G. L. Lin

An apparatus for studying spallation neutrons in the Aberdeen Tunnel laboratory

Abstract 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 611xa0m water equivalent (m.w.e.). The apparatus comprises 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 650xa0kg 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.

Measurement of cosmic-ray muons and muon-induced neutrons in the Aberdeen Tunnel Underground Laboratory

In this study, we have measured the muon flux and production rate of muon-induced neutrons at a depth of 611 m water equivalent. Our apparatus comprises three layers of crossed plastic scintillator hodoscopes for tracking the incident cosmic-ray muons and 760 L of a gadolinium-doped liquid scintillator for producing and detecting neutrons. The vertical muon intensity was measured to be Iμ = (5.7±0.6)×10–6 cm–2 s–1 sr–1. The yield of muon-induced neutrons in the liquid scintillator was determined to be Yn = (1.19 ± 0.08(stat) ± 0.21(syst)) × 10–4 neutrons/(μ•g•cm–2). A fit to the recently measured neutron yields at different depths gave a mean muon energy dependence of 0.76±0.03 for liquid-scintillator targets.