Low-energy excitations and $$\gamma $$-decay branchings in $$^{124}$$Sn via (p,p’$$\gamma $$) at $$E_p={15}\,\,\hbox {MeV}$$

The dipole response of the proton-magic nucleus $${}^{124}\hbox {Sn}$$ 124 Sn was previously investigated with electromagnetic and hadronic probes. Different responses were observed revealing the so-called isospin splitting of the Pygmy Dipole Resonance (PDR). Here we present the results of a new study of $${}^{124}\hbox {Sn}$$ 124 Sn using inelastic proton scattering at low energies to test an additional probe possibly exciting states of the PDR. The response to the new probe as well as the $$\gamma $$ γ -decay behavior of excited states were studied. The $${}^{124}\hbox {Sn}$$ 124 Sn (p,p’$$\gamma $$ γ ) experiment was performed at $$E_p = {15}\,\,\hbox {MeV}$$ E p = 15 MeV using the combined spectroscopy setup SONIC@HORUS at the Tandem accelerator of the University of Cologne. Proton-$$\gamma $$ γ coincidences were recorded, enabling a state-to-state analysis due to the excellent energy resolution for both particles and $$\gamma $$ γ rays. $$ J=1 $$ J = 1 states in the PDR region were populated in the present inelastic proton scattering experiment. Many $$\gamma $$ γ -decay branching ratios could be determined.

Lifetime Measurements at NCSR “Demokritos”

Proof-of-principle inelastic proton scattering measurements have been performed at NCSR “Demokritos”. Excited states in 64Zn and 92Mo were populated using the (p,p'γ) reaction with E(p) = 7 MeV. The reaction γ rays were detected using four HPGe detectors at eight separate angles, with respect to the beam-axis. From Doppler-shift attenuation of the ∞ rays, lifetimes for eight excited states in 64Zn and for the Iπ = 2^+_2 and 2^+_3 states in 92Mo were deduced. The lifetimes measured in 92Mo are in good agreement with adopted values whereas the lifetimes measured in 64Zn are typically longer than the literature values. Development of the experimental set-up and potential novel physics cases where this reaction could be used are briefly discussed.

Discovery of collective states in 208Pb by complete spectroscopy

Most neutron and proton bound states in 208Pb are described in the shell model as one-particle onehole configurations. Besides precise data obtained with the Q3D magnetic spectrograph of the MLL (Garching, Germany) an important reaction is the inelastic proton scattering via isobaric analog resonances in 209Bi. It yields amplitudes of neutron one-particle one-hole configurations with relative signs in each stateof 208Pb. The orthogonality, normality, and sum rule relations allow to investigate the completeness of the transformation matrices of one-particle one-hole configurations describing the states in 208Pb with spins from 0− to 14− and 0+ to 12+. By this method amplitudes of unobservable one-particle one-hole configurations can be determined.The comparison of spin, parity, and dominant particle-hole components thus derived in up to 30 states of a certain spin to shell model calculations allows to identify states described as collective excitations of the entire nucleus.