Abstract
A series of photon scattering experiments has been performed on the double-beta decay partners 76 Ge and 76 Se, in order to investigate their dipole response up to the neutron separation threshold. Gamma-ray beams from bremsstrahlung at the S-DALINAC and from Compton-backscattering at HIGS have been used to measure absolute cross sections and parities of dipole excited states, respectively. The HIGS data allows for indirect measurement of averaged branching ratios, which leads to significant corrections in the observed excitation cross sections. Results are compared to statistical calculations, to test photon strength functions and the Axel-Brink hypothesis.
Highlights
The focus will be on the present techniques to derive E1 strength distributions from a combination of nuclear resonance fluorescence (NRF) experiments using continuous bremsstrahlung beams in combination with nearly monoenergetic, fully polarized photon beams as available at the High Intensity Gamma-ray Source (HIGS) facility at TUNL, on the campus of Duke University
Some enhancement may exist around 7 MeV in excitation energy, but a conclusion on enhanced E1 strength at low energies depends strongly on the fit function and extrapolation used for the giant dipole resonance (GDR)
Statistical calculations have been performed and show good agreement with data when assuming a hybrid of KMF and SLO E1 photon strength functions (PSFs)
Summary
The focus will be on the present techniques to derive E1 strength distributions from a combination of nuclear resonance fluorescence (NRF) experiments using continuous bremsstrahlung beams in combination with nearly monoenergetic, fully polarized photon beams as available at the High Intensity Gamma-ray Source (HIGS) facility at TUNL, on the campus of Duke University. Results from a series of experiments on the nuclei 76Se and 76Ge, performed at the S-DALINAC facility at TU Darmstadt and at HIGS will be discussed. Data have been obtained for low-lying dipole excited states in this candidate pair for neutrino less double-beta (0ν2β) decay, which is potentially important in the discussion of γ-ray background in large-scale experiments searching for this rare (if existing) decay mode. We will focus on the PDR region, and compare the new data to calculations within a statistical approach.
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