A new Bonner-sphere set for high energy neutron measurements: Monte Carlo simulation

The usual Bonner sphere set consists of six to eight high density polyethylene spheres with diameters varying from 3 to 12 inches. Either a BF₃ counter, LiI scintillator, or ³He detector is located at the center of each sphere to detect the moderated neutrons. The responses of these spheres for high energy neutrons are very low even for the largest 12 inch sphere. To increase the response for high energy neutrons, high Z material such as Pb, W, TI, or Au can be added to the sphere to utilize the (n,xn) reaction of these materials. Monte Carlo simulations for the Pb-added case with a ³ He detector as an example will be presented. The response at high energy for this case is enhanced by a factor of 5 to 8 depending upon the sphere diameter