Timing test of the NeuRad neutron detector prototype∗

The NeuRad neutron detector is constructed out of scintillation fibers and is aimed on measuring the neutron heavy fragment angular correlations from exotic neutron decays. The results of the first test of NeuRad prototype timing properties are presented in this report. The EXPERT (EXotic Particle Emission and Radioactivity by Tracking) is a part of the physics program of the Super-FRS Experiment Collaboration [1]. The EXPERT experiments are aimed at studies of the unknown exotic nuclear systems beyond the proton and neutron drip-lines. These experiments will use the first half of the Super-FRS as a radioactive beam separator and its second half as a high-resolution spectrometer. NeuRad detector will provide precise information on angular correlations between nuclear-decay neutrons and the charged decay products measured by the rest of EXPERT setup. An information on angular correlations will be used to determine the decay energy of the precursor, its life time and mode of the decay. The detector is designed in order to provide sufficient detection efficiency and fine position resolution for neutrons at expected energies about 200-800 MeV interacting with the material of fibers, in particular, via elastic scattering. The detector will be constructed of scintillating fibers (≈ 10 units) with 3x3 mm cross section and the length of 1 m each, which will be grouped into bundles. Two multianode PMT’s will be mounted on each side of bundle, each side of fiber will be read out by one pixel. Bundles will be oriented along beam axis meaning that the frontal PMT will be penetrated by neutrons. The detector will be placed at distance of ≈ 30 m from the focal plane FRF1. Such setup will ensure total angular acceptance of the detector up to ±6 mrad which reflects low transfer momentum, corresponding to the decay energy expected at the range of 0.1-100 keV. One of the significant NeuRad characteristics is the time resolution. The first neutron hit has to be determined in order to distinguish between one multi-scattered neutron and the event with multiple neutrons. The longitudinal (z) position, which enhances angular resolution, will be extracted from the time difference between the signals collected on both sides of the detector. In order to obtain required angular resolution, a position resolution about 6 cm is needed. This corresponds to the time-uncertainty of ∼ 0.5 ns. Test measurements of timing characteristics has been performed