Measurement and analysis of the 241 Am neutron capture cross section at the n_TOF facility at CERN

PHYSICAL REVIEW C 97, 054616 (2018) Measurement and analysis of the 241Am neutron capture cross section at the n_TOF facility at CERN E. Mendoza,1,*D. Cano-Ott,1S. Altstadt,2S. Andriamonje,3J. Andrzejewski,4L. Audouin,5J. Balibrea,1V. Bécares,1 M. Barbagallo,6F. Bečvář,7F. Belloni,3B. Berthier,5E. Berthoumieux,3J. Billowes,8D. Bosnar,9M. Brugger,10 F. Calviño,11 M. Calviani,10 C. Carrapiço,12 F. Cerutti,10 E. Chiaveri,10,3M. Chin,10 N. Colonna,6G. Cortés,11 M. A. Cortés-Giraldo,13 M. Diakaki,14 I. Dillmann,15 C. Domingo-Pardo,2I. Durán,16 N. Dzysiuk,17 C. Eleftheriadis,18 A. Ferrari,10 K. Fraval,3 V. Furman,19 M. B. Gómez-Hornillos,11 S. Ganesan,20 A. R. García,1G. Giubrone,21 I. F. Gonçalves,12 E. González,1 A. Goverdovski,22 F. Gramegna,17 E. Griesmayer,23 C. Guerrero,10,13 F. Gunsing,3P. Gurusamy,20 T. Heftrich,2S. Heinitz,24 A. Hernández-Prieto,10,11 J. Heyse,25 D. G. Jenkins,26 E. Jericha,23 F. Käppeler,27 Y. Kadi,10 D. Karadimos,14 T. Katabuchi,28 V. Ketlerov,22 V. Khryachkov,22 P. Koehler,29 M. Kokkoris,14 J. Kroll,7M. Krtička,7C. Lampoudis,3C. Langer,2 E. Leal-Cidoncha,16 C. Lederer,30 H. Leeb,23 L. S. Leong,5J. Lerendegui-Marco,13 M. Licata,31,32 D. López,1R. Losito,10 A. Manousos,18 J. Marganiec,4T. Martínez,1C. Massimi,31,32 P. Mastinu,17 M. Mastromarco,6A. Mengoni,33 P. M. Milazzo,34 F. Mingrone,31 M. Mirea,35 W. Mondelaers,25 C. Paradela,16 A. Pavlik,30 J. Perkowski,4A. J. M. Plompen,25 J. Praena,13,36 J. M. Quesada,13 T. Rauscher,37 R. Reifarth,2A. Riego-Perez,11 M. Robles,16 F. Roman,35 C. Rubbia,10 J. A. Ryan,8 M. Sabaté-Gilarte,10,13 R. Sarmento,12 A. Saxena,20 P. Schillebeeckx,25 S. Schmidt,2D. Schumann,24 P. Sedyshev,19 G. Tagliente,6J. L. Tain,21 A. Tarifeño-Saldivia,21 D. Tarrío,16 L. Tassan-Got,5A. Tsinganis,10 S. Valenta,7G. Vannini,31,32 V. Variale,6P. Vaz,12 A. Ventura,31 M. J. Vermeulen,26 R. Versaci,10 V. Vlachoudis,10 R. Vlastou,14 A. Wallner,38 T. Ware,8 M. Weigand,2C. Weiss,23 T. Wright,8and P. Žugec9 (n_TOF Collaboration) 1Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), Spain 2Goethe University Frankfurt, Germany 3CEA Saclay, Irfu, Gif-sur-Yvette, France 4University of Lodz, Poland 5Institut de Physique Nucléaire, CNRS-IN2P3, Université Paris-Sud, Université Paris-Saclay, F-91406 Orsay Cedex, France 6Istituto Nazionale di Fisica Nucleare, Sezione di Bari, Italy 7Charles University, Prague, Czech Republic 8University of Manchester, United Kingdom 9Department of Physics, Faculty of Science, University of Zagreb, Croatia 10European Organization for Nuclear Research (CERN), Switzerland 11Universitat Politècnica de Catalunya, Spain 12Instituto Superior Técnico, Lisbon, Portugal 13Universidad de Sevilla, Spain 14National Technical University of Athens, Greece 15Technische Universität München, Garching, Germany 16University of Santiago de Compostela, Spain 17Istituto Nazionale di Fisica Nucleare, Sezione di Legnaro, Italy 18Aristotle University of Thessaloniki, Thessaloniki, Greece 19Joint Institute for Nuclear Research (JINR), Dubna, Russia 20Bhabha Atomic Research Centre (BARC), India 21Instituto de Física Corpuscular, Universidad de Valencia, Spain 22Institute of Physics and Power Engineering (IPPE), Obninsk, Russia 23Technische Universität Wien, Austria 24Paul Scherrer Institut (PSI), Villingen, Switzerland 25European Commission, Joint Research Centre, Geel, Retieseweg 111, B-2440 Geel, Belgium 26University of York, United Kingdom 27Karlsruhe Institute of Technology, Campus North, IKP, 76021 Karlsruhe, Germany 28Tokyo Institute of Technology, Japan 29Oak Ridge National Laboratory (ORNL), Oak Ridge, Tennessee 37831, USA 30University of Vienna, Faculty of Physics, Vienna, Austria 31Istituto Nazionale di Fisica Nucleare, Sezione di Bologna, Italy 32Dipartimento di Fisica e Astronomia, Università di Bologna, Italy 33Agenzia nazionale per le nuove tecnologie (ENEA), Bologna, Italy 34Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Italy 35Horia Hulubei National Institute of Physics and Nuclear Engineering, Romania 36Universidad de Granada, Spain 2469-9985/2018/97(5)/054616(21) 054616-1 Published by the American Physical Society E. MENDOZA et al. PHYSICAL REVIEW C 97, 054616 (2018) 37Department of Physics, University of Basel, Switzerland 38Australian National University, Canberra, Australia (Received 31 January 2018; published 24 May 2018) The 241Am(n,γ ) cross section has been measured at the n_TOF facility at CERN with the n_TOF BaF2Total Absorption Calorimeter in the energy range between 0.2 eV and 10 keV. Our results are analyzed as resolved resonances up to 700 eV, allowing a more detailed description of the cross section than in the current evaluations, which contain resolved resonances only up to 150–160 eV. The cross section in the unresolved resonance region is perfectly consistent with the predictions based on the average resonance parameters deduced from the resolved resonances, thus obtaining a consistent description of the cross section in the full neutron energy range under study. Below 20 eV, our results are in reasonable agreement with JEFF-3.2 as well as with the most recent direct measurements of the resonance integral, and differ up to 20–30% with other experimental data. Between 20 eV and 1 keV, the disagreement with other experimental data and evaluations gradually decreases, in general, with the neutron energy. Above 1 keV, we find compatible results with previously existing values. DOI: 10.1103/PhysRevC.97.054616 I. INTRODUCTION To improve the design of new advanced nuclear reactors and for determining their performance in the transmutation of nuclear waste, it is important to reduce the present neutron cross section uncertainties of minor actinides [1–3]. In particular, 241Am is one of the most abundant minor actinides in spent fuels, and capture is the dominant reaction in this nucleus at low neutron energies. In addition, the reprocessing of Am is technologically more advanced than for other minor actinides. Improved experimental cross section data for the 241Am(n,γ ) reaction was one of the objectives of the ANDES project within the Seventh Framework Programme of the European Commission. Therefore, four time-of-flight (TOF) measurements were planned and carried out. In this paper we present the results of one of these measurements. The other three have been already published: one of them, which is also a capture measurement, was performed with the same sample and in the same facility but with different γ-ray detectors [4]; the other two are a transmission and a capture measurement performed at JRC-Geel, with a different sample [5]. In addition there are several other measurements, both TOF and integral, which present significant discrepancies among one another. As a consequence, it is not surprising that there are also large discrepancies among the evaluated libraries. Indeed, these discrepancies are being investigated through an international collaborative working group organized by NEA-OECD [6]. The 241Am(n,γ ) cross section measurement presented in this paper was performed at the n_TOF facility at CERN [7] using the n_TOF Total Absorption Calorimeter (TAC). Capture cross section data were obtained for incident neutron energies between 0.2 eV and 10 keV. In Sec. II we describe the experimental setup. The data reduction procedures to derive *[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. the experimental capture yield, which will be made available for the EXFOR database [8], are presented in Sec. III.The results of a resonance shape analysis are reported in Sec. IV and compared with results of other experiments and evaluations in Sec. V. Finally, the conclusions of this work are presented in Sec. VI. II. THE EXPERIMENTAL SETUP A. The n_TOF facility at CERN The n_TOF facility at CERN [7,9,10] is a high instantaneous intensity pulsed neutron source designed to study neutronnucleus interactions for neutron kinetic energies ranging from a few meV to several GeV. Neutrons are produced every 1.2 s (or multiples of this interval) from spallation reactions by a20GeV/c proton beam delivered by the CERN Proton Synchrotron (PS) with 16 ns FWHM time resolution impinging on a 1.3 tonne cylindrical lead target 40 cm in length and 60 cm in diameter. The target is surrounded by a coolant circuit of 1-cm-thick water, followed by 4 cm of borated water (H2O+ 1.28% H3BO3, fraction in mass) which moderates the initially fast neutron spectrum.1At present neutrons travel through two evacuated beam lines, a horizontal and a vertical one at angles of 10◦and 90◦with respect to the direction of the proton beam, respectively. However, the vertical beam line [11] had not been built when this measurement was made in 2010. The horizontal beam line reaches a measuring station located at a distance of 182.3 m from the spallation target and has a length of 7.9 m. A sweeping magnet placed along the beam line prevents the charged particles from reaching the measuring station and two collimators give the appropriate shape to the neutron beam. There are about 1.2×105neutrons per nominal pulse of 7×1012 protons between 0.1 eV and 10 keV reaching the irradiation position. The energy dependence of the neutron beam was determined with three different detectors [12]: a 1The n_TOF facility was closed at the end of the 2004 campaign. It was opened again in 2009 (Phase-II), with a different lead block and coolant circuit, which are the ones described here. 054616-2 MEASUREMENT AND ANALYSIS OF THE 241Am … PHYSICAL REVIEW C 97, 054616 (2018) FIG. 1. Schematic view of part of the n_TOF Total Absorption Calorimeter. Modules in front of the beam pipe and the upper hemisphere of the neutron absorber are not shown. silicon flux monitor [13] (SiMon), a Micromegas gas detector [14], and a calibrated fission chamber from Physikalisch Technische Bundesanstalt (PTB) [15], which are based on the 6Li(n,t), 10B(n,α) and 235U(n,f ) standard reactions [16], respectively. The first two detectors were in place during the 241Am(n,γ ) measurement. The spatial distribution of the neutron beam at the irradiation position can be approximated by a two-dimensional (2D) Gaussian distribution with σx= σy=0.62 cm and does not vary significantly in the studied energy range [17,18]. The TOF response function, described in Ref. [7], is not very different from the one of the n_TOF Phase-I, whose more detailed description can be found in Ref. [19]. B. The detection system To detect the 241Am(n,γ ) events we used the n_TOF TAC [20]. This detector, shown in Fig. 1, consists of 40 BaF2crystals of 15 cm in length covering ∼95% of the solid angle and is used to detect in coincidence (nearly) all the γrays coming from the capture reactions. Each crystal is covered with two layers of 0.1-mm-thick Teflon foil and a 0.1-mm-thick polished aluminum sheet on the outside, to optimize the light collection. The crystals are also enclosed in 1-mm-thick 10B loaded carbon fiber capsules aimed at absorbing the scattered neutrons. Each of these capsules is coupled with an aluminum cylinder that houses a 12.7-cm Photonis XP4508B photomultiplier and a special voltage divider made at the Instituto Tecnológico e Nuclear in Lisbon that favors a fast signal recovery. The complete modules are attached to an aluminum honeycomb structure that holds the complete assembly. A neutron absorber made of borated polyethylene of 5- and 10-cm inner and outer radii, respectively, was placed in the center of the geometry, covering the inner surface of the TAC. The intensity of the neutron beam was monitored during the entire 241Am(n,γ ) campaign with the above-mentioned silicon flux monitor [13], which was mounted about 2 m upstream of the sample. This detector was used to normalize the different measurements to their total neutron beam intensity and also to confirm the stability of the energy profile of the neutron beam. The detector signals were recorded by a digital data acquisition system [21] based on Acqiris-DC270 digitizers with 8-bit resolution and operating most of the measurement at 250 MSamples/s, recording continuously for 32 ms for each neutron pulse, corresponding to a minimum neutron energy of 180 meV. Part of the measurement was performed with the digitizers operating at 500 MSamples/s, thus recording for 16 ms, corresponding to a minimum neutron energy of 0.7 eV. The data buffers were analyzed offline with dedicated pulse shape reconstruction algorithms. The algorithm used to analyze the BaF2signals returns for each signal the TOF, the area, and other parameters used to distinguish the detected particle type: γor α(the latter is produced by the decay of Ra impurities in the crystals). The algorithm is described in detail in Ref. [22], and a more accessible reference of a similar routine is Ref. [23]. Each BaF2detector was calibrated in energy from measurements performed with standard γ-ray sources (137Cs, 88Y, and Am/Be), and the gain drifts were monitored throughout the entire measurement with the position of peaks due to the detection of αparticles. An energy threshold of 300 keV was applied to each BaF2detector. This corresponds to the lowest value for which the energy calibration spectra were successfully reproduced by Monte Carlo simulations. The individual signals were grouped into TAC events using a coincidence window of 20 ns. Each TAC event is characterized by its TOF, total deposited energy (Esum) and crystal multiplicity (mcr), which is the number of detectors contributing to an event. The Esum and mcr values are used to apply cuts to the detected events in order to improve the capture-to-background ratio. In this paper, the word event always refers to these TAC events. C. The 241Am and auxiliary samples and measurements Thin powder samples of actinide oxides suffer from inhomogeneities [24–26] which can affect the resonance integrals (convolution with the neutron beam and self-shielding) and shape (due to self-shielding effects). For this reason, we took advantage of the technique developed at the Institute for Transuranium Elements (JRC-ITU) in Karlsruhe for producing homogeneous samples of actinide oxides mixed with an inert matrix. The sample was part of a set of 11 241Am samples produced by the JRC-ITU [27] for neutron total [5], capture [4,5], and (n,2n)[28] cross section measurements. Ten of these samples used Al2O3as inert matrix and the other one used Y2O3. Both Y and Al materials have similar properties from the neutronic point of view but for measuring above 1 keV Al has the advantage that resonances start at higher energies. The sample used for this experiment was made of 36.5 mg of 241AmO2infiltrated into a 305-mg Al2O3matrix. The fabrication procedure was as follows. Very small (10- to 100-μm) and porous alumina beads were introduced into a solution of the actinide in nitric acid. After some time, the beads absorbed a certain amount of actinide nitrates. Then the beads were dried and calcined, leading to a disperse mixture of AmO2inside the inert matrix. The powder was 054616-3 E. MENDOZA et al. PHYSICAL REVIEW C 97, 054616 (2018) TABLE I. Number of pulses and total number of counts in the silicon flux monitor dedicated to each measurement. Measurement No. pulses No. SiMon counts 241Am 1.41 ×1052.26 ×107 Dummy sample 2.63 ×1043.39 ×107 Al canning 3.27 ×1041.71 ×107 No sample 2.88 ×1044.43 ×106 Graphite 2.86 ×1033.42 ×106 241Am, beam off 4.32 ×103 No sample, beam off 5.85 ×103 197Au 1.09 ×1047.81 ×106 then pressed into a pellet of 342 mg and 12.26 mm in diameter for ensuring the mechanical stability, and encapsulated inside a 0.5-mm-thick Al canning. The mixture obtained in this way is very homogeneous, as it has been confirmed by different characterization techniques such as nondestructive xray radiographies or destructive α-particle autoradiographies, performed on slices of the pellets during the development of the methodology. The 241Am mass of the sample used in this work was 32.23(19) mg. The total amount of 241Am was determined by calorimetry at JRC Karlsruhe. The rest of the 241Am samples were prepared in a similar way, but with different 241Am contents. The masses of seven of these samples, none of them used in this work, were also measured at the JRC-Ispra [29], finding an excellent agreement with the measurements of the mass performed at JRC-ITU. Concerning impurities present in the sample, we detected 237Np (∼0.9 mg) and 240Pu (∼0.016 mg) during the resonance analysis. For the analysis the measured room temperature, 296 ±3K,wastakenas sample temperature. The sample was placed in the center of the TAC, glued on a 50-μm-thick kapton foil mounted in an aluminum ring with a diameter larger than the neutron beam. Due to the high sample activity (∼4 GBq), a 2-mm-thick Pb layer was placed around the neutron beam at the position of the sample in order to strongly reduce the amount of γrays originating in the sample decay and reaching the TAC. To determine the background, additional measurements with other samples were carried out. The list of samples included a dummy sample including the Al canning plus the Al2O3matrix, the Al canning, and a graphite sample 12 mm in diameter and 6 mm thick, which is used to determine the TAC response to sample scattered neutrons. We also performed measurements without beam and without sample (no sample, beam off), without beam but with the sample in place (241Am, beam off), and with neutron beam but without any sample. In addition, three 197Au samples were measured for normalization purposes. The number of pulses and total number of counts in the silicon flux monitor allocated to each of these measurements are summarized in Table I. III. DATA REDUCTION The data reduction process is similar to the one applied for previous measurements performed with the TAC [30–32]. 012345678910 Total deposited energy (MeV) 1 10 2 10 3 10 Counts/(pulse MeV) Am 241 Dummy sample Al canning Am - beam off 241 No sample - beam off )αB(n, 10 )γH(n, 1 ,p)αAl( 27 + Ra -decay)β( ,p)αAl( 27 )γAm(n, 241 )γAl(n, 27 FIG. 2. Total deposited energy in the TAC during the 241Am(n,γ ) and different background measurements. The data correspond to neutron energies between 1 and 10 eV and no cuts on mcr have been applied to the detected events. The capture yield is the fraction of incident neutrons that induce a (n,γ ) reaction and can be determined experimentally as Yn,γ (En)=Ctot(En)−Cbkg(En) ε(En)φ(En),(1) where Enis the neutron energy, Ctot(En) and Cbkg(En)are the number of total and background counts registered by the TAC, respectively, under certain Esum and mcr cuts, ε(En)isthe corresponding detection efficiency, and φ(En) is the intensity of the neutron beam intercepted by the sample. A. Background and selection of cuts in the detected events Background events in the 241Am(n,γ ) measurement can be attributed to two contributions: (i) events coming from neutron reactions in the 241Am nuclei, i.e., fission and elastic scattering, and (ii) the rest of the background, which results from the environmental background, the activity of the BaF2crystals, the sample activity, and the interaction of the neutron beam with all the materials except the 241Am nuclei. The latter contribution could be, in principle, obtained directly from the different background measurements summarized in Table I. The response of the TAC resulting from some of these measurements together with the one from a measurement with the 241Am sample, in terms of total deposited energy Esum, is presented in Fig. 2. A maximum deposited energy from 241Am(n,γ ) cascades is just above the neutron separation energy of 242Am, Sn(242Am) =5.5MeV. Other visible contributions are the 27Al(n,γ ) reaction, with Sn(28Al) =7.7 MeV, and the (n,γ ) and (n,α) reactions in 1H and 10B, respectively. The difference between the two measurements performed without the neutron beam is due to the sample activity, whose main contribution above 1 MeV is due to the interaction of the αparticles coming from the decay of the 241Am with the 27Al of the Al2O3matrix [33]. 054616-4 MEASUREMENT AND ANALYSIS OF THE 241Am … PHYSICAL REVIEW C 97, 054616 (2018) 1 10 2 10 3 10 4 10 Neutron energy (eV) 10 2 10 3 10 LnE)ΔCounts/(pulse Am 241 Dummy sample Al canning Am - beam off 241 No sample - beam off )γSm(n, FIG. 3. Number of events detected per pulse and per unit per unit lethargy (LnE, which means that the bin contents have been divided by the natural logarithm of the ratio between the upper and lower bin limits) in the 241Am(n,γ ) measurement as a function of the neutron energy, together with different background measurements. Only mcr >1and2.5<E sum <6 MeV events are shown. From Fig. 2it is easy to see that the capture-to-background ratio is significantly improved if the low (Esum <1MeV) and high (Esum >6 MeV) energy events are excluded from the analysis. This holds also for restrictions on mcr, because capture events have higher average multiplicity than the background ones. However, the more restricted the cuts are, the lower the detection efficiency becomes. In addition, there are pile-up effects induced by the high background counting rate which affect the detection of the capture signals (Sec. IIIB), and the more restricted the cuts are, the more important these effects become. A detailed analysis led to the optimum cuts of mcr >2 and 2.5<E sum <6 MeV, which were adopted in the present analysis. However, the capture yield has also been obtained for five additional combinations of cuts: 2.5<E sum <6 MeV and 3 <E sum <5 MeV, combined with mcr >0, mcr >1, and mcr >2. The differences between the six different yields were used to estimate uncertainties due to systematic effects in the results. The number of events detected per proton pulse for the same measurements as in Fig. 2, but with additional cuts in Esum and mcr, are presented in Fig. 3as a function of neutron energy. The difference between the measurements performed with the dummy and the Al canning samples should show only the effect of the interaction of the neutron beam with the Al2O3matrix. However, the results in Fig. 3reveal that an unexpected resonant behavior appears in the spectrum of the dummy sample. These resonances are due to Sm contamination. This contamination most likely comes from a glue used to repair the dummy sample, since it broke down before this 241Am(n,γ ) measurement was performed. Owing to this Sm contamination the background contribution of the Al2O3matrix could not be deduced directly from the dedicated background measurements, and some corrections which are described below were needed. The background components due to the Al canning and Al2O3matrix both have two components related to capture 1 10 2 10 3 10 Neutron energy (eV) 2− 10 1− 10 Capture yield + background Am 241 Dummy sample Background FIG. 4. Experimental 241Am(n,γ ) yield (non-background- subtracted) together with the calculated background, in blue, and the background obtained if the Sm impurities are not removed, in red. and neutron elastic scattering reactions in Al. The capture components are proportional to energy dependence of the Al(n,γ ) cross section, which at neutron energies of our interest is in first approximation proportional to the inverse of the neutron speed, i.e., E−1/2 n. The elastic components should have the same neutron energy dependence for both materials. From these assumptions it follows that BAl2O3(En)= αE−1/2 n+βBAlcanning(En), where αand βare constants and BAl2O3and BAlcanning are the background components related to the interaction of the neutron beam with the Al2O3matrix and with the Al canning, respectively. BAlcanning was easily obtained from the dedicated background measurements, and the αand β parameters were obtained by fitting BAl2O3(En)+B(Sm) to reproduce the measurement performed with the dummy sample. B(Sm) represents the contribution of the Sm impurities, which was deduced from the Sm(n,γ ) cross sections taken from the evaluated libraries. The resulting background is presented in Fig. 4. We used the background calculated in this way only up to 80 eV, where the influence of Sm impurities is quite strong in the resonance peaks and negligible in the valleys. Above 80 eV the contribution of the Sm is below 1%, so we took the background calculated from the dummy sample measurement, after subtracting the Sm contribution. The background related to elastic and fission reactions in the 241Am nuclei was estimated from the evaluated cross sections and the probability of detecting a scattered neutron and a fission reaction. The former probability, which depends on the neutron energy and on the Esum and mcr cuts, was obtained from the graphite sample measurement, under the assumption that the response of the TAC to neutrons scattered in carbon does not differ much from the response to neutrons scattered in 241Am. The probability of detecting a 241Am(n,f ) event was assumed to be similar to the probability of detecting a 235U(n,f ) event, which was determined in a 235U(n,γ ) measurement performed with the n_TOF TAC and a fission tagging detector [34]. Both contributions are very low in the energy range of interest and none of them introduces a sizable uncertainty in the measured 241Am(n,γ ) cross section. In particular, the fission cross section of 241Am is about 200 times lower than the capture cross section. The background due to the elastically scattered neutrons is also very low—less than 1% with respect 054616-5 E. MENDOZA et al. PHYSICAL REVIEW C 97, 054616 (2018) Total deposited energy (MeV) 012345678 Counts/(MeV ms) 0 2 4 6 8 10 12 Experimental Monte Carlo >0 cr m >1 cr m >2 cr m >3 cr m >4 cr m FIG. 5. Experimental (solid lines) and simulated (dotted lines) deposited energy spectra from 241Am capture cascades for different mcr cuts. The experimental data were obtained from the strong 241Am resonance at ∼0.3eV. to the capture reactions in the neutron energy range of interest for mcr >1ormcr >2 cuts. For mcr >0 the contribution is smaller than 1% only below 1 keV, and goes up to 2.5% at 10 keV. B. Detection efficiency The detection efficiency has been calculated from Monte Carlo simulations. The capture γ-ray cascades were generated with the DECAYGEN code [35], and transported into the TAC geometry (see Fig. 1) with a code based on the GEANT4 toolkit [36,37]. The results of the Monte Carlo code were then reconstructed in the same way as in the real experiment, including all the experimental effects such as the energy resolution of the crystals or the pile-up effects. The capture cascades generated by DECAYGEN depend on statistical models for the description of the level densities and photon strength functions. These models depend on some parameters, which were adjusted to reproduce the experimental deposited energy distributions for various mcr cuts. The quality of the results is illustrated in Fig. 5. A detailed description of the entire process is given in Ref. [38], and the method was also used in Refs. [31,32]. We did not find any significant difference in the shape of the deposited energy spectra among several resonances (Fig. 6), and thus it was assumed that the detection efficiency depends only on the applied cuts for Esum and mcr and not on the energy of the captured neutron. In addition, we know from previous works [38] that sizable differences in the Esum distributions lead to very small variations in the reconstructed efficiency. There is, however, a dependence of the detection efficiency on the TOF via pile-up effects, which are described below. The calculated efficiency values for the six different cuts used in this analysis are presented in Table II. For the estimation of the uncertainties in the detection efficiencies two main components were considered, as described in Refs. [38–40]: one related to the generation of capture cascades and other related to the uncertainties of the TAC FIG. 6. Deposited energy spectra (with mcr >2) from 241Am capture cascades for different resonances. The spectrum corresponding to the first resonance at 0.3 eV (solid lines) is compared to the spectra of the next eight resonances (dotted lines) at (a) 0.6, (b) 1.3, (c) 1.9, (d) 2.4, (e) 2.6, (f) 4.0, (g) 5.0, and (h) 5.4 eV. All the spectra have been normalized to the area. geometry. The first component was estimated by performing multiple simulations with different EM deexcitation patterns for the capture cascades and observing when the simulated spectra deviate from the experimental data. The second component was estimated by varying the geometry parameters and calculating the impact of such variations on the detection efficiencies. Concerning the pile-up effects, two different situations were considered. The first one is related to the high counting rate in the TAC due to capture cascades in the sample. This effect is very small (1%) for the 241Am(n,γ ) cascades; however, it must be corrected for in the 4.9 eV saturated resonance of 197Au, which is used for normalization (see Sec. IIIC). To correct for these pile-up effects we used the third method described and validated in Ref. [41]. TABLE II. Calculated capture detection efficiencies for the six different cuts in Esum and mcr considered in this work. The right-hand column shows the calculated-to-experimental ratio of the integrals of the deposited energy histograms shown in Fig. 5, normalized to the cuts of 2.5<E sum <6 MeV and mcr >0. Cuts Efficiency (%) Calc./Expt. 2.5<E sum <6.0MeV,mcr >0 61.1(9) 1 2.5<E sum <6.0MeV,mcr >1 56.7(9) 0.996 2.5<E sum <6.0MeV,mcr >2 36.5(7) 0.989 3.0<E sum <5.0MeV,mcr >0 42.1(8) 1.013 3.0<E sum <5.0MeV,mcr >1 39.8(8) 1.005 3.0<E sum <5.0MeV,mcr >2 26.6(7) 0.995 054616-6 MEASUREMENT AND ANALYSIS OF THE 241Am … PHYSICAL REVIEW C 97, 054616 (2018) 12345678910 Neutron energy (keV) 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 losses 1-f >2 cr <6 MeV, m sum 2.5<E >1 cr <6 MeV, m sum 2.5<E >0 cr <6 MeV, m sum 2.5<E FIG. 7. One minus the fraction of events lost (flosses) due to the pile-up induced by the background, as a function of the neutron energy and for three different Esum and mcr cuts. The second pile-up effect is induced by the high counting rate due to the background related to the neutron beam, which is a function of TOF and is the dominant component of the background except at the lowest neutron energies. When this counting rate becomes high enough (hundreds of counts per millisecond) then the background signals pile up with capture signals, thus modifying the probability of detecting them. We developed a new method of correcting for this effect which is based on the same methodology as in Ref. [41], i.e., in the offline manipulation of the digitized signals. In this case we copied the digitized signals obtained at low neutron energies (i.e., detected under a low background counting rate, with negligible pile-up) to a different TOF position in the digitized data buffer, corresponding to higher neutron energies and thus with higher background counting rates. The resulting artificially created data buffers were analyzed afterwards with the pulse shape reconstruction algorithms used for the standard analysis of the experiment. By comparing the results of the analyses obtained for the same signal but placed in different TOF positions in the digitized data buffers, it is possible to characterize the pile-up effects due to the background. This methodology will be described in more detail in a future publication [42]. The corrections of the capture yields due to this effect for three of the six different Esum and mcr cuts are presented in Fig. 7as a function of the neutron energy. As shown, the more restrictive the cuts in Esum and mcr applied to the detected events are, the higher is the fraction of events lost due to the background induced pile-up. C. Normalization The measurement was normalized by means of the saturated resonance method [43] to the strongest 197Au resonance at 4.9 eV. For this purpose we used three different 197Au samples, two of them with different thicknesses (250 and 50 μm) and with the same diameter as the 241Am sample (12.2 mm), and a third one with 50 μm thickness and a larger diameter 3 3.5 4 4.5 5 5.5 6 6.5 7 Neutron energy (eV) 0 0.2 0.4 0.6 0.8 1 1.2 Normalized capture yield Sample 1 - HIP Sample 1 - LIP Sample 2 - HIP Sample 3 - LIP pile-up corrected (b) 3 3.5 4 4.5 5 5.5 6 6.5 7 Neutron energy (eV) 0 0.2 0.4 0.6 0.8 1 1.2 Normalized capture yield Sample 1 - HIP Sample 1 - LIP Sample 2 - HIP Sample 3 - LIP not pile-up corrected (a) FIG. 8. (b) The experimental 197Au(n,γ ) yields obtained for the three different samples, sample 1 (250 μm thick, 12.2 mm diameter), sample 2 (50 μm thick, 12.2 mm diameter), and sample 3 (50 μm thick, 45 mm diameter), and the two beam pulse intensities, high (HIP) and low (LIP). The yields have been normalized to reproduce the results obtained from SAMMY using JEFF-3.2. (a) The same experimental data without performing pile-up corrections. covering the entire neutron beam. The three 197Au samples were measured with the nominal neutron beam intensity and also with an intensity 2.3 times smaller. The comparison with different count rates validated the pulse pile-up corrections, as showninFig.8. The measurement performed with the third 197Au sample cannot be directly used to normalize, since it has a different diameter than the 241Am sample. However, it can be included in the comparison and used to validate the pile-up corrections after re-normalizing it to the measurement performed with the sample with the same thickness but smaller radius. This renormalization was performed in the tail of the 197Au resonance, where no pulse pile-up corrections are needed. In Table III we present the normalization factors obtained from the different 197Au measurements. In all the cases we used the measurement performed with the thicker 197Au sample (sample 1) and with low intensity pulses to normalize the yields. Each of these normalization factors was obtained for 054616-7 E. MENDOZA et al. PHYSICAL REVIEW C 97, 054616 (2018) TABLE III. Normalization factors obtained by means of the saturated resonance method using three different 197Au samples and two different beam intensities. 197Au sample High intensity Low intensity Thickness Diameter pulses pulses (μm) (mm) Sample 1 250 12.20 0.986(8) 1.000(9) Sample 2 50 12.20 0.969(10) 0.975(11) Sample 3 50 45.00 0.968(8) different Esum and mcr cuts. The values and uncertainties in Table III are the mean and the standard deviation of the results of each case, respectively. All the normalization factors are compatible within two standard deviations. The measurement performed with the nominal neutron beam intensity and the largest diameter 197Au sample was not used because the pile-up correction method cannot handle the instantaneous counting rate as high as about four events per microsecond. The uncertainty in the normalization was estimated taking into account both the spread of the values and the uncertainties in Table III, obtaining an uncertainty of 1.5%. To this value we added the uncertainty due to the 197Au(n,γ ) detection efficiency. As for 241Am, it is estimated from the uncertainties associated with the generation of capture cascades (0.7% for 197Au) and of the simulated TAC geometry. However, the uncertainty due to the TAC geometry was not added in this case since it was already included in the uncertainty of the 241Am(n,γ ) detection efficiency, and it propagates in the same way, introducing a strong correlation between both detection efficiencies. If we make a quadratic sum of both quantities we obtain a total uncertainty of 1.7% in the normalization to the saturated resonance of 197Au. D. Uncertainties The uncertainties due to systematic effects in the capture yield were estimated in the following way. The quantities with larger uncertainties which affect the normalization process are the detection efficiency (2%), the normalization to the saturated resonance of 197Au discussed in the previous section (1.7%), and the sample mass (0.6%). If we make a quadratic sum of these quantities we obtain a total normalization uncertainty of 2.7%. In addition to the normalization uncertainty we have to consider the energy dependent uncertainty on the neutron fluence shape, which is 1% below 100 eV and 2% between 100 eV and 10 keV [12]. Other sources of uncertainty come from the determination of the background and from the pile-up corrections. We estimated the uncertainty due to both these effects at the same time from the differences between the resulting capture yields obtained with the different Esum and mcr cuts. In particular, we estimated it as the standard deviation calculated from the six different resulting yields. The result is presented in Fig. 9,as a function of neutron energy, together with the corresponding relative uncertainties due to counting statistics. Note that the size of the latter depends largely on the width of the neutron 1 10 2 10 3 10 4 10 Neutron energy (eV) 0 2 4 6 8 10 12 14 Uncertainty (%) Statistical Std. deviation FIG. 9. Standard deviation of the capture yield obtained from the six different Esum and mcr cuts mentioned in the text as a function of the neutron energy, together with the uncertainties due to counting statistics. energy intervals considered, whereas this dependency is much smaller in the standard deviation. The increase of the values at ∼6 keV is due to the first 27Al resonance. IV. CROSS SECTION ANALYSIS A. Analysis of the resolved resonance region The resolved resonance region (RRR) was analyzed with the SAMMY code (version 8.0.0) [19]. In the most recent evaluated libraries the RRR extends up to 150–160 eV, but we performed a resonance analysis up to 700 eV. We have fitted, using the Reich-Moore approximation, the energy E0and the neutron width nof each resonance, and the radiative capture width γonly when its uncertainty due to counting statistics was less than 10%. The resonance parameters of the negative resonances, the scattering radius, and all fission widths were taken from the JEFF-3.2 evaluation [44], after verifying that large variations of these parameters do not affect the resulting capture yield significantly. It was confirmed by the techniques described in Ref. [45] that all the resonances observed in the investigated energy range were s-wave resonances. As it was not possible to distinguish the total spin values J=2,3, only the gnvalues were determined, with g=(2J+1) (2I+1)(2j+1) , where J,I=5/2 and j=1/2 are the spins of the resonance, target nucleus, and neutron, respectively. The time-to-energy relation was obtained by adjusting the n_TOF time-of-flight effective distance to reproduce the energies of the resonances of 197Au in the JEFF-3.2 evaluation, yielding 185.59(2) m. Note that above a certain energy we are not fitting individual resonances but clusters of resonances in many cases, since it is not possible to resolve them accurately. However, having a resonant description of the cross section up to higher energies is useful for more accurate self-shielding calculations. Together with the 241Am resonances, we included in the SAMMY input the 237Np and 240Pu impurities and the 16O and 27Al of the AmO2compound and the Al2O3matrix. 16O and 27Al were included only to properly calculate selfshielding and multiple scattering effects. Detection efficiency for their cascades was set to zero, since their contributions were included in the calculation of the background. Indeed, 054616-8 MEASUREMENT AND ANALYSIS OF THE 241Am … PHYSICAL REVIEW C 97, 054616 (2018) 1 10 Neutron energy (eV) 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Capture Yield (a) 50 60 70 80 90 Neutron energy (eV) 0 0.005 0.01 0.015 0.02 0.025 0.03 Capture Yield (b) 120 130 140 150 160 Neutron energy (eV) 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 0.022 Capture Yield (c) 290 300 310 320 330 340 350 360 Neutron energy (eV) 0 0.002 0.004 0.006 0.008 0.01 Capture Yield (d) 420 430 440 450 460 470 480 490 500 Neutron energy (eV) 0 0.001 0.002 0.003 0.004 0.005 0.006 Capture Yield (e) 580600620640660680 Neutron energy (eV) 0 0.001 0.002 0.003 0.004 0.005 0.006 Capture Yield (f) FIG. 10. Examples of the fitted n_TOF capture yield, in different energy ranges. The data points correspond to the experimental capture yield and the solid line to the fit performed with SAMMY. we studied in detail the self-shielding and multiple scattering effects by comparing calculations performed with SAMMY, MCNP-6.1 [46], and GEANT4. In these calculations we obtained the theoretical capture yield under different conditions: with and without the Al canning, and with and without the Al2O3 matrix. We found that the results obtained with the three codes are in a reasonable agreement, better than 0.5%. They showed that the effect of the Al canning is negligible; the effect of the Al2O3matrix introduces an increase in the number of detected capture events by ∼1.5%, nearly constantly in the energy range of interest, and that the self-shielding due to the 241Am itself is small (<2%) except for the first three resonances, where it is around 10%. The n_TOF capture yield is presented together with the results of the SAMMY fit for several neutron energy ranges in Fig. 10. We obtained the mean values of the resonance parameters and their uncertainties due to counting statistics from the SAMMY analysis performed with the optimum cuts of mcr >2 and 2.5<E sum <6 MeV, together with their correlations. Total uncertainty of the resonance parameters due to systematic effects is given by three contributions: (i) the uncertainties due to systematic effects of the experimental yield (Sec. IIID), (ii) the uncertainty in the temperature of the sample, and (iii) the uncertainty due to the Doppler broadening model used in the fitting procedure. Concerning contribution (i), we performed independent resonance analysis for each of the six experimental data sets resulting from the different cuts mentioned before in order to take into account the contributions due to the determination of the background and due to the pile-up corrections. The uncertainty of each fitted parameter due to these two effects was estimated as the standard deviation of the different fitted values. An additional 2.7% normalization uncertainty was added to the gnparameters, since the area of each resonance is in good approximation proportional to gnwhen capture is the dominant reaction. The last two contributions, (ii) and (iii), were estimated by performing fits with three different sample temperatures, 293, 296, and 299 K, and with two different Doppler broadening models, the free gas model (FGM) and the crystal-lattice model (CLM) [19]. In the latter case, we used the phonon spectrum of UO2(SAMMY example file t124f.clm), since it has not been measured for AmO2. In both cases the uncertainties of each fitted parameter were estimated as the standard deviation of the 054616-9 E. MENDOZA et al. PHYSICAL REVIEW C 97, 054616 (2018) TABLE VII. (Continued.) E0gn±σstat ±σsys∗ (eV) (meV) (meV) (meV) 140.900 1.03 ±0.04 ±0.03 141.226 4.25 ±0.08 ±0.07 142.924 0.409 ±0.020 ±0.021 144.617 1.00 ±0.03 ±0.04 145.111 0.329 ±0.021 ±0.019 146.212 1.26 ±0.03 ±0.04 147.770 7.00 ±0.11 ±0.07 148.082 1.06 ±0.05 ±0.04 148.908 2.53 ±0.05 ±0.03 150.933 0.325 ±0.022 ±0.022 151.587 1.176 ±0.032 ±0.025 152.864 1.28 ±0.04 ±0.04 153.338 0.264 ±0.022 ±0.009 155.036 0.548 ±0.082 ±0.022 155.133 1.13 ±0.10 ±0.04 155.625 0.406 ±0.029 ±0.022 156.305 2.73 ±0.05 ±0.09 157.007 0.975 ±0.118 ±0.010 158.140 0.871 ±0.031 ±0.023 159.194 3.44 ±0.06 ±0.04 159.809 0.739 ±0.031 ±0.015 161.847 1.64 ±0.06 ±0.05 162.134 1.55 ±0.06 ±0.03 163.329 5.51 ±0.08 ±0.09 164.982 4.60 ±0.09 ±0.04 165.354 0.96 ±0.05 ±0.04 166.326 0.210 ±0.021 ±0.024 167.276 2.12 ±0.05 ±0.03 167.732 0.627 ±0.034 ±0.023 168.437 0.23 ±0.02 ±0.04 170.585 1.02 ±0.03 ±0.04 171.212 0.35 ±0.03 ±0.03 171.778 0.094 ±0.017 ±0.024 172.776 0.189 ±0.020 ±0.014 173.946 1.81 ±0.05 ±0.05 174.402 0.53 ±0.03 ±0.03 175.288 0.386 ±0.026 ±0.022 176.039 0.90 ±0.03 ±0.03 177.020 0.575 ±0.034 ±0.008 177.465 0.62 ±0.03 ±0.03 178.285 1.01 ±0.04 ±0.04 179.149 1.189 ±0.038 ±0.024 180.222 1.71 ±0.05 ±0.04 180.854 0.39 ±0.03 ±0.04 181.636 0.68 ±0.04 ±0.03 181.955 0.60 ±0.04 ±0.04 182.876 3.11 ±0.06 ±0.10 183.652 0.32 ±0.03 ±0.03 184.780 4.86 ±0.09 ±0.10 186.057 2.62 ±0.06 ±0.08 187.190 0.644 ±0.033 ±0.020 187.923 0.338 ±0.035 ±0.016 188.305 0.52 ±0.04 ±0.03 188.947 0.77 ±0.04 ±0.03 189.752 0.652 ±0.032 ±0.023 190.859 0.96 ±0.04 ±0.05 TABLE VII. (Continued.) E0gn±σstat ±σsys∗ (eV) (meV) (meV) (meV) 191.756 0.817 ±0.040 ±0.014 192.410 4.11 ±0.08 ±0.08 193.334 4.58 ±0.10 ±0.06 194.001 0.26 ±0.03 ±0.04 194.993 0.251 ±0.024 ±0.020 197.053 4.33 ±0.08 ±0.03 198.200 0.77 ±0.04 ±0.03 198.821 0.515 ±0.033 ±0.016 199.889 0.30 ±0.03 ±0.04 200.649 1.92 ±0.06 ±0.04 200.994 0.236 ±0.038 ±0.015 201.696 0.666 ±0.039 ±0.020 202.392 2.78 ±0.07 ±0.07 203.094 0.27 ±0.03 ±0.04 203.844 0.87 ±0.04 ±0.04 204.836 2.91 ±0.10 ±0.03 205.218 5.52 ±0.13 ±0.13 207.864 0.56 ±0.04 ±0.03 208.680 0.90 ±0.05 ±0.04 209.417 6.07 ±0.14 ±0.18 210.068 1.25 ±0.05 ±0.03 211.731 3.67 ±0.08 ±0.09 212.987 1.89 ±0.07 ±0.07 213.513 1.860 ±0.064 ±0.019 214.689 4.10 ±0.09 ±0.05 217.100 0.31 ±0.03 ±0.03 217.872 1.84 ±0.06 ±0.03 219.375 2.67 ±0.07 ±0.06 220.028 1.813 ±0.062 ±0.017 222.587 0.43 ±0.04 ±0.03 223.180 1.07 ±0.05 ±0.05 224.082 3.71 ±0.10 ±0.04 224.891 2.484 ±0.071 ±0.023 225.891 0.25 ±0.03 ±0.04 227.542 2.920 ±0.080 ±0.025 228.135 0.82 ±0.05 ±0.04 230.929 0.45 ±0.04 ±0.04 233.526 6.72 ±0.14 ±0.06 234.438 1.88 ±0.07 ±0.07 236.932 1.98 ±0.06 ±0.05 238.904 1.70 ±0.06 ±0.03 240.257 0.77 ±0.05 ±0.03 241.438 2.44 ±0.08 ±0.03 242.749 2.06 ±0.08 ±0.05 243.185 1.14 ±0.07 ±0.11 244.066 0.685 ±0.045 ±0.020 246.226 0.97 ±0.05 ±0.04 247.136 2.28 ±0.07 ±0.07 249.529 0.517 ±0.045 ±0.019 250.640 2.40 ±0.09 ±0.10 251.224 2.86 ±0.16 ±0.07 251.559 2.95 ±0.13 ±0.04 252.715 1.62 ±0.09 ±0.05 253.130 2.61 ±0.12 ±0.17 253.749 1.37 ±0.07 ±0.04 255.584 1.00 ±0.05 ±0.05 054616-16 MEASUREMENT AND ANALYSIS OF THE 241Am … PHYSICAL REVIEW C 97, 054616 (2018) TABLE VII. (Continued.) E0gn±σstat ±σsys∗ (eV) (meV) (meV) (meV) 256.810 0.56 ±0.05 ±0.04 257.709 0.40 ±0.04 ±0.04 259.770 6.33 ±0.15 ±0.06 260.804 1.79 ±0.08 ±0.06 261.927 2.21 ±0.08 ±0.07 263.043 0.84 ±0.06 ±0.03 264.019 1.31 ±0.07 ±0.03 264.751 2.13 ±0.08 ±0.06 266.078 0.66 ±0.05 ±0.04 267.467 1.59 ±0.07 ±0.06 268.644 2.12 ±0.08 ±0.07 269.770 3.20 ±0.12 ±0.07 270.422 4.68 ±0.15 ±0.06 271.801 0.87 ±0.06 ±0.04 272.836 1.28 ±0.07 ±0.03 274.660 6.63 ±0.27 ±0.20 274.991 3.47 ±0.19 ±0.08 275.825 1.091 ±0.066 ±0.022 276.891 0.52 ±0.05 ±0.03 277.622 0.520 ±0.052 ±0.022 278.444 0.35 ±0.04 ±0.04 279.683 0.45 ±0.05 ±0.03 281.087 3.54 ±0.14 ±0.06 281.496 1.85 ±0.13 ±0.05 282.152 0.95 ±0.10 ±0.13 282.624 1.77 ±0.12 ±0.04 283.427 14.3 ±0.4 ±0.4 284.777 1.79 ±0.08 ±0.05 286.125 2.38 ±0.11 ±0.10 286.635 3.35 ±0.15 ±0.07 287.512 1.36 ±0.08 ±0.04 288.824 2.29 ±0.10 ±0.05 289.557 4.39 ±0.19 ±0.09 290.043 2.89 ±0.13 ±0.09 291.167 0.98 ±0.07 ±0.08 292.604 2.24 ±0.10 ±0.07 293.502 1.08 ±0.07 ±0.08 294.957 2.16 ±0.09 ±0.05 296.389 3.692 ±0.129 ±0.022 297.113 3.85 ±0.14 ±0.03 297.828 0.47 ±0.06 ±0.04 298.738 2.95 ±0.12 ±0.08 299.794 7.44 ±0.20 ±0.08 300.692 3.07 ±0.12 ±0.07 302.205 4.99 ±0.14 ±0.06 303.832 1.36 ±0.08 ±0.03 304.581 1.21 ±0.08 ±0.04 305.831 0.85 ±0.06 ±0.04 307.162 3.09 ±0.11 ±0.07 307.996 0.69 ±0.07 ±0.04 309.017 3.34 ±0.16 ±0.06 309.435 1.78 ±0.13 ±0.03 310.297 2.16 ±0.10 ±0.03 311.782 2.27 ±0.10 ±0.04 313.515 1.96 ±0.10 ±0.07 314.334 2.96 ±0.12 ±0.10 TABLE VII. (Continued.) E0gn±σstat ±σsys∗ (eV) (meV) (meV) (meV) 316.734 3.51 ±0.14 ±0.08 317.480 2.45 ±0.14 ±0.13 318.143 1.41 ±0.10 ±0.07 320.480 3.03 ±0.12 ±0.04 321.888 1.62 ±0.10 ±0.10 322.911 1.33 ±0.09 ±0.06 324.375 5.88 ±0.22 ±0.19 325.565 3.51 ±0.14 ±0.14 326.670 1.37 ±0.10 ±0.09 327.790 0.98 ±0.08 ±0.03 331.615 0.75 ±0.09 ±0.05 332.411 1.72 ±0.12 ±0.13 333.215 1.18 ±0.11 ±0.12 334.461 5.7 ±0.3 ±0.3 335.318 2.03 ±0.15 ±0.12 335.928 1.49 ±0.13 ±0.04 338.935 2.95 ±0.16 ±0.09 339.791 1.77 ±0.12 ±0.21 341.228 4.13 ±0.18 ±0.17 342.307 1.95 ±0.13 ±0.14 343.636 1.42 ±0.13 ±0.11 344.393 5.22 ±0.27 ±0.18 345.304 7.60 ±0.30 ±0.16 346.030 1.26 ±0.16 ±0.05 346.506 0.75 ±0.13 ±0.06 347.324 7.10 ±0.29 ±0.13 349.619 2.09 ±0.13 ±0.07 350.786 3.20 ±0.15 ±0.06 351.796 1.17 ±0.11 ±0.09 353.017 2.62 ±0.17 ±0.06 353.570 3.32 ±0.21 ±0.19 354.463 0.85 ±0.10 ±0.09 355.478 1.00 ±0.10 ±0.08 356.455 0.84 ±0.09 ±0.04 357.618 3.37 ±0.15 ±0.05 359.245 6.16 ±0.23 ±0.12 360.333 3.32 ±0.16 ±0.13 361.707 8.3 ±0.4 ±0.3 362.392 4.65 ±0.27 ±0.19 363.371 7.90 ±0.31 ±0.24 364.366 26.7 ±1.3 ±1.4 366.635 0.98 ±0.09 ±0.09 368.154 0.59 ±0.08 ±0.07 369.525 0.85 ±0.09 ±0.05 370.540 3.5 ±0.2 ±0.3 373.233 5.06 ±0.23 ±0.13 373.770 1.47 ±0.14 ±0.13 375.380 4.06 ±0.17 ±0.12 376.492 1.44 ±0.13 ±0.08 377.201 1.67 ±0.13 ±0.06 378.874 2.05 ±0.13 ±0.04 380.894 3.97 ±0.17 ±0.18 382.094 2.17 ±0.14 ±0.09 384.583 5.18 ±0.25 ±0.08 385.346 2.58 ±0.18 ±0.11 386.159 3.04 ±0.21 ±0.19 054616-17 E. MENDOZA et al. PHYSICAL REVIEW C 97, 054616 (2018) TABLE VII. (Continued.) E0gn±σstat ±σsys∗ (eV) (meV) (meV) (meV) 386.895 6.80 ±0.28 ±0.15 387.830 3.22 ±0.16 ±0.16 390.607 2.40 ±0.15 ±0.04 391.891 3.3 ±0.2 ±0.3 393.776 1.85 ±0.14 ±0.09 394.658 3.26 ±0.17 ±0.07 395.744 1.13 ±0.13 ±0.06 396.430 6.11 ±0.30 ±0.22 397.600 3.92 ±0.20 ±0.09 398.674 2.08 ±0.14 ±0.05 399.960 7.70 ±0.28 ±0.22 401.820 5.90 ±0.23 ±0.19 402.848 0.42 ±0.08 ±0.05 404.031 1.48 ±0.12 ±0.16 405.147 1.36 ±0.12 ±0.07 406.150 0.96 ±0.11 ±0.09 407.114 2.38 ±0.15 ±0.11 408.196 1.89 ±0.16 ±0.07 408.740 1.80 ±0.16 ±0.19 410.499 0.88 ±0.10 ±0.03 411.916 0.61 ±0.08 ±0.10 413.379 1.23 ±0.12 ±0.03 414.133 1.30 ±0.13 ±0.04 415.045 1.59 ±0.13 ±0.06 416.520 2.53 ±0.16 ±0.14 417.401 3.26 ±0.20 ±0.16 418.461 2.59 ±0.16 ±0.14 420.736 3.55 ±0.20 ±0.10 421.492 3.63 ±0.21 ±0.12 422.557 1.60 ±0.13 ±0.11 424.394 3.55 ±0.20 ±0.08 425.530 3.83 ±0.20 ±0.15 426.576 3.24 ±0.19 ±0.17 427.435 1.22 ±0.14 ±0.10 428.397 5.1 ±0.3 ±0.3 429.110 1.14 ±0.14 ±0.08 430.104 2.50 ±0.16 ±0.11 431.257 3.96 ±0.20 ±0.14 433.440 5.68 ±0.32 ±0.17 434.155 5.28 ±0.27 ±0.09 435.342 0.730 ±0.104 ±0.023 436.307 2.00 ±0.16 ±0.12 437.268 0.24 ±0.06 ±0.03 438.289 1.07 ±0.12 ±0.07 439.190 1.33 ±0.15 ±0.10 440.037 4.37 ±0.32 ±0.23 440.706 8.53 ±0.40 ±0.23 441.959 1.82 ±0.15 ±0.03 443.090 2.56 ±0.17 ±0.08 444.791 9.56 ±0.44 ±0.12 446.497 8.48 ±0.36 ±0.16 447.369 3.28 ±0.20 ±0.13 449.100 0.362 ±0.105 ±0.010 449.371 2.91 ±0.21 ±0.06 450.493 1.03 ±0.13 ±0.09 451.659 2.06 ±0.31 ±0.09 TABLE VII. (Continued.) E0gn±σstat ±σsys∗ (eV) (meV) (meV) (meV) 451.932 2.78 ±0.35 ±0.07 453.112 17.9 ±0.9 ±0.7 454.607 4.2 ±0.2 ±0.3 456.905 2.21 ±0.19 ±0.11 457.735 8.64 ±0.44 ±0.24 458.529 6.28 ±0.32 ±0.14 460.092 2.5 ±0.2 ±0.3 461.227 2.48 ±0.18 ±0.20 462.924 2.46 ±0.20 ±0.11 463.765 2.05 ±0.20 ±0.13 464.611 3.8 ±0.2 ±0.4 466.045 9.9 ±0.5 ±0.6 466.979 5.43 ±0.39 ±0.20 467.743 7.8 ±0.4 ±0.3 469.044 3.29 ±0.21 ±0.05 471.752 2.14 ±0.16 ±0.18 472.975 2.76 ±0.20 ±0.19 474.037 1.37 ±0.16 ±0.09 475.064 9.4 ±0.5 ±0.4 476.170 2.2 ±0.2 ±0.3 479.858 11.7 ±0.5 ±0.7 481.165 6.44 ±0.39 ±0.06 481.910 2.01 ±0.19 ±0.19 483.764 6.83 ±0.32 ±0.10 484.965 5.8 ±0.3 ±0.3 486.259 3.17 ±0.24 ±0.25 487.008 3.92 ±0.29 ±0.17 488.159 4.4 ±0.2 ±0.4 489.906 2.82 ±0.22 ±0.22 490.787 2.04 ±0.23 ±0.16 491.767 15.5 ±0.7 ±0.6 493.472 2.08 ±0.17 ±0.17 494.968 1.21 ±0.15 ±0.07 495.758 1.08 ±0.15 ±0.14 496.723 2.51 ±0.20 ±0.22 498.708 1.90 ±0.19 ±0.19 499.499 6.19 ±0.32 ±0.08 502.333 1.48 ±0.16 ±0.10 503.540 6.19 ±0.38 ±0.16 504.243 6.0 ±0.4 ±0.3 505.747 1.13 ±0.15 ±0.17 506.853 1.63 ±0.17 ±0.10 508.072 1.49 ±0.16 ±0.09 509.519 1.87 ±0.18 ±0.09 510.964 3.1 ±0.2 ±0.3 512.842 3.40 ±0.22 ±0.20 515.115 1.54 ±0.17 ±0.18 516.675 5.5 ±0.3 ±0.4 518.719 12.7 ±0.7 ±0.7 521.371 4.45 ±0.27 ±0.10 522.472 2.60 ±0.21 ±0.18 525.323 3.62 ±0.26 ±0.06 526.327 1.18 ±0.16 ±0.11 527.682 0.66 ±0.13 ±0.06 528.996 11.4 ±0.6 ±0.5 529.606 2.56 ±0.31 ±0.20 054616-18 MEASUREMENT AND ANALYSIS OF THE 241Am … PHYSICAL REVIEW C 97, 054616 (2018) TABLE VII. (Continued.) E0gn±σstat ±σsys∗ (eV) (meV) (meV) (meV) 531.226 3.44 ±0.28 ±0.15 532.274 7.8 ±0.4 ±0.6 533.788 1.93 ±0.23 ±0.14 534.643 5.52 ±0.34 ±0.18 536.013 2.34 ±0.25 ±0.11 536.821 5.4 ±0.4 ±0.4 538.434 1.67 ±0.18 ±0.13 540.165 7.5 ±0.5 ±0.4 541.190 1.55 ±0.18 ±0.22 543.256 6.43 ±0.40 ±0.17 544.542 4.4 ±0.3 ±0.4 545.558 5.84 ±0.39 ±0.18 546.927 0.88 ±0.14 ±0.11 549.036 5.27 ±0.30 ±0.11 550.529 2.22 ±0.25 ±0.17 551.250 4.97 ±0.38 ±0.17 552.821 1.28 ±0.19 ±0.11 553.667 6.0 ±0.4 ±0.4 555.315 3.89 ±0.25 ±0.18 558.830 1.49 ±0.20 ±0.07 559.566 1.84 ±0.21 ±0.05 561.643 1.71 ±0.19 ±0.06 563.198 8.7 ±0.5 ±0.3 564.066 3.77 ±0.32 ±0.12 565.256 2.8 ±0.2 ±0.3 567.094 1.47 ±0.18 ±0.11 568.177 1.50 ±0.20 ±0.09 569.134 1.61 ±0.19 ±0.17 571.937 3.7 ±0.3 ±0.3 574.460 5.0 ±0.3 ±0.3 575.804 3.90 ±0.33 ±0.08 576.977 7.5 ±0.4 ±0.3 578.793 8.2 ±0.4 ±0.4 580.696 3.8 ±0.3 ±0.3 583.049 9.1 ±0.5 ±0.6 584.216 3.00 ±0.30 ±0.17 585.133 2.0 ±0.2 ±0.3 587.201 0.67 ±0.14 ±0.14 588.620 4.46 ±0.37 ±0.23 589.601 17.4 ±1.4 ±1.2 590.382 3.2 ±0.4 ±0.3 593.140 33.0 ±1.8 ±1.0 595.391 0.7 ±0.2 ±0.3 596.873 5.6 ±0.5 ±0.4 597.585 3.38 ±0.33 ±0.17 599.457 1.61 ±0.20 ±0.20 601.391 1.38 ±0.19 ±0.12 602.810 6.2 ±0.5 ±0.3 603.599 5.2 ±0.5 ±0.4 605.075 1.57 ±0.20 ±0.11 606.565 4.2 ±0.3 ±0.3 607.930 25 ±2±3 608.692 8.4 ±0.7 ±0.3 609.804 1.37 ±0.21 ±0.06 610.753 0.99 ±0.17 ±0.08 612.676 10.2 ±0.8 ±0.6 613.457 12.9 ±0.8 ±0.7 TABLE VII. (Continued.) E0gn±σstat ±σsys∗ (eV) (meV) (meV) (meV) 616.795 1.13 ±0.18 ±0.19 618.323 3.09 ±0.26 ±0.15 619.953 2.24 ±0.27 ±0.07 620.827 3.12 ±0.30 ±0.21 622.134 1.61 ±0.21 ±0.19 623.382 3.35 ±0.34 ±0.12 624.374 5.80 ±0.41 ±0.09 625.892 2.35 ±0.25 ±0.25 627.802 5.3 ±0.4 ±0.4 629.956 7.1 ±0.6 ±0.3 630.898 9.4 ±0.7 ±0.5 632.961 4.14 ±0.33 ±0.18 634.265 5.39 ±0.46 ±0.11 635.347 7.06 ±0.54 ±0.12 636.918 1.18 ±0.20 ±0.21 637.658 1.286 ±0.212 ±0.024 639.711 10.02 ±0.62 ±0.23 640.761 6.1 ±0.5 ±0.4 641.739 1.46 ±0.23 ±0.17 642.944 1.87 ±0.26 ±0.19 644.250 6.32 ±0.46 ±0.14 645.351 3.4 ±0.4 ±0.3 646.301 3.54 ±0.33 ±0.23 648.282 5.2 ±0.4 ±0.3 650.678 9.7 ±0.6 ±0.9 652.221 11.7 ±0.8 ±0.3 654.070 3.84 ±0.32 ±0.12 656.381 6.0 ±0.5 ±0.8 658.355 11.4 ±0.8 ±0.4 659.214 6.1 ±0.5 ±1.1 661.683 4.7 ±0.4 ±0.6 662.858 3.7 ±0.3 ±0.3 664.996 3.44 ±0.34 ±0.25 666.407 4.44 ±0.41 ±0.10 667.346 3.2 ±0.4 ±0.3 668.280 2.94 ±0.33 ±0.18 670.056 7.7 ±0.7 ±0.8 670.758 11.2 ±1.5 ±0.7 671.184 1.68 ±0.44 ±0.14 672.487 13.3 ±0.9 ±0.5 673.671 5.5 ±0.5 ±0.6 675.929 5.1 ±0.4 ±0.3 677.163 8.6 ±0.7 ±0.7 678.539 4.8 ±0.4 ±0.4 679.916 5.0 ±0.4 ±0.4 682.073 3.0 ±0.3 ±0.3 683.339 1.06 ±0.19 ±0.08 685.235 12.7 ±1.0 ±0.5 685.970 11.8 ±0.9 ±1.3 687.541 1.12 ±0.21 ±0.06 688.732 5.64 ±0.49 ±0.13 690.399 8.3 ±0.6 ±0.3 692.310 5.9 ±0.5 ±0.3 694.320 3.45 ±0.32 ±0.15 696.943 6.4 ±0.5 ±0.4 699.189 4.0 ±0.4 ±0.3 700.419 5.28 ±0.46 ±0.21 054616-19 E. 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