Code SAMMY Research Articles

Resolved resonance region evaluations of n+ 206,207,208Pb for fast spectrum applications

Resolved resonance region evaluations of the major isotopes of natural lead, 206Pb, 207Pb, 208Pb, have been performed to support the development of Generation IV reactors. Validation of nuclear data for lead fast reactors was performed with simulations of shielding benchmarks, integral critical benchmarks, and quasi-differential scattering measurements. Sensitivity analyses of these systems showed that elastic scattering reactions above 100 keV were the dominant reactions driving system performance. The resolved resonance regions (RRRs) of the lead isotopes extend past 100 keV, making the RRR an ideal starting point to evaluate lead cross sections. Since the R-matrix requires knowledge of bound, distant, and observed resonances, it was necessary to evaluate from 10−5eV up to the respective limit of the RRR. The 208Pb RRR evaluation was extended to 1.5 MeV in order to obtain resonance parameters used to calculate new elastic scattering angular distributions up to 1.5 MeV. Resonance parameter uncertainties and covariance were generated using the R-matrix code SAMMY. The new RRR parameters show a direct improvement to the scattering kernel below 1.5 MeV which in turn greatly improves fast critical experiments over ENDF/B-VIII.0.

Measurement and analysis of the neutron-induced total cross-sections of 209Bi from 0.3 eV to 20 MeV on the Back-n at CSNS* *Supported by the National Natural Science Foundation of China (12375296), the Key Laboratory of Nuclear Data Foundation (JCKY2022201C153), the National Key Research and Development Plan (2022YFA1603303), and the Natural Science Foundation of Hunan Province of China (2021JJ40444, 2020RC3054)

The neutron-induced total cross-section of 209Bi is crucial for the physical design and safety assessment of lead-based fast reactors, and the quality of experimental data should be improved for evaluation and application. A recent experiment was conducted on the back-streaming white neutron beamline (Back-n) at the China Spallation Neutron Source (CSNS) using the neutron total cross-section spectrometer (NTOX). The neutron energy was determined using a fast multi-cell fission chamber and the time-of-flight technique. Two high-purity bismuth samples, 6 mm and 20 mm in thickness, were chosen for neutron transmission measurements and comparisons. The neutron total cross-sections of 209Bi, ranging from 0.3 eV to 20 MeV, were derived considering neutron flight time determination, flight path calibration, and background subtraction. A comparison of the experimental results with the data in the ENDF/B-VIII.0 library showed fair agreement, and the point-wise cross-sections were found to be consistent with existing experimental data. Special attention was given to the determination of resonance parameters, which were analyzed using the R -matrix code SAMMY and Bayesian method in the 0.5 keV to 20 keV energy range. The extracted resonance parameters were compared to previously reported results and evaluated data. This study is recognized as the first one where the neutron total cross-section of bismuth across such a broad energy spectrum is measured in a single measurement or experiment, and it provides valuable data for the assessment of related reaction information for evaluated libraries and the advancement of lead-bismuth-based nuclear systems.

Measurement of the ^{181} Ta(n,gamma ) cross sections up to stellar s-process temperatures at the CSNS Back-n

The neutron capture cross section of ^{181} Ta is relevant to s-process of nuclear astrophysics, extraterrestrial samples analysis in planetary geology and new generation nuclear energy system design. The ^{181}Ta(n,gamma ) cross section had been measured between 1 eV and 800 keV at the back-streaming white neutron facility (Back-n) of China spallation neutron source(CSNS) using the time-of-flight (TOF) technique and hbox {C}_{6},hbox {D}_{6} liquid scintillator detectors. The experimental results are compared with the data of several evaluated libraries and previous experiments in the resolved and unresolved resonance region. Resonance parameters are extracted using the R-Matrix code SAMMY in the 1–700 eV region. The astrophysical Maxwell average cross section(MACS) from kT = 5 to 100 keV is calculated over a sufficiently wide range of neutron energies. For the characteristic thermal energy of an astrophysical site, at kT = 30keV the MACS value of ^{181}Ta is 834 ± 75 mb, which shows an obvious discrepancy with the Karlsruhe Astrophysical Database of Nucleosynthesis in Stars (KADoNiS) recommended value 766 ± 15 mb. The new measurements strongly constrain the MACS of ^{181}Ta(n,gamma ) reaction in the stellar s-process temperatures.

Resonance region evaluation of 16O for criticality safety and reactor applications

The intent of this paper is to present the resolved resonance evaluation of 16O in the energy range from thermal to 6 MeV. The newness of the present work is that recent cross-section data for the 16O(n,α) 13C reaction taken at the GELINA time-of-flight facility and transmission data obtained at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR ) were included in the evaluation. The evaluation was carried out with the SAMMY code. The evaluation was used to calculate critical benchmark experiment sensitive to the 16O cross sections.

Modernization efforts for the R-Matrix code SAMMY

The R-Matrix code SAMMY [1] is a widely used nuclear data evaluation code focused on the resolved range, which includes corrections for experimental effects. The code is still mostly written in FORTRAN 77 and uses a memory management system suitable for the time of its initial writing in 1984. A modernization effort is underway to update the code to modern software development practices. A continuous-integration testing framework was added to automate the large existing set of test cases. Improvements in memory management were implemented to make the code easier to maintain and enable enhancements. The resonance parameters and covariance information are now stored in C++ objects shared by SAMMY and AMPX [2], which is the processing code that generates nuclear data libraries for SCALE [3]. Further plans include switching to the Evaluated Nuclear Data File (ENDF) reading and writing routines in AMPX because these routines are more robust, easier to maintain, and support more features. Support for the new Generalized Nuclear Database Structure (GNDS) format [4] is also of interest. GNDS will share not only the resonance parameters but also the parameters associated with experimental correction in GNDS. The data are currently available in a binary SAMMY format, and the ability to export them to GNDS would make them more widely available and shareable. The next step will be to use the same resonance processing code at 0K in AMPX and SAMMY as an available formalism. Then, any improvements in the formalism can immediately be tested in SCALE because the reconstruction in AMPX will use the same cross section model. The new data library can then be used for testing using the VALID Benchmark suite [5] or other suitable benchmark suites.

140,142Ce Neutron Cross Section Resolved Resonance Region Evaluation

A resolved resonance region evaluation of 140,142Ce was conducted by Oak Ridge National Laboratory. Requested by the US Nuclear Criticality Safety Program, this evaluation is based on recent high-resolution transmission and capture high-resolution measurements of natCe and 142Ce conducted at JRC-Geel at the Geel Linear Accelerator facility. It is also based on recently measured thermal constants available from the EXFOR database [1]. Starting from the resonance parameters from the ENDF/B-VIII.0 library [2] and following a preliminary R-matrix analysis [3], an updated set of resonance parameters and corresponding covariance information was derived by the fit of these experimental datasets using the Reich–Moore approximation of the R-matrix theory, as implemented in the SAMMY code system [4]. The resolved resonance region upper energy limit for 140Ce was kept at 200 keV, whereas the 142Ce resonance region was extended from 13 to 26 keV. This new evaluation was found to be in good agreement not only with several integral quantities of interest to the reactor physics community, but also with the stellar Maxwellian-averaged cross section [5].

High accuracy, high resolution 235U(n,f) cross section from n_TOF (CERN) from 18 meV to 10 keV

The 235U(n,f) cross section was measured in a wide energy range (18 meV–170 keV) at the n_TOF facility at CERN, relative to 6Li(n,t) and 10B(n,α) standard reactions, with high resolution and accuracy, with a setup based on a stack of six samples and six silicon detectors placed in the neutron beam. In this paper we report on the results in the region between 18 meV and 10 keV neutron energy. A resonance analysis has been performed up to 200 eV, with the code SAMMY. The resulting fission kernels are compared with the ones extracted on the basis of the resonance parameters of the most recent major evaluated data libraries. A comparison of the n_TOF data with the evaluated cross sections is also performed from thermal to 10 keV neutron energy for the energy-averaged cross section in energy groups of suitably chosen width. A good agreement, within 0.5%, is found on average between the new results and the latest evaluated data files ENDF/B-VIII.0 and JEFF-3.3, as well as with respect to the broad group average fission cross section established in the framework of the standard working group of IAEA (the so-called reference file). However, some discrepancies, of up to 4%, are still present in some specific energy regions. The new dataset here presented, characterized by a unique combination of high resolution and accuracy, low background and wide energy range, can help to improve the evaluations from the Resolved Resonance Region up to 10 keV, also reducing the uncertainties that affect this region.

New experimental measurement of natSe(n, γ) cross section between 1 eV to 1 keV at the CSNS Back-n facility

The 74Se is one of 35 p-nuclei, and 82Se is a r-process only nucleus, and their (n, γ) cross sections are vital input parameters for nuclear astrophysics reaction network calculations. The neutron capture cross section in the resonance range of isotopes and even natural selenium samples has not been measured. Prompt γ-rays originating from neutron-induced capture events were detected by four C6D6 liquid scintillator detectors at the Back-n facility of China Spallation Neutron Source (CSNS). The pulse height weighting technique (PHWT) was used to analyze the data in the 1 eV to 100 keV region. The deduced neutron capture cross section was compared with ENDF/B-VIII.0, JEFF-3.2, and JENDL-4.0, and some differences were found. Resonance parameters were extracted by the R-matrix code SAMMY in the 1 eV–1 keV region. All the cross sections of natSe and resonance parameters are given in the datasets. The datasets are openly available at http://www.doi.org/10.11922/sciencedb.j00113.00019.

Neutron capture cross section of 169Tm measured at the CSNS Back-n facility in the energy region from 30 to 300 keV * *Supported by the National Natural Science Foundation of China (11790321, 11805282) and the National Key Research and Development Program of China (2016YFA0401601)

The capture cross sections of the 169Tm reaction were measured at the back streaming white neutron beam line (Back-n) of the China Spallation Neutron Source (CSNS) using four C6D6 liquid scintillation detectors. The background subtraction, normalization, and correction were carefully considered in the data analysis to obtain accurate cross sections. For the resonance at 3.9 eV, the R-matrix code SAMMY was used to determine the resonance parameters with the internal normalization method. The average capture cross sections of 169Tm for energy between 30 and 300 keV were extracted relative to the 197Au reaction. The measured cross sections of the 169Tm reaction were reported in logarithmically equidistant energy bins with 20 bins per energy decade with a total uncertainty of 5.4% – 7.0% in this study and described in terms of average resonance parameters using a Hauser-Feshbach calculation with fluctuations. The point-wise cross sections and the average resonance parameters showed fair agreement with the evaluated values of the ENDF/B-VIII.0 library in the energy region studied.

Resonance evaluation of Gadolinium isotopes

The objective of this paper is to present the results of an evaluation of the gadolinium isotopes with the main focus on the isotopes155Gd and157Gd. The evaluations were carried out in the resolved resonance region using the Reich-Moore formalism. The originality on the155Gd and157Gd evaluations is the addition of new high-resolution capture cross section measurements performed at the neutron time-of-flight, n_TOF facility for enriched samples and the statistical analysis of the resonance parameters. The resonance analysis was performed with the multilevel R-matrix code SAMMY together with the generalized least-squares technique based on the Bayes’ theory.

Cross section for the neutron radiative capture on Lu173 nuclei

We report the measurement of a neutron radiative cross section on a target with a high gamma activity, at the Los Alamos DANCE detector (Detector for Advanced Neutron Capture Experiments) for the first time. The $(n,\ensuremath{\gamma})$ reaction properties of the unstable $^{173}\mathrm{Lu}$ isotope were studied. Two experimental campaigns were needed to determine the $^{173}\mathrm{Lu}(n,\ensuremath{\gamma})$ cross section. They were performed at the Los Alamos Neutron Science Center (LANSCE) spallation neutron source facility. To this end, two targets were produced from an Hf sample using successively proton irradiation and chemical separations. They were composed of $^{173}\mathrm{Lu},^{174}\mathrm{Lu}$, and $^{175}\mathrm{Lu}$ isotopes. The two measurements were conducted at two-year intervals, taking advantage of the difference of the isotopic decay lifetimes in order to identify resonances from the $^{173}\mathrm{Lu}(n,\ensuremath{\gamma})$ and $^{174}\mathrm{Lu}(n,\ensuremath{\gamma})$ reactions. Just over one hundred new resonances were observed, the majority of which come from the $^{173}\mathrm{Lu}(n,\ensuremath{\gamma})$ reaction. Only a few of them were assigned to the $^{174}\mathrm{Lu}(n,\ensuremath{\gamma})$ reaction. As regards the $^{173}\mathrm{Lu}(n,\ensuremath{\gamma})$ reaction, the radiative neutron capture cross section was determined over the energy range from thermal neutron up to 200 eV. The parameters of resonances in the resolved resonance region were extracted with the sammy code while calculations with talys determined the capture cross section in the unresolved resonances region. At the keV region, we performed standard talys calculations as well as other microscopic investigations by substituting the standard talys photon strength function by another one from QRPA models.

Neutron capture yields and resonance parameters of dysprosium isotopes measured at Japan Proton Accelerator Research Complex

Neutron capture yields of dysprosium isotopes (161Dy, 162Dy, 163Dy, and 164Dy) were measured using the time-of-flight method with a NaI(Tl) spectrometer locate at 27.9m from the spallation neutron target in the ANNRI beamline at the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Research Complex. The resonance parameters were determined using the multilevel R-matrix Bayesian code SAMMY in the neutron energy range of 1 to 300eV. Five resonances of the 161Dy isotope, reported by Shin et al. but not presented in ENDF/B-VII.1, were confirmed in this study. One resonance of the 164Dy isotope presented in ENDF/B-VII.1 was not observed in this study. The measured average level spacings were $2.31\pm 0.23$ eV for 161Dy and $6.91\pm 0.69$ eV for 163Dy. The statistical distributions of the resonance parameters reasonably agreed with the Porter-Tomas distributions and multiple exit channel theory.

Transmission measurements and resonance parameter analysis for Mo-98 and Mo-100

Molybdenum can exist in many nuclear reactor components, including fuel, cladding, or as a high yield fission product. As a result, accurate isotopic nuclear data for molybdenum are important for reactor simulation. To this end, high-resolution time-of-flight neutron transmission measurements on highly enriched isotopic metallic samples of Mo-98 and Mo-100 were performed and data were reduced to transmission in the resolved resonance region from 10 eV to 53 keV for Mo-98 and 10 eV to 26.5 keV for Mo-100. Measurements were taken with Li-6 glass transmission detectors at 31 m and 100 m flight paths. The Bayesian R-matrix code SAMMY 8.0 was used to shape-fit the data and to extract resonance parameters from the transmission spectra. The newly fitted resonance parameters were compared with those given in ENDF/B-VII.1. The results represent a refinement of those given in the current evaluation due to the improvement in the experimental resolution in these measurements. The comparison included analysis of level statistics. The resonance parameters for Mo-98 show many differences with the current evaluations. The results of the analysis indicated missing levels in Mo-98 starting at 10 keV, which implies an inability to resolve all resonances at higher energies. The resonance parameters for Mo-100 agree well with the current evaluation. Level statistics analysis indicates there are few missing levels up to 26.5 keV.

Measurement and resonance analysis of the S33(n,α)Si30 cross section at the CERN n_TOF facility in the energy region from 10 to 300 keV

The S33(n,α)Si30 cross section has been measured at the neutron time-of-flight (n_TOF) facility at CERN in the neutron energy range from 10 to 300 keV relative to the B10(n,α)Li7 cross-section standard. Both reactions were measured simultaneously with a set of micromegas detectors. The flight path of 185 m has allowed us to obtain the cross section with high-energy resolution. An accurate description of the resonances has been performed by means of the multilevel multichannel R-matrix code sammy. The results show a significantly higher area of the biggest resonance (13.45 keV) than the unique high-resolution (n,α) measurement. The new parametrization of the 13.45-keV resonance is similar to that of the unique transmission measurement. This resonance is a matter of research in neutron-capture therapy. The S33(n,α)Si30 cross section has been studied in previous works because of its role in the production of S36 in stars, which is currently overproduced in stellar models compared to observations.2 MoreReceived 11 April 2018Revised 9 May 2018DOI:https://doi.org/10.1103/PhysRevC.97.064603Published 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.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNeutron physicsNuclear astrophysicsResonance reactionsTechniquesSpectrometers & spectroscopic techniquesNuclear Physics

Resonance analysis of 151,153Eu from neutron capture cross section measurements in the energy range from 1 to 20 eV

ABSTRACT The neutron capture cross sections of Europium-151 and Europium-153 have been measured by the time-of-flight method in the energy range from 0.005 to 100 eV using the Kyoto University Research Reactor Institute-Linear Accelerator (KURRI-LINAC). An assembly of Bismuth Germanate (BGO) scintillators was used to detect the prompt capture of γ rays. The absolute values of the neutron capture cross sections of 151Eu and 153Eu were deduced by normalizing the thermal capture cross sections in JENDL-4.0 and ENDF/B-VII.1, respectively. Then, we have obtained the resonance parameters of 20 resonances in 151Eu and 17 resonances in 153Eu using the code SAMMY. For the 3.36-eV resonance of 151Eu, the evaluated resonance peak area in JENDL-4.0 is about 95% smaller than the present result. For the 7.00-, 7.22-, and 7.42-eV resonance; we confirmed that there are significant differences between the measured peaks and evaluated peaks in JENDL-4.0, ENDF/B-VII.1, and JEFF-3.2. For the 153Eu, the evaluated resonance peak areas in JENDL-4.0, ENDF/B-VII.1, and JEFF-3.2 are about 15% larger than the measured resonance peak areas at the 2.46-, 3.29-, and 3.94-eV resonances.

Resonance parameter covariance representation: file32 versus file33

Sensitivity and uncertainty analysis in error propagation studies are carried out based on nuclear data uncertainty information available in the basic nuclear data libraries such as ENDF, JEFF, JENDL and others. The uncertainty files (covariance matrices) are generally obtained from analysis of experimental data. In the resonance region, the computer code SAMMY is used for analyses of experimental data and generation of resonance parameters. In addition to resonance parameters evaluation, SAMMY also generates resonance parameter covariance matrices (RPCM). The intent of this paper is to discuss the use of the RPCM in contrast to the use of a cross section covariance matrix (CSCM) representation. For so, the resonance evaluation for 48Ti in the resonance range from 10−5 eV to 400 keV is used. The RPCM is translated into two distinct CSCM by using a coarser and a finer group structures. The results are presented and discussions of the feasibility of using these covariance representations are depicted.

Resonance Analysis for Neutron Capture Cross Sections of Th-232

In recent years, a great interest has been taken in the thorium fuel cycle. The neutron capture reaction for 232Th is very important to evaluate the 233U production in the thorium fuel cycle.In the present study, we have carried out the resonance analysis of neutron capture cross sections of 232Th obtained by using the Kyoto University Research Reactor Institute – Linear Accelerator (KURRI-LINAC). We performed the resonance analysis using the code SAMMY for the 10 resolved resonances in the energy range from 20 to 210 eV. The obtained parameters for the 69.2-, 113.1-, 120.9- and 170.4-eV resonances are in disagreement with the evaluated values, whereas the parameters for other six resonances were in general agreement.In order to verify the validity for the resonance analysis, we also investigated the neutron self-shielding and multiple-scattering effects on the neutron capture cross sections obtained for 232Th samples with three different thicknesses. The correction factors were estimated by the Monte Carlo simulation using the evaluated cross sections in JENDL-4.0 and the cross section data revised by the present resonance analysis. The comparison between the capture cross sections corrected with the JENDL-4.0 is consistent with the resonance analysis results. Moreover, it was confirmed that the revised cross section data enable the correction factors to reproduce the experimental results for the 69.2- and 120.9-eV resonances. In the case of 170.4-eV resonance, the disagreement between the experimental results was not improved in this study. Therefore, further study is necessary to improve the resonance data.

Neutron capture measurements and resonance parameters of dysprosium

Neutron capture yields of dysprosium isotopes ( 161Dy, 162Dy, 163Dy, and 164Dy were measured using the time-of-flight method with a 16 segment sodium iodide multiplicity detector. The measurements were made at the 25m flight station at the Gaerttner LINAC Center at Rensselaer Polytechnic Institute. Resonance parameters were obtained using the multilevel R-matrix Bayesian code SAMMY. The neutron capture data for four enriched dysprosium isotopes and one natural dysprosium sample were sequentially fitted. New resonances not listed in ENDF/B-VII.1 were observed. There were 29 and 17 new resonances from 161Dy and 163Dy isotopes, respectively. Six resonances from 161Dy isotope, two resonances from 163Dy, and four resonances from 164Dy were not observed. The capture resonance integrals of each isotope were calculated with the resulting resonance parameters and those of ENDF/B-VII.1 in the energy region from 0.5eV to 20MeV and were compared to the capture resonance integrals with the resonance parameters from ENDF/B-VII.1. A resonance integral value of the natural dysprosium calculated with present resonance parameters was $ 1405 \pm 3.5$ barn. The value is $ \sim 0.3\%$ higher than that obtained with the ENDF/B-VII.1 parameters. The distributions of the present and ENDF/B-VII.1 neutron widths were compared to a Porter-Thomas distribution. Neutron strength functions for 161Dy and 163Dy were calculated with the present resonance parameters and both values were in between the values of “Atlas of Neutron Resonances” and ENDF/B-VII.1. The present radiation width distributions of 161Dy and 163Dy were fitted with the $ \chi^{2}$ distribution by varying the degrees of freedom.

Radiative neutron capture cross section from U236

The $^{236}\mathrm{U}(n,\ensuremath{\gamma})$ reaction cross section has been measured for the incident neutron energy range from 10 eV to 800 keV by using the Detector for Advanced Neutron Capture Experiments (DANCE) $\ensuremath{\gamma}$-ray calorimeter at the Los Alamos Neutron Science Center. The cross section was determined with the ratio method, which is a technique that uses the $^{235}\mathrm{U}(n,f)$ reaction as a reference. The results of the experiment are reported in the resolved and unresolved resonance energy regions. Individual neutron resonance parameters were obtained below 1 keV incident energy by using the $R$-matrix code sammy. The cross section in the unresolved resonance region is determined with improved experimental uncertainty. It agrees with both ENDF/B-VII.1 and JEFF-3.2 nuclear data libraries. The results above 10 keV agree better with the JEFF-3.2 library.

Rhenium resonance parameters from neutron capture and transmission measurements in the energy range 0.01 eV to 1 keV

Rhenium is a refractory metal with potential uses in nuclear reactor applications, particularly those at very high temperatures. Measurements have been made using natural samples. Natural rhenium consists of two isotopes: 185Re (37.40%) and 187Re (62.60%). The electron linear accelerator (LINAC) at the Rensselaer Polytechnic Institute (RPI) Gaerttner LINAC Center was used to explore neutron interactions with rhenium in the energy region from 0.01 eV to 1 keV. Neutron capture and transmission measurements were performed by the time-of-flight technique. Two transmission measurements were performed at flight paths of 15 m and 25 m with 6Li glass scintillation detectors. The neutron capture measurements were performed at a flight path of 25 m with a 16-segment sodium iodide multiplicity detector. Resonance parameters were extracted from the data using the multilevel R-matrix Bayesian code SAMMY. A table of resonance parameters and their uncertainties is presented. The uncertainties in resonance parameters were propagated from a number of experimental quantities using a Bayesian analysis. Uncertainties were also estimated from fitting each Re sample measurement individually. The measured neutron capture resonance integral for 185Re is (4 ± 1)% larger than ENDF/B-VII.1. The capture resonance integral for 187Re is (3 ± 1)% larger than ENDF/B-VII.1. Other findings from these measurements include: a decrease in the thermal capture cross section for 185Re of (2 ± 2)% from ENDF/B-VII.1; a decrease in the thermal capture cross section for 187Re of (3 ± 4)% from ENDF/B-VII.1; a decrease in the thermal total cross section for 185Re of (2 ± 2)% from ENDF/B-VII.1; and a decrease in the thermal total cross section for 187Re of (6 ± 5)% from ENDF/B-VII.1. Considering the uncertainties, none of the indicated changes in thermal cross sections represents a statistically significant change from ENDF/B-VII.1.