LENDA: A low energy neutron detector array for experiments with radioactive beams in inverse kinematics

The Low Energy Neutron Detector Array (LENDA) is a neutron time-of-flight (TOF) spectrometer developed at the National Superconducting Cyclotron Laboratory (NSCL) for use in inverse kinematics experiments with rare isotope beams. Its design has been motivated by the need to study the spin–isospin response of unstable nuclei using (p,n) charge-exchange reactions at intermediate energies ( > 100 MeV / u ). It can be used, however, for any reaction study that involves emission of low energy neutrons (150 keV to 10 MeV). The array consists of 24 plastic scintillator bars and is capable of registering the recoiling neutron energy and angle with high detection efficiency. The neutron energy is determined by the time-of-flight technique, while the position of interaction is deduced using the timing and energy information from the two photomultipliers of each bar. A simple test setup utilizing radioactive sources has been used to characterize the array. Results of test measurements are compared with simulations. A neutron energy threshold of < 150 keV , an intrinsic time (position) resolution of ∼ 400 ps ( ∼ 6 cm) and an efficiency > 20 % for neutrons below 4 MeV have been obtained.