Radiative neutron capture on 242Pu in the resonance region at the CERN n_TOF-EAR1 facility

PHYSICAL REVIEW C 97, 024605 (2018) Radiative neutron capture on 242Pu in the resonance region at the CERN n_TOF-EAR1 facility J. Lerendegui-Marco,1C. Guerrero,1,*E. Mendoza,2J. M. Quesada,1K. Eberhardt,3A. R. Junghans,4M. Krtiˇcka,5O. Aberle,6 J. Andrzejewski,7L. Audouin,8V. Bécares,2M. Bacak,9J. Balibrea,2M. Barbagallo,10 S. Barros,11 F. Beˇcváˇr,5C. Beinrucker,12 E. Berthoumieux,13 J. Billowes,14 D. Bosnar,15 M. Brugger,6M. Caamaño,16 F. Calviño,17 M. Calviani,6D. Cano-Ott,2 R. Cardella,6A. Casanovas,17 D. M. Castelluccio,18,19 F. Cerutti,6Y. H. Chen,8E. Chiaveri,6N. Colonna,10 G. Cortés,17 M. A. Cortés-Giraldo,1L. Cosentino,20 L. A. Damone,10,21 M. Diakaki,13 M. Dietz,22 C. Domingo-Pardo,23 R. Dressler,24 E. Dupont,13 I. Durán,16 B. Fernández-Domínguez,16 A. Ferrari,6P. Ferreira,11 P. Finocchiaro,20 V. Furman,25 K. Göbel,12 A. R. García,2A. Gawlik,7T. Glodariu,26 I. F. Gonçalves,11 E. González-Romero,2A. Goverdovski,27 E. Griesmayer,9 F. Gunsing,6,13 H. Harada,28 T. Heftrich,12 S. Heinitz,24 J. Heyse,29 D. G. Jenkins,30 E. Jericha,9F. Käppeler,31 Y. Kadi,6 T. Katabuchi,32 P. Kavrigin,9V. Ketlerov,27 V. Khryachkov,27 A. Kimura,28 N. Kivel,24 M. Kokkoris,33 E. Leal-Cidoncha,16 C. Lederer,22 H. Leeb,9S. Lo Meo,18,19 S. J. Lonsdale,22 R. Losito,6D. Macina,6J. Marganiec,7T. Martínez,2C. Massimi,19,34 P. Mastinu,35 M. Mastromarco,10 F. Matteucci,36,37 E. A. Maugeri,24 A. Mengoni,18 P. M. Milazzo,36 F. Mingrone,19 M. Mirea,26 S. Montesano,6A. Musumarra,20,38 R. Nolte,39 A. Oprea,26 N. Patronis,40 A. Pavlik,41 J. Perkowski,7 J. I. Porras,6,42 J. Praena,1,42 K. Rajeev,43 T. Rauscher,44,45 R. Reifarth,12 A. Riego-Perez,17 P. C. Rout,43 C. Rubbia,6 J. A. Ryan,14 M. Sabaté-Gilarte,1,6A. Saxena,43 P. Schillebeeckx,29 S. Schmidt,12 D. Schumann,24 P. Sedyshev,25 A. G. Smith,14 A. Stamatopoulos,33 G. Tagliente,10 J. L. Tain,23 A. Tarifeño-Saldivia,23 L. Tassan-Got,8A. Tsinganis,33 S. Valenta,5G. Vannini,19,34 V. Variale,10 P. Vaz,11 A. Ventura,19 V. Vlachoudis,6R. Vlastou,33 A. Wallner,46 S. Warren,14 M. Weigand,12 C. Weiss,6,9C. Wolf,12 P. J. Woods,22 T. Wright,14 and P. Žugec6,15 (n_TOF Collaboration) 1Dpto. Física Atómica, Molecular y Nuclear, Universidad de Sevilla, 41012 Seville, Spain 2Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), Spain 3Johannes Gutenberg-Universitt Mainz, 55128 Mainz, Germany 4Helmholtz-Zentrum Dresden-Rossendorf, D-01314 Dresden, Germany 5Charles University, Prague, Czech Republic 6European Organization for Nuclear Research (CERN), Switzerland 7University of Lodz, Poland 8Institut de Physique Nucléaire, CNRS-IN2P3, Univ. Paris-Sud, Université Paris-Saclay, F-91406 Orsay Cedex, France 9Technische Universität Wien, Austria 10Istituto Nazionale di Fisica Nucleare, Sezione di Bari, Italy 11Instituto Superior Técnico, Lisbon, Portugal 12Goethe University Frankfurt, Germany 13CEA Irfu, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France 14University of Manchester, United Kingdom 15Department of Physics, Faculty of Science, University of Zagreb, Zagreb, Croatia 16University of Santiago de Compostela, Spain 17Universitat Politècnica de Catalunya, Spain 18Agenzia nazionale per le nuove tecnologie (ENEA), Bologna, Italy 19Istituto Nazionale di Fisica Nucleare, Sezione di Bologna, Italy 20INFN Laboratori Nazionali del Sud, Catania, Italy 21Dipartimento di Fisica, Università degli Studi di Bari, Italy 22School of Physics and Astronomy, University of Edinburgh, United Kingdom 23Instituto de Física Corpuscular, Universidad de Valencia, Spain 24Paul Scherrer Institut (PSI), Villingen, Switzerland 25Joint Institute for Nuclear Research (JINR), Dubna, Russia 26Horia Hulubei National Institute of Physics and Nuclear Engineering, Romania 27Institute of Physics and Power Engineering (IPPE), Obninsk, Russia 28Japan Atomic Energy Agency (JAEA), Tokai-mura, Japan 29European Commission, Joint Research Centre, Geel, Retieseweg 111, B-2440 Geel, Belgium 30University of York, United Kingdom 31Karlsruhe Institute of Technology, Campus North, IKP, 76021 Karlsruhe, Germany 32Tokyo Institute of Technology, Japan 33National Technical University of Athens, Greece 34Dipartimento di Fisica e Astronomia, Università di Bologna, Italy 35Istituto Nazionale di Fisica Nucleare, Sezione di Legnaro, Italy 36Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Italy 2469-9985/2018/97(2)/024605(21) 024605-1 Published by the American Physical Society J. LERENDEGUI-MARCO et al. PHYSICAL REVIEW C 97, 024605 (2018) 37Dipartimento di Astronomia, Università di Trieste, Italy 38Dipartimento di Fisica e Astronomia, Università di Catania, Italy 39Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany 40University of Ioannina, Greece 41University of Vienna, Faculty of Physics, Vienna, Austria 42University of Granada, Spain 43Bhabha Atomic Research Centre (BARC), India 44Centre for Astrophysics Research, University of Hertfordshire, United Kingdom 45Department of Physics, University of Basel, Switzerland 46Australian National University, Canberra, Australia (Received 2 November 2017; published 6 February 2018) The spent fuel of current nuclear reactors contains fissile plutonium isotopes that can be combined with uranium to make mixed oxide (MOX) fuel. In this way the Pu from spent fuel is used in a new reactor cycle, contributing to the long-term sustainability of nuclear energy. However, an extensive use of MOX fuels, in particular in fast reactors, requires more accurate capture and fission cross sections for some Pu isotopes. In the case of 242Pu there are sizable discrepancies among the existing capture cross-section measurements included in the evaluations (all from the 1970s) resulting in an uncertainty as high as 35% in the fast energy region. Moreover, postirradiation experiments evaluated with JEFF-3.1 indicate an overestimation of 14% in the capture cross section in the fast neutron energy region. In this context, the Nuclear Energy Agency (NEA) requested an accuracy of 8% in this cross section in the energy region between 500 meV and 500 keV. This paper presents a new time-of-flight capture measurement on 242Pu carried out at n_TOF-EAR1 (CERN), focusing on the analysis and statistical properties of the resonance region, below 4 keV. The 242Pu(n,γ ) reaction on a sample containing 95(4) mg enriched to 99.959% was measured with an array of four C6D6detectors and applying the total energy detection technique. The high neutron energy resolution of n_TOF-EAR1 and the good statistics accumulated have allowed us to extend the resonance analysis up to 4 keV, obtaining new individual and average resonance parameters from a capture cross section featuring a systematic uncertainty of 5%, fulfilling the request of the NEA. DOI: 10.1103/PhysRevC.97.024605 I. MOTIVATION The future of nuclear energy points to the use of innovative nuclearsystems suchas acceleratordrivensystems andGen-IV reactors aimed at the reduction of the nuclear waste. The burned fuel from current thermal reactors can be recycled in order to separate the plutonium from the spent fuel. This plutonium contains around 66% of 239Pu and 241Pu (together), which are fissile and can be thus combined with natural or depleted uranium to make the mixed oxide (MOX) fuel. In this way the Pu from spent fuel and the depleted uranium, otherwise considered as waste, are used in a new reactor cycle, contributing to the long-term sustainability of nuclear energy. The use of MOX fuels has already been established on an industrial scale in thermal power reactors in several countries, but a more efficient use can be achieved in fast reactors [1]. The design and operation of these innovative systems require improved knowledge of the neutron cross sections of some of the isotopes present in the new fuel compositions such as the MOX [2]. Among the neutron cross sections that *[email protected] Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. need to be improved in terms of accuracy, the NEA Subgroup WPEC-26 [3] recommends that the capture cross section of 242Pu should be measured with an accuracy of 8–10 % in the energy range between 2 keV and 500 keV (see Table I), which includes both the resolved and unresolved resonance regions. The first attempts to measure the 242Pu(n,γ ) reaction were made in 1973 and 1975, when Poortmans et al. [4] and Hockenbury et al. [5] used the time-of-flight technique for measurements below 1.3 keV at the CBNM linear accelerator (Geel,Belgium)and between 6and87 keVatRPI(Troy,USA), respectively. A few years later, Wisshak and Käppeler [6,7] measured the cross section in the unresolved resonance region in two energy intervals, 10–90 keV and 50–250 keV. Recently, another time-of-flight measurement was carried out with the DANCE detector at LANSCE by Buckner et al. [8], covering the region from thermal to 40 keV but resolving resonances only up to 500 eV due to the limited neutron energy resolution of the DANCE facility. Their results, with a final systematic uncertainty around 6%, show a fairly good agreement with the evaluations in the resonance region and a systematic reduction of 20–30 % above 1 keV compared to ENDF/B-VII [9] (it is to be noted that JEFF-3.2 [10] is in agreement with ENDF/B-VII around 1 keV but 10–20 % larger at ∼10 keV). The comparison of the measurements in the keV region shows differences of about 35%. Indeed, interpretations with the JEFF-3.1 library of the PROFIL and PROFIL-2 experiments carried out in the fast reactor PHENIX have shown an overestimation of about 14% of the 242Pu integral capture cross 024605-2 RADIATIVE NEUTRON CAPTURE ON 242Pu IN THE … PHYSICAL REVIEW C 97, 024605 (2018) TABLE I. Current and required (NEA) accuracy of the 242Pu(n,γ ) cross section for innovative nuclear systems. ADS: accelerator driven system. SFR: sodium fast reactor. Ref. Nuclear Energy Accuracy (%) device range Current Required HPRL [14] (MOX fuel) 0.5 eV–2 keV a8 WPEC-26 [3] ADS 9–25 keV 35 10 WPEC-26 [3] SFR 2–500 keV 35 8 aCurrent accuracy not stated. Improved accuracy below 2 keV is required to extract accurate individual and average resonance parameters (see text for details). section from 1 keV–1 MeV [11–13]. Aiming at improving the evaluation of the fast energy range in terms of average parameters, the NEA, in its Nuclear Data High Priority Request List (HPRL) [14], requests high-resolution capture measurements with improved accuracy below 2 keV (see Table I). This should also allow us to solve the present discrepancies among average resonance parameters in the literature (see Table VII). In order to respond to the target accuracies required by the NEA in different energy ranges, listed in Table I,anew time-of-flight measurement of the capture cross section of 242Pu was proposed and approved by the CERN INTC [18] in 2013. The measurement was carried out at n_TOF-EAR1 in 2015 and preliminary results have been already presented in Refs. [19,20]. While the measurement has provided data from thermal up to at least 200 keV, this paper deals only with the analysis of the resolved resonance region, which has been extended from 1.3 keV to 4 keV. In the next section we describe brieflythe n_TOF-EAR1facility,the samples andthe detection setup. The data analysis towards the capture yield is described in Sec. III. Last, the analysis of the individual resonances and their statistical properties are discussed in Secs. IV and V, respectively. II. MEASUREMENT AT N_TOF A. n_TOF facility at CERN The neutron beam at n_TOF is generated through spallation of 20 GeV/c protons extracted in pulses from the CERN Proton Synchrotron and impinging on cylindrical lead target 40 cm in length and 60 cm in diameter. These pulses feature a nominal intensity of 7 ×1012 protons, delivered with a time spread of σ=7 ns at a maximum frequency of 0.83 Hz. The resulting high-energy (MeV-GeV) spallation neutrons are partially slowed down in a surrounding water layer to produce a white neutron beam that expands in energy from thermal to a few GeV. The neutrons travel towards the two experimental areas along two beam lines: EAR1 at 185 m (horizontal) [21] and EAR2 at 19 m (vertical) [22]. Each of the experimental areas is better suited for different type of measurements depending on the specific requirements in terms of flux and resolution. While EAR1 features a better time (i.e., neutron energy) resolution, the shorter vertical beam line of EAR2 provides a poorer resolution but currently the highest instantaneous white neutron flux worldwide (see Ref. [23]), FIG. 1. Sketch of the sample assembly composed of seven thin 242Pu deposits on 10 μm thick Al backings (see text for details). which makes it especially well suited for measuring highly radioactive and/or small mass samples (see, for instance, Ref. [24]). The measurement of the 242Pu(n,γ ) at n_TOF, aiming at describing accurately the resonance region and not affected by a high radioactivity background, was therefore performed at EAR1. B. 242Pu and ancillary measurements The sample preparation was carried out within the EC CHANDA project [25] by the JGU University of Mainz and the HZDR research center in Germany. The material used was 99.959% pure 242Pu (main impurities: 2 ×10−4 and 2 ×10−5of 240Pu and 244Pu, respectively) provided by ORNL. A set of seven thin targets 45 mm in diameter, in order to cover the complete neutron beam, were prepared by electrodeposition of 95(4) mg of 242Pu on thin (10 μm) aluminumbackingswitha50nmTicoating,resultingintargets with an average areal density of 850 μg/cm2of 242Pu, with variations between targets within 7% (see Ref. [26]forthe details).Thetargetthicknesshomogeneity,studiedbymeansof alpha radiography, was found to be 75%, leading to an overall thickness inhomogeneity of the seven targets combined below 0.1%. The assembly of seven thin targets, sketched in Fig. 1, features a total backing thickness of only 70 μm. This value is significantly smaller than in previously used actinide targets at n_TOF (see, for instance, Refs. [27–29]) and results in a reduced neutron capture and scattering associated background. During the experiment, with a total number of 3.17 ×1018 protons (i.e., approximately one month long), most (64%) of the beam time was allocated to measure the Pu target. The background induced by the sample assembly was determined with an exact replica of the Pu target without the Pu deposits using 24% of the beam time. This replica will be called the dummy target hereafter. The background caused by the γ rays in the beam was assessed by using a lead (1 mm thick) 024605-3 J. LERENDEGUI-MARCO et al. PHYSICAL REVIEW C 97, 024605 (2018) target that scatters photons without perturbing significantly the neutron beam. The measurement of a thick (100 μm) gold target with the same diameter as the 242Pu one was used for normalization via the saturated resonance method [30], and a measurement with no target in the beam was used to estimate the background level in the lead and gold measurements. Last, measurements without beam were carried out without and with the242Putargetsinplacefordeterminingtheenvironmentaland 242Pu activity backgrounds. The details about the background subtraction and normalization are given in Sec. IIIA. C. Detection setup As of today, two different detection systems are available at n_TOF for capture experiments. The full γ-ray cascade can be detected using the 4πBaF2total absorption calorimeter (TAC) [31], or just one of the γrays of each cascade (total energy detection technique, see Sec. IIIB) is detected with an array of four low neutron sensitivity C6D6detectors [32]. The array of four C6D6was chosen for this measurement mainly because these detectors suffer significantly less from the so-called γflash (i.e., prompt γrays produced in the spallation reactions) than the TAC, due to their fast response and light components, thus allowing us to measure up to the maximum required neutron energy (see Table I). The setup of four detectors looking at the target from a backward position (135° with respect to the beam) in order to minimize the background from scattered in-beam γrays is shown in the top panel of Fig. 2. The bottom panel shows the corresponding geometry implemented in the Monte Carlo simulation with FIG. 2. Top: Array of four C6D6detectors used to detect the γ-ray cascades emitted following the neutron capture on the 242Pu sample. Bottom: Geometry implemented in GEANT4 to simulate the response of the detection setup. the GEANT4 toolkit [33,34] used for assessing the detection efficiency (see Sec. IIIB). Two additional detectors are used at n_TOF for monitoring the proton and neutron beams. A wall current monitor (so-called PKUP) measures the intensity of the proton beam in each pulse. The neutron beam is monitored with the SiMon system [35], an array of four silicon detectors placed outside the beam and looking at a thin enriched lithium fluoride foil for detecting the products of the 6Li(n,α) reaction, whose cross section is considered a standard from thermal energy to 1 MeV. The pulse-by-pulse intensities provided by these two detectors have been found to be proportional within 0.5%, which sets the accuracy in the scaling when comparing or combining different measurements, for instance for background subtraction and normalization. Eachof thedetectors inthe capturesetup andthe beammonitoring system is connected to one channel of the n_TOF Data acquisition system [36], which features 12-bit digitizers samplingat 900 MSamples/sduring 100 ms followingthe arrival of the proton pulse to the spallation target (i.e., recording signals of reactions induced by neutrons for energies down to 18 meV). The full data movies are automatically transferred from the DAQ computers to the CERN Advanced Storage manager (CASTOR) for their long-term storage and off-line analysis. III. ANALYSIS A. Data reduction The digitized signals recorded by the n_TOF DAQ and stored in CASTOR are analyzed using the pulse shape analysis routine described in Ref. [37]. In particular, the C6D6signals are analyzed by comparing each of them with reference pulse shapes characteristic of each detector (see Refs. [37,38]for details). The amplitude, area and time-of-flight of each identified detector signal are stored together with the information on the proton pulse (date, time, type, and intensity). The corresponding neutron energy is then calculated using the nonrelativistic formula: En=1 2mnL0+λ(En) t−t02 ,(1) where mnis the neutron mass, L0is the flight path from the target exit to the experimental area, tis the signal time, t0 is the start time (calculated from the arrival of the γflash to each detector), and λ(En) is an energy-dependent equivalent moderation length, related to the resolution function of the facility. The neutron energy dependence of λreflects the fact that neutrons of a given energy are not produced instantaneously with the arrival of the proton beam but take some time to be produced, moderated, and transported outside the spallation target assembly (see Ref. [39] for a more detailed explanation). Accurate amplitude-to-energy calibrations and gain stability checks for the four C6D6detectors were performed on a weekly basis using 137Cs, 88Y, 241Am/9Be, and 244Cm/13C calibration sources. The small time-dependent gain shifts observed were corrected for and, as a result, the weighted (defined in Sec. IIIB) counting rates remained constant within 0.5% along the full length of the experiment (one month). 024605-4 RADIATIVE NEUTRON CAPTURE ON 242Pu IN THE … PHYSICAL REVIEW C 97, 024605 (2018) Neutron energy (eV) 1 10 2 10 3 10 4 10 5 10 Counts/(bin pulse) 4− 10 3− 10 2− 10 1− 10 Total counts Beam-on background (dummy) Beam-off background Total background Deposited energy (MeV) 0123456 Counts/(bin pulse) 2− 10 1− 10 1Total counts Beam-on background (dummy) Total beam-off background Total background Total counts Beam-on background (dummy) Beam-off background Total background < 4 keV n 1 eV < E Deposited energy (MeV) 0123456 Counts/(bin pulse) 4− 10 3− 10 2− 10 1− 10 Total counts Beam-on background (dummy) Total beam-off background Total background Total counts Beam-on background (dummy) Beam-off background Total background < 3.1 eV n 2.1 eV < E FIG. 3. Unweighted counting rates per pulse for the 242Pu and background measurements as a function of the neutron energy in the full energy range measured at n_TOF-EAR1 (top). Energy deposition in the C6D6detectors corresponding to the full neutron energy range analyzed in this paper (1 eV–4 keV) (middle) and with neutron energy cuts to select just the largest resonance (2.67 eV) (bottom). The measured counting rates as a function of neutron energy (with energy deposited in the detectors Edep larger than 150 keV) are displayed in the top panel of Fig. 3, where it is observed that the beam-off background (constant in time) dominatesonly below10 eV. Thebeam-dependent background (dotted red line), determined with the measurement of the dummy target, is the major contribution to the counting rate at higher energies. The dashed green (light gray) curve in this figure shows the level of the overall background, in which the in-beam γ-ray background is also included. The latter, although strongly suppressed due to the inclusion of 10Bin the moderator (see Ref. [21]), is still a relevant source of backgroundespeciallyintheunresolvedresonanceregion[19]. Last, the counting rate increases at neutron energies above 306 keV. This is related to the opening of the first inelastic channel above the γ-ray energy detection threshold. The middle and bottom panels of Fig. 3show the measured counting rates as a function of the deposited γ-ray energy. While the middle panel contains data for all the neutron energy rangeunderstudy, thebottom panelcorresponds justto neutron energies inside the first capture resonance (2.1–3.3 eV). The latter hence shows an enhanced capture to background ratio compared to the detector response integrated over the full neutron energy range of the resonance region. The spectra of deposited energy indicate that the beam-off, i.e., the room and 242Pu sample activity background are mainly low energy γ rays while the high-energy γ-ray background is related to the beam (dummy). Besides neutron capture, two additional neutron-induced reactions in 242Pu can contribute to the measured counting rate: neutron scattering and fission. Considering the elastic scattering, the cross section is 10–100 times larger than capture but the C6D6detectors have a negligible neutron sensitivity (4 orders of magnitude below the efficiency for capture). Therefore, the neutron scattering contribution has been considered negligible. As for the fission, the efficiency of the detection array is slightly larger than for capture due to the larger γ-ray multiplicity. However, it is also considered negligible since the fission cross section in the energy range of interest remains on average 3 orders of magnitude below the one of capture with the exception of few resonances excluded from the resonance analysis (see Sec. IV), B. Total energy detection technique The detection efficiency depends, in general, on the cascade pattern (i.e., the γ-ray energies and multiplicities). To avoid this dependency, neutron capture measurements with C6D6 detectors are analyzed following the total energy detection (TED) technique [40,41]. This is based on two principles: (i) The efficiency of the detectors must be low enough so that at most one γray per cascade is detected. The total efficiency for detecting a cascade εcbecomes εc=1− i (1 −εi)≈ i εi,(2) εibeing the efficiency to detect a γray of the cascade. The sum goes over all emitted gammas i. (ii) The efficiency to detect each γray is proportional to its energy Ei(εi=k·Ei), hence: εc=k i Ei=k·Ec.(3) 024605-5 J. LERENDEGUI-MARCO et al. PHYSICAL REVIEW C 97, 024605 (2018) Under these two conditions the efficiency for detecting a cascadeisproportional totheknownenergyofthecascade (Ec) and independent of the actual decay path. However, the second requirement is not fulfilled by C6D6detectors and therefore a mathematical manipulation of the detector response is needed to achieve the proportionality between detection efficiency and γ-ray energy: the counts recorded at each deposited energy are weighted by a factor dependent on its energy (pulse height), given by the so-called weighting function (WF). This is known as the pulse height weighting technique (PHWT) [41]. Following the prescription from Ref. [41], the WF for each sample (242Pu and 197Au) has been calculated from the detector response to monoenergetic γrays from 50 keV–10 MeV obtained via Monte Carlo simulations of the detection system carried out with a GEANT4 application developed for this purpose [42]. The very detailed geometry implemented in GEANT4, displayed in Fig. 2, includes even details of the Pu target assembly in order to consider, among other effects, the attenuation of photons in the 242Pu targets and backings as well as the neutron self-shielding for the largest resonances. The resulting WFs, calculated to have a proportionality constant k=1inEq.(3), are third- to fourth-degree polynomials (depending on the sample). The application of these WFs to the response of the detectors allows satisfying the proportionality condition εi=k·Eiwithin 1% for all the simulated γ-ray energiesbetween0.1and10 MeV.Thecorrectionsandsystematic uncertainties associated to this technique are discussed in the following section. C. Corrections to the detection efficiency The application of the PHWT results in a detection efficiency numerically equal to the energy of the capture cascade [Eq. (3) with k=1]. This is in principle independent of the decay pattern, but there are actually some effects and corrections to be considered: (i) the possible detection of more than one γray (multiple counting) from a cascade in our detection setup, fmc; (ii) the counts lost below the detection threshold in γ-ray energy, fthr; and (iii) the probability of internal conversion leading to the emission of nondetectable electrons instead of γrays, fce. The associated corrections fmc,fthr, and fce are calculated with the help of Monte Carlo simulations of the detection system response to capture cascades. The cascade generator CAPTUGENS [43] was used to generate realistic cascades emitted by the compound nuclei 243Pu and 198Au at an excitation energy Sn,consideringinbothcasesacompletelyknownlevelscheme, γ-ray transition probabilities, and internal conversion factors (all from ENSDF [44]) below a certain excitation energy Ecut (400 keV for 243Pu and 1600 keV for 198Au), and then a statisticalmodel (based on leveldensity parametersand photon strength functions) to generate transitions starting above Ecut. The statistical parameters were taken from Refs. [45] and [46]for198Au and 243Pu, respectively. The generated cascades were coupled to the GEANT4 application developed to simulate the detector response for the PHWT, resulting in the good Deposited energy (MeV) 01234567 counts/(bin pulse) 10 2 10 3 10 4 10 5 10 Captugens + Geant4 ) @ 2.67 eVγPu(n, 242 Deposited energy (MeV) 01234567 Counts/(bin pulse) 10 2 10 3 10 4 10 5 10 Captugens + Geant4 ) @ 4.9 eVγAu(n, 197 FIG. 4. Top: Energy deposited spectrum in the C6D6in the 2.67 eV 242Pu(n,γ ) resonance compared to the simulated response. Bottom: Experimental response compared to the simulated one for the 4.9eVresonanceof197Au(n,γ )crosssection.Thelow-energyfraction missing in the experimental spectra fthr is corrected according to the simulations. agreement between the experimental and simulated responses shown in Fig. 4for both 242Pu(n,γ ) and 197Au(n,γ ) cascades. The correction factors are calculated by comparing the efficiency from the simulation of cascades when each of these effects is included with respect to the expected value εc=Ec, given by Eq. (3) with k=1. The fmc correction, below 0.5%, is already applied during the analysis by considering only one of the simultaneously detected γrays (i.e., belonging to the same capture cascade). fthr and fce have been calculated for several detection thresholds, showing that fce is at most 0.4% for the minimum threshold of 150 keV applied in the subsequent analysis. Therefore only fthr is sizable and quite different for each isotope, ranging up to 15% and 8% for 242Pu(n,γ ) and 197Au(n,γ ), respectively, for energy thresholds smaller than 250 keV. In order to keep this correction small, a threshold of 150 keV was used for the analysis. The values of correction factors obtained and their associated uncertainties are summarized in Table II. Thevalidation ofthesecorrectionsisassessedbycomparing the corresponding corrected counting rates for different energy 024605-6 RADIATIVE NEUTRON CAPTURE ON 242Pu IN THE … PHYSICAL REVIEW C 97, 024605 (2018) TABLE II. Yield correction factors related to the deviations from the PHWT theory, being just fthr sizable with the actual experimental conditions.Theuncertainties inthetable arederived fromthestatistics in the simulations. Ethr fthr fce fmc 250 keV 200 keV 150 keV 150 keV 242Pu 1.150(4) 1.121(4) 1.090(3) 1.004(3) 0.995(3) 197Au 1.078(3) 1.066(3) 1.052(3) 1.001(3) 0.998(3) 242Pu/197Au 1.067(4) 1.052(4) 1.035(4) thresholds.Theresultsforthresholdsbetween 150and250keV agree within 0.2% and 1% for 197Au(n,γ ) and 242Pu(n,γ ), respectively. Therefore, a systematic uncertainty of 1.5% has been estimated for these corrections. Additionally, the simulated cascades allow to estimate the deviation from the PHWTtheorygivenbyEq.(3) relatedtotheperformanceofthe weighting functions. The deviation is found to be within 0.5% for both the 242Pu and Au samples and this value is considered as the associated uncertainty. D. Capture yield The neutron capture yield is the probability for an incident neutron to undergo a capture reaction and is related to the capture σγand total σtot cross sections as: Y(En)=(1 −e−nσtot )σγ σtot ,(4) where nrepresent the sample’s areal density. Under the thin target approximation nσtot 1, which applies in this measurement with the exception of the largest resonance, the capture cross section can be directly extracted from the experimentally obtained capture yield Y=nσγ. The latter is calculated as: Y(En)=fmcfthrfce fSRM ·Cw(En)−Bw(En) (En)·εc ,(5) Cwand Bwbeing the weighted distributions of total and background counts per pulse obtained from the measured counting rates displayed in Fig. 3,(En) the total number of neutrons of a given energy Enreaching n_TOF-EAR1 in each pulse [47], εcthe detection efficiency [see Eq. (3)] and fmc, fthr, and fce the correction factors to the efficiency discussed intheprevioussection.Last,fSRM istheabsolutenormalization factor obtained via the saturated resonance method (SRM) [30] using the first (4.9 eV) resonance of 197Au. The 100 μm thicknessof thegold targetissuch thatthis resonancesaturates, i.e., almost all neutrons undergo at least one interaction, and this saturation level provides the means to normalize the 242Pu capture yield. The saturated resonance of 197Au has been fitted for each detector to extract individual normalization factors fSRM, as listed in Table III. Figure 5shows the fit of this resonance in the average yield of the four detectors using the SAMMY code [48]. The deviations in fSRM between the individual detectors are related mainly to uncertainties in the efficiency and in the positioning (distance and angle) of the detectors with respect to the target. Both effects affect equally to the 197Au and 242Pu TABLE III. Normalization factors fSRM obtained for each detector from the fit of the 197Au(n,γ ) 4.9 eV saturated resonance using the SAMMY code. The right column presents the ratios of the individual normalized 242Pu 2.67 eV resonance kernels, Ynorm, with respect to the average value of the four detectors, Ynorm. The uncertainties in the table are due the uncertainty in the fit of the saturated resonance and the counting statistics. fSRM Ynorm/ (Ethr =150 keV) Ynorm C6D6-1 0.853(3) 1.012(4) C6D6-2 0.994(3) 1.003(4) C6D6-3 0.891(3) 0.990(4) C6D6-4 0.914(3) 0.995(4) All C6D60.914(2) measurements and therefore cancel out with this normalization method.Averificationofthecorrectnessof theindividualfSRM comes from the fact that the 2.67 eV resonance kernels in the normalized 242Pu yields from individual detectors agree with the average within about 1%, as presented in Table III. The systematic uncertainties from different sources contributing to the resulting yield are summarized in Table IV.The uncertainty related to the relative positioning along the beam line of the 197Au and 242Pu samples is assumed to be ±1 mm, leading to a 1.5% additional uncertainty in the normalization. Table IV also includes the energy-dependent uncertainty of the neutronfluxshape,1%below100eV and2%athigher energies [47]. It is to be noted that the uncertainty in the background subtraction is considered negligible because it does not affect the analysis of individual resonances. The resulting quadratic sum of partial systematic uncertainties in the 242Pu yield is 3.2% or smaller. An additional uncertainty of 4% related to the determination of the sample mass has to be considered Yield 0.2 0.4 0.6 0.8 1)γAu(n, 197 SAMMY Fit Neutron energy (eV) 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8 Residuals 4− 2− 0 2 4 FIG. 5. Saturated resonance at 4.9 eV in the experimental capture yield of 197Au fitted with the SAMMY code. The average of the four detectors is shown. 024605-7 J. LERENDEGUI-MARCO et al. PHYSICAL REVIEW C 97, 024605 (2018) TABLE IV. Summary of the estimated individual systematic uncertainties contributing to the final uncertainty in the 242Pu capture yield grouped according to their origin. The uncertainty in the sample mass contributes additionally in the extraction of the cross section from the capture yield. The upper limit in the total systematic uncertainties corresponds to the energy range 100 eV <E n<4keV. General group Partial origin Syst. unc. (%) Neutron flux Flux shape (En<100 eV) 1 Flux shape (100 eV <E n<4 keV) 2 Efficiency (PHWT) Efficiency correction factors 1.5 Deviation PHWT theory 0.5 Gain shift 0.5 Normalization Deviation yields individual detectors 1 Relative position Au/Pu 1.5 Beam monitors 0.5 Sample mass 4 Total (capture yield) <3.2 Total (cross section) <5.1 in the subsequent extraction of the capture cross section. The resulting systematic uncertainty in the cross section is 5.1% or smaller, clearly lower than the 8% required by the NEA for the design and operation of advanced nuclear devices (see Table I). One last consideration in the calculation of the yield is relatedtothe statisticalfluctuations.The captureyieldobtained using the prescription of the PHWT shows enhanced statistical fluctuations, especially in the resonances with few counts, with respect to those related to counting statistics. These enhanced fluctuations,inherentinthePHWTmethod,limitthemaximum energy of analyzable resonances. In order to expand the energy range in the subsequent resonance analysis, we have verified that for 242Pu (may be true for heavy 0+nuclei, in general), the cascade spectrum is the same independently of the neutron energy. Thus, the unweighted yield scaled with the appropriate averageweighting factor, which accounts for the efficiency and the associated corrections described in this section, is perfectly compatible within the uncertainties with the one extracted following the usual PHWT method. Given all of the above, the unweighted scaled yield has been chosen for the analysis in Sec. IV. IV. RESONANCE ANALYSIS A. Individual resonance parameters Once the capture yield has been obtained, the resonance analysis is performed using the SAMMY code [48], which allows fitting experimental time-of-flight data using the Reich- MooreapproximationtotheR-matrixtheory.Thecodefeatures different models to consider experimental effects such as self-shielding, multiple scattering, residual background, and Doppler and resolution broadenings. A total of 251 resonances have been observed and analyzed between 1 eV and 4 keV, leaving out of our analysis the few resonances where fission contributes significantly (see Table VIII). In order to extract the individual resonance parameters, first the spin of all resonances have been set to J=1/2 (meV) γ Γ 23 23.5 24 24.5 25 25.5 26 26.5 27 27.5 28 (meV) n Γ 2 2.02 2.04 2.06 2.08 2.1 2.12 2.14 2.16 2.18 2.2 (meV) γ Γ 20 21 22 23 24 25 26 27 28 29 30 (meV) n Γ 45 50 55 60 65 70 FIG. 6. Two-dimensional (2D) plots showing the evolution of the reduced χ2of the fit (color scale) as a function of the n-γvalues for the 2.67 eV (top) and 53.5 eV (bottom) resonances. (assumed to be s-waves) since 242Pu is an even-even target. Then, the fission widths have been fixed to the values measured by Auchampaugh et al. [49] or Weigmann et al. [50], assuming a value of 0.01 meV for the rest, as recommended in JEFF-3.2 (see Table VIII). The radiative capture width is expected to be a constant (actually, it is expected from statistical model to fluctuate around the average value with a rms of about ∼3% [51]). In order to determine the value of γ, a systematic studyof the χ2ofthe SAMMY calculations (experimentalcature yield vs. parameterized yield as a function of γand n)was carried out among the largest resonances below 1.5 keV, using those showing a well-bound γaround the minimum χ2to computetheaverageγ.Theaveragevalueγresultingfrom this analysis has been used as a fixed parameter for the analysis of all the other resonances, where the only free parameters are the resonance energy and neutron width. An example of the mentioned distributions of the reduced χ2(i.e., χ2over the number of experimental points) as a function of the radiative and neutron width values is given in Fig. 6for the two largest resonances, both showing a well-bound minimum. While this method worked for the majority of the fitted resonances, some SAMMY fits of resonances with nγ, featuring a very low sensitivity to nin the fit, converged after many iterations towards too large nvalues, inconsistent with the evaluated resonance parameters extracted from a multichannel analysis of all available measurements. For those cases, the nwas 024605-8 RADIATIVE NEUTRON CAPTURE ON 242Pu IN THE … PHYSICAL REVIEW C 97, 024605 (2018) Neutron energy (keV) 0.332 0.334 0.336 Yield 0 0.001 0.002 0.003 0.004 This work JEFF 3.2 : 28.5, 70 meV n Γ, γ Γ : 24.9, 125 meV n Γ, γ Γ Neutron energy (keV) 0.591 0.592 0.593 0.594 0.595 0.596 Yield 0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016 This work JEFF 3.2 : 28.2, 38 meV n Γ, γ Γ : 18.8, 230 meV n Γ, γ Γ Neutron energy (keV) 0.792 0.794 0.796 0.798 Yield 0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 This work JEFF 3.2 : 24.7, 200 meV n Γ, γ Γ : 23.8, 300 meV n Γ, γ Γ FIG. 7. Example of the sensitivity of resulting SAMMY fits to different combination of nand γshowing the compatibility of the fit with overestimated n(red/dark gray) compared to the fit with a nvalue consistent with evaluations (green/light gray). JEFF-3.2 is also shown as a reference (dotted blue line). bound to a smaller value consistent with the evaluations and then the γwas fitted. Figure 7shows the most extreme cases where one can see that a large reduction in ndoes not compromise the quality of the fit. The difficulties to adjust non capture data are due to the absence of transmission data withthe same sample to constrain the value ofnin the SAMMY calculation. Regarding the Doppler model used in the calculations with SAMMY, this plays a role only at low energies. Indeed, the analysis of the lowest-energy resonance with the commonly employed free gas model (FGM) is not satisfactory, giving, for instance, a reduced χ2of 4.7. The use of the more realistic crystal lattice model (CLM), in this case with a uranium oxide phonon description (SAMMY example file 124d), results in a better fit, as shown in Fig. 8, with a reduced χ2of only 1.9. Regarding the second largest resonance, at 53.5 eV, the fits are excellent with both models and the extracted radiative kernels agree within 0.1%. Therefore the resonances at higher energies were all analyzed using the FGM, since the difference with Yield 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 This work SAMMY CLM SAMMY FGM JEFF 3.2 CLM Residuals 10− 5− 0 5 10 Neutron energy (eV) 2.58 2.6 2.62 2.64 2.66 2.68 2.7 2.72 2.74 2.76 Residuals 10−5−0 5 10 FIG. 8. SAMMY fits and residuals of the largest 242Pu capture resonance using free gas (FGM) and a crystal lattice (CLM) models to describe the Doppler broadening. The fit obtained using the resonance parameters in JEFF-3.2 or ENDF/B-VII.1 (CLM) is shown as a reference. respect to the results with the CLM are negligible but the computing time is significantly reduced. The resulting list of individual resonance parameters and radiative kernels up to 4 keV is presented in Table VIII of Appendix. In this table several resonances are marked as possible pwaves. The criterion for marking possible p-wave resonances is based on the probability of occurrence of p-wave resonances (see next section). Figure 9shows several energy ranges of the measured capture yield below 1.3 keV together withthecorresponding SAMMY fitandthe yieldscorresponding to the ENDF/B-VII [9] and JEFF-3.2 [10] evaluated cross sections. The good neutron energy resolution of n_TOF-EAR1 combined with the high statistics of the new capture data have allowed us to extend the resolved resonance region up to 4 keV, which is significantly higher than the current limit in the evaluations, which are based on the resonance parameters reported in Refs. [4,49,50]. This extension is illustrated in Figs. 9–10, showing SAMMY fits from just above the current 920 eV and 1.3 keV energy limit for resonance parameters in ENDF/B-VII.1 [9] and JEFF-3.2 [10], respectively, up to 4 keV. In the resonance analysis above 1.3 keV, the energies and neutron widths in Refs. [49,50] were used as initial parameters for the fit and to help identifying small resonances. B. Comparison to evaluated cross sections The different resonances displayed in Fig. 9are illustrative examples of resonances currently present in the evaluations that can be confirmed (75) or rejected (7) according to the new capturedata.Forinstance,we confirmthe presenceof adoublet at 504 eV, as already suggested by Poortmans et al. [4], but we do not see the resonance at 14 eV listed in evaluations, confirming what Buckner et al. reported [8]. In addition, 19 new resonances have been identified within JEFF-3.2’s resonance region (some examples in Fig. 9). Since these new resonances are usually weak, some of them are most likely p-wave resonances, as it is discussed in Sec. V. The quantitative cross-section comparison between the results of this work and of JEFF-3.2 is made in terms of radiative kernel (RK), calculated from the resonance parameters as: RK=gJ γn γ+n+f ,(6) 024605-9 J. LERENDEGUI-MARCO et al. PHYSICAL REVIEW C 97, 024605 (2018) TABLE VIII. (Continued.) Energy J γgJnfRKn_TOF/JEFF n_TOF/DANCE (eV) (meV) (meV) (meV) (meV) 149.838(3)a0.5 24.8 13.71(20) 0.0554 8.9(8) 0.983(9) 1.19(10) 163.69(21)a0.5 24.8 0.49(4) 0.01 0.48(4) 0.91(7) 0.93(11) 205.022(3)a0.5 23.7(3) 52.0(19) 0.0548 16.29(24) 1.093(16) 1.10(6) 210.24(5)a0.5 24.8 0.3(4) 0.01 0.29(4) 0.7(10) 0.71(12) 215.488(7)a0.5 24.8 5.48(14) 0.184 4.48(9) 0.991(21) 0.89(7) 219.54(6)a,d,e (0.5) 24.8 0.28(4) 0.01 0.28(4) 0.97(15) 1.10(9) 232.942(8)a0.5 24.8 5.61(17) 0.131 4.58(11) 1.09(3) 1.19(21) 264.7(7)a,d,e (0.5) 24.8 0.36(6) 0.01 0.36(6) 0.95(16) 1.00(19) 272.41(8)a,d,e (0.5) 24.8 0.32(6) 0.01 0.32(6) 1.9(4) 2.0(4) 273.786(7)a0.5 24.8 14.8(5) 0.102 9.35(19) 1.001(20) 0.97(7) 275.07(9)a,d,e (0.5) 24.8 0.27(6) 0.01 0.27(6) 1.6(4) 1.6(4) 281.2(13)a,d,e (0.5) 24.8 0.16(5) 0.01 0.16(5) 1.3(4) 1.2(4) 298.873(10)a0.5 24.8 9(3) 0.01 6.65(18) 1.06(3) 1.04(9) 303.727(8)a0.5 26.6(13) 17.8(5) 0.067 10.6(3) 1.09(3) 1.04(7) 317.53(11)b,d (0.5) 24.8 0.33(9) 0.01 0.33(8) – – 320.096(7)a0.5 26.7(4) 230(16) 0.017 23.9(4) 1.121(17) 1.36(5) 328.97(14)b,d (0.5) 24.8 0.2(8) 0.01 0.2(8) – – 332.642(8)a0.5 28.5(7) 70(5) 0.018 20.3(6) 0.95(3) 0.97(8) 341.97(13)b,d (0.5) 24.8 0.39(1) 0.01 0.39(11) – – 374.484(19)a0.5 24.8 6.2(3) 0.01 5(19) 0.99(4) 0.96(9) 380.52(19)a,d,e (0.5) 24.8 0.18(7) 0.01 0.18(7) 0.7(3) 0.7(3) 382.548(10)a0.5 22.7(6) 50(4) 0.085 15.6(5) 1.02(3) 0.98(7) 400.19(4)a0.5 24.8 1.97(18) 0.01 1.83(16) 1.21(10) 1.10(14) 410.845(18)a0.5 24.8 8.7(4) 0.01 6.47(23) 1.15(4) 1.05(9) 424.27(3)a0.5 24.8 4.6(3) 0.18 3.86(19) 1.11(5) 1.11(11) 425.68(17)a,d,e (0.5) 24.8 0.31(11) 0.01 0.31(11) 1.1(4) 1.1(4) 468.42f,c,d 0.5 24.2 0.03 30 – – – 473.73(9)a,e 0.5 24.8 1.2(19) 0.32 1.13(17) 1.24(19) 1.20(22) 482.896(16)a0.5 28.2(17) 23.5(12) 0.42 12.7(5) 1.16(5) 1.13(9) 486.97(19)b,d (0.5) 24.8 0.34(12) 0.01 0.34(12) – – 495.11(21)a,d,e (0.5) 24.8 0.29(12) 0.01 0.29(11) 1.1(4) 1.08(4) 504.033(21)g0.5 24.8 29(6) 0.19 13.6(13) – – 504.749(16)g,b 0.5 24.8 60(10) 0.19 17.9(9) – – 536.81(14)a0.5 25.9(8) 96(11) 0.043 20.4(7) 1.18(4) – 548.81(17)a0.5 22.3(9) 74(10) 0.077 17.1(8) 0.92(4) – 576.532(16)a0.5 24.8 44(4) 0.01 16.2(5) 1.21(4) – 591.02(15)b,d (0.5) 24.8 1.02(24) 0.01 0.98(22) – – 595.427(20)a0.5 28.2(17) 38(3) 0.021 16.2(8) 1.28(6) – 598.65(18)b,d (0.5) 24.8 0.95(25) 0.021 0.92(23) – 600.21(3)a0.5 24.8 10.4(8) 0.102 7.3(4) 1.11(6) – 604.48(16)b,d (0.5) 24.8 0.99(24) 0.1 0.95(22) – – 611.14(3)a0.5 24.8 13.1(10) 0.064 8.6(4) 1.08(6) – 639.44(7)a0.5 24.8 4.3(4) 0.04 3.7(3) 0.98(9) – 660.27(13)b,d (0.5) 24.8 0.78(22) 0.066 0.76(20) – – 670.28(3)a0.5 24.8 15.5(13) 0.051 9.6(5) 1.14(6) – 693.56(3)a0.5 29.1(20) 40(4) 0.24 16.8(9) 1.25(7) – 712.18(3)a0.5 25.9(11) 121(29) 0.163 21.3(12) 1.27(7) – 713.9(16)b,d (0.5) 24.8 1.6(4) 0.01 1.5(3) – – 727.71(9)a0.5 24.8 3.8(5) 0.05 3.3(4) 1.17(14) – 737.23(3)a0.5 26.1(12) 105(20) 0.45 20.8(11) 1.06(6) – 748.04(19)b,d (0.5) 24.8 1.3(3) 0.05 1.2(3) – – 755.75(3)a,c 0.5 21.5 130 1.6 – – – 762.8(5)a,c 0.5 24.2 5.6 440 – – – 789.28(4)a,c 0.5 24.2 64 1.6 – – 794.52(3)a0.5 24.7(11) 201(78) 0.043 22(13) 1.02(6) – 825.28(9)a0.5 24.8 6(8) 0.21 4.8(5) 1.24(14) – 831.91(21)b,d (0.5) 24.8 1.4(4) 0.01 1.3(4) – – 024605-16 RADIATIVE NEUTRON CAPTURE ON 242Pu IN THE … PHYSICAL REVIEW C 97, 024605 (2018) TABLE VIII. (Continued.) Energy J γgJnfRKn_TOF/JEFF n_TOF/DANCE (eV) (meV) (meV) (meV) (meV) 838.45(4)a0.5 25.3(21) 39(5) 0.041 15.3(11) 1.17(8) – 857.09(4)a0.5 27(3) 34(4) 0.093 15.2(11) 1.13(8) – 866.38(6)a0.5 24.8 12.5(14) 0.043 8.4(6) 1.16(9) – 873.74(11)b0.5 24.8 6.1(9) 0.043 4.9(6) – – 879.64(4)a0.5 23.2(17) 59(10) 0.027 16.6(12) 0.97(7) – 887.31(5)a0.5 28(4) 23.0(24) 0.0155 12.6(11) 0.99(8) – 908.4(3)b,d (0.5) 24.8 0.8(3) 0.01 0.8(3) – – 913.31(21)b,d (0.5) 24.8 1.8(5) 0.01 1.7(4) – – 923.73(5)a0.5 21.4(17) 59(12) 0.029 15.7(12) 1.14(9) – 936.76(8)a0.5 24.8 10.8(15) 0.01 7.6(7) 1(9) – 950.35(8)a0.5 24.8 12.4(16) 0.01 8.4(7) 0.92(8) – 978.81(8)a0.5 24.8 12.9(18) 0.01 8.6(8) 0.94(9) – 1005.34(5)a0.5 31(3) 43(6) 0.01 18.0(15) 1.16(9) – 1024.04(25)b,d (0.5) 24.8 2.2(7) 0.01 2(6) – – 1031.36(5)a0.5 23.4(23) 46(8) 0.01 15.5(14) 0.98(9) – 1046.19(6)a0.5 20.6(15) 118(47) 0.01 17.5(15) 0.87(8) – 1063.55(6)a0.5 24.8 44(8) 0.01 16.2(10) 1.16(7) – 1088.99(6)a0.5 27.4(16) 200(77) 0.01 24.1(17) 1.12(8) – 1130.47(12)a0.5 24.8 12.7(20) 0.01 8.5(9) 1.2(13) – 1148.96(7)a0.5 23.4(14) 300(146) 0.01 21.7(14) 0.97(6) – 1185.47(13)a0.5 24.8 11.4(19) 0.01 7.9(9) 0.93(11) – 1198.78(7)a0.5 23.2(20) 95(33) 0.01 18.6(18) 0.97(9) – 1207.75(7)a0.5 24.8 49(10) 0.01 16.7(12) 1.11(8) – 1229.92(15)b0.5 24.8 8.8(18) 0.01 6.6(10) – – 1239.1(3)b,d (0.5) 24.8 2.3(8) 0.01 2.1(7) – – 1249.31(14)a0.5 24.8 11.1(20) 0.01 7.8(10) 1.18(15) – 1268.96(10)a0.5 24.8 26(5) 0.01 12.9(11) 1.01(9) – 1288.33(9)a0.5 23(3) 59(16) 0.01 16.6(18) 0.97(10) – 1330.64(9)b0.5 24.8 67(20) 0.01 18.5(15) – – 1342.22(10)b0.5 24.8 33(7) 0.01 14.3(13) – – 1351.5(4)b,d (0.5) 24.8 1.7(8) 0.01 1.6(7) – – 1354.03(14)b0.5 24.8 18(4) 0.01 10.5(13) – – 1368.19(8)b0.5 24.8 210(95) 0.01 22.7(11) – – 1393.75(25)b0.5 24.8 6.2(16) 0.01 5.0(10) – – 1405.81(25)b0.5 24.8 6.5(16) 0.01 5.2(10) – – 1414.3(4)b,d (0.5) 24.8 2.1(8) 0.01 2(7) – – 1433.3(14)b0.5 24.8 19(4) 0.01 10.9(14) – – 1455.55(9)b0.5 24.8 103(40) 0.01 20.4(16) – – 1503.71(17)b0.5 24.8 17(4) 0.01 10.3(14) – – 1509.97(19)b0.5 24.8 12(3) 0.01 8.2(13) – – 1527.4(3)b,d (0.5) 24.8 3.9(14) 0.01 3.4(10) – – 1540.04(21)b0.5 24.8 12(3) 0.01 8(13) – – 1560.5(3)b,d (0.5) 24.8 4.6(16) 0.01 3.9(12) – – 1567.35(12)b0.5 24.8 499(195) 0.01 24.3(5) – – 1578.5(3)b,d (0.5) 24.8 5.1(15) 0.01 4.3(11) – – 1598.4(4)b0.5 24.8 7.2(22) 0.01 5.6(13) – – 1623.39(12)b0.5 24.8 106(42) 0.01 20.5(16) – – 1642.26(13)b0.5 24.8 62(21) 0.01 18.1(17) – – 1654.26(22)b0.5 24.8 15(4) 0.01 9.6(15) – – 1675.8(3)b0.5 24.8 7.1(20) 0.01 5.6(12) – – 1687.7(3)b0.5 24.8 8.4(24) 0.01 6.3(13) – – 1696.7(14)b0.5 24.8 55(18) 0.067 17.4(18) – – 1708.93(13)b0.5 24.8 199(85) 0.001 22.6(11) – – 1723.9(4)b,d (0.5) 24.8 3.7(14) 0.1 3.2(11) – – 1739.9(4)b,d (0.5) 24.8 7(3) 0.1 5.3(17) – – 1740.7(3)b0.5 24.8 9(3) 0.1 6.4(18) – – 1752.6(3)b0.5 24.8 8.6(25) 0.51 6.3(13) – – 024605-17 J. LERENDEGUI-MARCO et al. PHYSICAL REVIEW C 97, 024605 (2018) TABLE VIII. (Continued.) Energy J γgJnfRKn_TOF/JEFF n_TOF/DANCE (eV) (meV) (meV) (meV) (meV) 1763.6(18)b0.5 24.8 37(10) 0.017 15.1(17) – – 1779(4)b,d (0.5) 24.8 6.3(21) 0.51 4.9(13) – – 1807.4(3)b0.5 24.8 7.6(23) 0.13 5.9(13) – – 1838.1(4)c0.5 – – – – – – 1845.8(3)b0.5 24.8 11(3) 0.01 7.6(15) – – 1863.11(20)b0.5 24.8 34(10) 0.49 14.4(17) – – 1882.81(17)b0.5 24.8 303(130) 0.056 23.5(8) – – 1892.2(3)b0.5 24.8 15(4) 0.96 9.4(16) – – 1897.3(4)b,d (0.5) 24.8 7(3) 1 5.6(15) – – 1906.05(22)b0.5 24.8 33(11) 0.01 14.4(20) – – 1914(4)b,d (0.5) 24.8 5.6(21) 0.01 4.6(14) – – 1928.82(18)b0.5 24.8 361(159) 0.01 23.8(7) – – 1947.2(4)b,d (0.5) 24.8 6.3(24) 0.01 5.1(15) – – 1953.2(4)b,d (0.5) 24.8 5.5(21) 0.01 4.5(14) – – 1974.6(3)b0.5 24.8 10(3) 0.01 7.2(18) – – 1983.85(19)b0.5 24.8 71(27) 0.01 18.8(19) – – 2006.25(20)b0.5 24.8 86(35) 0.01 19.6(18) – – 2018.2(4)b,d (0.5) 24.8 9(3) 0.01 6.6(18) – – 2023.35(19)b0.5 24.8 187(88) 0.01 22.4(13) – – 2038.41(20)b0.5 24.8 99(41) 0.01 20.3(17) – – 2057.21(19)b0.5 24.8 183(86) 0.01 22.4(13) – – 2068.1(4)b0.5 24.8 9(3) 0.01 6.7(19) – – 2074.5(4)b0.5 24.8 12(4) 0.01 8(19) – – 2082.2(4)b0.5 24.8 13(4) 0.01 8.5(20) – – 2115.71(23)b0.5 24.8 77(31) 0.01 19.1(20) – – 2121(3)b0.5 24.8 18(6) 0.01 10.4(21) – – 2141.1(4)b0.5 24.8 11(4) 0.01 7.6(20) – – 2166.5(3)b0.5 24.8 21(7) 0.01 11.6(22) – – 2186.8(23)b0.5 24.8 120(53) 0.01 21(16) – – 2209.9(3)b0.5 24.8 47(18) 0.01 16.6(22) – – 2223.3(3)b0.5 24.8 28(10) 0.01 13.2(23) – – 2229.6(4)b0.5 24.8 12(5) 0.01 8(22) – – 2265.2(3)b0.5 24.8 37(14) 0.01 15.1(23) – – 2271(4)b0.5 24.8 13(5) 0.01 8.4(22) – – 2276.5(3)b0.5 24.8 226(108) 0.01 22.9(11) – – 2291.8(5)b,d (0.5) 24.8 8(3) 0.01 6.3(19) – – 2303.7(3)b0.5 24.8 36(14) 0.01 14.8(24) – – 2311.3(3)b0.5 24.8 239(119) 0.01 23(11) – – 2315(4)b0.5 24.8 18(7) 0.01 10.4(25) – – 2338.6(3)b0.5 24.8 86(39) 0.01 19.7(21) – – 2351.9(5)b0.5 24.8 43(22) 0.01 16(3) – – 2359.9(4)b0.5 24.8 14(6) 0.01 9.1(23) – – 2366.9(5)b0.5 24.8 12(5) 0.01 8.1(22) – – 2384.6(4)b0.5 24.8 19(7) 0.01 11(24) – – 2401.6(4)b0.5 24.8 33(13) 0.01 14.4(25) – – 2424.7(4)b0.5 24.8 14(6) 0.01 9.2(25) – – 2431.1(4)b0.5 24.8 17(7) 0.01 10.1(24) – – 2446.4(4)b0.5 24.8 34(14) 0.01 14.7(25) – – 2459.7(4)b0.5 24.8 21(8) 0.01 11.6(25) – – 2471(4)b0.5 24.8 41(17) 0.01 15.8(24) – – 2497.9(3)b0.5 24.8 88(39) 0.01 19.8(20) – – 2525.7(5)b0.5 24.8 12(5) 0.01 8.3(23) – – 2538.9(4)b0.5 24.8 18(7) 0.01 11(3) – – 2549.4(5)b0.5 24.8 19(7) 0.01 10.7(24) – – 2563.7(3)b0.5 24.8 178(83) 0.01 22.3(13) – – 2605.2(4)b0.5 24.8 39(16) 0.01 15.5(24) – – 024605-18 RADIATIVE NEUTRON CAPTURE ON 242Pu IN THE … PHYSICAL REVIEW C 97, 024605 (2018) TABLE VIII. (Continued.) Energy J γgJnfRKn_TOF/JEFF n_TOF/DANCE (eV) (meV) (meV) (meV) (meV) 2623(4)b0.5 24.8 17(8) 0.01 10(3) – – 2637.4(3)b0.5 24.8 230(108) 0.01 23(11) – – 2702.6(5)b0.5 24.8 167(82) 0.11 22.1(14) – – 2703.6(5)b0.5 24.8 147(71) 0.11 21.7(15) – – 2736.2(4)b0.5 24.8 163(73) 0.094 22(13) – – 2745.5(6)b,d (0.5) 24.8 11(4) 1.5 7.3(19) – – 2758.7(4)b0.5 24.8 124(61) 0.031 21.1(18) – – 2794.2(5)b0.5 24.8 28(11) 0.01 13(3) – – 2811.1(5)b0.5 24.8 14(7) 0.01 9(3) – – 2816.8(5)b0.5 24.8 23(10) 0.01 12(3) – – 2871.6(4)b0.5 24.8 494(237) 0.01 24.2(6) – – 2889.5(5)b0.5 24.8 19(9) 0.01 11(3) – – 2904.8(5)b0.5 24.8 21(10) 0.01 12(3) – – 2916.5(4)b0.5 24.8 249(118) 0.01 23.1(10) – – 2931.7(5)b0.5 24.8 44(19) 0.01 16(3) – – 2941.3(4)b0.5 24.8 63(28) 0.01 18.1(23) – – 2947.7(4)b0.5 24.8 68(31) 0.01 18.6(23) – – 2974.3(4)b0.5 24.8 86(39) 0.01 19.7(20) – – 2993.9(4)b0.5 24.8 68(30) 0.01 18.5(22) – – 3002.7(4)b0.5 24.8 115(57) 0.01 20.9(19) – – 3012.6(5)b0.5 24.8 34(15) 0.01 15(3) – – 3045.6(5)b0.5 24.8 21(10) 0.01 11(3) – – 3058.4(5)b0.5 24.8 60(28) 0.01 18(3) – – 3076.8(5)b0.5 24.8 89(41) 0.01 19.8(20) – – 3137.3(5)b0.5 24.8 62(28) 1.2 17.8(24) – – 3145(5)b0.5 24.8 340(167) 1.22 23.6(8) – – 3159.1(5)b0.5 24.8 143(67) 0.01 21.6(15) – – 3178.6(5)b0.5 24.8 85(39) 0.01 19.6(21) – – 3192.5(6)b,d (0.5) 24.8 16(7) 0.01 10(3) – – 3197(5)b0.5 24.8 37(17) 0.01 15(3) – – 3215.8(6)b0.5 24.8 40(19) 0.01 16(3) – – 3219.5(5)b0.5 24.8 112(55) 0.01 20.8(19) – – 3228.5(5)b0.5 24.8 62(29) 0.01 18.1(24) – – 3250.6(5)b0.5 24.8 68(31) 0.01 18.5(23) – – 3270.1(5)b0.5 24.8 52(24) 0.01 17(3) – – 3282.5(5)b0.5 24.8 55(26) 0.01 17(3) – – 3326.3(5)b0.5 24.8 188(90) 0.01 22.5(13) – – 3378.8(5)b0.5 24.8 72(34) 0.01 18.8(23) – – 3408.7(6)b0.5 24.8 25(12) 0.01 13(3) – – 3416.9(5)b0.5 24.8 187(97) 0.009 22.4(14) – – 3426.3(6)b0.5 24.8 51(24) 0.01 17(3) – – 3442.4(6)b0.5 24.8 31(14) 0.01 14(3) – – 3456.7(5)b0.5 24.8 233(116) 0.13 23(11) – – 3477.7(5)b0.5 24.8 118(57) 0.11 21(18) – – 3491.7(6)b0.5 24.8 105(52) 0.28 20.5(20) – – 3501.4(6)b0.5 24.8 236(115) 0.36 23(11) – – 3513.1(5)b0.5 24.8 127(60) 0.01 21.2(17) – – 3524.8(5)b0.5 24.8 157(76) 0.2 21.9(15) – – 3533.6(6)b0.5 24.8 59(28) 0.01 18(3) – – 3545.5(6)b0.5 24.8 28(14) 0.01 13(3) – – 3560.8(6)b0.5 24.8 43(20) 0.01 16(3) – – 3586.8(6)b0.5 24.8 321(156) 0.18 23.6(8) – – 3624.9(7)b,d (0.5) 24.8 12(6) 0.29 8(3) – – 3656.1(6)b0.5 24.8 161(79) 0.67 21.9(15) – – 3664.8(6)b0.5 24.8 40(20) 0.01 16(3) – – 3674.2(6)c0.5 – – – – – – 3705.3(7)b,d (0.5) 24.8 14(7) 0.01 9(3) – – 024605-19 J. LERENDEGUI-MARCO et al. PHYSICAL REVIEW C 97, 024605 (2018) TABLE VIII. (Continued.) Energy J γgJnfRKn_TOF/JEFF n_TOF/DANCE (eV) (meV) (meV) (meV) (meV) 3727.9(6)b0.5 24.8 200(180) 0.05 22.7(15) – – 3742.3(6)b0.5 24.8 76(36) 0.01 19.1(23) – – 3764.1(6)b0.5 24.8 48(23) 0.01 17(3) – – 3777.4(7)b0.5 24.8 370(182) 0.21 23.8(8) – – 3794.7(6)b0.5 24.8 84(40) 0.07 19.5(22) – – 3806.3(6)b0.5 24.8 70(34) 0.07 18.7(24) – – 3816.5(7)b0.5 24.8 115(55) 0.015 20.9(18) – – 3818.6(6)b0.5 24.8 452(229) 0.015 24.1(7) – – 3841.3(7)b,g 0.5 24.8 37(25) 0.05 15(4) – – 3843.7(6)b,g 0.5 24.8 57(35) 0.05 18(3) – – 3882.5(6)b0.5 24.8 88(42) 0.01 19.8(21) – – 3909.3(7)b0.5 24.8 25(12) 0.01 13(3) – – 3926.2(6)b0.5 24.8 64(31) 0.01 18.3(25) – – 3938.3(6)b0.5 24.8 57(27) 0.01 18(3) – – 3959.6(6)b0.5 24.8 72(37) 0.01 19(3) – – aIncluded in JEFF-3.2. bNot included in JEFF-3.2. cLarge (Non-negligible) fission width: Not analyzed, parameters in the table from JEFF-3.2 (En<1.3 keV). dp-wave candidate: Spin could not be assigned. ep-wave resonance in ENDF/B-VII.1. fResonance in JEFF-3.2 below the experimental threshold in 0: Neither confirmed nor rejected. gDoublet. 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