High accuracy 234U(n,f) cross section in the resonance energy region

EPJ Web of Conferences 146, 04057 (2017) DOI: 10.1051/epjconf/201714604057 ND2016 High accuracy 234U(n,f) cross section in the resonance energy region E. Leal-Cidoncha1,a,I.Dur ´ an1, C. Paradela1,31, L. Tassan-Got2, L. Audouin2, L.C. Leal3, C. Le Naour2, G. Noguere4, D. Tarr´ ıo1,33, L.S. Leong2,S.Altstadt 5, J. Andrzejewski6, M. Barbagallo7,V.B ´ ecares8,F.Be ˇ cv´ aˇ r9, F. Belloni31, E. Berthoumieux10, J. Billowes12, V. Boccone11, D. Bosnar13, M. Brugger11, M. Calviani11, F. Calvi˜ no14, D. Cano-Ott8, C. Carrapic¸o15, F. Cerutti11, E. Chiaveri11,M.Chin 11, N. Colonna7,G.Cort ´ es14,M.A.Cort ´ es-Giraldo16, M. Diakaki10, C. Domingo-Pardo18, R. Dressler19, C. Eleftheriadis21,A.Ferrari 11,K.Fraval 10, S. Ganesan22,A.R.Garc ´ ıa8, G. Giubrone18,M.B.G ´ omez-Hornillos14, I.F. Gonc¸alves15,E.Gonz ´ alez-Romero8, E. Griesmayer23, C. Guerrero16, F. Gunsing10, P. Gurusamy22,A.Hern ´ andez-Prieto11, D.G. Jenkins24, E. Jericha23, Y. Kadi11,F.K ¨ appeler25, D. Karadimos17,N.Kivel 19, M. Kokkoris17,M.Krti ˇ cka9,J.Kroll 9, C. Lampoudis21, C. Langer5, C. Lederer5,26, H. Leeb23, R. Losito11, A. Mallick22, A. Manousos21, J. Marganiec6,T.Mart ´ ınez8, C. Massimi27, P.F. Mastinu20, M. Mastromarco7, M. Meaze7, E. Mendoza8, A. Mengoni28, P.M. Milazzo29, F. Mingrone27,M.Mirea 30, W. Mondelaers31, A. Pavlik26, J. Perkowski6, A. Plompen31, J. Praena34, J.M. Quesada16, T. Rauscher35,32,R.Reifarth 5,A.Riego 14, M.S. Robles1, F. Roman11, C. Rubbia11, M. Sabat´ e-Gilarte11,16, R. Sarmento15, A. Saxena22, P. Schillebeeckx31, S. Schmidt5, D. Schumann19, G. Tagliente7,J.L.Tain 18, A. Tsinganis11, S. Valenta9, G. Vannini27, V. Variale7,P.Vaz 15, A. Ventura28,R.Versaci 11, M.J. Vermeulen24, V. Vlachoudis11,R.Vlastou 17,A.Wallner 36,T.Ware 12, M. Weigand5, C. Weiß11, T. Wright12,P. ˇ Zugec13, and the n TOF Collaboration 1Universidade de Santiago de Compostela (USC), Spain 2Centre National de la Recherche Scientifique/IN2P3 - IPN, Orsay, France 3IRSN/PSN-EXP, Fontenay-aux-Roses, France 4CEA, Cadarache, France 5Johann-Wolfgang-Goethe Universit¨ at, Frankfurt, Germany 6Uniwersytet L´ odzki, Lodz, Poland 7Istituto Nazionale di Fisica Nucleare, Bari, Italy 8Centro de Investigaciones Energeticas Medioambientales y Tecnol´ ogicas (CIEMAT), Madrid, Spain 9Charles University, Prague, Czech Republic 10 Commissariat ` al’´ Energie Atomique (CEA) Saclay - Irfu, Gif-sur-Yvette, France 11 European Organization for Nuclear Research (CERN), Geneva, Switzerland 12 University of Manchester, Oxford Road, Manchester, UK 13 Department of Physics, Faculty of Science, University of Zagreb, Croatia 14 Universitat Politecnica de Catalunya, Barcelona, Spain 15 Instituto Tecnol´ ogico e Nuclear, Instituto Superior T´ ecnico, Universidade T´ ecnica de Lisboa, Lisboa, Portugal 16 Universidad de Sevilla, Spain 17 National Technical University of Athens (NTUA), Greece 18 Instituto de F´ ısica Corpuscular, CSIC-Universidad de Valencia, Spain 19 Paul Scherrer Institut, Villigen PSI, Switzerland 20 Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, Italy 21 Aristotle University of Thessaloniki, Thessaloniki, Greece 22 Bhabha Atomic Research Centre (BARC), Mumbai, India 23 Atominstitut, Technische Universit¨ at Wien, Austria 24 University of York, Heslington, York, UK 25 Karlsruhe Institute of Technology, Campus Nord, Institut f¨ ur Kernphysik, Karlsruhe, Germany 26 University of Vienna, Faculty of Physics, Austria 27 Dipartimento di Fisica, Universit` a di Bologna, and Sezione INFN di Bologna, Italy 28 Agenzia nazionale per le nuove tecnologie, l’energia e lo sviluppo economico sostenibile (ENEA), Bologna, Italy 29 Istituto Nazionale di Fisica Nucleare, Trieste, Italy 30 Horia Hulubei National Institute of Physics and Nuclear Engineering - IFIN HH, Bucharest, Magurele, Romania 31 European Commission JRC, Institute for Reference Materials and Measurements, Retieseweg 111, 2440 Geel, Belgium 32 Department of Physics and Astronomy, University of Basel, Basel, Switzerland 33 Department of Physics and Astronomy, Uppsala University, Sweden 34 Universidad de Granada (UGRAN), Spain e-mail: [email protected] c The Authors, published by EDP Sciences. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). EPJ Web of Conferences 146, 04057 (2017) DOI: 10.1051/epjconf/201714604057 ND2016 35 Centre for Astrophysics Research, School of Physics, Astronomy, Mathematics, University of Hertfordshire, UK 36 Research School of Physics and Engineering, Australian National University, Australia Abstract.New results are presented of the 234U neutron-induced fission cross section, obtained with high accuracy in the resonance region by means of two methods using the 235U(n,f) as reference. The recent evaluation of the 235U(n,f) obtained with SAMMY by L. C. Leal et al. (these Proceedings), based on previous nTOF data [1], has been used to calculate the 234U(n,f) cross section through the 234U/235U ratio, being here compared with the results obtained by using the n TOF neutron flux. 1. Introduction The 234U isotope is present in the uranium-enriched fuel of current reactors and is also produced during the thorium-fuel cycle. Because of its relatively low (n,f) cross section, data found in current nuclear databases could be sufficient for a first evaluation of critical reactors as well as for Accelerator Driven Systems. Nevertheless, a detailed assessment of relevant integral reactor quantities requires a more precise and complete set of basic nuclear data for this important isotope. Experimental datasets available in EXFOR as well as data in the evaluated libraries [2] show discrepancies. The ENDF/B-VII.1 and JENDL-4.0 evaluations are shifted in energy and some resonances are missing in one of the two databases. In the Resolved Resonance Region (RRR), both evaluations are based on the experimental data of James et al. [3], but JENDL-4.0 includes also the resonance parameters provided by Dridi et al. [4] for the capture reaction and the fission cross section of Heyse et al. [5] for the 5.17 eV resonance. Above 1.5 keV, in the Unresolved Resonance Region (URR), the fission data of James et al. and the capture data of Pennington were used in ENDF/B-VII.1 whereas JENDL- 4.0 used the experimental data sets mentioned in Ref. [2]. The 234U(n,f) cross section data presented in this work, in the neutron energy range from 3 eV up to 10 MeV, have been measured at the Neutron Time-of-Flight (n TOF) facility at CERN with an improved detection setup based on Parallel Plate Avalanche Counters (PPACs). 2. The experimental setup The 234U(n,f) cross section was measured in 2012 during the so-called Phase-II at the CERN-n TOF facility [6] using ten PPACs consisting of one central anode with a very fast signal (time resolution ∼500 ps) and two segmented cathodes, used to measure the two coordinates of the fission fragment (FF) hit [7]. The targets, which consisted of thin radioactive layers electrodeposited on an aluminium foil, were interleaved with ten PPAC detectors. The data here presented correspond to three 234U and two 235U targets. The thickness of the Al backing was 2.0 µm for the 234U and one 235U and 0.7 µm for the second 235U target. There was a slight isotopic contamination in the 235U targets of 234U (0.74%), 236U (0.27%) and 238U (6.28%), as well as a 235U (0.077%) content in the 234U targets, which has been subtracted during the data analysis. The n TOF spallation target in previous PPAC experiments, performed during the Phase-I [1,8]used normal water as the neutron moderator, which was changed to borated water in the last campaign of Phase- II when the data presented in this work have been taken. Important differences in the neutron flux are observed below hundreds of eV depending on the type of moderator material [9]. The PPAC configuration was also modified in Phase-II. The detectors and targets were tilted by 45◦with respect to the neutron beam direction in order to reach up to 90◦ angular acceptance of the FF detection compared to the 60◦ achieved with the perpendicular setup used in Phase-I, see Ref. [7] for details. 3. Data analysis and results The fission cross section (σ) is related to the number of detected fission events (C) per unit of incident neutron energy (En) by: C(En)x=σ(En)x·(En)·Nx·(1) where is the neutron fluence, is the detection efficiency and N is the areal density of a target (x) of radius R. 3.1. 235U(n,f) cross section As the neutron fluence received by the targets during the experiment is not accurately known, the 235U(n,f) has been used as a reference in the 234U(n,f) cross section calculation. However, the n TOF neutron flux shape was known [10] and was normalised with Eq. (1)usingthe 235U(n,f) cross section area of 246.4 ±1.2 b ·eV given by the IAEA in the neutron energy interval from 7.8 to 11 eV as explained in Ref. [1]. The 235U(n,f) cross section, obtained as the mean value of both 235U targets, is compared in Fig. 1with the recent evaluation presented in this conference by L. C. Leal et al., based on the data of Paradela et al. [1], and with the ENDF/B-VII.1 database. The averaged integral cross sections, calculated with the Analysis of Geel Spectrum (AGS) code [11], are provided in Table 1where the ratios of the n TOF data to those in each column are given in parentheses for different energy regions. 3.2. 234U(n,f) cross section The 234U(n,f) cross section is calculated in this work by means of two methods, both based on the fact that all targets receive the same neutron flux and assuming that the efficiency of all detectors is the same within the uncertainties we are dealing with. With the first method (nTOF1), the 235U(n,f) cross section obtained in the previous subsection has been used as a reference. The normalisation factor is inversely proportional to N5·so, assuming that the efficiency is the same for all detectors, we can get the 234U(n,f) cross section via the relation between the areal densities of the samples given by: N4=N5·m4·M5 m5·M4 (2) 2 EPJ Web of Conferences 146, 04057 (2017) DOI: 10.1051/epjconf/201714604057 ND2016 Table 1. 235U(n,f) averaged integral cross sections. En[eV] n TOF [b] Paradela [b] Leal [b] IAEA [b] ENDF/B-VII.1 [b] 100–200 21.13 21.31(0.99) 21.02(1.01) 21.17(1.00) 20.32(1.04) 200–300 20.70 20.82(0.99) 20.77(1.00) 20.69(1.00) 20.60(1.01) 300–400 13.02 12.90(1.01) 13.22(0.99) 13.14(0.99) 12.81(1.02) 400–500 13.66 13.68(1.00) 13.49(1.01) 13.78(0.99) 13.29(1.03) 500–600 15.51 15.30(1.01) 15.20(1.02) 15.17(1.02) 14.87(1.04) 600–700 11.50 11.56(1.00) 11.53(1.00) 11.51(1.00) 11.24(1.02) 700–800 11.12 11.05(1.01) 11.10(1.00) 11.10(1.00) 10.88(1.02) 800–900 8.236 8.305(0.99) 8.150(1.01) 8.213(1.00) 7.977(1.03) 900–1000 7.440 7.529(0.99) 7.370(1.01) 7.502(0.99) 7.240(1.03) 1000–2000 7.359 7.318(1.01) 7.290(1.01) 7.303(1.01) 7.138(1.03) 2000–3000 5.390 5.237(1.03) 5.330(1.01) 5.386(1.00) 5.290(1.02) 3000–4000 4.758 4.740(1.00) 4.790(0.99) 4.784(0.99) 4.778(1.00) 4000–5000 4.250 4.216(1.01) 4.270(1.00) 4.261(1.00) 4.207(1.01) 5000–6000 3.745 3.808(0.98) 3.820(0.98) 3.838(0.98) 3.905(0.96) 6000–7000 3.374 3.214(1.05) 3.350(1.01) 3.291(1.03) 3.287(1.03) 7000–8000 3.203 3.140(1.02) 3.210(1.00) 3.236(0.99) 3.158(1.01) 8000–9000 2.916 2.934(0.99) 3.090(0.94) 3.009(0.97) 2.940(0.99) 9000–10000 3.072 3.071(1.00) 3.060(1.00) 3.120(0.98) 3.043(1.01) 10 20 En (eV) 1 10 100 1000 f(b) n_TOF (this work) L. C. Leal ENDF/B-VII.1 Figure 1. 235U(n,f) cross section data. The dashed vertical lines correspond to the normalisation limits. The second method (nTOF2) is based on the ratio of the number of fission events obtained for the 234U and 235U samples, using the 235U(n,f) cross section evaluated by L.C. Leal et al., with Eq. (1), where the neutron flux and the efficiency cancel. The cross section obtained by the first method is compared in Fig. 2with the experimental data provided by EXFOR and with the ENDF/B-VII.1 and JENDL-4.0 evaluations. The data presented in this work have better resolution than the others, being closer to the previous nTOF data measured by Paradela et al. [8]. A slight energy offset is observed between the ENDF/B-VII.1 and JENDL-4.0 evaluations in addition to differences in the cross sections. This energy shift is also observed between the evaluations and the experimental data, being more pronounced in the case of the JENDL-4.0 database. Above the RRR some groups of fission resonances are observed in the experimental data, which are not evaluated in the databases, as can be seen in Fig. 3. The averaged integral cross sections calculated with both methods are given in Table 2for different energy regions, compared with Paradela et al., ENDF/B-VII.1 and JENDL-4.0. The ratios of the first column data over the values in the other columns are given in parentheses. On 4.8 4.9 55.1 5.2 5.3 5.4 5.5 En (eV) 0 5 10 15 20 25 30 f(b) n_TOF1 (this work) James (1977) Heyse (2007) Paradela (2010) ENDF/B-VII.1 JENDL-4.0 550 560 570 580 590 En (eV) 0 5 10 15 20 f(b) Figure 2. 234U(n,f) cross section data in different energies of the RRR. average, the differences between n TOF1and the other columns in Table 2are respectively 0.9% (n TOF2), −18% (Paradela), −76% (ENDF/B-VII.1) and −73% (JENDL- 4.0). 3.3. Conclusions The 234U(n,f) cross section data has been obtained by means of two approaches, being in very nice agreement between them. When comparing these data with the 3 EPJ Web of Conferences 146, 04057 (2017) DOI: 10.1051/epjconf/201714604057 ND2016 Table 2. 234U(n,f) averaged integral cross sections. En[eV] n TOF1[mb] n TOF2[mb] Paradela [mb] ENDF/B-VII.1 [mb] JENDL-4.0 [mb] 100–120 365.8 343.9(1.06) 344.2(1.06) 255.0(1.43) 243.1(1.51) 120–160 26.82 26.65(1.01) 20.08(1.34) 12.81(2.09) 12.34(2.17) 160–220 80.79 79.33(1.02) 74.80(1.08) 55.08(1.47) 52.80(1.53) 220–300 61.69 60.00(1.03) 46.08(1.34) 35.98(1.71) 27.01(2.28) 300–400 84.45 77.81(1.09) 76.33(1.11) 55.92(1.51) 41.95(2.01) 400–520 486.3 490.7(0.99) 458.2(1.06) 338.5(1.44) 244.7(1.99) 520–660 498.9 507.3(0.98) 473.9(1.05) 367.2(1.36) 268.1(1.86) 660–820 153.3 164.2(0.93) 142.6(1.08) 103.5(1.48) 74.14(2.07) 820–1000 32.92 34.28(0.96) 26.26(1.25) 19.98(1.65) 15.63(2.11) 1000–1200 28.71 29.93(0.96) 22.11(1.30) 13.23(2.17) 5.858(4.90) 1200–1600 22.36 22.99(0.97) 17.01(1.31) 11.57(1.93) 9.282(2.41) 1600–2200 8.131 8.112(1.00) 5.996(1.36) 5.597(1.45) 5.486(1.48) 2200–3000 7.908 7.721(1.02) 5.201(1.52) 3.873(2.04) 9.862(0.80) 3000–4000 12.42 12.43(1.00) 9.068(1.37) 6.887(1.80) 9.757(1.27) 4000–5200 25.55 26.59(0.96) 21.02(1.22) 8.661(2.95) 12.78(2.00) 5200–6600 8.379 9.204(0.91) 8.335(1.01) 10.63(0.79) 10.56(0.79) 6600–8200 54.02 55.04(0.98) 57.33(0.94) 12.83(4.21) 25.54(2.12) 8200–10000 6.113 6.404(0.95) 7.013(0.87) 13.23(0.46) 11.99(0.51) 6500 7000 7500 8000 8500 En (eV) 0 0.2 0.4 0.6 0.8 1 f (b) Figure 3. 234U(n,f) cross section data in the 7 keV energy region. 100 1000 10000 En (eV) 1 10 Ratio 0.5 5 n_TOF1 / n_TOF2 n_TOF1 / Paradela n_TOF1 / ENDF/B-VII.1 n_TOF1 / JENDL-4.0 Figure 4. Ratio of the 234U(n,f) integral cross sections averaged over the energy ranges given in Table 2. experimental data provided by EXFOR, a better resolution is observed in the present data, having a shape very close to the previous n TOF data in [8]. Huge discrepancies have been found in the cross sections and energies with the evaluations in the ENDF/B-VII.1 and JENDL-4.0 libraries. The averaged integral cross section ratios given in parentheses in Table 2are shown in Fig. 4,differing by factors of 0.5 to 5. It is worth to mention the good agreement between both experimental methods, the difference of −18% with respect to Paradela et al. [8] and the severe disagreement with the evaluated libraries. References [1] C. Paradela et al., The EPJ Conferences 111, 02003 (2016) [2] www-nds.iaea.org [3] G.D. James et al., Phys. Rev. C 15, 2083 (1977) [4] W. Dridi, PhD. Thesis (CEA/Saclay) (2006) [5] J. Heyse et al., Nucl. Sci. Eng. 156, 211 (2007) [6] F. Gunsing et al., CERN-Proceedings-2015-001, cds.cern.ch/record/2115398 [7] D. Tarr´ ıo et al., Nucl. Instrum. Meth. A 743,79 (2014) [8] C. Paradela et al., Phys. Rev. C 82, 034601 (2010) [9] M. Barbagallo et al., EPJ A 49(12), 1–11 (2013) [10] n TOF internal communication [11] B. Becker et al., Data reduction and uncertainty propagation of time-of-flight spectra with AGS J. of Instrumentation 7, P11002-19 (2012) 4