The neutron yield from thick target of Pb irradiated with 250 MeV protons has been studied experimentally.The Pb target was surrounded by a water bath, where this size effectively contained most of the neutrons emittedfrom the target. The moderated neutrons were measured by the activity induced in an array of Au activation foils(with or without Cd cover). The axial coordinates of the foils without Cd cover were Z = -15, -10, -5, 0, 5, 10, 15,20 cm along the target axial, and the radial coordinates of the foils were R = 7.5, 12.5, 17.5, 22.5 and 27.5 cm abovethe target axial. The Au-foil activities were determined by measuring the peak intensities of the 412 keV line from198Au[1], and the results are shown in Fig. 1.
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