Altstadt, S.

Andrzejewski, J.

Audouin, L.

Barbagallo, M.

Belloni, F.

Berthoumieux, E.

Bečvář, F.

Billowes, J.

Bosnar, D.

Brugger, M.

Bécares, V.

Calviani, M.

Calviño, F.

Cano-Ott, D.

Carrapiço, C.

Cerutti, F.

Chiaveri, E.

Chin, M.

Colonna, N.

Cortés, G.

Cortés-Giraldo, M. A.

Diakaki, M.

Domingo-Pardo, C.

Durán, I.

Dzysiuk, N.

Eleftheriadis, C.

Ferrari, A.

Fraval, K.

Furman, V.

Ganesan, S.

García, A. R.

Giubrone, G.

González, E.

Gonçalves, I. F.

Goverdovski, A.

Griesmayer, E.

Guerrero, C.

Gunsing, F.

Gurusamy, P.

Gómez-Hornillos, M. B.

Heftrich, T.

Heinitz, S.

Hernández-Prieto, A.

Heyse, J.

Jenkins, D. G.

Jericha, E.

Kadi, Y.

Karadimos, D.

Katabuchi, T.

Ketlerov, V.

Khryachkov, V.

Koehler, P.

Kokkoris, M.

Kroll, J.

Krtička, M.

Käppeler, F.

Lampoudis, C.

Langer, C.

Leal-Cidoncha, E.

Lederer, C.

Leeb, H.

Leong, L. S.

Lerendegui-Marco, J.

Licata, M.

Losito, R.

Manousos, A.

Marganiec, J.

Martínez, T.

Massimi, C.

Mastinu, P.

Mastromarco, M.

Mendoza, E.

Mengoni, A.

Milazzo, P. M.

Mingrone, F.

Mirea, M.

Mondelaers, W.

Paradela, C.

Pavlik, A.

Perkowski, J.

Plompen, A. J. M.

Praena, J.

Quesada, J. M.

Rauscher, T.

Reifarth, R.

Riego-Perez, A.

Robles, M.

Roman, F.

Rubbia, C.

Ryan, J. A.

Sabaté-Gilarte, M.

Sarmento, R.

Saxena, A.

Schillebeeckx, P.

Schmidt, S.

Schumann, D.

Sedyshev, P.

Tagliente, G.

Tain, J. L.

Tarifeño-Saldivia, A.

English

n_TOF Collaboration

Vermeulen, M. J.

KITopen

EPJ Web of Conferences 146, 11054 (2017) DOI: 10.1051/epjconf/201714611054ND2016The 236U neutron capture cross-section measured at the n TOFCERN facilityM. Mastromarco1,a, M. Barbagallo1, M.J. Vermeulen2, N. Colonna1, S. Altstadt3, J. Andrzejewski4, L. Audouin5,V. Bécares6, F. Bečvář7, F. Belloni8, E. Berthoumieux8, J. Billowes9, D. Bosnar10, M. Brugger11, F. Calviño12,M. Calviani11, D. Cano-Ott6, C. Carrapiço13, F. Cerutti11, E. Chiaveri11,8, M. Chin11, G. Cortés12, M.A. Cortés-Giraldo14,M. Diakaki15, C. Domingo-Pardo16, I. Durán17, N. Dzysiuk18, C. Eleftheriadis19, A. Ferrari11, K. Fraval8, V. Furman20,M.B. Gómez-Hornillos12, S. Ganesan21, A.R. Garcı́a6, G. Giubrone16, I.F. Gonçalves13, E. González6, A. Goverdovski22,E. Griesmayer23, C. Guerrero11, F. Gunsing8, P. Gurusamy21, T. Heftrich3, S. Heinitz24, A. Hernández-Prieto11,12,J. Heyse25, D.G. Jenkins2, E. Jericha23, F. Käppeler27, Y. Kadi11, D. Karadimos15, T. Katabuchi28, V. Ketlerov22,V. Khryachkov22, P. Koehler29, M. Kokkoris15, J. Kroll7, M. Krtička7, C. Lampoudis8, C. Langer3, E. Leal-Cidoncha17,C. Lederer30, H. Leeb23, L.S. Leong5, J. Lerendegui-Marco14, M. Licata31,32, R. Losito11, A. Manousos19, J. Marganiec4,T. Martı́nez6, C. Massimi31,32, P. Mastinu18, E. Mendoza6, A. Mengoni33, P.M. Milazzo34, F. Mingrone31, M. Mirea35,W. Mondelaers25, C. Paradela17, A. Pavlik30, J. Perkowski4, A.J.M. Plompen25, J. Praena14, J.M. Quesada14,T. Rauscher36, R. Reifarth3, A. Riego-Perez12, M. Robles17, F. Roman35, C. Rubbia11, J.A. Ryan9, M. Sabaté-Gilarte11,14,R. Sarmento13, A. Saxena21, P. Schillebeeckx25, S. Schmidt3, D. Schumann24, P. Sedyshev20, G. Tagliente1, J.L. Tain16,A. Tarifeño-Saldivia16, D. Tarrı́o17, L. Tassan-Got5, A. Tsinganis11, S. Valenta7, G. Vannini31,32, V. Variale1, P. Vaz13,A. Ventura31, R. Versaci11, V. Vlachoudis11, R. Vlastou15, A. Wallner37, T. Ware9, M. Weigand3, C. Weiss23, T. Wright9,P. Žugec10, and the n TOF Collaboration1 Istituto Nazionale di Fisica Nucleare, Sezione di Bari, Italy2 University of York, UK3 Goethe University Frankfurt, Germany4 University of Lodz, Poland5 Institut de Physique Nucléaire, CNRS-IN2P3, Univ. Paris-Sud, Université Paris-Saclay, 91406 Orsay Cedex, France6 Centro de Investigaciones Energeticas Medioambientales y Tecnológicas (CIEMAT), Spain7 Charles University, Prague, Czech Republic8 CEA Saclay, Irfu, Gif-sur-Yvette, France9 University of Manchester, UK10 University of Zagreb, Croatia11 European Organization for Nuclear Research (CERN), Switzerland12 Universitat Politècnica de Catalunya, Spain13 Instituto Superior Técnico, Lisbon, Portugal14 Universidad de Sevilla, Spain15 National Technical University of Athens, Greece16 Instituto de Fı́sica Corpuscular, Universidad de Valencia, Spain17 University of Santiago de Compostela, Spain18 Istituto Nazionale di Fisica Nucleare, Sezione di Legnaro, Italy19 Aristotle University of Thessaloniki, Thessaloniki, Greece20 Joint Institute for Nuclear Research (JINR), Dubna, Russia21 Bhabha Atomic Research Centre (BARC), India22 Institute of Physics and Power Engineering (IPPE), Obninsk, Russia23 Technische Universität Wien, Austria24 Paul Scherrer Institut (PSI), Villingen, Switzerland25 European Commission, Joint Research Centre, Geel, Retieseweg 111, 2440 Geel, Belgium26 Karlsruhe Institute of Technology, Campus North, IKP, 76021 Karlsruhe, Germany27 Tokyo Institute of Technology, Japan28 Oak Ridge National Laboratory (ORNL), Oak Ridge, TN 37831, USA29 University of Vienna, Faculty of Physics, Vienna, Austria30 Istituto Nazionale di Fisica Nucleare, Sezione di Bologna, Italy31 Dipartimento di Fisica e Astronomia, Università di Bologna, Italy32 Agenzia nazionale per le nuove tecnologie (ENEA), Bologna, Italyae-mail: mario.mastromarco@ba.infn.itc© 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, 11054 (2017) DOI: 10.1051/epjconf/201714611054ND201633 Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Italy34 Horia Hulubei National Institute of Physics and Nuclear Engineering, Romania35 Department of Physics, University of Basel, Switzerland36 Australian National University, Canberra, AustraliaAbstract. The 236U isotope plays an important role in nuclear systems, both for future and currently operatingones. The actual knowledge of the capture reaction of this isotope is satisfactory in the thermal region, but it isconsidered insufficient for Fast Reactor and ADS applications. For this reason the 236U(n, γ ) reaction cross-section has been measured for the first time in the whole energy region from thermal energy up to 1 MeVat the n TOF facility with two different detection systems: an array of C6D6 detectors, employing the totalenergy deposited method, and a 4π total absorption calorimeter (TAC), made of 40 BaF2 crystals. The twon TOF data sets agree with each other within the statistical uncertainty in the Resolved Resonance Region upto 800 eV, while sizable differences (up to  20%) are found relative to the current evaluated data libraries.Moreover two new resonances have been found in the n TOF data. In the Unresolved Resonance Region upto 200 keV, the n TOF results show a reasonable agreement with previous measurements and evaluated data.1. Introduction236U plays an important role in nuclear systems, bothinnovative or already in use. In the current reactors basedon U/Pu it is important in the neutron balance in the coreand in the equilibrium fuel composition. Regarding thefuture reactors based on the Th/U cycle, 236U plays thesame role as 242Pu in the traditional fuel cycle, thereforeits contribution to the fraction of absorbed neutrons isrelevant. The actual knowledge of the capture cross-sectionof 236U is considered satisfactory in the thermal region,but insufficient for Fast Reactors and ADS applications;in these cases the target accuracy is 10% [1], which istherefore the aim of the present measurement.Major data libraries are based on a few experimentalmeasurements characterized by poor accuracy andresolution and covering incomplete energy ranges. Apartfor the low-energy 1/v region, where the major evaluationslike JENDL-4.0, ENDF/B-VII.1 and JEFF-3.2 show asmooth trend and are in agreement between each otherwithin a few percent, discrepancies are observed betweenevaluated data and experimental results, in particular inthe Resolved Resonance Region (RRR), which are wellabove the required accuracy. Moreover, the RRR is limitedto 1.5 keV in most of the libraries, while it extends upto 4.0 keV in JENDL-4.0. In the Unresolved ResonanceRegion (URR), evaluated cross-section below 200 keV areconsistent to each other, although experimental data showsome discrepancies, while above 200 keV both evaluationsand experimental data show large variations.The present situation is therefore unacceptable forfuture nuclear applications. This situation motivateda new measurement of the capture cross-section of236U at the CERN n TOF facility [2]. To reducesystematic uncertainties, the measurement was carried outwith two independent detection techniques based on aTotal Absorption Calorimeter [3] and a pair of C6D6detectors [4].2. The experimental setupThe C6D6 detectors, characterized by a low neutronsensitivity and γ -ray effciency, are mounted at 135◦ withrespect to the sample; they rely on the use of the PulseHeight Weigting Technique [5] which requires that atmost one γ -ray per capture event is detected. The seconddetection system (TAC), made of 40 BaF2 crystals andcharacterized by high geometric and intrinsic effciciency,allows detection and reconstruction of the full γ -raycascade of the capture event. However, due to its largesensitivity to neutrons and to the γ -flash, it was notpossible to collect data above a few tens of keV.The uranium sample consists of a high purity presseddisk pellet 99.85% enriched in 236U3O8 with a total massof 399 mg. Known contaminants are 0.05% of 235U and0.1% of 238U. The pressed pellet is placed inside a diskshaped capsule made of high purity and normal aluminum.A capsule without sample inside, called “dummy”, wasbuilt with the same dimensions of the aluminum capsule.The sample was inserted between two thin kapton foils andthis assembly was glued on a carbon fiber frame mountedon the remotely-controlled sample exchanger togetherwith other samples used for the determination of thebackground: an “empty” sample, made of just the kaptonfoils, the dummy sample, a nat Pb sample for in-beam γ -rays and a natural gold sample used for normalizationpurposes. All samples were made with the same diameteras the U3O8 pellet.3. Results3.1. The resolved resonance regionThe background-subtracted capture yield measured withthe C6D6 setup is shown in Fig. 1. The resolvedresonance region was analyzed by means of the R-matrixcode SAMMY. The yield has been parametrized viathe Reich-Moore approximation; experimental effects asDoppler broadening, sample scattering, isotopic correctionfor contaminants, self-shielding and n TOF resolutionfunction are properly taken into account within theSAMMY code.In the SAMMY fit a residual constant background wasconsidered that was probably due to an underestimatedcontribution of the aluminum capsule. However, in theResolved Resonanance Region, this component is only 0.04% in the extracted capture yield.In the fitting procedure for the Resonance ShapeAnalysis (RSA), the resonance energy (ER) and bothpartial widths (γ and n) were allowed to vary. While theresulting 236U resonance parameters are not very accurate,this procedure provides an accurate value for the capturekernel, gγ n/. As a starting point for the SAMMY fits,the resonance parameters from the JENDL-4.0 data library2EPJ Web of Conferences 146, 11054 (2017) DOI: 10.1051/epjconf/201714611054ND2016Neutron energy (eV)1 10 210 310 410 510Capture yield-410-310-210-1101Figure 1. Capture yield obtained after normalization andbackground subtraction. The n TOF data shown here arecollected with C6D6 detection system.Neutron energy (eV)30 32 34 36 38 40 42 44Capture yield00.10.20.30.40.50.60.70.86D6CSAMMYJENDL-4.0ENDF/B-VII.1Figure 2. Comparison between C6D6 data fitted by SAMMY andmajor data libraries.Neutron energy (eV)75 75.5 76 76.5 77 77.5 78 78.5Capture yield00.0020.0040.0060.0080.016D6CSAMMYJENDL-4.0ENDF/B-VII.1Figure 3. Structure at 76.7 eV in the C6D6 data compared withmajor data libraries. The resulting SAMMY fit is also shown.were taken for the C6D6 and from ENDF/B-VII.1 for theTAC analysis.Although structures are present, the lower statisticsof C6D6 comparated to the TAC data does not allowto analyze resonance above 800 eV with a statisticaluncertainty on the capture kernel below 40%. An exampleof the fitted yield of C6D6 data is shown in Fig. 2.Two structures at 76.7 and 362.9 eV not present inmajor data libraries have been found in the C6D6 dataset, as shown in Figs. 3 and 4, and were confirmed bythe TAC measurement. A possible candidate is a 237Npcontamination in the sample as a result of the captureNeutron energy (eV)356 358 360 362 364 366 368Capture yield00.0020.0040.0060.0080.016D6CSAMMYJENDL-4.0ENDF/B-VII.1Figure 4. Structure at 362.9 eV of C6D6 data compared withmajor data libraries. The resulting SAMMY fit is also shown.Neutron energy (eV)0 100 200 300 400 500 600 700 800Kernel ratio00.20.40.60.811.21.41.61.82 / TAC6D6CFigure 5. Comparison between the capture kernels determinedfrom the C6D6 and TAC data.Neutron energy (eV)0 100 200 300 400 500 600 700 800Kernel ratio00.20.40.60.811.21.41.61.822.2  / JENDL-4.06D6C / ENDF/B-V.II.16D6CFigure 6. Comparison between capture kernels obtained fromthe C6D6 measurement with the corresponding values from datalibraries.reaction on 236U(n, γ )237U followed by β-decay. However,since there is no evidence of other, stronger resonances of237Np in the analyzed energy range, these resonances couldbe attributed to 236U.The capture kernel is sensitive to systematic effectsrelated to the experimental setup, in particular to theneutron sensitivity. In the present analysis, these effectshave been correctly taken into account, as demonstratedby Fig. 5, where the ratio between the capture kernelscalculated from the resonance parameters obtained fromC6D6 and from the TAC data is shown. The goodagreement between the two datasets and the resultingaverage difference of less than 1% confirms that the3EPJ Web of Conferences 146, 11054 (2017) DOI: 10.1051/epjconf/201714611054ND2016Neutron energy (eV)410 510) cross-section (b)γU(n,23600.20.40.60.811.21.41.61.826D6CENDF/B-VII.1JENDL-4.0Figure 7. Comparison between C6D6 data and major datalibraries in the URR.Neutron energy (eV)410 510) cross-section (b)γU(n,23600.20.40.60.811.21.41.61.826D6CKazakov (1988)Adamchuk (1987)Buleeva (1985)Carlson (1970)Barry (1961)Figure 8. Comparison between C6D6 data and previous results inthe URR.capture yield in both independent analyses was consistentand reliable.A comparison of the capture kernels measured atn TOF with the ones calculated from data libraries (seeFig. 6) shows a deviation of 16% relative to JENDL-4.0and of 23% relative to ENDF/B-V.II.1. Between 800 eVand 1.5 keV, the resonance analysis has been performedonly on the TAC data. Structures above 1.5 keV are presentin both data sets, confirming the structures in the evaluatedcross section of JENDL-4.0. However, in this case the lowstatistics makes it difficult to perform a resonance analysisabove 1.5 keV neutron energy.3.2. The unresolved resonance regionRegarding the unresolved resonance region, a comparisonbetween the C6D6 average cross-section data and majordata libraries shown in Fig. 7 reveals that in this energyrange the present results agree to better than 5% with majorevaluations up to 700-800 keV. Due to the prompt γ -flashand inelastic reactions, data above this energy range are notvery reliable.The two structures in the data at 5.9 and 34.7 keVare not due to the 236U(n, γ ) reaction, but are consistentwith the 27Al(n, γ ) reactions in the capsule, which areaffected by a sizable uncertainty. This result and theconstant background found in the RRR, indicate that thecontribution of the aluminum capsule to the total captureyield is underestimated.A comparison with previous results shown in Fig. 8,indicates that the present data, apart from the discrepanciesdue to the aluminum structures, agree better than 7% withmost of the previous measurements up to 700–800 keV.As a final remark, it should be considered that thepresent data, affected by a systematic uncertainty around7%, are certainly the most accurate obtained so far inthis energy region that is particularly important for thedevelopment of fast reactors.References[1] V.G. Pronyavev, Assessment of Nuclear DataNeeds for Thorium and other Advanced Cycles,INDC(NDS), IAEA (1999)[2] C. Guerrero et al., Eur. Phys. J. A 49, 27 (2013)[3] C. Guerrero et al., Nucl. Instr. and Meth. A 608, 424–433 (2009)[4] R. Plag et al., Nucl. Instr. and Meth. A 496, 425–436(2003)[5] A. Borella et al., Nucl. Instr. and Meth. A 577, 626–640 (2007)4

The $^{236}$U neutron capture cross-section measured at the n_TOF CERN facility

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The $^{236}$ U neutron capture cross-section measured at the n_TOF CERN facility

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The $^{236}$ U neutron capture cross-section measured at the n_TOF CERN facility