Pulse-height Weighting Technique Research Articles

Measurement of the neutron capture cross sections of rhenium up to stellar s - and r -process temperatures at the China Spallation Neutron Source Back-n facility

The neutron capture measurement of natural rhenium was performed with the time-of-flight technique at the Back-n facility of the China Spallation Neutron Source in the energy range from 1 to 500 eV of the resolved resonance region (RRR) and from 5 to 400 keV in the unresolved resonance region (URR). Prompt γ-rays originating from neutron-induced capture events were detected by four C6D6 detectors. The pulse height weighting technique and the double-bunch unfolding method based on the Bayesian theory were used in the data analysis. To obtain reliable measurement results, background subtraction, normalization, and corrections were carefully considered. The multilevel R-matrix Bayesian code was used to extract the resonance parameters in the RRR. An absence of resonance near 392 eV is observed in our measurement, which has been observed in previous works. The average cross sections in the URR of natural rhenium relative to Au197 were obtained in logarithmical equidistant energy bins with 20 bins per energy decade. The code was used to describe the average cross sections in the URR; the Maxwellian-averaged cross sections (MACSs) of Re185 and Re187 are given from kT=5 to 100 keV. At a thermal energy of kT=30 keV, the MACS value for Re185 (1469±127 mb) is in good agreement with the Karlsruhe Astrophysical Database of Nucleosynthesis in Stars (KADoNIS) recommended value (1535±62 mb) within the error bars. By contrast, the value of 1361±118 mb for Re187 shows a discrepancy with the recommended value (1160±57 mb). Published by the American Physical Society 2024

Measurements of keV-Neutron capture cross sections and capture gamma-ray spectra of 74,76,78,80,82Se

ABSTRACT The neutron capture cross sections and capture γ -ray spectra of 74,76,78,80,82Se were measured in a region from 15 to 100 keV and around 550 keV. A neutron time-of-flight method was used with a ns-pulsed neutron source based on the 7Li(p,n)7Be reaction and a large anti-Compton NaI(Tl) γ -ray spectrometer. A pulse-height weighting technique was applied to the observed γ -ray pulse-height spectra to obtain capture yields. The capture cross sections of 74,76,78,80Se were derived with uncertainties from 4.0 to 5.5% and those of 82Se were derived with uncertainties of 6.5–27% by using the standard capture cross sections of 197Au. The present results of 78,82Se were the first experimental ones above the resolved resonance region. The present results were compared with previous measurements and the evaluated values in JENDL-5.0 and ENDF/B-VIII.0. The evaluations of JENDL-5.0 differ from the present results of 74,76,78,80Se and 82Se by 0.9–51% and 6.9–120%, respectively. The capture γ -ray spectra of 74,76,78,80,82Se were derived by unfolding the observed capture γ -ray pulse-height spectra. The present results were the first experimental ones in the keV region.

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.

A Segmented Total Energy Detector (sTED) optimized for (n, [formula omitted]) cross-section measurements at n_TOF EAR2

The neutron time-of-flight facility n_TOF at CERN is a spallation source dedicated to measurements of neutron-induced reaction cross-sections of interest in nuclear technologies, astrophysics, and other applications. Since 2014, Experimental ARea 2 (EAR2) is operational and delivers a neutron fluence of ∼4⋅107 neutrons per nominal proton pulse, which is ∼50 times higher than the one of Experimental ARea 1 (EAR1) of ∼8⋅105 neutrons per pulse. The high neutron flux at EAR2 results in high counting rates in the detectors that challenged the previously existing capture detection systems. For this reason, a Segmented Total Energy Detector (sTED) has been developed to overcome the limitations in the detector’s response, by reducing the active volume per module and by using a photo-multiplier (PMT) optimized for high counting rates. This paper presents the main characteristics of the sTED, including energy and time resolution, response to γ-rays, and provides as well details of the use of the Pulse Height Weighting Technique (PHWT) with this detector. The sTED has been validated to perform neutron-capture cross-section measurements in EAR2 in the neutron energy range from thermal up to at least 400 keV. The detector has already been successfully used in several measurements at n_TOF EAR2.

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.

Measurements of the Neutron Total and Capture Cross Sections and Derivation of the Resonance Parameters of 181Ta

The neutron total and capture cross sections of 181Ta were measured at the Accurate Neutron-Nucleus Research Measurement Instrument of the Materials and Life Science Experimental Facility in the Japan Proton Accelerator Research Complex to improve the accuracy of the current resonance parameters. The total cross section was determined from the transmission measurement in the energy range from 0.2 to 150 eV. The capture cross section was derived from the capture yield using the pulse height weighting technique in the energy range from thermal to 150 eV. The thermal neutron capture cross section was measured as 21.3 ± 0.3 ( stat ) ± 0.6 ( sys ) b. The obtained transmission and capture cross section were simultaneously fitted using the resonance analysis code REFIT, and the resonance parameters for resonances below 150 eV were evaluated. The present resonance parameters were compared to reported measurements.

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.

Fast-neutron capture cross section data measurement of minor actinides for development of nuclear transmutation systems

The neutron capture cross sections of 237Np, 243Am and 241Am in the keV energy region were measured by the time-of-flight method at the Japan Proton Accelerator Research Complex (J-PARC). Characterization of the minor actinide samples were made to reduce the uncertainties of the cross section. A neutron beam filter system was developed and installed in ANNRI to solve the double-bunch mode issue of J-PARC. The pulse-height weighting technique was employed to determine the neutron capture cross sections. The neutron capture cross sections of 237Np, 243Am and 241Am were determined with higher accuracies than the past experiments.

Neutron capture measurements with high efficiency detectors and the Pulse Height Weighting Technique

Neutron capture cross section measurements in time-of-flight facilities are usually performed by detecting the prompt γ-rays emitted in the capture reactions. One of the difficulties to be addressed in these measurements is that the emitted γ-rays may change with the neutron energy, and therefore also the detection efficiency. To deal with this situation, many measurements use the so called Total Energy Detection (TED) technique, usually in combination with the Pulse Height Weighting Technique (PHWT). With it, it is sought that the detection efficiency depends only on the total energy of the γ-ray cascade, which does not vary much with the neutron energy. This technique was developed in the 1960s and has been used in many neutron capture experiments to date. One of the requirements of the technique is that γ-ray detectors have a low efficiency. This has meant that the PHWT has been used with experimental setups with low detection efficiencies. However, this condition does not have to be fulfilled by the experimental system as a whole. The main goal of this work is to show that it is possible to measure with a high efficiency detection system that uses the PHWT, and how to analyze the measured data.

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.

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.

Measurement of 232Th (n, γ) cross section at the CSNS Back-n facility in the unresolved resonance region from 4 keV to 100 keV

The neutron capture cross section of 232Th was measured at the neutron time-of-flight facility Back-n of China Spallation Neutron Source (CSNS) for the first time. The measurement was performed with 4 hydrogen-free deuterated benzene C6D6 liquid scintillation detectors, in the ES#2 experiment station on the beam line, at a distance of about 76 m from the neutron-production assembly. The total energy detection principle in combination with the pulse height weighting technique (PHWT) was applied to analyze the measured data. Results of the 232Th (n, γ) reaction cross section in the unresolved resonance region from 4 keV to 100 keV were obtained, which shows a good agreement with the existing experimental data from EXFOR, as well as with the evaluated data from the ENDF/B-VIII.0 and CENDL-3.1. In addition, the excitation function of 232Th (n, γ)233Th reaction in the unresolved resonance region was theoretically calculated by using the code TALYS-1.95. By fitting the experimental cross section and theoretical data, the average parameters in the unresolved resonance region were extracted. The datasets are openly available at http://dx.doi.org/10.11922/sciencedb.j00113.00015.

Measurements of the 107 Ag neutron capture cross sections with pulse height weighting technique at the CSNS Back-n facility

Silver indium cadmium (Ag–In–Cd) control rod is widely used in pressurized water reactor nuclear power plants, and it is continuously consumed in a high neutron flux environment. The mass ratio of 107Ag in the Ag–In–Cd control rod is 41.44%. To accurately calculate the consumption value of the control rod, a reliable neutron reaction cross section of the 107Ag is required. Meanwhile, 107Ag is also an important weak r nucleus. Thus, the cross sections for neutron induced interactions with 107Ag are very important both in nuclear energy and nuclear astrophysics. The (n, γ) cross section of 107Ag has been measured in the energy range of 1–60 eV using a back streaming white neutron beam line at China spallation neutron source. The resonance parameters are extracted by an R-matrix code. All the cross section of 107Ag and resonance parameters are given in this paper as datasets. The datasets are openly available at http://www.doi.org/10.11922/sciencedb.j00113.00010.

Neutron capture cross section measurements for <sup>nat</sup>Lu with different thickness

The C<sub>6</sub>D<sub>6</sub> detection system coupling with the pulse height weighting technique is widely used for experimentally measuring the neutron capture cross section. The thickness of sample used in the experiment directly affects the neutron beam time and the reliability of the experimental data. In the present work, we compare the lutetium (Lu) neutron capture reaction cross sections among the samles with different thickness, obtained by the C<sub>6</sub>D<sub>6</sub> detection system of the back-streaming white neutron beam line at China spallation Neutron Source (CSNS back-n). The light response of the detection system is simulated with the consideration of the sample thickness by GEANT4 Monte Carlo simulation code. The 4<sup>th</sup> order polynomial pulse weight functions for different samples are determined by using the above light response function. In the experiment, the high precision capture yield distributions in the resonance energy region are obtained by measuring the longer flight distance and background. The experimental resonance parameters are deduced by analyzing the capture yield distribution with the R-matrix theory. The comparisons of the results of capture yield and the resonance parameters between the two groups show that the resonance curve of 1.06mm <sup>nat</sup>Lu sample changes due to its thickness effect, and there is a large difference between the experimental resonance parameters and ENDF/B-VIII.0 database. However, the experimental results of 0.207mm <sup>nat</sup>Lu sample can well accord with the ENDF/B-VIII. 0 data.

Neutron capture and total cross-section measurements and resonance parameter analysis of niobium-93 below 400 eV

ABSTRACT Neutron capture yields and transmission ratios of 93Nb were measured by applying the time-of-flight method using the Accurate Neutron-Nucleus Reaction measurement Instrument of the Materials and Life Science Experimental Facility at the Japan Proton Accelerator Research Complex. Nb metal foils were used as samples. Germanium gamma-ray and Li-glass neutron detectors were used for capture yields and transmission ratio measurements, respectively. The pulse height weighting technique was applied to deduce the capture cross-sections from 0.01 to 400 eV, and the thermal-neutron capture cross-section was determined to be 0.97 ± 0.11 b. The total cross-sections were derived from transmission ratios ranging from 0.2 to 400 eV. The resonance parameters of 93Nb below 400 eV were determined based on the obtained capture cross-sections and transmission ratios using the resonance analysis code, REFIT, and compared with the parameters given by past measurements and the evaluated nuclear data library, JENDL-4.0.

KeV-region analysis of the neutron capture cross-section of 237Np

ABSTRACT Neutron capture cross-section measurements for Np have been conducted with the Accurate Neutron Nucleus Reaction Measurement Instrument (ANNRI) at the Materials and Life Science Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC) using neutrons with energy ranging from thermal energy to 1 MeV. A time-of-flight (TOF) method using a NaI(Tl) detector was employed and the data were analyzed based on the pulse-height weighting technique in order to derive the neutron capture cross-section. The absolute capture cross-section was determined using the first resonance from JENDL-4.0 together with the total neutron flux derived from a Au sample measurement in which the first resonance was completely saturated. Both normalization techniques present agreement within 1. The present results are also compared evaluated data libraries. There is a discrepancy of 10–25 discrepancy from 0.5 to 20 keV with JENDL-4.0. Nonetheless, above this energy JENDL-4.0 seems to reproduce the present data better as the results agree within uncertainties up to 500 keV. The cross-section results contain uncertainties below 4 from 0.5 to 30 keV. However, the total uncertainty increases to over 8 above 30 keV. Along with the cross-section measurement, theoretical calculations with the CCONE code were performed to reproduce the present results.

Measurements of the neutron capture cross section of 243Am around 23.5 keV

ABSTRACT The neutron capture cross section of 243Am was measured by the time-of-flight method with a pulsed neutron beam from a spallation neutron source of the Japan Proton Accelerator Research Complex. An Fe neutron beam filter was used to make the incident neutron beam quasi-monoenergetic around 23.5 keV. The neutron capture γ-rays were detected with a NaI(Tl) detector. The pulse height weighting technique was employed to derive the neutron capture cross section from the pulse height spectrum. The cross section was determined relative to the capture cross section of 197Au of JENDL-4.0. The obtained neutron capture cross section of 243Am was 2.52 ± 0.14 b, determined with a much smaller uncertainty than those of past measurements.

Introduction of a C6D6detector system on the Back-n of CSNS

Radiative neutron capture cross sections are very important in the field of basic physics research and nuclear device R&D. The Back-n white neutron beam line of China Spallation Neutron Source (CSNS) is the first spallation neutron beam line in China. On the purpose for radiative neutron capture cross section measurement, a C6D6detector system was built in the Back-n experimental station. The pulse height weighting technique (PHWT) was used to make the system’s detective efficiency independent of the cascade path and the energy of cascade gamma rays. The neutron energy spectrum was measured for the energy between 1eV and 80keV with a6Li loaded ZnS scintillation detector. Besides, a testing experiment with197Au and169Tm samples was carried out to examine this system. According to the preliminary results, this C6D6detector system can be used to perform neutron capture cross section measurement.

Measurement of the neutron capture cross-section of 237Np using ANNRI at MLF/J-PARC

The neutron capture-cross section of 237Np was measured using the Accurate Neutron-Nucleus Reaction Measurement Instrument (ANNRI) with special emphasis in the region of interest for the core design of Accelerator-Driven Systems (ADS), from 0.5 to 500 keV. A neutron time-of-flight method was employed using the NaI(Tl) spectrometer in the ANNRI beamline at the Japanese Proton Accelerator Research Complex (J-PARC) together with the pulse-height weighting technique. The cross-section was determined by normalizing the results to JENDL-4.0 cross-section data at the first resonance of 237Np. In the 0.5 to 500 keV range, the present preliminary results present better agreement with previous experiments of Weston et al [3]. Experimental data from Esch et al [6] is about 15% lower than the present results. In comparision with evaluated data, ENDF/B-VIII.0 offers better agreement from 0.5 to 10 keV than with JENDL-4.0. From 0.5 to 10 keV JENDL-4.0 underestimates the present results by 10-15%. Nontheless, over 10 keV energy JENDL-4.0 shows good agreement up to 500 keV. The present preliminary cross-section has uncertainties of about 5% from 0.5 to 35 keV, a value lower than the uncertainties present in JENDL-4.0 of 6-10%. However, over 35 keV the total uncertainties steadily increase and amount to 10% at 500 keV.

Neutron capture cross-section measurement and resolved resonance analysis of 237Np

ABSTRACTThe neutron capture cross-section of 237Np has been measured in the neutron energy region from 10 meV to 500 eV. A neutron time-of-flight method was employed using the NaI(Tl) spectrometer in the ANNRI beamline at the Japanese Proton Accelerator Research Complex (J-PARC). The experimental capture yield was derived using the pulse-height weighting technique and an energy-dependent cross-section was obtained relative to the incident neutron spectrum derived from a 10B(n, )7Li reaction yield. The absolute cross-section was determined by normalizing the results to JENDL-4.0 cross-section data at the first resonance of 237Np. The thermal cross-section was measured to be 177.6 ± 3.8 b. The resolved resonance region was analyzed with the REFIT code. An average radiation width = 40.3 ± 0.5 meV, a mean level spacing D0 = 0.60 ± 0.02 eV and a neutron strength function 104S0 = 1.02 ± 0.12 were obtained.