  In this paper, we describe the design, construction and performance of an
apparatus installed in the Aberdeen Tunnel laboratory in Hong Kong for studying
spallation neutrons induced by cosmic-ray muons under a vertical rock
overburden of 611 meter water equivalent (m.w.e.). The apparatus comprises of
six horizontal layers of plastic-scintillator hodoscopes for determining the
direction and position of the incident cosmic-ray muons. Sandwiched between the
hodoscope planes is a neutron detector filled with 650 kg of liquid
scintillator doped with about 0.06% of Gadolinium by weight for improving the
efficiency of detecting the spallation neutrons. Performance of the apparatus
is also presented.
