproduction of both total and partial cross sections. The accuracy of the calculation made it possible to check the spin assignment of some states in 75As. In the case of the 1075 keV state, a double state with spins and parities of 3/2- and 5/2- is needed to explain the experimental partial cross sections. A change in parity from 5/2+ to 5/2- is required for the state at 401 keV. Furthermore, in the case of 74Ge, studying the combination of total and partial cross sections made it possible to test the gamma width, which is essential in the calculation of the astrophysical 74

Determination of 141Pr(alpha,n)144Pm cross sections at energies of relevance for the astrophysical p-process using the gamma-gamma coincidence method

As(n,gamma)75As rate.

Mixed-symmetry octupole and hexadecapole excitations in the N = 52 isotones

The reaction 141 Pr(α,n) 144 Pm was investigated between Eα = 11 MeV and 15 MeV with the activation method using the γγ coincidence method with a segmented clover-type high-purity Germanium (HPGe) detector. Measurements with four other HPGe detectors were additionally made. The comparison proves that the γγ coincidence method is an excellent tool to investigate cross sections down to the microbarn range. The (α,n) reaction at low energy is especially suited to test α + nucleus optical-model potentials for application in the astrophysical p process. The experimentally determined cross sections were compared to Hauser-Feshbach statistical model calculations using different optical potentials and generally an unsatisfactory reproduction of the data was found. A local potential was constructed to improve the description of the data. The consequences of applying the same potential to calculate astrophysical ( γ,α ) rates for 145 Pm and 148 Gd were explored. In summary, the data and further results underline the problems in global predictions of α + nucleus optical potentials at astrophysically relevant energies.

The high-efficiency γ-ray spectroscopy setup γ3 at HIγS

Background: Excitations with mixed proton-neutron symmetry have been previously observed in the N=52 isotones. Besides the well-established quadrupole mixed-symmetry states (MSS), octupole and hexadecapole MSS have been recently proposed for the nuclei Zr92 and Mo94. Purpose: The heaviest stable N=52 isotone Ru96 was investigated to study the evolution of octupole and hexadecapole MSS with increasing proton number. Methods: Two inelastic proton-scattering experiments on Ru96 were performed to extract branching ratios, multipole mixing ratios, and level lifetimes. From the combined data, absolute transition strengths were calculated. Results: Strong M1 transitions between the lowest-lying 3- and 4+ states were observed, providing evidence for a one-phonon mixed-symmetry character of the 32(-) and 42+ states. Conclusions: sdg-IBM-2 calculations were performed for Ru96. The results are in excellent agreement with the experimental data, pointing out a one-phonon hexadecapole mixed-symmetry character of the 42+ state. The 31-||M1||32(-) matrix element is found to scale with the 2s+||M1||2ms+ matrix element.

Investigation of α-induced reactions on the p nucleus Yb168

The existing Nuclear Resonance Fluorescence (NRF) setup at the HI{\gamma}S facility at the Triangle Universities Nuclear Laboratory at Duke University has been extended in order to perform {\gamma}-{\gamma} coincidence experiments. The new setup combines large volume LaBr3:Ce detectors and high resolution HPGe detectors in a very close geometry to offer high efficiency, high energy resolution as well as high count rate capabilities at the same time. The combination of a highly efficient {\gamma}-ray spectroscopy setup with the mono-energetic high-intensity photon beam of HI{\gamma}S provides a worldwide unique experimental facility to investigate the {\gamma}-decay pattern of dipole excitations in atomic nuclei. The performance of the new setup has been assessed by studying the nucleus \sulfur at 8.125 MeV beam energy. The {\gamma}-decay branching ratio from the

Measurement of the Re187(α,n)Ir190 reaction cross section at sub-Coulomb energies using the Cologne Clover Counting Setup

1^+

In-beam experiments on (p, γ) and (a, γ) reactions for the astrophysical p process

level at 8125.4 keV to the first excited

Investigation of octupole vibrational states in 150 Nd via inelastic proton scattering (p,p 'gamma)

2^+

Study of mixed-symmetry excitations in 96Ru via inelastic proton-scattering

state was determined to 15.7(3)%.

First test results of the digital data acquisition at the HORUS spectrometer

Abstract Cross sections for the Yb 168 ( α , γ ) Hf 172 and Yb 168 ( α , n ) Hf 171 reactions were measured by means of the activation method using α particles with energies between 12.9 MeV and 15.1 MeV. The spectroscopy of the γ rays emitted by the reaction products was performed using three different HPGe detector types, namely clover-type high-purity germanium detectors, a low-energy photon spectrometer detector, and a coaxial high-purity germanium detector. The results were compared to Hauser–Feshbach statistical model calculations. Within certain assumptions, astrophysical conclusions could be drawn concerning the production of the p nucleus Yb 168 . The data in this work can serve as a contribution to the current very fragmentary experimental data base for charged-particle induced reactions. In addition, the absolute intensity for nine γ-ray transitions following the electron capture decay of Hf 171 could be derived.