Measurement of the neutron induced fission cross section on transuranic (TRU) elements at the n_TOF facility at CERN

Measurement of the Neutron Induced Fission Cross Section on Transuranic (TRU) Elements at the n_TOF Facility at CERN Cite as: AIP Conference Proceedings 947, 43 (2007); https:// doi.org/10.1063/1.2813848 Published Online: 31 October 2007 P. F. Mastinu, U. Abbondanno, G. Aerts, H. Álvarez, F. Álvarez-Velarde, S. Andriamonje, J. Andrzejewski, P. Assimakopoulos, L. Audouin, G. Badurek, P. Baumann, F. Becvár, E. Berthoumieux, F. Calviño, M. Calviani, D. Cano-Ott, R. Capote, C. Carrapiço, P. Cennini, V. Chepel, E. Chiaveri, N. Colonna, G. Cortes, A. Couture, J. Cox, M. Dahlfors, S. David, I. Dillman, C. Domingo-Pardo, W. Dridi, I. Duran, C. Eleftheriadis, M. Embid-Segura, L. Ferrant, A. Ferrari, R. Ferreira-Marques, K. Fujii, W. Furman, I. Goncalves, E. González-Romero, F. Gramegna, C. Guerrero, F. Gunsing, B. Haas, R. Haight, M. Heil, A. Herrera-Martinez, M. Igashira, E. Jericha, F. Käppeler, Y. Kadi, D. Karadimos, D. Karamanis, M. Kerveno, P. Koehler, E. Kossionides, M. Krticka, C. Lampoudis, H. Leeb, A. Lindote, I. Lopes, M. Lozano, S. Lukic, J. Marganiec, S. Marrone, T. Martínez, C. Massimi, A. Mengoni, P.M. Milazzo, C. Moreau, M. Mosconi, F. Neves, H. Oberhummer, S. O'Brien, J. Pancin, C. Papachristodoulou, C. Papadopoulos, C. Paradela, N. Patronis, A. Pavlik, P. Pavlopoulos, L. Perrot, M. T. Pigni, R. Plag, A. Plompen, A. Plukis, A. Poch, J. Praena, C. Pretel, J. Quesada, T. Rauscher, R. Reifarth, C. Rubbia, G. Rudolf, P. Rullhusen, J. Salgado, C. Santos, L. Sarchiapone, I. Savvidis, C. Stephan, G. Tagliente, J. L. Tain, L. Tassan-Got, L. Tavora, R. Terlizzi, G. Vannini, P. Vaz, A. Ventura, D. Villamarin, M. C. Vincente, V. Vlachoudis, R. Vlastou, F. Voss, S. Walter, M. Wiescher, and K. Wisshak ARTICLES YOU MAY BE INTERESTED IN Study of Neutron-Induced Fission Cross Sections of U, Am, and Cm at n_TOF AIP Conference Proceedings 1265, 477 (2010); https:// doi.org/10.1063/1.3480244 Measurement of 139La(n,γ) Cross Section at n_TOF AIP Conference Proceedings 831, 551 (2006); https:// doi.org/10.1063/1.2201012 Implications of 151Sm(n,γ) Cross Section at n_TOF AIP Conference Proceedings 947, 43 (2007); https://doi.org/10.1063/1.2813848 947, 43 © 2007 American Institute of Physics. AIP Conference Proceedings 831, 502 (2006); https:// doi.org/10.1063/1.2200996 Measurement of the Neutron Induced Fission Cross Section on Transuranic (TRU) Elements at the n_TOF Facility at CERN P. F. Mastinu , U. Abbondanno , G. Aerts , H. Alvarez-^, F. Alvarez-Velarde , S. Andriamonje^, J. Andrzejewski^, P. Assimakopoulos™, L. Audouin', G. Badurek", P. Baumann^, F. Becvar^^, E. Berthoumieux^, F. Calvino , M. Calviani38, D. Cano-Ott^, R. Capote^^'l^, C. Carrapifo^^'^, P. Cenninil^^ V. Chepell"^, E. Chiaveril^^ N. Colonnal^, G Cortes^^, A. Couture^O, J. Cox^O, M. Dahlfors^^, S. David'^, I. Dillman^l, C. Domingo-Pardo22, W. Dridi^, I. Duran^, C. Eleftheriadis^-', M. Embid-Segura^, L. Ferrant'', A. Ferrari^", R. FerreiraMarques^', K. Fujii , W. Furman^^, I. Goncalves^', E. Gonzalez-Romero^, F. Gramegna^^, C. Guerrero^, F. Gunsing^, B. Haas^^, R. Haight^", M. HeiF , A. Herrera-Martinez^", M. Igashira^', E. Jericha", F. Kappeler^ , Y. Kadi^", D. Karadimos", D. Karamanis", M. Kerveno", P. Koehler^", E. Kossionides^", M. Krticka^^, C. Lampoudis^^'^, H. Leeb^, A. Lindote^^, I. Lopes^^, M. Lozano^^ S. Lukic'^, J. Marganiec^, S. Marrone^^, T. Martinez^, C. Massimi^^, A. Mengoni^^'l^, P.M. Milazzo^, C. Moreau^, M. Mosconi^l, F. Neves^^, H. Oberhummer", S. O'Brien^^, J. Pancin^, C. Papachristodoulou", C. Papadopoulos-' , C. Paradela-', N. Patronis", A. Pavlik-'^, P. Pavlopoulos-'-', L. Perrot^, M.T. Pigni^, R. Plag^l, A. Plompen^^ ^ Plukis^, A. Poch^^, J. Praenal2, c. Pretel^^, J. Quesada^^, T. Rauscher^^, R. Reifarth^^, c. Rubbia^^, G Rudolf^, P. Rullhusen34, j. Salgado^^, C. Santos^^, L. Sarchiapone^^, I. Savvidis^-', C. Stephan', G. Tagliente^^, J.L. Tain^^, L. Tassan-Got', L. Tavora^^, R. Terlizzi^", G. Vannini-^^, P. Vaz^^, A. Ventura-'', D. Villamarin^, M.C. Vincente^, V. Vlachoudis^'^, R. Vlastou^^, F. Voss^l, S. Walter^l, M. Wiescher^O, K. Wisshak^l Istituto Nazionale di Fisica Nucleare, Trieste, Italy ^CEA/Saclay - DSM/DAPNIA, Gif-sur-Yvette, France Universidade de Santiago de Compostela, Spain Centra de Investigaciones Energeticas Medioambientales y Tecnologicas, Madrid, Spain University of Lodz, Lodz, Poland CP947, VII Latin American Symposium on Nuclear Physics and Applications edited by R. Alarcon, P. L. Cole, C. Djalali, and F. Umeres © 2007 American Institute of Physics 978-0-7354-0461-8/07/$23.00 43 University ofloannina, Greece Centre National de la Recherche Scientiflque/IN2Pi - IPN, Orsay, France o Atominstitut der Osterreichischen Universitdten,Technische Universitdt Wien, Austria Centre National de la Recherche Scientiflque/IN2Pi - IReS, Strasbourg, France Charles University, Prague, Czech Republic Universidad Politecnica de Madrid, Spain Istituto Nazionale di Fisica Nucleare(INFN), Laboratori Nazionali di Legnaro, Italy International Atomic Energy Agency (IAEA), Nuclear Data Section, Vienna, Austria Universidad de Sevilla, Spain Instituto Tecnologico e Nuclear(ITN), Lisbon, Portugal CERN, Geneva, Switzerland 17 LIP - Coimbra & Departamento de Fisica da Universidade de Coimbra, Portugal Istituto Nazionale di Fisica Nucleare, Bari, Italy Universitat Politecnica de Catalunya, Barcelona, Spain 20 University of Notre Dame, Notre Dame, USA 21 Forschungszentrum Karlsruhe GmbH (FZK), Institut fiir Kernphysik, Germany 22 Instituto de Fisica Corpuscular, CSIC-Universidad de Valencia, Spain Aristotle University ofThessaloniki, Greece Joint Institute for Nuclear Research, Frank Laboratory of Neutron Physics, Dubna, Russia Centre National de la Recherche Scientifique/IN2Pi - CENBG, Bordeaux, France Los Alamos National Laboratory, New Mexico, USA 27 Tokyo Institute of Technology, Tokyo, Japan Oak Ridge National Laboratory, Physics Division, Oak Ridge, USA ^^NCSR, Athens, Greece Dipartimento di Fisica, Universitd di Bologna, and Sezione INFN di Bologna, Italy National Technical University of Athens, Greece Institut fiir Isotopenforschung und Kernphysik, Universitdt Wien, Austria 33 Pole Universitaire Leonard de Vinci, Paris La Defense, France ^'*CEC-JRC-IRMM, Geel, Belgium Department of Physics and Astronomy - University of Basel, Basel, Switzerland Universitd degli Studi Pavia, Pavia, Italy ^^ENEA, Bologna, Italy Dipartimento di Fisica, Universitd di Padova, and INFN Laboratori Nazionali di Legnaro, Italy Abstract. During the 2004 campaign, the n_TOF collaboration measured neutron fission cross sections for ^''U, ^'"'^''^Am, ^''^Cm, as well as the fission standards ^'^-^'^u, using a sealed Fission Ionization Chamber (FIC). The setup included a total of 16 targets and 18 electrodes mounted together in a 50-cm length chamber, allowing the measurements of all isotopes at the same time, thus in the same experimental conditions. A brief description of the facility and of the detector setup will be presented followed by the preliminary results of the analysis of ^'^U, ^''U, and ^''^Cm from thermal energies up to some tenths of MeV. PACS: 01.30.Cc + 14.20.Dh +28.20.-V +25.85.-W 44 INTRODUCTION Recently, potential climate problems related to the greenhouse-gas effect have triggered a renewed interest in nuclear energy production, mainly because nuclear power is the only energy source that combines the attributes of large-scale electricity production, and zero greenhouse gas emissions during the production process. In addition, many countries consider nuclear energy a strategic component of a diverse energy portfolio to meet fast-growing electricity demand and decrease dependence on foreign governments/companies. However, before becoming truly competitive, nuclear energy will have to solve problems related with safe operation, and waste production during its full life cycle. Although much progress has been made towards safer operation during the last few decades, radiotoxicity of the produced waste remains an important issue. The most significant contributions come from plutonium and minor actinides such as ^^^Np, 9zll 9zl^ 9zlS • Am, and Cm, whose half lives span from himdreds to tens of thousand of years. A possible solution to the waste problem could derive from incineration or transmutation in subcritical reactors, like Accelerator Driven Systems (ADS), or in critical systems, like future Gen-IV fast nuclear reactors. The incineration process rehes on neutron induced fission of Trans Uranic Element (TRU's,) and neutron capture on fission fragments. Another possible way to reduce production of minor actinides is to use fissile ^^^U in the thorium fuel cycle instead of the currently adopted ^^^U; the lower mass of the fertile ^^^Th leads to a production of a smaller amount of actinides. Of crucial importance for a feasibility study as well as to find the best parameters for the safe operation of such reactors, is precise knowledge of the neutron induced cross sections on a large variety of isotopes over a large energy range. Nuclides of interest span the range from the heavier minor actinides to lighter fission fragments and structural materials. To provide these neutron induced cross section data, a neutron Time of Fhght facility (n_TOF) has been built at CERN, the European Organization for Nuclear Research. THE n_TOr FACILITY The n_TOF facility is driven by a 20 GeV/C proton beam from the CERN proton synchrotron (PS). A white neutron source, spanning the energy range from thermal to 300 MeV is produced via spallation reactions when the PS proton beam strikes a 80x80x60 cm^ lead block. A 6-cm thick layer of light water surroimding the lead block acts both as a coolant as well as a moderator. The main characteristics of the facility are a wide energy range, low and well characterized backgrounds, excellent energy resolution (the flight path is 187.5 m) and very high instantaneous neutron flux (3 10^ n/cm^/pulse with fission collimator); a crucial feature when making measurements on radioactive samples. The PS proton beam has a width of 6 ns, and can be operated either in dedicated (7 lO'^ protons/pulse) or parasitic mode (4 lO'^ proton/pulse) with 45 a duty cycle of 0.8 Hz. Different detectors can be used in the experimental hall to measure the neutron flux [1], and capture and fission cross sections [2]. THE EXPERIMENTAL SET UP Fission events are identified by detecting one fission fragment (FF), in a Fast Ionization Chamber (FIC). Inside the FIC, a stack of several parallel-plates are separated by 5mm and surroimded by a mixture of argon and tetrafluoromethane gas (90% Ar+10% CF4) at 720 mbar pressure. There are 16 targets and 18 electrodes in total, spanning 50 cm in length, thus allowing a simultaneous measurement of the fission cross sections of several isotopes. Each target consisted of a stainless steel holder with a 100-^m thick aluminum foil backing, and very a thin layer of target material (4-450 |ig/cm^) deposited on both sides over a circular area 80 mm diameter [2]. EVENT SELECTION AND DATA ANALYSIS An amplitude threshold was used to discriminate FF signals from backgroimd (mostly due to alpha decay of the radioactive samples) in the FIC (see figure I). Amplitude distribution for various isotopes 100 120 140 160 180 200 Amplitude (ch.) FIGURE 1: Amplitude distribution of FIC signals. The second peak for ^''^Cm was due to the a decay of the nucleus, which was less pronounced for the Uranium isotopes because of their lower activity. The last peak is due to saturation. The shape of the FF distribution is a convolution of the one fragment detection and the poor energy resolution of the FIC detector. A simple energy threshold worked well for low activity samples such as ^^^U and U. However, for Cm a higher threshold was needed, which cut out some low energy FF events; thus, a subsequent normalization to a known cross section was needed in this case. The neutron flux . 235T The neutron flux was derived from our U measurement using the latest ENDF/BVII.0 evaluation Because of the unknown efficiency of the FIC detector, the convolution of the neutron flux and the efficiency is reported in figure 2, although the efficiency is expected to be close to 100% for the applied threshold. As expected, the 46 flux shape is very similar to that measured with the capture setup, having peaks near thermal energy and 1 MeV (the latter due to evaporation from spallation products) and an isolethargic flux shape in between. n_TOF neutron flux, fission setup, from U FIGURE 2:n_TOF neutron flux measured with fission collimator. The flux was calculated using the standard ^'^U cross section taken from ENDF/B-VII.O. RESULTS . 233T The resultant U fission cross section, using a threshold cutoff at channel 40 (see Fig. 1) is shown in Fig. 3. The same threshold was used in calculating the neutron flux. ^^U(n,f) cross section FIGURE 3: ^''U(n,f) cross sections from n_TOF data (dots) and ENDF/B-VII.O (solid curve). In general, there is good agreement between the two except that some dips in our data are more pronounced than in the evaluation, suggesting that our background may be lower than that in the measurements on which the evaluation is based. The ^''^Cm sample had an activity of 0.4 GBq, with alpha and spontaneous fission decay, so a simple higher energy threshold could not reject all the background. The main alpha backgroimd rejection was obtained using a threshold at channel 80. Further alpha and spontaneous fission backgroimd subtraction was accomplished using runs without neutron beam and applying the same energy threshold. Our data were normalized to previous results at thermal energy using an average weighted value of all available data [3-5]. The contribution due to the 6.6% of ^"'"'Cu in the sample was subtracted. Our data are compared to the ENDF/B-VII.O evaluation in Fig. 4. 47 FIGURE 4: ^*^Cm{n,i) cross sections from riTOF (dots) and ENDF/B-VII.O (solid curve) from 0.035 eV to 1 MeV. In the inset, n_TOF data (dots) are compared to those from White et al. [6] (solid curve) from 20 to 60 eV. There is a significant difference (up to 10%) between our data and ENDF/B VI in the energy region from thermal to 20 eV. There is better agreement at higher energies, although the peak-to-valley ratio differs by about 20% for some resonances. As shown in the upper panel of figure 4, our data are in good agreement with those of White et al [6]. CONCLUSIONS We have reported preliminary neutron induced fission cross section OTT 9zlS measurements for U and Cm from thermal energy to 1 MeV. Our results are, in general, in good agreement with the latest ENDF/B-VII.O evaluation. These results demonstrate the capability to perform high precision fission cross section measurements on highly radioactive samples at the n_TOF facility. Also, the neutron flux with the fission collimator at n_TOF was determined using the well known ^^^U(n,y) cross section. Detailed imcertainty estimation and resonance fitting using the R-matrix code SAMMY are in progress. REFERENCES 1. S. Marrone et al. Nucl. Instr. and Methods. A, 517 ( 2004) 389. 2. U. Abbondanno et al, n_TOFPerformance Report, CERN/INTC-O-011, INTC-(2002-037). 3. C. Browne et al, Nucl. Sci. Eng. 65 (1978) 166. 4. V. D. Gavrilov et al, Atomnaya Energiya 41 (1975) 185. 5. R. W. Benjamin et al, Nucl. Sci. Eng. 47 (1972) 203. 6. R. M. White and J. C. Browne, Nuclear Cross Sections for Technology, J.L. Fowler, C.H. Johnson, CD. Bowman eds. (U.S. Department of Commerce, Washington 1980), NBS Special Publication 594, p.496, and R. M. White et al, Nucl. Data for Science and Technology, K.H. Bockhoff ed. (Reidel, Dordrecht, 1983), p.218. 48