Karsten Vogt

Concentration of electric dipole strength below the neutron separation energy in N=82 nuclei

Abstract The semi-magic nuclei 138 Ba, 140 Ce, and 144 Sm have been investigated in photon scattering experiments up to an excitation energy of about 10 MeV. The distribution of the electric dipole strength shows a resonance like structure at energies between 5.5 and 8 MeV exhausting up to 1% of the isovector E1 Energy Weighted Sum Rule.

Experimental simulation of a stellar photon bath by bremsstrahlung: the astrophysical gamma-process

The nucleosynthesis of heavy proton-rich nuclei in a stellar photon bath at temperatures of the astrophysical

Measurement of the (gamma, n) cross section of the nucleus Au-197 close above the reaction threshold

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Measurement of the (y,n) reaction rates of the nuclides 190Pt, 192Pt, and 198Pt in the astrophysical y process

-process was investigated where the photon bath was simulated by the superposition of bremsstrahlung spectra with different endpoint energies. The method was applied to derive (

The s-process branching at W-185

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Polarization sensitivity of a segmented HPGe detector up to 10 MeV

,n) cross sections and reaction rates for several platinum isotopes.The nucleosynthesis of heavy proton-rich nuclei in a stellar photon bath at temperatures of the astrophysical gamma-process was investigated where the photon bath was simulated by the superposition of bremsstrahlung spectra with different endpoint energies. The method was applied to derive (gamma,n) cross sections and reaction rates for several platinum isotopes

NAIS: Nuclear activation-based imaging spectroscopy

The cross section and the astrophysical reaction rate of the reaction Au-197(gamma,n)Au-196 have been measured close above the reaction threshold at E-thr = 8.071 MeV using the method of photoactivation. The results are compared to those of several previous measurements as well as to theoretical calculations. The relevance of the reaction Au-197(gamma,n)Au-196 as a standard for photoactivation experiments is discussed

Photoreactions in nuclear astrophysics

The nucleosynthesis of heavy neutron-deficient nuclei in a stellar photon bath at the temperatures relevant for the astrophysical gamma process was investigated. In order to derive (gamma,n) cross sections and reaction rates, the stellar photon bath was simulated by the superposition of several bremsstrahlung spectra with different endpoint energies. As a first test for this method, the (gamma,n) reaction rates of the platinum isotopes 190Pt, 192Pt, and 198Pt were derived. The results are compared to other experimental data and theoretical calculations.

Nucleosynthesis by photon-induced reactions

The neutron capture cross section of the unstable nucleus W-185 has been derived from experimental photoactivation data of the inverse reaction W-186(gamma, n) W-185. The new result of sigma = 687 +/- 110 mbarn confirms the theoretically predicted neutron capture cross section of W-185 of sigma approximate to 700 mbarn at kT = 30 keV. A neutron density in the classical s-process of n(n) = (3.8(-0.9)(+1.1)) x 10(8) cm(-3) is derived from the new data for the W-185 branching. In a stellar s-process model, one finds a significant overproduction of the residual s-only nucleus Os-186.

E1 strength in N = 82 nuclei

Abstract Linear γ-ray polarization can be measured using segmented germanium detectors. The polarization sensitivity of the Compton scattering process leads to asymmetries in the signals of a segmented detector. We have measured the polarization sensitivity of a four-fold segmented large volume germanium detector up to photon energies of approximately 10 MeV for the first time. The detector and its performance are compared to smaller Compton polarimeters which have been analyzed in previous work. A possible application of the described Compton polarimeter will be parity assignments in photon scattering experiments.