Neutron Capture Yields Research Articles

Measurement of the neutron capture cross section of 185Re in the keV energy region

ABSTRACT Despite various applications of Rhenium in nuclear science and engineering, there have been limited measurements of the neutron capture cross section of 185Re in the keV energy region, with existing data showing discrepancies. To address this, the study employed the time-of-flight method to measure the neutron capture cross section of 185Re. The prompt γ-rays from the neutron capture reactions were detected using a NaI(Tl) detector. The pulse-height weighting technique was employed to determine the neutron capture yield. The measured cross-section values were determined relative to the neutron capture cross section of 197Au in the energy range from 15 to 90 keV. Additionally, the obtained results were corrected for neutron transport effects and impurities. The results of the measurement provided improved accuracy compared to previous studies, contributing to the nuclear data for the capture cross section of 185Re in the keV energy range.

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.

The Stellar 72Ge(n, γ) Cross Section for weak s-process: A First Measurement at n_TOF

The slow neutron capture process (s-process) is responsible for producing about half of the elemental abundances heavier than iron in the universe. Neutron capture cross sections on stable isotopes are a key nuclear physics input for s-process studies. The 72Ge(n, γ) Maxwellian-Averaged Cross Section (MACS) has an important influence on the production of isotopes between Ge and Zr in the weak s-process in massive stars and so far only theoretical estimations are available. An experiment was carried out at the neutron time-of-flight facility n_TOF at CERN to measure the 72Ge(n, γ) reaction for the first time at stellar neutron energies. The capture measurement was performed using an enriched 72GeO2 sample at a flight path length of 184 m, which provided high neutron energy resolution. The prompt gamma rays produced after neutron capture were detected with a set of liquid scintillation detectors (C6D6). The neutron capture yield is derived from the counting spectra taking into account the neutron flux and the gamma-ray detection efficiency using the Pulse Height Weighting Technique. Over 70 new neutron resonances were identified, providing an improved resolved reaction cross section to calculate experimental MACS values for the first time. The experiment, data analysis and the new MACS results will be presented including their impact on stellar nucleosynthesis, which was investigated using the post-processing nucleosynthesis code mppnp for a 25 solar mass model.

Measurements of the Neutron Capture Cross Section of Am-243 with the ANNRI beamline, MLF/J-PARC

The neutron capture cross section of 243Am from thermal to 100 keV was measured using the Accurate Neutron-Nucleus Reaction Measurement Instrument (ANNRI) at the Japan Proton Accelerator Research Complex (J-PARC). The time-of-flight (TOF) method using a NaI(Tl) detector was employed in these measurements and the pulse-height weighting technique was used to derive the neutron capture yield. The preliminary cross section was determined by normalizing the results to JENDL-4.0 cross section data at the third resonance of 243Am. In the thermal energy, the preliminary result is in good agreement with the two latest experimental data measured by the TOF and the activation methods but higher than the evaluated values in JENDL-5.

Experimental determination of the neutron resonance peak of Er162 at 67.8 eV

Er162 is one of the p nuclei in nuclear astrophysics, and its (n,γ) cross sections are important input parameters in nuclear astrophysics network calculations. Resonance data for Er162(n,γ)Er163 at 67.8 eV is currently not present in the EXFOR database; however, it is included in the ENDF/B VIII.0 database. The (n,γ) cross section of Ernat has been measured in the energy range of 1–100 eV at the Back-n facility in the China Spallation Neutron Source. However, due to the influence of the in-beam γ background of the Back-n Facility, it is has not been possible to observe the neutron resonance peak of Er162 at 67.8 eV. A general simulation method is proposed for quantifying the in-beam γ-ray background. By subtracting the in-beam γ-ray background, the neutron-capture yields of Er162 are obtained within the energy range of 20–100 eV. The neutron resonance parameters of Er162 at 67.8 eV are then extracted successfully. It is found that Γγ=101.15±10.08 meV and Γn=2.79±0.28 meV, which are consistent with the ENDF/B VIII.0 database. However, the 51.4-eV resonance peak of Er162(n,γ) is currently unobserved.Received 31 July 2022Revised 17 October 2022Accepted 5 December 2022DOI:https://doi.org/10.1103/PhysRevC.106.065804©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNuclear astrophysicsNuclear reactionsNucleon induced nuclear reactionsRadiative captureResonance reactionsProperties150 ≤ A ≤ 189TechniquesNuclear data analysis & compilationNuclear Physics

241Am Neutron Capture Cross Section in the keV region using Si and Fe-filtered neutron beams

ABSTRACT The neutron capture cross-section of 241Am was measured in the keV neutron range using the recently implemented neutron filtering system of the Accurate Neutron-Nucleus Reaction Measurement Instrument (ANNRI) beamline in the materials and life science (MLF) facility of the Japan Proton Accelerator Research Complex (J-PARC). Filter arrays consisting of 20 cm of nat Fe and nat Si were employed in separate measurements to provide filtered neutron beams with averaged neutron energies of 23.5 (Fe), 51.5 and 127.7 (Si) keV. The present 241Am results were obtained relative to the 197Au neutron capture yield by applying the total energy detection principle together with the pulse-height weighting technique. The 241Am neutron capture cross-section was determined as 2.72(29) b at 23.5 keV, 2.14(26) b at 51.5 keV and 1.32(10) b at 127.7 keV with total uncertainties in the range of 8 to 12%, much lower in comparison to the latest time-of-flight experimental data available.

Unravelling UBC 274: A morphological, kinematical, and chemical analysis of a disrupting open cluster

Context.Open clusters in the process of disruption help to understand the formation and evolution of the Galactic disk. The wealth and homogeneity ofGaiadata have led to the discovery of several open clusters with signs of disruption. Detailed chemical information for these clusters is essential in order to study the timescales and interplay between the star formation process and cluster disruption.Aims.We perform a morphological, kinematic, and chemical analysis of the disrupting cluster UBC 274 (2.5 Gyr,d = 1778 pc), to study its global properties.Methods.We use HDBSCAN to obtain a new membership list up to 50 pc from its centre and up to magnitudeG = 19 usingGaiaEDR3 data. We use high-resolution and high signal-to-noise spectra to obtain atmospheric parameters of six giants and sub-giants, and individual abundances of 18 chemical species.Results.The cluster has a highly eccentric (0.93) component, tilted ∼10 deg with respect to the plane of the Galaxy, which is morphologically compatible with the results of a test-particle simulation of a disrupting cluster. Our abundance analysis shows that the cluster has a sub-solar metallicity of [Fe/H] = −0.08 ± 0.02. Its chemical pattern is compatible with that of Ruprecht 147, of similar age but located closer to the Sun, with the remarkable exception of neutron-capture elements, which present an overabundance of [n/Fe] ∼ 0.1.Conclusions.The cluster’s elongated morphology is associated with the internal part of its tidal tail, following the expected dynamical process of disruption. We find a significant sign of mass segregation, where the most massive stars appear 1.5 times more concentrated than other stars. The cluster’s overabundance of neutron-capture elements can be related to the metallicity dependence of the neutron-capture yields due to the secondary nature of these elements, predicted by some models. UBC 274 presents a high chemical homogeneity at the level of 0.03 dex in the sampled region of its tidal tails.

Neutron capture cross section measurements of 241Am at the n_TOF facility

Neutron capture on 241Am plays an important role in the nuclear energy production and also provides valuable information for the improvement of nuclear models and the statistical interpretation of the nuclear properties. A new experiment to measure the 241Am(n, γ) cross section in the thermal region and the first few resonances below 10 eV has been carried out at EAR2 of the n_TOF facility at CERN. Three neutron-insensitive C6D6 detectors have been used to measure the neutron-capture gamma cascade as a function of the neutron time of flight, and then deduce the neutron capture yield. Preliminary results will be presented and compared with previously obtained results at the same facility in EAR1. In EAR1 the gamma-ray background at thermal energies was about 90% of the signal while in EAR2 is up to a 25 factor much more favorable signal to noise ratio. We also extended the low energy limit down to subthermal energies. This measurement will allow a comparison with neutron capture measurements conducted at reactors and using a different experimental technique.

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.

Measurements of neutron total and capture cross sections of 241Am with ANNRI at J-PARC

ABSTRACT Neutron total and capture cross sections of 241Am have been measured with a new data acquisition system and a new neutron transmission measurement system installed in Accurate Neutron Nucleus Reaction measurement Instrument at Materials and Life Science Experimental Facility of Japan Proton Accelerator Research Complex. The neutron total cross sections of 241Am were determined by using a neutron time-of-flight (TOF) method in the neutron energy region from 4 meV to 2 eV. The thermal total cross section of 241Am was derived with an uncertainty of 2.9%. A pulse-height weighting technique was applied to determine neutron capture yields of 241Am. The neutron capture cross sections were determined by the TOF method in the neutron energy region from the thermal to 100 eV, and the thermal capture cross section was obtained with an uncertainty of 4.1%. The evaluation data of JENDL-4.0 and JEFF-3.2 were compared with the present results.

The quality of megavoltage photon beams measured by the ratio of photoactivation and neutron capture yields

The activities of products of two photonuclear reactions (113In(γ,γ’)113mIn and 115In(γ,γ’)115mIn) and neutron capture (115In(n, γ)116mIn) were measured. The measurements were made to verify that obtained activities (as well as some of their ratios) change sufficiently with the change of the energy, so that the activation of the indium could be recommended as a sensitive test for the control of the endpoint energy (and beam quality) of bremsstrahlung beams in an energy region usually used in radiation therapy. Mikrotron photon beam was used for photoactivation, and the source of neutrons was the mikrotron tungsten target itself, at energies higher than threshold for (γ, n) reaction. At lower energies, neutrons were produced in Be target inserted in photon beam. It was obtained that sensitive index of endpoint energy variation can be obtained in a broad energy region from 5 MeV to 23 MeV by different combinations of saturation activities of three reaction products. The described measurements can be used to develop a very sensitive and simple method in a routine quality control of photon beams of megavoltage devices used in radiotherapy.

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.

Neutron Capture Measurements and Resonance Analysis of Dysprosium

The electron linear accelerator facility at the Rensselaer Polytechnic Institute was used to measure neutron capture yields of dysprosium with the time-of-flight method in the neutron energy region from 10 eV to 1 keV. The neutron capture experiments were made at a flight path length of 25.5 m with a 16-section NaI multiplicity detector. High purity isotopic samples of 161Dy, 162Dy, 163Dy, 164Dy as well as one natural dysprosium sample with thickness of 0.508 mm were used in this measurement. Resonance parameters were extracted from the data using simultaneous fit with the multilevel R-matrix Bayesian code SAMMY 8.0. New resonances are proposed, and other resonances previously identified in the literature have been revised. The present results are compared with other evaluated values of ENDF/B-VII.1 and JENDL 4.0.

Au197(n,γ) cross section in the resonance region

The (n,γ) cross section of Au197 has been measured at n-TOF in the resolved resonance region, up to 5keV, with the aim of improving the accuracy in an energy range where it is not yet considered standard. The measurements were performed with two different experimental setup and detection techniques, the total energy method based on C6D6 detectors, and the total absorption calorimetry based on a 4π BaF2 array. By comparing the data collected with the two techniques, two accurate sets of neutron-capture yields have been obtained, which could be the basis for a new evaluation leading to an extended cross-section standard. Overall good agreement is found between the n-TOF results and evaluated cross sections, with some significant exceptions for small resonances. A few resonances not included in the existing databases have also been observed. © 2010 The American Physical Society.

High energy resolution measurement of the 238U neutron capture yield from 1 to 100 keV

The purpose of this work is the precise determination of the 238U neutron capture yield (i.e. the probability of neutron capture) as a function of neutron energy with the highest available neutron energy resolution. The motivation for this undertaking arises from the central role played by the 238U neutron capture process in the neutron balance of both thermal reactors and fast breeder reactors. The present measurement was performed using the Oak Ridge Electron Linear Accelerator (ORELA) facility. The pulsed beam of neutrons from the ORELA facility is collimated on a sample of 238U. The neutron capture rate in the sample is measured, as a function of neutron time-of-flight (TOF) by detecting the γ-rays from the 238U(n, γ) 239U reaction with a large γ-ray detector surrounding the 238U sample. At each energy, the capture yield is proportional to the observed capture rate divided by the measured intensity of the neutron beam. The constant of proportionality (the normalization constant) is obtained from the ratio of theoretical to experimentally measured areas under small 238U resonances where the resonance parameters have been determined from high-resolution 238U transmission measurements. The cross section for the reaction 238U(n, γ) 239U can be derived from the measured capture yield if one applies appropriate corrections for multiple scattering and resonance self-shielding. Some 200 238U neutron resonances in the energy range from 250 eV to 10 keV have been observed which had not been detected in previous measurements.

Neutron capture measurements on radioactive93Zr

Neutron capture measurements made on a sample of fission-product zirconium containing 20%93Zr(t1/2=1.5×106a) at the Oak Ridge Electron Linear Accelerator time-of-flight facility resulted in the identification of 138 resonance peaks for the93Zr isotope at neutron energies up to 21.5 keV. Average capture cross sections from 20 to 300 keV were derived by subtracting neutron capture yields of the stable zirconium isotopes90, 91, 92, 94, 96Zr and additional backgrounds. The average cross sections found were significantly less than those of JENDL-1. While generally 30% higher than those of ENDF/B —V below 60 keV, the binned data overlapped the smooth ENDF/B —V curve. The average for a Maxwellian neutron spectrum withkT=30 keV is (95±10) mb and the resonance contribution to the capture resonance integral is (15.0±0.5)b.

Neutron-Capture Cross Sections of the Stable Lead Isotopes

Neutron-capture yields for several samples of separated lead isotopes were obtained at the Oak Ridge electron linear accelerator, in the neutron energy range above 2.5 keV. These were analyzed for resonance-capture areas and parameters. The data are included in a new evaluation of lead cross-section data.[NUCLEAR REACTIONS $^{204,206,207,208}\mathrm{Pb}(n,\ensuremath{\gamma})$, ${E}_{n}>2.5$ keV, measured ${\ensuremath{\sigma}}_{n,\ensuremath{\gamma}}$; deduced levels, ${E}_{\ensuremath{\gamma}}$, $\ensuremath{\Gamma}$, ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}$, averages, R.I., enriched targets, resolution \ensuremath{\sim}0.2%.]

Neutron Resonance Parameters ofMo92

Neutron transmission and total neutron-capture yields were measured using the time-of-flight technique at the Oak Ridge electron linear accelerator facility using enriched samples of $^{92}\mathrm{Mo}$. A total of 42 resonances were observed for neutron energies less than 32 keV. 12 are assigned to $s$-wave interactions, while 23 are assigned to $p$-wave interactions. The resonant energies, neutron widths, radiation widths, and spins are deduced. The average $s$- and $p$-wave radiation widths are equal to 0.178\ifmmode\pm\else\textpm\fi{}0.015 eV and 0.24\ifmmode\pm\else\textpm\fi{}0.03 eV, respectively. The $s$-wave neutron strength function is (0.65\ifmmode\pm\else\textpm\fi{}0.26)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$, while the $p$-wave strength function is (3.3\ifmmode\pm\else\textpm\fi{}1.1)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$.