Thermal Neutron Capture Cross Section Research Articles

Measurements of neutron capture cross-sections for nuclides of interest in decommissioning: 45Sc, 63Cu, 64Zn, 109Ag, and 113In

ABSTRACT As nuclear facilities are dismantled in decommissioning, various and large amounts of waste are generated. Even more inconveniently, they are radioactive waste due to neutron activation. Thus, the neutron capture cross-sections of nuclides targeted for decommissioning are required to evaluate the radioactivity produced. The present study selected 45Sc, 63Cu, 64Zn, 109Ag and 113In among targeted nuclides, and performed the measurements of thermal-neutron capture cross-sections by an activation method at the Kyoto University Research Reactor. The thermal-neutron capture cross-sections were derived on the basis of Westcott’s convention. The present results were obtained as follows: 27.18 ± 0.28 barn for 45Sc(n,γ)46Sc, 4.34 ± 0.06 barn for 63Cu(n,γ)64Cu, 0.719 ± 0.011 barn for 64Zn(n,γ)65Zn, 4.05 ± 0.05 barn for 109Ag(n,γ)110mAg and 8.53 ± 0.27 barn for 113In(n,γ)114Inm1+m2 reactions. The results for 45Sc and 64Zn support evaluated cross-section data within the limits of uncertainties, while those for the other nuclides were slightly different from evaluated ones. The obtained results are useful not only for the evaluation of isotope production, but also for the consideration of those nuclides as flux monitors, as an alternative to Au and Co.

Novel integrated structure and function of Mg–Gd neutron shielding materials

Abstract As the lightest metal structural materials, magnesium (Mg) alloys offer extensive application potential. Gadolinium (Gd), as the primary alloying element in Mg alloys and recognized for its notable thermal neutron capture cross-section, is considered one of the most efficient neutron absorbers. Thus, the Mg–Gd alloy is highly expected to emerge as a material with remarkable neutron absorption capacity. Hence, in this study, the thermal neutron-shielding capabilities of Mg–Gd alloys were comprehensively examined by fabricating four as-cast Mg–xGd alloys with varying compositions (x = 0, 5, 10, and 15 wt%). The obtained results were further corroborated by sophisticated modeling and calculations using SuperMC. The results revealed a direct correlation between the thermal neutron absorption capacity of the Mg–Gd alloys and the increase in Gd content, with a noteworthy neutron attenuation factor of 22.33. Moreover, in an Au ion irradiation experiment conducted at 200°C, the Mg–15Gd alloy exhibited exceptional radiation resistance, with a displacement per atom (dpa) of 10. The matrix and second-phase regions were devoid of any cavity formation. Instead, a finite number of dislocation rings were observed, forming both leaf-like and granular Gd-rich nanoscale precipitates. This study underscores the versatility of Mg–Gd alloys as efficient neutron shielding materials and structural materials tailored for applications demanding radiation resistance in diverse environments.

Gadolinium Concentration Measurement with an Atomic Absorption Spectrophotometer

Abstract Because gadolinium (Gd) has the highest thermal neutron capture cross section, resulting in an 8 MeV gamma cascade upon capture, it has been proposed for dissolution in water Cherenkov detectors to achieve efficient neutron tagging capabilities. Whereas metallic Gd is insoluble in water, several compounds are very easy to dissolve. Gadolinium sulfate, Gd2(SO4)3, has been thoroughly tested and proposed as the best candidate. Accurate measurement of its concentration, free of doubt from impurities in water, is crucial. An atomic absorption spectrophotometer (AAS) is a device that suits this purpose and is widely used to measure the concentration of many elements. In this study, we describe three different approaches to measure Gd sulfate concentrations in water using an AAS: doping samples with potassium and lanthanum, and employing tantalum and tungsten platforms.

Probing and controlling oxygen impurity diffusion in h-BN semi-bulk crystals

Combining its unique features of ultrawide bandgap (UWBG) and two-dimensional nature, h-BN has been explored for emerging applications such as deep ultraviolet optoelectronic devices and single photon emitters. One of the unusual applications of h-BN is for solid-state neutron detectors by utilizing the property of high thermal neutron capture cross section of B-10 as well as its UWBG properties. Although a record high detection efficiency of 59% has been attained by h-BN detectors, the understanding/minimization of defects and impurities is still needed to further advance the h-BN material and detector technologies. We report metal organic chemical vapor deposition growth and oxygen (O) impurity diffusion in thick h-BN. The diffusion coefficient (D) of O impurities has been measured via the evolution of an oxygen related emission with the etching depth, providing a value of D of ∼ 2 × 10−13 cm2/s at 1450 °C and supporting the interpretation that oxygen in h-BN is a substitutional donor. A multiple-buffer-layer approach was employed to mitigate to a certain degree the issue of oxygen diffusion from sapphire substrate during growth. It was demonstrated that the performance of h-BN neutron detectors fabricated from the wafer incorporating multiple buffer layers was significantly improved, as manifested by the enhanced thermal neutron detection efficiency. The advancement of the crystal growth technology of h-BN semi-bulk crystals creates applications in optoelectronic and power electronic devices utilizing the UWBG semiconductor properties of h-BN, while high efficiency h-BN neutron detectors have the potential to supplant the traditional He-3 gas detectors in various application areas by offering the obvious advantages of UWBG semiconductor technologies.

Methodologies for 176Lu-176Hf Analysis of Zircon Grains from the Moon and Beyond.

Zircons are found in extraterrestrial rocks from the Moon, Mars, and some differentiated meteorite parent-bodies. These zircons are rare, often of small size, and have been affected by neutron capture induced by cosmic ray exposure. The application of the 176Lu-176Hf decay system to zircons from planetary bodies such as the Moon can help establish the chronology of large-scale differentiation processes such as the crystallization of the lunar magma ocean. Here, we present methods to measure the isotopic composition of Hf of extraterrestrial zircons dated using ID-TIMS U-Pb after chemical abrasion. We introduce a 2-stage elution scheme to separate Hf from Zr while preserving the unused Zr fraction for future isotopic analysis. The effect of neutron capture is also re-examined using the latest thermal neutron capture cross sections and epithermal resonance integrals. Our tests show that the precision of Hf isotopic analyses is close to what is theoretically attainable. We have tested this method to a limited set of zircon grains from lunar rocks returned by the Apollo missions (lunar soil 14163, fragmental polymict breccia 72275, and clast-rich breccia 14321). The model ages align with previously reported values, but further work is needed to assess the chronology of lunar magma ocean crystallization as only a handful of small zircons (5 zircons from 3 samples) were analyzed, and the precision of the analyses can be improved by measuring more and larger lunar zircon grains.

Cosmic implications of the reaction: a nuclear astrophysical perspective

We conducted a comprehensive study of the neutron capture cross section of within the relevant astrophysical energy range. Through rigorous R-matrix analysis, we determined the Maxwellian-averaged cross section to be 11.98 0.25 μb at kT = 30 keV. This result is approximately four times higher than the thermal neutron capture cross section estimated in earlier studies assuming the law. The implications of our findings extend to the region of inhomogeneous Big-Bang models in nuclear astrophysics, where understanding the behaviour of neutron capture cross sections plays a crucial role in elucidating the intricate processes that shaped the early universe.

Evaluation of the thermal neutron capture cross section and the resonance integral of the 70Zn(n,γ)[formula omitted]Zn reaction

Radiative neutron capture is studied in the 70Zn(n,γ)71m,gZn reaction in order to determine the thermal neutron capture cross sections for the reactions. The resonance integrals are calculated to facilitate corrections for the epithermal neutron component. Thermal cross sections for thermal neutrons and resonance integrals for epithermal neutrons (from cadmium cut-off energy 0.5 eV to 0.1 MeV with filter and without filter) are evaluated.

Thermal neutron capture cross-section and resonance integral measurements of 186W(n,γ)187W reaction using the thermal column neutron source at the Dalat research reactor

The thermal neutron radiative capture cross-section (σ0) and the resonance integral (I0) of the reaction 186W(n,γ)187W were measured by the thin foil activation method using the well thermalized neutron source at the graphite thermal column facility of the Dalat research reactor. The activities of the irradiated target and monitor samples were measured using a high resolution HPGe gamma-ray spectrometer. The recent updated values of gamma-rays intensities and decay half-life of the 187W nucleus were applied in this experiment to substantially improve the cross-section results compared to the previous measurements. The thermal neutron capture cross- section and the resonance integral of the 186W(n,γ)187W reaction were determined relative to the standard reaction 197Au(n,γ)198Au. The values obtained are 31.76 ± 0.63 and 429.2 ± 25.6 barns for σ0 and I0 respectively. Our results and previous measured values are compared, and discrepancies are discussed.

Characterization of the DHC Crack Parameters in Zirconium Alloys

"Zirconium alloys are used in heavy water-cooled reactors due to their low thermal neutron capture cross-section and good mechanical and corrosion properties. At the beginning of their operation, hydrogen was identified as an embrittlement agent. The source of the embrittlement was hydride precipitates that formed as platelets. Hydrides were associated with the cracks and the process was called Delayed Hydride Cracking – DHC. This research aims to develop a reproducible procedure concerning DHC KIH parameter measurements on Zirconium claddings, by using the Pin Loading Test (PLT) technique. Experimental activities including sample preparation, adding hydrogen, testing and results are presented in detail. "

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.

Recent Progress in Gd-Containing Materials for Neutron Shielding Applications: A Review.

With the rising demand for nuclear energy, the storage/transportation of radioactive nuclear by-products are critical safety issues for humans and the environment. These by-products are closely related to various nuclear radiations. In particular, neutron radiation requires specific protection by neutron shielding materials due to its high penetrating ability to cause irradiation damage. Herein, a basic overview of neutron shielding is presented. Since gadolinium (Gd) has the largest thermal neutron capture cross-section among various neutron absorbing elements, it is an ideal neutron absorber for shielding applications. In the last two decades, there have been many newly developed Gd-containing (i.e., inorganic nonmetallic-based, polymer-based, and metallic-based) shielding materials developed to attenuate and absorb the incident neutrons. On this basis, we present a comprehensive review of the design, processing methods, microstructure characteristics, mechanical properties, and neutron shielding performance of these materials in each category. Furthermore, current challenges for the development and application of shielding materials are discussed. Finally, the potential research directions are highlighted in this rapidly developing field.

Measurements of capture cross-section of 93Nb by activation method and half-life of 94Nb by mass analysis

ABSTRACT The thermal-neutron capture cross section (σ 0 ) and resonance integral (I 0 ) for93Nb were measured by an activation method; a half-life of 94Nb was derived by mass analysis. Niobium-93 samples were irradiated with the use of the hydraulic conveyer installed in the research reactor in Institute for Integral Radiation and Nuclear Science, Kyoto University. Gold-aluminum and cobalt-aluminum alloy wires were used to monitor thermal-neutron fluxes and Westcott’s indexes at the irradiation position. A 25-μm-thick gadolinium foil was used to separate reactions ascribed to thermal neutrons. Its thickness provided a cut-off energy of 0.133 eV. In order to attenuate the radioactivity of 182Ta produced by impurities, the Nb samples were cooled for nearly 2 years. The induced radio activity in the monitors and Nb samples was measured by gamma-ray spectroscopy. In the analysis based on Westcott’s convention, the σ 0 and I 0 values were calculated as 1.11 ± 0.04 barns and 10.5 ± 0.6 barns, respectively. After the γ-ray measurements, mass analysis was applied to the Nb samples to obtain the reaction rate. By combining data obtained by both γ-ray spectroscopy and mass analysis, a half-life of 94Nb was determined as (2.00 ± 0.15) ×104 years.

Characterization of thermal neutron distribution of an Am–Be neutron source setup by CdZnTe detector

Owing to the developments in prompt gamma neutron activation analysis (PGNAA) and prompt gamma ray activation imaging (PGAI), it is necessary to develop an online thermal neutron distribution measurement method. The CdZnTe detector is considered as an alternative thermal neutron detector because of its high thermal neutron capture cross section. In this study, the thermal neutron field of an 241Am–Be neutron source was determined by CdZnTe detector. The intrinsic neutron detection efficiency of CdZnTe detector was calculated by using indium foil activation, and the value was 3.65%. Then the characteristics of neutron source were conducted with the calibrated CdZnTe detector. The thermal neutron fluxes in front of beam port were measured at several distances ranging from 0 cm up to 28 cm. Thermal neutron field at distances of 1 cm and 5 cm were also measured. The experimental data were then compared with Monte Carlo simulation. The results demonstrated that the simulated data agree well with experimental measurements.

A study on characteristics of background gamma spectrum from LaCl3 detector in pulsed neutron logging

The scintillator detectors such as LaCl3(Ce) play an important role in some fields of scientific research, environment, safeguards, medicine, security and industry due to its superior energy resolution and exceptional luminescence properties, etc. However, Cl element in a LaCl3 crystal produces uncertainty of determining oil saturation in pulsed neutron logging because of the background spectrum caused by secondary gamma ray from the reaction of Cl nuclei with the neutron. In this paper, we employed Monte Carlo method to simulate secondary gamma ray generated LaCl3 crystal induced by thermal neutron with different borehole and formation conditions and establish a reference spectrum of Cl element. The relations between elemental window or peak areas counts and borehole and formation conditions were also investigated. The background was obtained by combining the reaction rate derived from thermal neutron capture cross section for Cl element and neutron flux with the reference spectrum. The results indicate that the contribution of secondary gamma ray to measuring spectrum decreases with formation porosity, limestone content, borehole diameter, and water salinity increasing. Nevertheless, the relative peak areas of Cl at different energies remain constant, indicating that the logging conditions have less of an effect on the background spectrum shape. As evidenced by the measured spectra in the sandstone and limestone calibration wells processed, the peaks of Si and Ca elements are enhanced while the peaks of Cl element are weakened. After subtracting detector background, the computations of oil saturation based on calibration wells are 38% more accurate than the original method.

Neutron capture cross-section measurement by mass spectrometry for Pb-204 irradiated in JRR-3

ABSTRACT Reliable neutron capture cross sections of lead isotopes are necessary for the development of lead or lead-bismuth cooled fast reactors. Although 204Pb has the smallest natural abundance in stable Pb isotopes, its neutron capture cross-section data are important because a long-lived radionuclide 205Pb (T1/2 = 17.3 million years) is produced by a neutron capture reaction on 204Pb. This study applied a mass spectrometry method to measure the neutron capture cross section of 204Pb. An enriched 204Pb sample was irradiated for 24 days with a neutron flux on the order of 1013 n/cm2/sec at the Japan Research Reactor-3. The irradiated 204Pb sample was analyzed by thermal ionization mass spectrometry to obtain the isotopic ratio between 205Pb and 204Pb. Consequently, the thermal-neutron capture cross-section of 204Pb was found to be 0.536 ± 0.030 barns.

The new Device for Indirect Capture Experiments on Radionuclides at LANSCE: Efforts on measuring the resonance(s) responsible for the extremely large 88Zr (n,γ) cross section

The thermal neutron capture cross section of 88Zr was recently reported to be the second largest in nature with the largest resonance integral measured. Presumably, these very large values are caused by a resonance or resonances very near thermal energy. Determining their energies and widths, and hence the shape of the cross section away from thermal energies,is useful for applications. The short half-life (83.4 days) and associated large background, renders direct measurements of the neutron capture cross section impossible using current techniques. However, it is possible to measure the total neutron cross section, and hence the resonance properties, using the newly commissioned Device for Indirect Capture Experiments on Radionuclides (DICER) at the Los Alamos Neutron Science Center (LANSCE). Transmission measurements are utilized as a surrogate method to perform capture measurements. The 88Zr needed for a DICER measurement was produced at the Isotope Production Facility (IPF) and cleanly separated from the production target material. A description of the new instrument, efforts and preliminary results on 88Zr will be presented.

Am-241 thermal neutron capture cross section and neutron capture resonance integral from reactor activation and oscillation measurements

In order to validate the neutron capture cross section in 241Am, comparisons of calculations with activation experiments at the TRIGA reactor at JSI and pile oscillation measurements at the MINERVE reactor at CEA Cadarache were done. The results suggest that the evaluation in the new test library JEFF-4T1 on average provide an improvement of the C/E results compared to the existing nuclear data library releases. However, due to some discrepancies, additional experiments at JSI as well as further development of the computational model of the JSI TRIGA reactor are planned to improve the accuracy and reliability of the neutron activation analysis and the nuclear data inferred from them.

Measurement of neutron capture cross sections for the 174Yb(n,γ)175Yb reaction at thermal and epithermal energies

Herein, we measured the thermal neutron capture cross section (σ0) and resonance integral (I0) of the 174Yb(n,γ)175Yb reaction relative to those of the reference reaction 197Au(n,γ)198Au. Measurements were conducted based on the activation method using pulsed neutrons combined with the Cd ratio method and offline γ-ray spectrometry. Pulsed neutrons were generated on a 100 MeV electron linac of the Pohang Accelerator Laboratory, Korea. Yb samples and Au monitors were irradiated with and without a 0.5 mm Cd cover to absorb thermal neutrons. The neutron flux was determined via the 115In(n,γ)116mIn reaction. The induced activities of the reaction products were measured using a gamma spectrometer based on a well-calibrated HPGe detector. For the 174Yb(n,γ)175Yb reaction, the thermal neutron capture cross section and resonance integral cross-section were obtained as σ0,Yb = 70.5 ± 4.2 b and I0,Yb = 54.1 ± 4.2 b, relative to the corresponding values of σ0,Au = 98.65 ± 0.09 b and I0,Au = 1550 ± 28 b for the 197Au(n,γ)198Au reference reaction. The obtained results were compared with the measured and evaluated data.

Europium doped Gd2O3 and GdBO3 scintillators for thermal neutron detection

Neutron detectors used in various applications in nuclear security and nuclear safety are mostly based on the 3He technology. Unfortunately, in the last few years, the market of 3He has encountered huge problems in matching the supply and demand leading to an exponential increase in the price and a serious strategic problem of resources. To guarantee the availability of detection systems for nuclear security, the last decade has been driven by the quest for exploring alternative technologies to replace 3He based detectors. Gadolinium (natGd) is a promising rare earth element which has the largest capture cross-section for thermal neutrons among all stable elements due to the contributions of the isotopes 155Gd and 157Gd. This paper describes the fabrication of Gd2O3:Eu3+ and GdBO3:Eu3+ phosphors as scintillators for thermal neutron detection. The samples were evaluated using photoluminescence, SEM analysis, and pulse height spectra recorded from a D–D neutron source. The recorded spectrum was compared to a FLUKA simulation of the characteristic K X-ray emission following neutron capture.

Fluid Identification Derived from Formation Chlorine Measurements and Reservoir Characterization of Tight Carbonate in Sichuan Basin, China

Summary Natural gas production in the Sichuan Basin reached 30×109 m3 in 2020, but the shortfall between this and the production goal of 50×109 m3 in 2025 requires further exploration. The complex mineralogy and low porosity in tight carbonate reservoirs reduce the accuracy of formation water saturation calculations from Archie’s equation, which brings uncertainties to the reservoir characterization. Therefore, it is necessary to incorporate other methods as supplements to methods based on resistivities. In this paper, we outline a method that incorporates wireline-induced gamma spectroscopy, nuclear magnetic resonance (NMR), array dielectric, and borehole images. Spectroscopy is not only used to estimate the mineralogy of the reservoir, but it also provides measurements, such as chlorine concentration and thermal neutron capture cross section (sigma). The amount of chlorine in the formation is proportional to the water volume in the reservoir, hence formation water saturation. Sigma is also an indicator of the formation water saturation. It enables formation water saturation calculation without resistivity measurements. Case studies are presented from carbonate reservoirs in the Sichuan Basin, China. A robust and comprehensive petrophysical description of mineralogy, porosity, pore geometry, free fluid volume, rock type, and formation water saturation is presented. Calculation of formation water saturation from chlorine and sigma proves to be successful in both water-based mud and oil-based mud (OBM) environments. The depth of investigation (DOI) of chlorine from spectroscopy is about 8 to 10 in. for 90% of the signal. The various DOIs of different measurements must be considered when performing the fluid identification. Bound fluid saturation can reach more than 50% in tight carbonate reservoirs. Formation water saturation is not the only factor that determines the fluid type. Free fluid saturation from NMR must also be incorporated. Finally, a robust methodology integrating formation water saturation derived from dielectric and spectroscopy, and free fluid saturation derived from NMR shows great advantage in fluid identification in tight carbonate reservoirs. In this paper, we discuss a novel combination of wireline logging tools for fluid identification in a tight carbonate reservoir in the Sichuan Basin. It reduces the uncertainty when estimating formation water saturation and when resistivity measurements are suppressed in OBM environments. The gas zones identified by the new method have promising predictions of gas production. This workflow can also be applied to other tight carbonate plays in China.