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Understanding the neutron background is essential for determining the neutron yield from nuclear reactions. In the analysis presented here, the shadow bars are placed in front of neutron detectors to determine the energy dependent neutron background fractions. The measurement of neutron spectra with and without shadow bars is important to determine the neutron background more accurately. The neutron background, along with its sources and systematic uncertainties, are explored with a focus on the impact of background models and their dependence on neutron energy., 7 pages, 10 figures

Experimental information on fragment emissions is important in understanding the dynamics of nuclear collisions and in the development of transport model simulating heavy-ion collisions. The composition of complex fragments emitted in the heavy-ion collisions can be explained by statistical models, which assume that thermal equilibrium is achieved at collision energies below 100 MeV/u. Our new experimental data together with theoretical analyses for light particles from Sn+Sn collisions at 270 MeV/u, suggest that the hypothesis of thermal equilibrium breaks down for particles emitted with high transfer momentum. To inspect the system's properties in such limit, the scaling features of the yield ratios of particles from two systems, a neutron-rich system of ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ and a nearly symmetric system of ${}^{108}\mathrm{Sn}+{}^{112}\mathrm{Sn}$, are examined in the framework of the statistical multifragmentation model and the antisymmetrized molecular dynamics model. The isoscaling from low energy particles agree with both models. However the observed breakdown of isoscaling for particles with high transverse momentum cannot be explained by the antisymmetrized molecular dynamics model.

NeuLAND is the neutron detector used by the R3B collaboration, which is part of the NUSTAR collaboration at the FAIR facility. NeuLAND is used for the detection of fast neutrons in the range of 200 MeV- 1000 MeV and is composed of plastic scintillators. Neutrons can undergo hadronic scattering with the scintillator material to produce charged particles, which in turn can be detected by their scintillation light. The high granularity of the detector allows for an accurate reconstruction of the primary interaction points of the neutrons. With these interaction points and with the information from the other detectors in the R3B setup, the reaction at the target can be kinematically reconstructed. This reconstruction is the tool that enables the R3B collaboration to study complex reactions. However, particles produced through reactions of the incoming radioactive beam with other R3B detectors may also enter NeuLAND’s active volume and generate a significant background. In this paper, Monte Carlo simulations are utilized to explore possible reduction techniques of this background. In particular, the reduction of the charged-particle component of this background through the use of a VETO wall is explored for the initial setup of the R3B experiment. The list of physics processes considered and their implementation in the simulations are tested against experimental data to ensure that conclusions about the background reduction are meaningful. Extensive simulations show that the use of a VETO wall is, in many situations, not necessary.