Spallation yields of neutrons produced in thick lead/bismuth targets by protons at incident energies of 420 and 590 MeV

Spallation-neutron yields for protons at E-p = 420 and 590 MeV incident on thick Pb/Bi targets have been measured via activation analysis of An and Mn foils at the PSI proton irradiation facility. The data were obtained with the water-bath method, in a novel variant that incorporates a detailed MCNPX simulation in the analysis procedure. They include slow-neutron fluence distributions at E-p = 300, 420 and 590 MeV, Cd-ratio distributions at E-p = 300 MeV and total n/p values of 6.0 +/- 0.3 and 9.6 +/- 0.4 at 420 and 590 MeV, respectively. The latter are in line with neutron-yield systematics for protons on thick Pb-targets, which are found to vary with remarkable regularity over a broad range of incident energies. The results of the present work, along with those obtained recently by various groups on thin and thick-target neutron spectra, neutron-multiplicities and the radio-nuclide inventory produced, constitute a database pertinent to the design and optimization of new, high-intensity spallation-neutron sources at these proton energies. (C) 2003 Elsevier B.V. All rights reserved.