Measurements at n_TOF of the neutron capture cross section of minor actinides relevant to the nuclear waste transmutation

Measurements at n_TOF of the Neutron Capture Cross Section of Minor Actinides Relevant to the Nuclear Waste Transmutation Cite as: AIP Conference Proceedings 769, 1442 (2005); https://doi.org/10.1063/1.1945275 Published Online: 13 June 2005 D. Cano-Ott, U. Abbondanno, G. Aerts, H. Álvarez, F. Àlvarez-Velarde, S. Andriamonje, J. Andrzejewski, P. Assimakopoulos, L. Audouin, G. Badurek, P. Baumann, F. Bečvář, J. Benlliure, E. Berthoumieux, F. Calviño, R. Capote, A. Carillo de Albornoz, P. Cennini, V. Chepel, E. Chiaveri, N. Colonna, G. Cortes, D. Cortina, A. Couture, J. Cox, S. David, R. Dolfini, C. Domingo-Pardo, W. Dridi, I. Duran, M. Embid-Segura, L. Ferrant, A. Ferrari, L. Fitzpatrick, R. Ferreira-Marques, H. Frais-Koelbl, K. Fujii, W. Furman, I. Goncalves, R. Gallino, E. Gonzalez-Romero, A. Goverdovski, F. Gramegna, E. Griesmayer, C. Guerrero, F. Gunsing, B. Haas, R. Haight, M. Heil, A. Herrera-Martinez, M. Igashira, S. Isaev, E. Jericha, Y. Kadi, F. Käppeler, D. Karamanis, D. Karadimos, M. Kerveno, V. Ketlerov, P. Koehler, V. Konovalov, E. Kossionides, M. Krtička, C. Lamboudis, H. Leeb, A. Lindote, I. Lopes, M. Lozano, S. Lukic, J. Marganiec, L. Marques, S. Marrone, P. Mastinu, A. Mengoni, P. M. Milazzo, C. Moreau, M. Mosconi, F. Neves, H. Oberhummer, S. O’Brien, M. Oshima, J. Pancin, C. Papachristodoulou, C. Papadopoulos, T. Papaevangelou, C. Paradela, N. Patronis, A. Pavlik, P. Pavlopoulos, G. Perdikakis, L. Perrot, R. Plag, A. Plompen, A. Plukis, A. Poch, C. Pretel, J. Quesada, T. Rauscher, R. Reifarth, M. Rosetti, C. Rubbia, G. Rudolf, P. Rullhusen, J. Salgado, L. Sarchiapone, 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, H. Wendler, M. Wiescher, K. Wisshak, and The n_TOF Collaboration ARTICLES YOU MAY BE INTERESTED IN Measurement of the 232Th Neutron Capture Cross Section at the CERN n_TOF Facility AIP Conference Proceedings 769, 1470 (2005); https://doi.org/10.1063/1.1945282 New Measurement of the Capture Cross Section of Bismuth and Lead Isotopes AIP Conference Proceedings 769, 1521 (2005); https://doi.org/10.1063/1.1945294 The n_TOF Facility at CERN: Performances and First Physics Results AIP Conference Proceedings 769, 724 (2005); https://doi.org/10.1063/1.1945110 AIP Conference Proceedings 769, 1442 (2005); https://doi.org/10.1063/1.1945275 769, 1442 © 2005 American Institute of Physics. Measurements at n_TOF of the Neutron Capture Cross Section of Minor Actinides Relevant to the Nuclear Waste Transmutation D. Cano-Ott20 1 , U. Abbondanno14,G.Aerts 7,H.Álvarez 24, F. Àlvarez-Velarde20, S. Andriamonje7, J. Andrzejewski33, P. Assimakopoulos9, L. Audouin 5G. Badurek1,P.Baumann 6,F.Beˇcváˇr31, J. Benlliure24, E. Berthoumieux7, F. Calviño25, R. Capote23, A. Carillo de Albornoz30, P. Cennini4, V. Chepel17,E.Chiaveri 4, N. Colonna13,G.Cortes 25,D.Cortina 24, A. Couture29,J.Cox 29,S.David 5,R.Dolfini 15, C. Domingo-Pardo21, W. Dridi7,I.Duran 24, M. Embid-Segura20,L.Ferrant 5, A. Ferrari4, L. Fitzpatrick4,R.Ferreira-Marques 17, H. Frais-Koelbl3,K.Fujii 13,W.Furman 18, I. Goncalves30, R. Gallino36, E. Gonzalez-Romero20, A. Goverdovski19, F. Gramegna12,E.Griesmayer 3, C. Guerrero20, F. Gunsing7, B. Haas32, R. Haight27,M.Heil 8, A. Herrera-Martinez4, M. Igashira37,S.Isaev 5,E.Jericha 1,Y.Kadi 4, F. Käppeler8, D. Karamanis9, D. Karadimos9, M. Kerveno,6, V. Ketlerov19, P. Koehler28, V. Konovalov18, E. Kossionides39,M.Krtiˇcka31, C. Lamboudis10, H. Leeb1, A. Lindote17, I. Lopes17,M.Lozano 23, S. Lukic6, J. Marganiec33, L. Marques30, S. Marrone13,P.Mastinu 12, A. Mengoni4, P.M. Milazzo14, C. Moreau14, M. Mosconi8,F.Neves 17,H.Oberhummer 1, S. O’Brien29, M. Oshima38,J.Pancin 7, C. Papachristodoulou9, C. Papadopoulos40, T. Papaevangelou4, C. Paradela24, N. Patronis9, A. Pavlik2, P. Pavlopoulos34, G. Perdikakis40,L.Perrot 7,R.Plag 8,A.Plompen 16, A. Plukis7,A.Poch 25,C.Pretel 25, J. Quesada23,T.Rauscher 26, R. Reifarth27,M.Rosetti 11, C. Rubbia15, G. Rudolf6,P.Rullhusen 16, J. Salgado30, L. Sarchiapone4, C. Stephan5, G. Tagliente13,J.L.Tain 21, L. Tassan-Got5,L.Tavora 30, R. Terlizzi13, G. Vannini35, P. Vaz30,A.Ventura 11, D. Villamarin20,M.C.Vincente 20, V. Vlachoudis4,R.Vlastou 40 F. Voss8, H. Wendler4, M. Wiescher29,K.Wisshak 8 The n_TOF Collaboration 1Atominstitut der Österreichischen Universitäten,Technische Universität Wien, Austria  2Institut für Isotopenforschung und Kernphysik, Universität Wien, Austria  3Fachhochschule Wiener Neustadt, Wiener Neustadt, Austria  4CERN, Geneva, Switzerland  5Centre National de la Recherche Scientifique/IN2P3 - IPN, Orsay, France  6Centre National de la Recherche Scientifique/IN2P3 - IReS, Strasbourg, France  7CEA/Saclay - DSM, Gif-sur-Yvette, France  8Forschungszentrum Karlsruhe GmbH (FZK), Institut für Kernphysik, Germany  9University of Ioannina, Greece  10Aristotle University of Thessaloniki, Greece  11ENEA, Bologna, Italy  12Laboratori Nazionali di Legnaro, Italy  13Istituto Nazionale di Fisica Nucleare, Bari, Italy  14Istituto Nazionale di Fisica Nucleare, Trieste, Italy  15Università degli Studi Pavia, Pavia, Italy  16CEC-JRC-IRMM, Geel, Belgium  17LIP - Coimbra & Departamento de Fisica da Universidade de Coimbra, Portugal  18Joint Institute for Nuclear Research, Frank Laboratory of Neutron Physics, Dubna, Russia  19Institute of Physics and Power Engineering, Kaluga region, Obninsk, Russia  20Centro de Investigaciones Energeticas Medioambientales y Technològicas, Madrid, Spain  21Consejo Superior de Investigaciones Cientificas - University of Valencia, Spain  22Universidad Politecnica de Madrid, Spain  23Universidad de Sevilla, Spain  24Universidade de Santiago de Compostela, Spain  25Universitat Politecnica de Catalunya, Barcelona, Spain  26Department of Physics and Astronomy - University of Basel, Basel, Switzerland  27Los Alamos National Laboratory, New Mexico, USA  28Oak Ridge National Laboratory, Physics Division, Oak Ridge, USA  29University of Notre Dame, Notre Dame, USA  30Instituto Tecnológico e Nuclear, Lisbon, Portugal  31Charles University, Prague, Czech Republic  32Centre National de la Recherche Scientifique/IN2P3 - CENBG, Bordeaux, France  33University of Lodz, Lodz, Poland  34Pôle Universitaire Léonard de Vinci, Paris La Défense, France  35Dipartimento di Fisica, Università di Bologna, and Sezione INFN di Bologna, Italy  36Dipartimento di Fisica Generale, Università di Torino and Sezione INFN di Torino, I-10125 Torino, Italy  37Tokyo Institute of Technology, Tokyo, Japan  38Japan Atomic Energy Research Institute, Tokai-mura, Japan  39NCSR, Athens, Greece  40National Technical University of Athens, Greece Abstract. Accurate and reliable neutron-capture cross-section data for actinides are necessary for the proper design, safety regulation, and precise performance assessment of transmutation devices such as Fast Critical Reactors or Accelerator Driven Systems. In particular, the neutron-capture cross sections of 237Np, 240Pu, and 243Am play a key role in the design and optimization of a strategy for the Nuclear Waste Transmutation. The listed cross sections have been measured in 2004 at n_TOF with a high accuracy due to a combination of features unique in the world: high instantaneous neutron fluence and excellent energy resolution of the n_TOF facility, innovative Data Acquisition System based on flash ADCs, and the use of a high-performance BaF2Total Absorption Calorimeter as a detection device. 1442 CP769, International Conference on Nuclear Data for Science and Technology, edited by R. C. Haight, M. B. Chadwick, T. Kawano, and P. Talou © 2005 American Institute of Physics 0-7354-0254-X/05/$22.50 INTRODUCTION Nuclear waste is one the main issues for the public perception of nuclear-energy production and for the sustainability of this energy source. Nuclear waste transmutation has been proposed as a way to reduce substantially (by a factor of 1/100 or more) the radiotoxicity inventory of the long-livedcomponent of the nuclear waste, mainly the trans-uranium actinides. Actinide transmutation is proposed to take place by fission in nuclear systems like critical reactors or subcritical Accelerator Driven Systems (ADS). In most of the scenarios, the use of fast-neutron energy spectra and specific fuel compositions, highly enriched in high-mass trans-uranium actinides, is proposed. 2000 40000 8000 100006000 0 50 100 150 200 250 Pulse shape reconstructions of the BaF2 signals Digitised BaF2 signals time (ns) signal amplitude (flash ADC counts) FIGURE 1. Digitised BaF2signals and the corresponding reconstruction after the pulse-shape analysis. The detailed engineering designs, safety evaluations, and the detailed performance assessment of dedicated transmutation ADS and critical reactors (i.e., with fuels highly enriched in transuranic isotopes) require more precise and complete basic nuclear data [1]. Of crucial importance is the composition of the fuels proposed for transmutation devices, with a large concentration of minor actinides and high-mass plutonium isotopes. These isotopes with smaller relevance for the operation of present reactors will play an important role in the neutronics of the transmuters and for its transmutation performance. 1correspondingauthor:[email protected] EXPERIMENT Isotopically enriched targets of minor actinides are available only in small amounts, typically of the order of 1- 100 mg. Even for these small amounts, the activity of the samples represents major difficulties related both to the experimental techniques and the radioprotection aspects. FIGURE 2. View of the Total Absorption Calorimeter as it is implemented in the code GEANT4 [8] used for the MC simulations. The targets of 237Np (43.3 mg, 1.29 MBq), 240Pu (51.2 mg, 458 MBq), and 243Am (10 mg, 75 MBq) measured at n_TOF have been all assembled in thesame way: the radioactive material is sandwiched by two thin Al layers (total mass < 75 mg) and canned inside a 0.35- mm-thick Ti canning with ISO 2919 certification (requested by the safety regulations at CERN). Their isotopic purity has been determined by γ -ray spectrometry and is >98% in all cases. In capture measurements at n_TOF [2] with a 4-cm- diameter neutron beam spot, the instantaneous fluence amounts to 105neutrons/cm2/pulse for neutron energies between 0.1 eV and 20 GeV. This is one of the key features for measuring the (n, γ ) cross section of lowmass and highly radioactive isotopes with a good signal- to-noise ratio. During the measurements, the repetition rate of the PS was on average 3-4 proton pulses for a PS supercycle of 16.4 s. In addition, the n_TOF facility provides an excellent energy resolution of 10  3to 10  4 at a 185-m flight path between the Pb spallation target and the counting station. The capture cross-section measurements at n_TOF have been done relative to the standard capture cross 1443 section 197Au(n, γ ). For this reason, several independent monitors were used permanently for a proper normalization between the 197Au(n, γ ) and main measurements. (eV) n E 2 10 3 10 -5 10 -4 10 -3 10 counts (normalised to the flux monitor rate) RAW DATA from the 237Np(n,γ) measurement at n_TOF 2.) Background due to the Ti canning + 1.) 1.) Room + target frame background 3.) 43.3 mg of 237Np + 2.) 3000 bins/decade FIGURE 3. Raw data from the 237Np (n, γ ) measurement in the resolved resonance region between 10 eV and 1 keV. Below, the background due to the Ti canning and the empty TAC (without any sample in the beam). (eV) n E 2 10 3 10 -5 10 -4 10 -3 10 counts (normalised to the flux monitor rate) RAW DATA from the 240Pu(n,γ) measurement at n_TOF 2. ) Background due to the Ti canning + 1.) 1.) Room + target frame background 3.) 51.2 mg of 240Pu + 2.) 3000 bins/decade FIGURE 4. Raw data from the 240Pu (n, γ ) measurement in the resolved resonanceregion between10 eV and1 keV. Below, the background due to the Ti canning and the empty TAC (without any sample in the beam). The Data Acquisition system (DAQ) [3] used in the measurements consists of 54 channels of highperformance flash ADCs [4]. Each channel has 8 Mbytes of memory and was operated at a sampling rate of 500 M samples/s, thus allowing recording of the full detector history for neutron energy ranges between 0.3 eV and 20 GeV. After zero suppression and data formatting, the raw data are sent to CERN’s massive storage facility CASTOR [5] via several Gigabit links. In parallel, especially designed pulse-shape analysis routines run on a PC farm and extract from the digitized detector signals the necessary information for the data analysis. The n_TOF DAQ offers unique features such as an extremely low dead time (< 10 ns), good signal analysis, and pileup discrimination among others, resulting in an excellent mechanism for controllingall kinds of systematic uncertainties associated with the detector’s behavior. The quality of the reconstruction for digitised BaF2 signals (two scintillation components τ short =0.7 ns and τ long=620 ns) is shown in Fig. 1. The neutron capture detection system consists of a segmented Total Absorption Calorimeter made of 40 BaF2crystals with 10B loaded carbon fibre capsules and placed at a 185-m flight path from the spallation source. The TAC has a nearly 100% detection efficiency for electromagnetic cascades (i.e., capture events) and good energy resolution (14% at 662 keV and 6% at 6.1 MeV). The radioactive targets are placed at the geometric center of the TAC and surrounded by a C12H2004(6Li)2neutron absorber placed inside the inner hole of the TAC. The neutron absorber and the 10B loaded carbon fibre capsules reduce the sensitivityof the detector to the scattered neutrons, do not reduce the capture detection efficiency (even though they lower the total absorption efficiency), and also help in attenuating the low-energy component (10-100 keV) of the sample radioactivity. For the measurement of 243Am, a cylindrical Pb shielding of 1 mm thickness around the target and outside the beam was necessary for suppressing the strong γ -activity with energies about 100-200 keV. Figure 2 shows a view of the experimental setup as it is implemented in the code GEANT4 [8] used for the detailed MC simulations of the TAC. The performance of the TAC has been investigated both experimentally (with standard calibration sources and the reference 197Au(n, γ ) cross section) and by Monte Carlo simulations [6, 7]. Furthermore, all sources of background have been measured and are being simulated for performing the background corrections necessary for an accurate capture cross-section analysis. RESULTS The capture data for 237Np, 240Pu were taken during August and September 2004, and the 243Am measurement is expected to finish in October 2004. For this reason, the data analysis is at a very early stage. However, a simple analysis of the raw data with full statistics indicates promisingresults. In the resolved resonance region, a large number of resonances are observed with good statistics in both the raw data for 237Np and 240Pu shown in Fig. 3 and 4, respectively. Furthermore, the level of the background there is fairly low, thus allowing us to conclude already that the extraction of accurate resonance parameters is possible. As is shown in Fig. 5 and 6, the cross-section analysis in the unresolved resonance region will require a more detailed study and subtraction of the background, dominated mainly by the effect of the Ti 1444 canning of the samples. However, clear capture signals are visible in the TAC energy-deposition spectra. The background due to the empty Ti canning and other minor sources has been measured with high statistics and will be subtracted from the main measurement, thus leading to an accurate value of the capture cross section up to 100 keV. (eV) n 1 10 2 10 3 10 4 10 5 10 E counts (normalised to the flux monitor rate) -4 10 -3 10 -2 10 RAW DATA from the 237Np(n,γ) measurement at n_TOF 200 bins/decade 2.) Background due to the Ti canning + 1.) 1.) Room + target frame background 3.) 43.3 mg of 237Np + 2.) FIGURE 5. Raw data from the 237Np (n, γ ) measurement in the energy range between 0.7 eV and 300 keV. Below, the background due to the Ti canning and the empty TAC (without any sample in the beam). (eV) n E 1 10 2 10 3 10 4 10 5 10 -4 10 -3 10 -2 10 -1 10 RAW DATA from the 240Pu(n,γ) measurement at n_TOF counts (normalised to the flux monitor rate) 2. ) Background due to the Ti canning + 1.) 1.) Room + target frame background 3.) 51.2 mg of 240Pu + 2.) 200 bins/decade FIGURE 6. Raw data from the 240Pu (n, γ ) measurement in the energy range between 0.7 eV and 300 keV. Below, the background due to the Ti canning and the empty TAC (without any sample in the beam). CONCLUSIONS The neutron capture cross-section measurements of 237Np, 240Pu, and 243Am have been performed at the n_TOF facility at CERN. A high-performance Total Absorption Calorimeter made of 40 BaF2crystals was used for this purpose. The raw data for 237Np and 240Pu are extremely promising in the resolved resonance region, where a large number of resonances has been observed with good statistics for both isotopes. Furthermore, the capture events can be clearly distinguished from the background at neutron energies up to 100 keV, thus allowing the conclusion that it will be possible to extract the capture cross section up to 100 keV after a careful background subtraction. Last, 237Np and 240Pu are the first two capture crosssection measurements on highly radioactive and lowmass actinides with the Total Absorption Calorimeter at n_TOF . They are a clear experimental validation of the good performance of the n_TOF facility, data acquisition system, and TAC and allow design of even more ambitious experiments for the near future. ACKNOWLEDGMENTS This work is part of the European Commission 5th Framework Programme project NTOF-ND-ADS under contract FIKW-CT-2000-00107. REFERENCES 1. Accelerator Driven Systems and Fast Reactors in Advanced Nuclear Fuel Cycles, ISBN 92-64-18482-1 ENEA/OECD Report, 2002 2. U. Abbondanoet al., "n_TOF Performance Report,” CERN/INTC- O-011, INTC-2002-037 3. R. Plag et al., submitted to Nucl. Instrum. Methods A (2004). 4. http://www.acqiris.com 5. http://castor.web.cern.ch/castor 6. M. Heil et al. Nucl. Instrum. Methods A 459(2001) 229 7. D. Cano-Ott et al., "Monte Carlo Simulation of the 4 π Total Absorption Calorimeter at n_TOF,” n_TOF internal report (2003) 8. S.Agostinelli et al.,Nucl. Instrum. Methods A, 506, (2003), p. 250-303. 1445