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Scattering of neutrons with energies ranging from 20 to 200 MeV was observed in an organic plastic scintillator array as a test for accuracy of simulation by two GEANT4-based models. The experiment was conducted at the LANSCE WNR facility at Los Alamos National Laboratory using a collimated neutron beam of well-defined energy and trajectory impinging on 16 BC-408 plastic scintillator detectors arranged in a horizontal array 2 detectors tall and 8 deep. Results from neutron scattering observations include hit-multiplicity distributions, beam attenuation depth, crosstalk events, scattering angle, attenuation depth between hits, and dark-scattering of neutrons from carbon nuclei, all as a function of the incident neutron energy. Measurement results are compared with predictions from two GEANT4-based Monte Carlo simulations, and agreement varies considerably over neutron energy, becoming poor at higher energies, pointing to needed improvement in simulation of neutrons in plastic scintillator. [ABSTRACT FROM AUTHOR]

The spin-orbit splitting between neutron 1 p orbitals at 33Si has been deduced using the single-neutron-adding (d , p) reaction in inverse kinematics with a beam of 32Si, a long-lived radioisotope. Reaction products were analyzed by the newly implemented SOLARIS spectrometer at the reaccelerated-beam facility at the National Superconducting Cyclotron Laboratory. The measurements show reasonable agreement with shell-model calculations that incorporate modern cross-shell interactions, but they contradict the prediction of proton density depletion based on relativistic mean-field theory. The evolution of the neutron 1 p -shell orbitals is systematically studied using the present and existing data in the isotonic chains of N = 17 , 19, and 21. In each case, a smooth decrease in the separation of the 1 p 3 / 2 - 1 p 1 / 2 orbitals is seen as the respective p -orbitals approach zero binding, suggesting that the finite nuclear potential strongly influences the evolution of nuclear structure in this region. [ABSTRACT FROM AUTHOR]

An active target detector array, ANASEN, has been developed for nuclear reaction studies with rare isotope beams at low energies. It aims at measurements of the excitation functions for proton and α - particle elastic and inelastic scattering and direct measurements of ( α , p) reactions with exotic nuclei in inverse kinematics. ANASEN is composed of three types of charged particle detectors. The length of the active area is 340 mm and the total covered area is 1300 cm 2 (almost 3 π steradian solid angle coverage) providing high efficiency for experiments with low intensity radioactive beams. A mix of 78 conventional electronics channels (for Proportional Counter and CsI-detectors) and 480 dedicated high-density ASICs electronics channels for the silicon detector are used for readout. [ABSTRACT FROM AUTHOR]

The study of neutron-unbound systems using invariant mass spectroscopy is often performed using low-intensity radioactive ion beams. Low reaction yields can be countered by using thick targets but at the expense of larger uncertainties in the reconstructed invariant mass. We present a new segmented target designed to address this trade-off. It is composed of three ∼ 4 mm thick passive beryllium targets interleaved between four 140 μ m thick position sensitive silicon detectors. In the first experiment to use this new system the half-life of two-neutron unbound 26 O was measured to be T 1 ∕ 2 = 5. 0 − 2. 2 + 1. 7 (stat) ± 1. 7 (syst) ps, which agrees with a previous measurement made by the MoNA Collaboration. [ABSTRACT FROM AUTHOR]