Measurements of neutron yields and spatial distributions in U/Pb, Pb and Hg thick targets bombarded by 0.5 and 1.0 GeV protons

Measurements have been carried out on neutron yields and spatial distributi ons in U/Pb, Pb and Hg thick targets and the surrounding paraffin moderator s bombarded by 0.533 and 1.0 GeV protons. CR-39 detectors were deployed on the surfaces of targets and moderators to record the neutrons produced in t he targets. The measurements show that: (1) Neutron yield of Hg target is less than U/Pb and Pb targets on bombardm ent by protons. Neutron yield ratio of U/Pb and Pb to Hg target are 2.01 +/ -0.10 and 1.76 +/-0.33, respectively. This means that Hg target is less pre ferable in order to get more secondary neutrons. (2) Neutron yields along 20 cm thick targets decrease approximately linearl y with the thickness through which the incident protons have penetrated. Th e lower the incident energy, the steeper the decrease of neutron yield. (3) Secondary neutron spectra for different incident energies are close to beach other, while some differences have been observed. (C) 2001 Elsevier S cience Ltd. All rights reserved.