highly efficient plastic-scintillator array constructed for decay and transfer reaction experimental setups that require neutron detection. The versatile and modular design allows for customizable experimental setups including beta-delayed neutron spectroscopy and (d,n) transfer reactions in normal and inverse kinematics. The neutron energy and prompt-photon discrimination is determined through the time of flight technique. Fully digital data acquisition electronics and integrated triggering logic enables some VANDLE modules to achieve an intrinsic efficiency over 70% for 300-keV neutrons, measured through two different methods. A custom Geant4 simulation models aspects of the detector array and the experimental setups to determine efficiency and detector response. A low detection threshold, due to the trigger logic and digitizing data acquisition, allowed us to measure the light-yield response curve from elastically-scattered carbon nuclei inside the scintillating plastic from incident neutrons with kinetic energies below 2 MeV.
The γ-strength functions and level densities in the quasi-continuum of 147,149 Sm isotopes have been extracted from particle-γ coincidences using the Oslo method. The nuclei of interest were populated via (p,d) reactions on pure 148,150 Sm targets and the reaction products were recorded by the Hyperion array. An upbend in the low-energy region of the γSF has been observed. The systematic analysis of the γSF for a range of Sm isotopes highlights the interplay between scissors mode and the upbend. Shell-model calculations show reasonable agreement with the experimental γSFs and confirm the correspondence between the upbend and scissors mode.
Electromagnetic observables are able to give insight into collective and emergent features in nuclei, including nuclear clustering. These observables also provide strong constraints for ab initio theory, but comparison of these observables between theory and experiment can be difficult due to the lack of convergence for relevant calculated values, such as E2 transition strengths. By comparing the ratios of E2 transition strengths for mirror transitions, we find that a wide range of ab initio calculations give robust and consistent predictions for this ratio. In order to experimentally test the validity of these ab initio predictions, we performed a Coulomb excitation experiment to measure the B(E2; 3/2 − → 1/2 − ) transition strength in 7 Be for the first time. A B(E2; 3/2 − → 1/2 − ) value of 26( 6) stat ( 3) syst e 2 fm 4 was deduced from the measured Coulomb excitation cross section. This result is used with the experimentally known 7 Li B(E2; 3/2 − → 1/2 − ) value to provide an experimental ratio to compare with the ab initio predictions. Our experimental value is consistent with the theoretical ratios within 1σ uncertainty, giving experimental support for the value of these ratios. Further work in both theory and experiment can give insight into the robustness of these ratios and their physical meaning.
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