Neutron Induced Fission Cross-Sections of 240 Pu and 243 Am in the Energy Range 1 - 200 MeV A.B. LAPTEV 1* , A.Yu. DONETS 2 , A.V. FOMICHEV 2 , A.A. FOMICHEV 3 , R.C. HAIGHT 4 , O.A. SHCHERBAKOV 1,5 , S.M. SOLOVIEV 2 , Yu.V. TUBOLTSEV 6 , A.S. VOROBYEV 1 1 Petersburg Nuclear Physics Institute, Gatchina, Leningrad district, 188300, Russia 2 V.G. Khlopin Radium Institute, St. Petersburg, 194021, Russia 3 Saint Petersburg State University, St. Petersburg, 198504, Russia 4 Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, USA 5 Japan Nuclear Cycle Development Institute, Tokai-mura, Ibaraki 319-1194, Japan 6 A.F. Ioffe Physico-Technical Institute, St. Petersburg, 194021, Russia During the last several years, the measurements of neutron-induced fission cross-sections of actinides and stable isotopes have been performed at the GNEIS facility. At present, the new series of experiments for measurements of fission cross-section ratios relative to 235 U have been began for 240 Pu, 243 Am and nat W in a wide energy range of incident neutrons from 1 MeV to 200 MeV. The measurements were performed using the multiplate ionization chamber and time-of-flight technique. The first results of this measurement in case of 240 Pu and 243 Am are presented in comparison with the other data. 1. Introduction There is a long-standing need for information about fission reactions of heavy nuclei induced by particles at intermediate energies. But regular experimental studies of fission and the evaluations of nuclear data in this energy region have begun comparatively recently mainly due to the new technological applications of fission reaction, as well as due to the increased capabilities of the modern neutron sources and experimental techniques. Among new applications, the most important for fission at intermediate energies are accelerator-driven systems such as those proposed for transmuting nuclear waste, especially actinides, and for energy generation. The solution of the tasks mentioned above leads to increased requirements on accuracy and reliability of relevant nuclear data, which are not fulfilled as yet 1) . Fission cross sections in the energy range 20 to several hundred MeV have been measured with spallation neutron sources at the WNR/LANSCE facility at Los Alamos and at the GNEIS facility 2) . At GNEIS, the measurements have been continued in the framework of the ISTC Project 609-97 using the 1-GeV proton synchrotron facility of PNPI at Gatchina. During 1997-99 the fission cross-sections of 233 U, 238 U, 232 Th, 237 Np, 239 Pu, nat Pb and 209 Bi have been measured relative to 235 U in the energy range 1-200 MeV 3,4) . It should be also noted that the measurements in separate energy points above 20 MeV were continued at some other accelerators, e.g. at the cyclotrons of Uppsala University (Sweden) 5) and Catholic University of Louvain (Belgium) 6) . In addition, the n_TOF collaboration team has announced its intention to begin such measurement at the new developed neutron pulsed source at CERN 7) . The purpose of the present investigation is to measure neutron-induced fission cross-sections of 240 Pu, 243 Am and nat W relative to 235 U in the energy range from 1 to 200 MeV at the neutron spectrometer GNEIS. Measurements are performed in the framework of new ISTC Project 1971. The first new results of this measurement for 240 Pu and 243 Am are presented in this article in comparison with the other data. The very first results of this measurement in the case of 240 Pu have been published earlier 8) . * Corresponding author, E-mail: laptev@pnpi.spb.ru