Resonance Shape Analysis Research Articles

241Am Neutron Capture Cross Section Measurement using the NaI(Tl) spectrometer of the ANNRI beamline of J-PARC

ABSTRACT The neutron capture cross-section of 241Am was measured from 10 meV to about 500 keV using the NaI(Tl) spectrometer of the Accurate Neutron-Nucleus Reaction Measurement Instrument (ANNRI) beamline in the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). The total energy detection principle was applied in conjunction with the pulse-height weighting technique to derive the neutron capture yield. The present cross-section results were normalized using a 197Au sample measurement by applying the saturated resonance method. The thermal cross section was measured to be 708 ± 22 b, in agreement with the evaluation in JENDL-5 of 709 b within uncertainties. In the keV region, the evaluated libraries of JENDL-5, ENDF/B-VIII.0 and JEFF-3.3 are in good agreement with the present results over 10 keV but show values lower by 30% to 70% below that energy. Moreover, the results of a resonance shape analysis of the resolved resonance region are also provided in the present paper.

Time-of-flight measurements of MINERVE samples containing fission products and neutron absorbing isotopes

The zero-power reactor MINERVE (CEA Cadarache) was designed to perform reactivity worth measurements by the oscillation technique. The various experimental programs, undertaken for the last thirty years, involved cylindrical samples with a diameter of about 1 cm and a height ranging from a few cm to 10 cm. Most of the samples are composed of UO2 pellets mixed with a high neutron absorbing nuclide, i.e. fission product, actinide, in a double-sealed Zry-4 container. An experimental program started in 2015 in collaboration with the Joint Research Centre of Geel to study the MINERVE samples at the time-of-flight facility GELINA by the neutron transmission technique. The two main objectives consist of checking both the composition of the MINERVE samples provided by the manufacturer and the quality of the resonance parameters recommended in the evaluated neutron data library JEFF-3.3. The pioneer experiments on MINERVE samples containing 107Ag and 109Ag revealed a substantial Tungsten contamination that was not reported by the manufacturer. Such a Tungsten contamination is related to the manufacturing process of the sample pellets. The observed Tungsten contaminations lead to non-negligible increases of the C/E ratios up to a few percent. second experimental campaign on MINERVE samples containing 99Tc provided useful insight on the quality of the 99Tc resonance parameters measured at the GELINA facility at the end of the 90s. The ongoing program continuing through 2022 will deliver data for samarium (natural, 147, 149, 152), neodymium (natural,143,145), gadolinium (natural, 155), europium (151, 153), rhodium (103), cesium (133), hafnium (180), dysprosium (160, 161, 162, 163, 164) and erbium (168, 170). The present work focuses on the data analysis technique developed for long cylindrical samples with a diameter smaller than the neutron beam, and on the grain size distribution model implemented in the resonance shape analysis REFIT.

Zr92(n,γ) and ( n ,tot) measurements at the GELINA and n_TOF facilities

Background: Stellar nucleosynthesis of elements heavier than iron is driven by neutron capture processes. Zr92 is positioned at a strategic point along the slow nucleosynthesis path, given its proximity to the neutron magic number N=50 and its position at the matching region between the weak and main slow processes. Purpose: In parallel with recent improved astronomical data, the extraction of accurate Maxwellian averaged cross sections (MACSs) derived from a more complete and accurate set of resonance parameters should allow for a better understanding of the stellar conditions at which nucleosynthesis takes place. Methods: Transmission and capture cross section measurements using enriched Zr92 metallic samples were performed at the time-of flight facilities GELINA of JRC-Geel (BE) and n_TOF of CERN (CH). The neutron beam passing through the samples was investigated in transmission measurements at GELINA using a Li-glass scintillator. The γ rays emitted during the neutron capture reactions were detected by C6D6 detectors at both GELINA and n_TOF. Results: Resonance parameters of individual resonances up to 81 keV were extracted from a combined resonance shape analysis of experimental transmissions and capture yields. For the majority of the resonances the parity was determined from an analysis of the transmission data obtained with different sample thicknesses. Average resonance parameters were calculated. Conclusions: Maxwellian averaged cross sections were extracted from resonances observed up to 81 keV. The MACS for kT=30keV is fully consistent with experimental data reported in the literature. The MACSs for kT≲15keV are in good agreement with those derived from the ENDF/B-VIII.0 library and recommended in the KADoNiS database. For kT higher than 30 keV differences are observed. A comparison with MACSs obtained with the cross sections recommended in the JEFF-3.3 and JENDL-4.0 libraries shows discrepancies even for kT≲15keV.5 MoreReceived 21 February 2020Revised 7 January 2022Accepted 7 February 2022DOI:https://doi.org/10.1103/PhysRevC.105.025805Published 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 AreasHydrostatic stellar nucleosynthesisNeutron physicsNuclear astrophysicsNuclear reactionsRadiative captureResonance reactionsProperties90 ≤ A ≤ 149TechniquesNuclear data analysis & compilationNuclear Physics

Neutron capture cross sections of curium isotopes measured with ANNRI at J-PARC

ABSTRACT The neutron capture cross sections of and were measured for the neutron energy range of 1–1000 eV via the neutron time-of-flight method with Accurate Neutron-Nucleus Reaction measurement Instrument (ANNRI) at Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). The world’s most intense neutron pulses from the Japan Spallation Neutron Source (JSNS) enable the accurate measurement of neutron capture cross sections. Besides, single-bunched neutron pulses allow the analysis in a higher neutron energy region than the previous measurement at ANNRI. The resonance analyses were performed up to 1000 eV by using a resonance shape analysis code REFIT. The spectra of prompt gamma-rays from neutron capture reactions of and were also obtained, and 43 and 10 prompt gamma-ray peaks from () and () reactions were newly observed, respectively.

Resonance parameters of Gd isotopes derived from capture measurements at GELINA

Neutron capture yields for $$^{{155}}\hbox {Gd}$$, $$^{{156}}\hbox {Gd}$$, $$^{{157}}\hbox {Gd}$$, $$^{{158}}\hbox {Gd}$$, and $$^{{160}}\hbox {Gd}$$ were determined applying the total energy detection principle technique using four $$\hbox {C}_{{6}}\hbox {D}_{{6}}$$ liquid scintillators and a $$^{{10}}\hbox {B}$$-loaded ionization chamber. Time-of-flight experiments were carried out at a 30 m flight path station of the GELINA facility using enriched samples. Parameters for resonances in the energy region between 5 and 500 eV were obtained from a resonance shape analysis with REFIT. Resonance integrals for $$^{{155}}\hbox {Gd}$$ and $$^{{157}}\hbox {Gd}$$ derived from the parameters are 1511 (25) b and 801 (19) b, respectively. Average level spacings, average radiation widths and neutron strength functions were derived. The results were compared with data that are reported in the literature and recommended in evaluated data libraries.

107Ag and 109Ag resonance parameters for neutron induced reactions below 1 keV

Neutron transmission and capture measurements have been performed at the time-of-flight (TOF) facility GELINA of the EC-JRC-Geel, using metallic discs of natural silver with different thicknesses. Resonances of neutron interactions with 107Ag and 109Ag were analysed in the energy region below 1 keV applying the Reich-Moore approximation of the R-Matrix theory. Discrepancies between the experimental data and calculations based on the neutron resonance parameters recommended in the main neutron cross section libraries (JEFF, ENDF/B, JENDL) were observed. Improved resonance parameters were determined by a resonance shape analysis using the REFIT code. The resonance energy, neutron (Γn) and radiation (Γγ) width were adjusted in a simultaneous fit to transmission and capture yield spectra below 100 eV. Above 100 eV fixed average radiation widths (Γγ107=140 meV, Γγ109 = 130 meV) were used and the neutron width Γn was adjusted to only the capture yield data. Capture resonance integral I0 were calculated from the parameters derived in this work (I0,107 = 101.20 b, I0,109 = 1515.24 b) and compared with those calculated using the cross sections recommended in the main libraries. Discrepancies in I0 for 107Ag are mainly due to difference in the parameters of the resonances at 16.4 eV, 41.6 eV, 173.9 eV and 202.8 eV. In case of 109Ag differences are mainly due to the difference in parameters of the resonance at 5.2 eV.

Cross section measurements of 155,157Gd(n,$\gamma$γ) induced by thermal and epithermal neutrons

Neutron capture measurements on $^{155}$Gd and $^{157}$Gd were performed using the time-of-flight technique at the n\_TOF facility at CERN. Four samples in form of self-sustaining metallic discs isotopically enriched in $^{155}$Gd and $^{157}$Gd were used. The measurements were carried out at the experimental area (EAR1) at 185 m from the neutron source, with an array of 4 C$_6$D$_6$ liquid scintillation detectors. The capture cross sections of $^{155}$Gd and $^{157}$Gd at neutron kinetic energy of 0.0253 eV have been estimated to be 62.2(2.2) kb and 239.8(9.3) kb, respectively, thus up to 6\% different relative to the ones reported in the nuclear data libraries. A resonance shape analysis has been performed in the resolved resonance region up to 180 eV and 300 eV, respectively, in average resonance parameters have been found in good agreement with evaluations. Above these energies the observed resonance-like structures in the cross section have been tentatively characterised in terms of resonance energy and area up to 1 keV.

Pretreatment Texture Analysis of Routine Magnetic Resonance Images and Shape Analysis of the Diffusion Tensor Predict Volumetric Response after Radiosurgery for Meningiomas

Tumor progression after stereotactic radiosurgery remains a major complication in WHO grade I meningiomas, with figures reported between 5-10%. According to our previous study, Diffusion Tensor Imaging (DTI) parameters can differentiate between meningioma subtypes and predict the reduction in volume of meningiomas after SRS. However DTI is still not frequently performed for SRS. The objective of this study was to identify those parameters from routine T1- and T2-weigted Magnetic Resonance (MR) sequences, and as well as from DTI, which predict best volume changes of meningiomas after Gamma Knife Radio-Surgery (GKRS) treatment. In 32 patients (mean age 58y) with meningiomas (mean volume 8.80cm3, mean dose 14.2Gy), routine 3 Tesla MR images as well as 11 different DTI parameter maps, including skewness of tensor shape, were measured before SRS. A total of 104 parameters derived from first level texture analysis of the pre-treatment MR images, including calculation of mean, standard deviation, 2.5 and 97.5 percentiles, kurtosis and skewness of data histograms on a voxel-wise basis, were correlated with lesion volume change after a mean follow up period of 3 years (19.5 – 63.3 months). Mean volume change rate per month after SRS was 0.92%. 1 (3%) meningioma progressed, 5 (16%) meningiomas stayed stable and 26 (81%) regressed. Several DTI-derived parameters correlated significantly with meningioma volume change. The parameter to predict best response of SRS was the 2.5 percentile value of the planar spherical index of the diffusion tensor (correlation coefficient -0.682, p≤0.001), whereas from the non-DTI parameters, only standard deviation of T2-weighted data correlated significantly with tumor volume change (correlation coefficient 0.505, p≤0.05). Other factors, like original tumor size, prescription dose and patient’s age, did not present significant correlation. WHO grade I Meningiomas differ in tissue homogeneity and in radiosensitivity. DTI-derived parameters show a higher correlation to shrinkage of meningioma volume after SRS than data from T1- and T2-weigted sequences. Combinations of standard deviation of T2 and DTI parameters can further improve correlation. If only routine MR images are available, standard deviation of T2-weighted images may be considered to predict volumetric response of meningiomas after SRS.

Neutron capture cross section measurements for 238U in the resonance region at GELINA

Measurements were performed at the time-of-flight facility GELINA to determine the 238U(n,\( \gamma\)) cross section in the resonance region. Experiments were carried out at a 12.5 and 60m measurement station. The total energy detection principle in combination with the pulse height weighting technique was applied using C6D6 liquid scintillators as prompt \( \gamma\)-ray detectors. The energy dependence of the neutron flux was measured with ionisation chambers based on the 10B(n,\( \alpha\)) reaction. The data were normalised to the isolated and saturated 238U resonance at 6.67 eV. Special procedures were applied to reduce bias effects due to the weighting function, normalization, dead time and background corrections, and corrections related to the sample properties. The total uncertainty due to the weighting function, normalization, neutron flux and sample characteristics is about 1.5%. Resonance parameters were derived from a simultaneous resonance shape analysis of the GELINA capture data and transmission data obtained previously at a 42m and 150m station of ORELA. The parameters of resonances below 500 eV are in good agreement with those resulting from an evaluation that was adopted in the main data libraries. Between 500 eV and 1200 eV a systematic difference in the neutron width is observed. Average capture cross section data were derived from the experimental capture yield in the energy region between 3.5 keV and 90 keV. The results are in good agreement with an evaluated cross section resulting from a least squares fit to experimental data available in the literature prior to this work. The average cross section data derived in this work were parameterised in terms of average resonance parameters and included in a least squares analysis together with other experimental data reported in the literature.

Partial-wave analysis ofn+Am241reaction cross sections in the resonance region

Cross sections for neutron-induced reactions of $^{241}\text{Am}$ in the resonance region have been evaluated. Results of time-of-flight cross section experiments carried out at the GELINA, LANSCE, ORELA and Saclay facilities have been combined with optical model calculations to derive consistent cross sections from the thermal energy region up to the continuum region. Resolved resonance parameters were derived from a resonance shape analysis of transmissions, capture yields, and fission yields in the energy region up to 150 eV using the refit code. From a statistical analysis of these parameters, a neutron strength function (${10}^{4}{S}_{0}=1.01\ifmmode\pm\else\textpm\fi{}0.12$), mean level spacing (${D}_{0}=0.60\ifmmode\pm\else\textpm\fi{}0.01$ eV) and average radiation width ($\ensuremath{\langle}{\mathrm{\ensuremath{\Gamma}}}_{{\ensuremath{\gamma}}_{0}}\ensuremath{\rangle}=43.3\ifmmode\pm\else\textpm\fi{}1.1$ meV) for $s$-wave resonances were obtained. Neutron strength functions for higher partial waves ($lg0$) together with channel and effective scattering radii were deduced from calculations based on a complex mean-field optical model potential, applying an equivalent hard-sphere scattering radius approximation.

Impact of systematic effects on results of neutron resonance transmission analysis

The impact of systematic effects on the areal density derived from a neutron resonance transmission analysis (NRTA) is investigated by measurements at the time-of-flight facility GELINA. The experiments were carried out at a 25m station using metallic natural Cu discs with different thicknesses. To derive the areal density from a fitting to the experimental transmission, the resonance shape analysis code REFIT was used. Large bias effects were observed using recommended resonance parameters. Therefore, neutron resonance parameters, in particular resonance energies and neutron widths, were derived from the transmission data obtained with a 0.25mm thick Cu metallic sample. These parameters were used to study the impact of the resonance strength and sample thickness on the accuracy of the areal density derived by NRTA.

CONRAD Evaluation Code: Development Status and Perspectives

CONRAD is an object-oriented code developed at CEA Cadarache since 2005 to treat issues occurring during the data assimilation process. The last new features of the code in terms of experimental, theoretical and interface aspects are presented in this paper. The experimental descriptions capabilities have been enhanced thanks to the implementation of both analytical (Chi-Square, Gaussian) and Monte-Carlo resolution functions which are required for neutron resonance shape analysis. On the theoretical aspects, efforts have been focused on the fast energy region with the wrapping of the ECIS and TALYS codes and the management of optical model and statistical parameters. These new features make it possible for CONRAD to currently perform evaluations from 0 to 20 MeV. Concerning the interfacing developments, a multigroup cross-sections generating tool and an ENDF parser have been recently improved to produce multigroup cross-section covariance matrices in the frame of the JEFF project. Several examples and comparisons with other codes (SAMMY, REFIT) are provided to validate each development.

Neutron transmission and capture cross section measurements for 241Am at the GELINA facility

Resonance parameters for neutron-induced reactions on 241Am below 110 eV have been determined. The parameters result from a resonance shape analysis of transmission and capture data measured at the time-of-flight facility GELINA, with the accelerator operating at a 50 Hz repetition rate. The transmission experiments were carried out at a 25 m station using a Li glass scintillator. The capture experiments were performed at a 12.5 m station by applying the total energy detection principle in combination with the pulse height weighting technique using a pair of C6D6 detectors. The normalization of the capture data was determined by a combined least squares adjustment of the transmission and capture data. From the adjusted resonance parameters a capture cross section of 749 ± 35 b for a neutron energy of 0.0253 eV and an average radiation width of 〈Γ γ 〉 = 42.0 meV for s-wave resonances were obtained. A missing-level analysis for s-wave neutron resonances within the statistical model results in compatible values with previous estimates. The neutron widths obtained in this work are approximately 22% larger compared to other experimental data and evaluated data libraries. Also the thermal capture cross section is larger than most of the recommended values. However, the resonance parameter file presented in this work is consistent with results of both integral experiments and of the experimentally determined resonance integrals.

Evaluation of stable tungsten isotopes in the resolved resonance region

In the last decade benchmark experiments and simulations, together with newly obtained neutron cross section data, have pointed out deficiencies in evaluated data files of W isotopes. The role of W as a fundamental structural material in different nuclear applications fully justifies a new evaluation of 182, 183, 184, 186 W neutron resonance parameters. In this regard transmission and capture cross section measurements on natural and enriched tungsten samples were performed at the GELINA facility of the EC-JRC-IRMM. A resonance parameter file used as input in the resonance shape analysis was prepared based on the available literature and adjusted in first instance to transmission data.

Recent Developments in the CONRAD Code regarding Experimental Corrections

The CONRAD code is an object-oriented software tool developed at CEA Cadarache since 2005 to deal with problems arising during the evaluation process (data assimilation and analysis, physical modelling, propagation of uncertainties…). This paper will present recent developments concerning the experimental corrections, which are required when a neutron resonance shape analysis is performed. Several experimental aspects are detailed in this work:

Resonance neutron-capture cross sections of stable magnesium isotopes and their astrophysical implications

We have measured the neutron capture cross sections of the stable magnesium isotopes 24,25,26Mg in the energy range of interest to the s process using the neutron time-of-flight facility n_TOF at CERN. Capture events from a natural metal sample and from samples enriched in 25Mg and 26Mg were recorded using the total energy method based on C62H6 detectors. Neutron resonance parameters were extracted by a simultaneous resonance shape analysis of the present capture data and existing transmission data on a natural isotopic sample. Maxwellian-averaged capture cross sections for the three isotopes were calculated up to thermal energies of 100 keV and their impact on s-process analyses was investigated. At 30 keV the new values of the stellar cross section for 24Mg, 25Mg, and 26Mg are 3.8±0.2 mb, 4.1±0.6 mb, and 0.14±0.01 mb, respectively.5 MoreReceived 9 January 2012DOI:https://doi.org/10.1103/PhysRevC.85.044615©2012 American Physical Society

Average radiation widths of levels in natural xenon isotopes

Average radiation widths 〈Γγ〉 for the stable xenon isotopes have been estimated using neutron resonance spectroscopic information deduced from high-resolution capture and transmission data measured at the electron linear accelerator GELINA of the Institute for Reference Materials and Measurements (IRMM) in Geel, Belgium. The combination of conventional Neutron Resonance Shape Analysis techniques (NRSA) with high-energy model calculations in a simple Bayesian learning method permit to calculate a consistent local systematic in the xenonʼs mass region (Z=54) from A=124 to A=136.

Interpretation of pile-oscillation measurements by the integral data assimilation technique

The Integral Data Assimilation (IDA) was designed to deduce values of infinite dilute neutron cross-sections from specific integral measurements. Performances of the IDA procedure are demonstrated with pile-oscillation measurements carried out on 155Gd in the pool type reactor MINERVE (CEA Cadarache, France). At low neutron energies, the Integral Data Assimilation is based on the Neutron Resonance Shape Analysis technique routinely used in neutron spectroscopy measurements. As a result of the IDA analysis, a value of (61 900±1500) b has been obtained for the 155Gd thermal capture cross-section at ( E th =25.3 meV).

Investigations for the use of the fast digitizers with [formula omitted] detectors for radiative capture measurements at GELINA

The relatively long dead time in conventional data acquisition systems that provide simultaneously the pulse height and the time information for the detected events hinders cross-section measurements with high count rates. This is the case for capture cross-section measurements at the time-of-flight facility GELINA using high radioactive samples or thick samples of materials having strong resonances. Either the high average count rate (e.g. due to the radioactivity of the sample) or the high instantaneous count rate for strong resonances results in a large dead time correction. One solution to reduce the impact of the dead time is the use of a data acquisition system based on fast digitizers. The performances of two commercial digitizers (CAEN N172B and Acqiris DC282), coupled to a C 6 D 6 scintillator, have been tested in terms of pulse height linearity and resolution, dead time and time resolution. The signal processing was done on-line obtaining simultaneously the pulse height and time information for each detected event. With both digitizers a comparable pulse height linearity and resolution has been obtained as with a conventional system. The total dead time of both digital systems is at least a factor 5 shorter than the one for the conventional system. The main difference in performance between the two digitizers is the time resolution. For a relatively large scintillator, a time resolution of about 2 ns has been achieved with the DC282 module and the conventional system while the time resolution was limited to 15 ns with the CAEN N1728B module. For most nuclei a 15 ns time resolution is sufficient to perform resonance shape analysis. Therefore, the CAEN N1728B module can be used for the majority of capture cross-section measurements at GELINA. However, for nuclei with low level density, for which the resolved resonance region extends to the keV-region, a better time resolution is required and the Acqiris DC282 module has to be used.

Assessment and Propagation of the 237Np Nuclear Data Uncertainties in Integral Calculations by Monte Carlo Techniques

A new method to produce covariance or dispersion matrices for the resonance parameters of neutron cross sections was developed. The technique uses resonance shape analysis in association with Monte Carlo treatment of the uncertainties. The method was implemented in the error propagation tool MCFIT. This program provides a user-friendly textual interface for the shape analysis code REFIT. It was designed to take into account the main sources of uncertainties involved in time-of-flight measurements. Its capability is illustrated with the simultaneous analysis of 237Np capture and transmission data. The covariance matrix obtained in this work was used to interpret oscillation measurements of 237Np samples carried out in the Minerve reactor located at Cadarache.