PHYSICAL REVIEW C 71, 044617 (2005) Reaction mechanisms of fast neutrons on stable Mo isotopes below 21 MeV P. Reimer, 1,2 V. Avrigeanu, 3 S. V. Chuvaev, 4 A. A. Filatenkov, 4 T. Glodariu, 3 A. Koning, 5 A. J. M. Plompen, 1,∗ S. M. Qaim, 2 D. L. Smith, 6 and H. Weigmann 1 1 European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg, B-2440 Geel, Belgium 2 Institut f ¨ ur Nuklearchemie, Forschungszentrum J¨ ulich GmbH, D-52425 J¨ ulich, Germany 3 “Horia Hulubei” National Institute for Physics and Nuclear Engineering, P.O. Box MG-6, 76900 Bucharest, Romania 4 V. G. Khlopin Radium Institute, 2nd Murinski Avenue 28, St. Petersburg 194021, Russia 5 Nuclear Research and Consultancy Group, P.O. Box 25, NL-1755 ZG Petten, The Netherlands 6 Nuclear Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439 (Received 31 August 2004; published 29 April 2005) A large number of new measurements with the activation technique were performed for (n,2n) and neutron-induced Z = 1,2 reaction cross sections on the stable molybdenum isotopes in the energy range from 13.5 to 21 MeV. First results were obtained for the 92 Mo(n,2n) 91 Mo m , 92 Mo(n,α) 89 Zr m , 94 Mo(n,2n) 93 Mo m , 95 Mo(n,p) 95 Nb m , 96 Mo(n,p) 96 Nb, 96 Mo(n,x ) 95 Nb m , 97 Mo(n,p) 97 Nb, 97 Mo(n,p) 97 Nb m , 97 Mo(n,x ) 96 Nb, 98 Mo(n,p) 98 Nb m , 98 Mo(n,x ) 97 Nb, 98 Mo(n,x ) 97 Nb m , and 100 Mo(n,α) 97 Zr reactions, above 16 MeV. A significant number of high-accuracy 14 MeV measurements were performed which are in good agreement with the measurements above 16 MeV for reactions studied in both energy ranges. The rather complete database for the molybdenum isotopes was analyzed with two different sets of consistent model calculations: a local and a global approach. The global approach (a blind calculation with the TALYS code) provides a good overall description of the dominant reaction channels, although the (n,α) reactions for the heavy isotopes are overpredicted. The local approach (an adjusted calculation with the STAPRE-H code) describes the shapes and magnitudes of the excitation functions well from the reaction thresholds up to 21 MeV using a consistent parameter set, which was optimized based on all experimental information for the nuclei at hand and their immediate neighbors. The agreement between experimental and calculated data is, in general, good both at the maxima and at the tails of the excitation functions, and both for total activation cross sections of a particular channel and for cross sections leading to isomers, showing the viability of the level densities, the optical models, and the γ widths. Comparison of the two model calculations with the data indicates the relevance of an appropriate treatment for preequilibrium (PE) α-particle emission for the description of the data above 14 MeV. Comparison between the model calculations shows largely different PE deuteron emission contributions to the total (Z = 1, A = 1) cross sections with an additional marked difference in energy dependence. This suggests that emission spectra around 20 MeV are required to establish the magnitude of the PE deuteron emission contribution to this process. New γ -ray strength functions were established by verification against average (n,γ ) data and were demonstrated to give good agreement with the measured isomer production cross sections. DOI: 10.1103/PhysRevC.71.044617 PACS number(s): 24.10.−i, 24.60.Dr, 25.40.−h, 28.20.−v I. INTRODUCTION Direct, preequilibrium (PE) and statistical processes should be considered in order to account for reaction channels that are open in fast-neutron interactions in the energy range up to 20 MeV. To assess the impact of different model assumptions and determine the optimum parameters that are needed to describe these processes comprehensively, measurements that address the systematics of the dominant reaction channels are essential. Molybdenum is an excellent structural metal at elevated temperatures. As a consequence, it has a wide potential for use in neutronic applications such as an accelerator-driven system or a controlled nuclear fusion device. However, despite the large amount of data measured in the case of the 92 Mo isotope, there are still many discrepancies even between recent measurements. Three evaluations performed rather recently ∗ Corresponding author. Email address: arjan.plompen@cec.eu.int. show differences of up to ∼50% [1,2] and ∼65% [2,3] for the (n,p) and (n,α) reactions, respectively. The present work concerns additional systematic measure- ments for neutron-induced reactions on Mo target nuclei from 13 to 21 MeV. These measurements are part of a larger measurement campaign to study the systematics of (n,2n) and Z = 1,2 reaction cross sections, from 14 to 21 MeV [4–7], where relatively few experimental data exist. The new and existing measured data for the Mo isotopes provide a good basis for the study of the systematics of the dominant reaction channels. Here, two sets of model calculations are compared with the measured data and with each other. For the first, parameters were determined previ- ously by looking for a best overall description of the available data for the entire range from aluminum to bismuth (global approach). For the second, parameter choices were optimized in the present work for the nuclei of immediate relevance of the reactions studied, together with their immediate neighbors (local approach), respecting known Z and A dependences and the available experimental information. 0556-2813/2005/71(4)/044617(20)/$23.00 044617-1 ©2005 The American Physical Society