Pre-equilibrium reactions on the stable tungsten isotopes at low energy

摘要

Excitation functions were measured for the W-180(n, 2n) W-179m, W-182(n, P) Ta-182, W-182(n, P) Ta-182m2, W-182(n, alpha) Hf-179m2, W-183 (n, P) Ta-183, W-183 (n, alpha) Hf-180m, W-184(n, P) Ta-184, W-184 (n, alpha) Hf-181, W-186(n, P) Ta-186, W-186(n, alpha) Hf-183, W-186(n, n'alpha) Hf-182m, and W-186(n, 2n) W-185 reactions from 13.4 to 14.9 MeV. The data of these reactions that are dominant for neutron-induced activation in tungsten were in most cases either defective or incomplete. The experimental results are compared with the results of calculations including all activation channels for the stable W isotopes up to a neutron incident energy of 20 MeV, using two global- and one local-parameter approaches which take into account direct reaction, pre-equilibrium emission (PE), and compound nucleus contributions. The sensitivity of the calculated cross sections to various model approaches and parameters is derived and discussed also in connection with the deviation from unity of calculated-to-experimental activity ratios from benchmark experiments with natural W irradiated by D-T fusion neutrons. The particular importance of the charged-particle emission in this atomic-mass range for PE model validation is discussed and the need for additional data for incident energies above 15 MeV is demonstrated. (c) 2005 Elsevier B.V. All rights reserved.