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.
The one-neutron knockout from ^{52}Ca in inverse kinematics onto a proton target was performed at ∼230 MeV/nucleon combined with prompt γ spectroscopy. Exclusive quasifree scattering cross sections ...to bound states in ^{51}Ca and the momentum distributions corresponding to the removal of 1f_{7/2} and 2p_{3/2} neutrons were measured. The cross sections, interpreted within the distorted-wave impulse approximation reaction framework, are consistent with a shell closure at the neutron number N=32, found as strong as at N=28 and N=34 in Ca isotopes from the same observables. The analysis of the momentum distributions leads to a difference of the root-mean-square radii of the neutron 1f_{7/2} and 2p_{3/2} orbitals of 0.61(23) fm, in agreement with the modified-shell-model prediction of 0.7 fm suggesting that the large root-mean-square radius of the 2p_{3/2} orbital in neutron-rich Ca isotopes is responsible for the unexpected linear increase of the charge radius with the neutron number.
Directed and elliptic flows of neutrons and light charged particles were measured for the reaction 197Au+197Au at 400 MeV/nucleon incident energy within the ASY-EOS experimental campaign at the GSI ...laboratory. The detection system consisted of the Large Area Neutron Detector LAND, combined with parts of the CHIMERA multidetector, of the ALADIN Time-of-flight Wall, and of the Washington-University Microball detector. The latter three arrays were used for the event characterization and reaction-plane reconstruction. In addition, an array of triple telescopes, KRATTA, was used for complementary measurements of the isotopic composition and flows of light charged particles. From the comparison of the elliptic flow ratio of neutrons with respect to charged particles with UrQMD predictions, a value \gamma = 0.72 \pm 0.19 is obtained for the power-law coefficient describing the density dependence of the potential part in the parametrization of the symmetry energy. It represents a new and more stringent constraint for the regime of supra-saturation density and confirms, with a considerably smaller uncertainty, the moderately soft to linear density dependence deduced from the earlier FOPI-LAND data. The densities probed are shown to reach beyond twice saturation.
In order to study the role of pions and clustering phenomena in nuclei, two experiments have been performed using the AGOR accelerator facility. In collisions of two nuclei a pion and a fused nucleus ...were produced. The examined reactions were 4He(3He,pi0)7Be and 6Li(4He,pi0)10B at beam energies about 10 MeV above the coherent pion production threshold (256 MeV and 236.4 MeV, respectively). Since the available energy is well below the pion production threshold in an elementary nucleon-nucleon process, a highly coherent mechanism is needed. We identified the reaction by measuring the fused system in the magnetic spectrometer and the produced neutral pions in the Plastic Ball detection system with large acceptance. Our experimental setup provided the exclusive cross sections by identifying all products in overdetermined kinematics. Here we present the preliminary results of the ongoing analysis for the second reaction. About 700 events fulfilling the kinematical conditions for an outgoing 10B and a pi0 decaying with large opening angle have been selected. Angular distribution of neutral pions will be discussed.
The elliptic-flow ratio of neutrons with respect to protons in reactions of neutron rich heavy-ions systems at intermediate energies has been proposed as an observable sensitive to the strength of ...the symmetry term in the nuclear Equation Of State (EOS) at supra-saturation densities. The recent results obtained from the existing FOPI/LAND data for 197Au+197Au collisions at 400 MeV/nucleon in comparison with the UrQMD model allowed a first estimate of the symmetry term of the EOS but suffer from a considerable statistical uncertainty. In order to obtain an improved data set for Au+Au collisions and to extend the study to other systems, a new experiment was carried out at the GSI laboratory by the ASY-EOS collaboration in May 2011.
SiΛvio: A trigger for Λ-hyperons Münzer, Robert; Berger, Martin; Fabbietti, Laura ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2014, Letnik:
745
Journal Article
Recenzirano
Odprti dostop
As online trigger for events containing Λ hyperons in p+p collisions at 3.1GeV a silicon-based device has been designed and built. This system has been integrated close to the target region within ...the FOPI spectrometer at GSI and was also employed as a tracking device to improve the vertex reconstruction of secondary decays. The design of the detector components, read-out, the trigger capability as well as the tracking performance are presented. An enrichment factor of about 14 was achieved for events containing a Λ-hyperon candidate.
PDF
