Capture Cross Section Measurements Research Articles

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.

Measurements of effective actinides neutron capture cross sections in a cadmium-filtered epithermal neutron spectrum

I (G.J.Y.) was a graduate student the first time I met Dr. Salvatores in February 1994 in Cadarache, France. He was teaching a class (in French) on fast reactor physics. Among us was a bright Chinese student who had come to learn reactor physics the French way. The student’s French was a little less than perfect, so I was surprised when, at the end of the class, he raised his hand and asked Dr. Salvatores, “Are you really French?” Dr. Salvatores looked at him and replied with a smile, “Eh, non, je ne suis qu’un pauvre paysan italien!” (No, I’m only a poor Italian peasant!) The class had a good laugh. It did not take long for me to realize Dr. Salvatores was more than just a “pauvre paysan italien”. Massimo would later become my Ph.D. director, and we had many occasions to meet and share laughs around the world over the next 25 years. He was an outstanding scientist, mentor, and bon vivant. He was a model and an inspiration for several generations of French nuclear reactor physicists involved in the development of fast reactors and advanced fuel cycles. Dr. Salvatores initiated the integral experiment that is the subject of this article.

Thermal-neutron capture cross-section measurement of Tantalum-181 using graphite thermal column at KUR

ABSTRACT Using an activation method with a well-thermalized neutron field, it is principally possible to drive a thermal-neutron capture cross-section without considering an epithermal neutron component. We demonstrated neutron capture cross-section measurements using the graphite thermal column (TC-Pn) of the Kyoto University Research Reactor. First, in order to confirm that the graphite thermal column was a well-thermalized neutron field, neutron irradiation was performed with neutron flux monitors: 197Au, 59Co, 45Sc, 63Cu, and 98Mo. The TC-Pn was confirmed to be extremely thermalized on the basis of Westcott’s convention, because the thermal-neutron flux component took a constant value regardless of the sensitivity of each flux monitor to epithermal neutrons. Next, as a demonstration, the thermal-neutron capture cross-section of 181Ta(n,γ)182m+gTa reaction was measured using the graphite thermal column, and then derived to be 20.5 ± 0.4 barn, which supported the evaluated value of 20.4 ± 0.3 barn. The 181Ta nuclide could be useful as a flux monitor that complements the sensitivity between 197Au and 98Mo monitors.

Radiative Neutron Capture Cross-Section Measurement of Ge Isotopes at n_TOF CERN Facility and Its Importance for Stellar Nucleosynthesis

This manuscript summarizes the results of radiative neutron capture cross-section measurements on two stable germanium isotopes, 70Ge and 73Ge. Experiments were performed at the n_TOF facility at CERN via the time-of-flight technique, over a wide neutron energy range, for all stable germanium isotopes (70,72,73,74, and 76). Results for 70Ge [Phys. Rev. C 100, 045804 (2019)] and 73Ge [Phys. Lett. B 790, 458 (2019)] are already published. In the field of nuclear structure, such measurements allow to study excited levels close to the neutron binding energy and to obtain information on nuclear properties. In stellar nucleosynthesis research, neutron induced reactions on germanium are of importance for nucleosynthesis in the weak component of the slow neutron capture processes.

Machine Learning aided 3D-position reconstruction in large LaCl3 crystals

We investigate five different models to reconstruct the 3D γ-ray hit coordinates in five large LaCl3(Ce) monolithic crystals optically coupled to pixelated silicon photomultipliers. These scintillators have a base surface of 50 × 50 mm2 and five different thicknesses, from 10 mm to 30 mm. Four of these models are analytical prescriptions and one is based on a Convolutional Neural Network. Average resolutions close to 1–2 mm fwhm are obtained in the transverse crystal plane for crystal thicknesses between 10 mm and 20 mm using analytical models. For thicker crystals average resolutions of about 3–5 mm fwhm are obtained. Depth of interaction resolutions between 1 mm and 4 mm are achieved depending on the distance of the interaction point to the photosensor surface. We propose a Machine Learning algorithm to correct for linearity distortions and pin-cushion effects. The latter allows one to keep a large field of view of about 70%–80% of the crystal surface, regardless of crystal thickness. This work is aimed at optimizing the performance of the so-called Total Energy Detector with Compton imaging capability (i-TED) for time-of-flight neutron capture cross-section measurements.

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.

Measurements of neutron capture cross-sections for 187Re isotope around 14 MeV neutrons and theoretical calculations of excitation functions

The cross-sections of the 187Re(n,γ)188mRe and 187Re(n,γ)188gRe reactions were measured at the four neutron energies of 13.5, 14.1, 14.4 and 14.8 MeV through the activation method and using off-line γ-ray spectrometry. The previously developed formulas were used to subtract the effects of γ rays with close energies and the contribution from the excited state. A high-resolution γ-ray spectrometer with high-purity germanium detector was used to measure the induced γ activities. The simulation computations of the excitation functions concerning the above-mentioned two nuclear reactions were performed by adopting the nuclear theoretical model program system Talys-1.9. The theoretical excitation curves in the incident neutron energy range from 2.53 × 10−8 to 20 MeV were acquired. The fitting line of our results in the neutron energy range of 13.5–14.8 MeV, within experimental uncertainty, agrees very well with the theoretical excitation curve based on the computer code Talys-1.9.

Measurement of the thermal neutron capture cross section by Be9 using the neutron flux from a nuclear research reactor and the AMS technique

We report on the measurement of the thermal neutron capture cross section by $^{9}\mathrm{Be}$, using $^{14}\mathrm{N}$ as a benchmark for the development of our protocol, which implies the combination of two precise techniques: neutron activation in a nuclear research reactor and accelerator mass spectrometry (AMS). Beryllium oxide (BeO), graphite, and uracil (${\mathrm{C}}_{4}{\mathrm{H}}_{4}{\mathrm{N}}_{2}{\mathrm{O}}_{2}$) samples were irradiated at the TRIGA MARK III nuclear research reactor facility at Instituto Nacional de Investigaciones Nucleares (ININ), M\'exico. Later on, isotopic concentrations were quantified by AMS at Laboratorio de Espectrometr\'{\i}a de Masas con Aceleradores (LEMA) of the Instituto de F\'{\i}sica, Universidad Nacional Aut\'onoma de M\'exico (IF-UNAM), Mexico. Cross sections for the $^{9}\mathrm{Be}(n,\ensuremath{\gamma})^{10}\mathrm{Be}$ and $^{14}\mathrm{N}(n,p)^{14}\mathrm{C}$ nuclear reactions were extracted for thermal neutrons.

Partial cross sections of 181Ta(n,γ) using BEGe detectors

Heavy nuclei are mainly synthesised by a sequence of neutron captures and β-decays. The corresponding neutron energies in the different astrophysical sites range from 1keV to 1MeV. By using the activation technique, small neutron capture cross sections can be studied. A sample is irradiated by a quasi-stellar neutron spectrum in order to produce radioactive isotopes. The decay of the radioactive nuclei can be detected by their characteristic gamma rays. For this purpose, sensitive experimental detector equipment is needed.Two Broad Energy Germanium Detectors (BEGe) were recently built up at the Goethe University Frankfurt. The first measurement of the partial neutron capture cross sections for the reaction 181Ta(n,γ) has been performed by using the activation technique.

80Se(n,γ) cross-section measurement at CERN n TOF

Radiative neutron capture cross section measurements are of fundamental importance for the study of the slow neutron capture (s-) process of nucleosynthesis. This mechanism is responsible for the formation of most elements heavier than iron in the Universe. Particularly relevant are branching nuclei along the s-process path, which are sensitive to the physical conditions of the stellar environment. One such example is the branching at 79Se (3.27 × 105 y), which shows a thermally dependent β-decay rate. However, an astrophysically consistent interpretation requires also the knowledge of the closest neighbour isotopes involved. In particular, the 80Se(n,γ) cross section directly affects the stellar yield of the “cold” branch leading to the formation of the s-only 82Kr. Experimentally, there exists only one previous measurement on 80Se using the time of flight (TOF) technique. However, the latter suffers from some limitations that are described in this presentation. These drawbacks have been significantly improved in a recent measurement at CERN n TOF. This contribution presents a summary of the latter measurement and the status of the data analysis.

Neutron capture measurement at the n TOF facility of the 204Tl and 205Tl s-process branching points

Neutron capture cross sections are one of the fundamental nuclear data in the study of the s (slow) process of nucleosynthesis. More interestingly, the competition between the capture and the decay rates in some unstable nuclei determines the local isotopic abundance pattern. Since decay rates are often sensible to temperature and electron density, the study of the nuclear properties of these nuclei can provide valuable constraints to the physical magnitudes of the nucleosynthesis stellar environment. Here we report on the capture cross section measurement of two thallium isotopes, 204Tl and 205Tl performed by the time-of-flight technique at the n TOF facility at CERN. At some particular stellar s-process environments, the decay of both nuclei is strongly enhanced, and determines decisively the abundance of two s-only isotopes of lead, 204Pb and 205Pb. The latter, as a long-lived radioactive nucleus, has potential use as a chronometer of the last s-process events that contributed to final solar isotopic abundances.

A first prototype of C[formula omitted]D[formula omitted] total-energy detector with SiPM readout for neutron capture time-of-flight experiments

Low efficiency total-energy detectors (TEDs) are one of the main tools for neutron capture cross section measurements utilizing the time-of-flight (TOF) technique. State-of-the-art TEDs are based on a C6D6 liquid-scintillation cell optically coupled to a fast photomultiplier tube. The large photomultiplier tube represents yet a significant contribution to the so-called neutron sensitivity background, which is one of the most conspicuous sources of uncertainty in this type of experiments. Here we report on the development of a first prototype of a TED based on a silicon-photomultiplier (SiPM) readout, thus resulting in a lightweight and much more compact detector. Apart from the envisaged improvement in neutron sensitivity, the new system uses low voltage (+28 V) and low current supply (∼50 mA), which is more practical than the ∼kV supply required by conventional photomultipliers. One important difficulty hindering the earlier implementation of SiPM readout for this type of detector was the large capacitance for the output signal when all pixels of a SiPM array are summed together. The latter leads to long pulse rise and decay times, which are not suitable for time-of-flight experiments. In this work we demonstrate the feasibility of a Schottky-diode multiplexing readout approach, that allows one to preserve the excellent timing properties of SiPMs, hereby paving the way for their implementation in future neutron TOF experiments.

Background study for [formula omitted] cross section measurements with C[formula omitted]D[formula omitted] detectors at CSNS Back-n

The Back-n beam line of the China Spallation Neutron Source is the first white neutron facility in China. One of its goals is to perform radiative neutron capture cross-section (σnγ) measurements. To study the experimental backgrounds of this new facility, a measurement of the σnγ of 197Au was carried out with a C6D6 detector system at Back-n. Time-dependent backgrounds induced by the scattered neutrons and in-beam gamma-rays were measured and analyzed with natC and natPb samples. The black resonance filter technique was employed to evaluate the shape of the backgrounds and perform the normalization. Besides, Monte Carlo simulations of these backgrounds were carried out with the Geant4 toolkit. The simulated results were compared with the experimental ones and the good agreement found allowed us to validate the background evaluation method.

Formation and dissociation reactions of complexes involving interstitial carbon and oxygen defects in silicon

We present a detailed first-principles study which explores the configurational space along the relevant reactions and migration paths involving the formation and dissociation of interstitial carbon-oxygen complexes, $\mathrm{C_{i}O_{i}}$ and $\mathrm{C_{i}O_{2i}}$, in silicon. The formation/dissociation mechanisms of $\mathrm{C_{i}O_{i}}$ and $\mathrm{C_{i}O_{2i}}$ are found as occurring via capture/emission of mobile $\mathrm{C_{i}}$ impurities by/from O-complexes anchored to the lattice. The lowest activation energies for dissociation of $\mathrm{C_{i}O_{i}}$ and $\mathrm{C_{i}O_{2i}}$ into smaller moieties are 2.3 eV and 3.1 eV, respectively. The first is compatible with the observed annealing temperature of $\mathrm{C_{i}O_{i}}$ , which occurs at around 400 $^{\circ}$C, and below the threshold for $\mathrm{O_{i}}$ diffusion. The latter exceeds significantly the measured activation energy for the annealing of $\mathrm{C_{i}O_{2i}}$ ($E_{\mathrm{a}}=2.55$ eV). We propose that instead of dissociation, the actual annealing mechanism involves the capture of interstitial oxygen by $\mathrm{C_{i}O_{2i}}$, thus being governed by the migration barrier of $\mathrm{O_{i}}$ ($E_{\mathrm{m}}=2.53$ eV). The study is also accompanied by measurements of hole capture cross sections and capture barriers of $\mathrm{C_{i}O_{i}}$ and $\mathrm{C_{i}O_{2i}}$. In combination with previously reported data, we find thermodynamic donor transitions which are directly comparable to the first-principles results. The two levels exhibit close features, conforming to a model where the electronic character of $\mathrm{C_{i}O_{2i}}$ can be described by that of $\mathrm{C_{i}O_{i}}$ perturbed by a nearby O atom.

Measurement of 232Th neutron capture cross-sections in the energy range of 2.0–5.0 MeV by using the neutron activation technique

The 232Th(n,γ)233Th neutron capture reaction cross-sections at the neutron energies of 4.36 ± 0.06 MeV, 3.52 ± 0.41 MeV and 2.06 ± 0.34 MeV have been measured using the activation method and off-line gamma-ray spectrometric technique. The neutrons were generated by T(p,n)3He reaction and the 197Au(n, γ)198Au was used as a monitor reaction to determine neutron flux. The effects of multiple scattering, flux attenuation, gamma-ray self-absorption and neutron flux fluctuation have been corrected in the experiment. The excitation function of the 232Th(n,γ)233Th reaction was also theoretically calculated using the TALYS-1.9 code. The experimental results were compared with the evaluated data, the calculated data and the previous experimental data.

A compact fission detector for fission-tagging neutron capture experiments with radioactive fissile isotopes

In the measurement of neutron capture cross-sections of fissile isotopes, the fission channel is a source of background which can be removed efficiently using the so-called fission-tagging or fission-veto technique. For this purpose a new compact and fast fission chamber has been developed. The design criteria and technical description of the chamber are given within the context of a measurement of the 233U(n, γ) cross-section at the n_TOF facility at CERN, where it was coupled to the n_TOF Total Absorption Calorimeter. For this measurement the fission detector was optimized for time resolution, minimization of material in the neutron beam and for alpha-fission discrimination. The performance of the fission chamber and its application as a fission tagging detector are discussed.

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 and total cross-section measurements of 155Gd and 157Gd at ANNRI in J-PARC

Neutron capture and total cross sections of 155Gd and 157Gd were measured with the neutron time-of-flight method in Accurate Neutron-Nucleus Reaction measurement Instrument at Material and Life Science Experimental Facility of the Japan Proton Accelerator Research Complex using the NaI (Tl) spectrometer and Li-glass detectors. Preliminary cross sections were obtained in the neutron energy region from 4 meV to 100 meV. The derived cross sections agree with evaluated values in JENDL 4.0 and the experimental results by Mastromarco but were not consistent with those by Leinweber.

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.