Excitation and $ \gamma$-decay coincidence measurements at the GRAF beamline for studies of pygmy and giant dipole resonances

Abstract

Physical studies of electric dipole excitations in atomic nuclei e.g. the structure of pygmy dipole resonances and isovector giant dipole resonances are attracting much attention recently. In this article, we describe a technical development in the coincidence measurement of the excitation processes with the Grand Raiden high-resolution magnetic spectrometer and the $ \gamma$-decay processes by the CAGRA and SC$ \gamma$ LLA efficient $ \gamma$-detector arrays at the Research Center for Nuclear Physics at Osaka University. Specifically, we describe how we developed a new beamline (GRAF), for $ \gamma$ detection at the target position by placing the spectrometer at an angle of $ 4.5-19.0^\circ$ and by transporting the primary beam to a well-shielded beam dump. Experimental conditions and representative data are shown for each of the two $ \gamma$-detector arrays.