High resolution γγ-spectroscopy at the Big-Bite Spectrometer

An array of HPGe detectors has been set up at the Big-Bite Spectrometer at AGOR cyclotron of KVI Groningen to allow coincident measurements of the γγ-decay of nuclei excited in inelastic hadron scattering at 100–400 MeV incident energies. Compared to previous experiments, where NaI detectors have been used, the energy resolution of the γγ-detection could be improved by more than one order of magnitude to about ΔEγ/Eγ=0.2%ΔEγ/Eγ=0.2% in the energy region of interest. The coincident measurement of the γγ-decay in inelastic hadron scattering experiments is very useful for the separation of nearby excitations, the assignment of multipolarities, the determination of branching ratios and to study the isospin character of bound excitations. The experimental setup and the results of a first (α,α′γ)(α,α′γ) test experiment at Eα=136MeV on 58Ni are presented.