Capture Cross Section Research Articles

Measurements of neutron capture cross-section for nuclides of interest in decommissioning (II): 58Fe(n,γ)59Fe

ABSTRACT As nuclear facilities are dismantled in decommissioning, large amounts of various waste are generated. Even more inconveniently, such waste is radioactive due to neutron activation. Thus, the neutron capture cross-sections of nuclides targeted in decommissioning are required to evaluate the radioactivity produced. In this work, 58Fe nuclide was selected among objective nuclides for decommissioning, and its thermal-neutron capture cross-section was measured by a neutron activation method at the graphite thermal column of Kyoto University Research Reactor in 5-MW operation. The thermal-neutron capture cross-section was derived using Westcott’s convention. The present work obtained 1.36 ± 0.03 barns for the58Fe(n,γ)59Fe reaction. The present result supports the JENDL-5 evaluation within 2σ. If updated with currently recommended nuclear data, some of the reported past data would support the present result.

Investigation of traps in halide vapor-phase epitaxy-grown β-Ga2O3 epilayers/n+-Ga2O3 using deep-level transient spectroscopy

Abstract A detailed investigation of deep traps in halide vapor-phase epitaxy (HVPE)-grown β-Ga2O3 epilayers has been done by performing deep-level transient spectroscopy (DLTS) from 200 K to 500 K on Pt/β-Ga2O3 and Ni/β-Ga2O3 Schottky diodes. Similar results were obtained with a fill pulse width of 100 ms irrespective of the different Schottky metal contacts and epilayers. Two electron traps at E2 (E C–E T = 0.65 eV) and E3 (E C–E T = 0.68–0.70 eV) with effective capture cross-sections of 4.10 × 10−14 cm2 and 5.75 × 10−15 cm2 above 300 K were observed. Below 300 K, a deep trap with a negative DLTS signal peak was also observed at E1 (E C–E T = 0.34–0.35 eV) with a very low capture cross-section of 3.28 × 10−17 cm2. For a short pulse width of 100 μs, only two electron traps, E2 and E3, at energies of 0.72 eV and 0.73 eV were observed, and one order of higher corresponding effective capture cross-sections. All traps were found to be unaffected by the electric field during the field-dependent DLTS study. From the filling pulse width dependence DLTS study, a decrease in the capacitance transient amplitude with the increasing pulse width was observed opposite to the capture barrier kinetics of the traps and attributed to the emission of carriers during the capture process. Trap concentrations were found to be high at the interface using depth profiling DLTS. Based on the available literature, it is suggested that these traps are related to FeGa, Fe-related centers, and complexes with hydrogen or shallow donors, and might be affected or generated during metallization by the electron beam evaporator and chemical mechanical polishing.

Regulation of CN-related optical transitions and non-radiative capture cross-section by biaxial strain in AlN

Carbon-related 4.7 eV absorption band and small in-plane strains in AlN may have some significant effects on its application in optoelectronic devices. Based on the accurate hybrid density functional calculation, we investigate the transition energy levels, photo-transition processes, and hole capture cross-sections of CN defect. We propose that the transition from −1 to 0 charge states of CN defect may be responsible for the 4.7 eV absorption band in AlN. In addition, the CN defect-related absorption and emission peaks are linearly dependent on the biaxial strain in the range of −3% to +3%, and the hole non-radiative capture rate by the CN center at the −3% biaxial strain is only 3.65% of that at the +3% biaxial strain. This work provides an effective approach for regulating the charge carrier capture ability of the defect center and improving device performance.

Neutron capture cross-section of p-nucleus 74Se in the keV region using the activation method

Neutron capture cross-section of p-nucleus 74Se in the keV region using the activation method

Investigation of defect states in AlGaN/GaN high electron mobility transistors by small-signal admittance analysis

We have performed a small-signal admittance analysis to extract trap parameters in an AlGaN/GaN high electron mobility transistor-on-Si. Whereas the admittance in the accumulation- and depletion-bias regimes is primarily due to the interface traps, the admittance near the threshold voltage and below is due to mono-energetic traps inside GaN. The density extracted for threading dislocation-related 1D traps at ≈0.22 eV below the GaN conduction band edge is similar to that previously reported by reverse-biased gate leakage analysis of the analyzed device. Our analysis suggests additional 1D traps of comparatively lower density ≈4×1014cm−3 but considerably large capture cross section ≈8×10−14cm2 in the GaN layer at ≈0.31 eV below the conduction band. The AlGaN trap density is considerably larger near the AlGaN/GaN interface than in the bulk AlGaN. The AlGaN traps mainly contribute to the voltage stretch; their admittance contribution is negligible. Gate leakage dominates the conductance at lower frequencies.

Suppressing Nonradiative Recombination through Dielectric Screening of Defects in Crystalline Carbon Nitride for Enhanced Photocatalytic Activity.

Abundant defect-induced nonradiative recombination greatly reduces the charge separation efficiency in photocatalysts. Dielectric screening of defects has been proven to be an effective strategy to improve the charge separation efficiency; however, it has been rarely reported in photocatalysis. Here, a developed calcium poly(heptazine imide) (CaPHI) is utilized as a model photocatalyst to explore the dielectric screening of defects. Through embedding potassium ions in CaPHI, the dipole moment and polarity of the PHI structure are increased, thus enhancing the dielectric constant and enabling the dielectric screening of defects. In addition, compared to the original CaPHI, the optimized Ca/KPHI exhibits a 79.3% reduction in defect capture cross-section, and a decrease in the nonradiative recombination rate from 0.6224 to 0.1452 ns-1, thus achieving an apparent quantum efficiency of 51.4% for H2 production at 420 nm. This proposed dielectric screening strategy effectively addresses the issue of slow carrier transport and separation caused by defect-induced nonradiative recombination in photocatalysts.

Resonance and surfactant effects on the interaction of a rising bubble and a sedimenting particle in an oscillating fluid

This paper considers the interaction of a rising bubble and a sedimenting fine particle in a liquid with a soluble surfactant subjected to the gravity field, forced flow, and vibrations. The frequency of vibrations is close to the resonance value. The particle motion trajectories are calculated, taking into account its inertia, fluid viscosity, Basset force, buoyancy force, and the mean force acting on the particle due to the inhomogeneity of the pulsating field. The collision efficiency is evaluated, and the cross sections of the sedimenting particles captured by the rising bubble are found. It is demonstrated that even at low vibration intensity but in the presence of a weak surfactant effect, a significant increase in the probability of particle–bubble collision and in the capture cross section can be achieved. The obtained results can be used to intensify the flotation processes by ultrasonic treatment.

The Photoionization Processes of Deep Trap Levels in n-GaN Films Grown by MOVPE Technique on Ammono-GaN Substrates

In this paper, we present various theoretical models that accurately approximate the spectral density of the optical capture cross-section (σe0) obtained through the analysis of photo-capacitance transients using the deep-level optical spectroscopy (DLOS) technique applied to semi-transparent Ni/Au Schottky barrier diodes (SBDs) fabricated on n-GaN films. The theoretical models examined in this study involved a variety of approaches, from the Lucovsky model that assumes no lattice relaxation to more sophisticated models such as the Chantre–Bois and the Pässler models, which consider the electron–phonon coupling phenomenon. By applying theoretical models to the experimentally determined data, we were able to estimate the photoionization (E0), trap level position (ET), and Franck–Condon (dFC) energy, respectively. In addition, the results of our analysis confirm that the photoionization processes of deep traps in n-GaN grown by the metal–organic vapor-phase epitaxy technique (MOVPE) are strongly coupled to the lattice. Moreover, it was shown that the Pässler model is preferred for the accurate determination of the individual trap parameters of defects present in n-GaN films grown on an Ammono-GaN substrate. Finally, a new trap level, Ec-1.99 eV with dFC = 0.15, that has not been previously reported in n-GaN films grown by MOVPE was found.

A new hybrid gadolinium nanoparticles-loaded polymeric material for neutron detection in rare event searches

Experiments aimed at direct searches for WIMP dark matter require highly effective reduction of backgrounds and control of any residual radioactive contamination. In particular, neutrons interacting with atomic nuclei represent an important class of backgrounds due to the expected similarity of a WIMP-nucleon interaction, so that such experiments often feature a dedicated neutron detector surrounding the active target volume. In the context of the development of DarkSide-20k detector at INFN Gran Sasso National Laboratory (LNGS), several R&D projects were conceived and developed for the creation of a new hybrid material rich in both hydrogen and gadolinium nuclei to be employed as an essential element of the neutron detector. Thanks to its very high cross-section for neutron capture, gadolinium is one of the most widely used elements in neutron detectors, while the hydrogen-rich material is instrumental in efficiently moderating the neutrons. In this paper results from one of the R&Ds are presented. In this effort the new hybrid material was obtained as a poly(methyl methacrylate) (PMMA) matrix, loaded with gadolinium oxide in the form of nanoparticles. We describe its realization, including all phases of design, purification, construction, characterization, and determination of mechanical properties of the new material.

Determination of Temperature‐ and Carrier‐Dependent Surface Recombination in Silicon

Knowledge regarding the temperature dependence of the surface recombination at the interface between silicon and various dielectrics is critically important as it 1) provides fundamental information regarding the interfaces and 2) improves the modeling of solar cell performance under actual operating conditions. Herein, the temperature‐ and carrier‐dependent surface recombination at the silicon–oxide/silicon and aluminum–oxide/silicon interfaces in the temperature range of 25−90 °C using an advanced technique is investigated. This method enables to control the surface carrier population from heavy accumulation to heavy inversion via an external bias voltage, allowing for the decoupling of the bulk and surface contributions to the effective lifetime. Thus, it offers a simple and versatile manner to separate the chemical passivation from the charge‐assisted population control at the silicon/dielectric interface. A model is established to obtain the temperature dependence of the capture cross sections, a critical capability for the optimization of the dielectric layers and the investigation of the fundamental properties of the passivation under field operating conditions.

An improved method for evaluating fracture density using pulsed neutron capture logging

Fracture density is a critical fracture evaluation parameter for the optimization and production prediction of hydraulic fracturing models. Nonradioactive tracer (NRT) techniques have successfully used a quantitative fracture density method based on neutron-induced gamma rays from formation elements. Furthermore, fracture density can be calculated using the formation capture cross section before and after hydraulic fracturing based on pulsed neutron capture logging. However, the response sensitivity of the macroscopic scattering cross section to the fractures decreases when the fracture density is high due to the neutron self-shielding phenomenon. Therefore, an improved fracture density evaluation method is applied, which combines the macroscopic capture cross section and the neutron self-shielding correction factor. In the new method, the peak area of titanium from the captured gamma spectrum is used to obtain a neutron self-shielding correction factor to improve the sensitivity of fracture density determination. Furthermore, the response of capture cross-section variation to fracture density at various tagged proppant concentrations and formation backgrounds is investigated. The findings indicate that the tagged proppant concentration influences the detection limit of fracture density and the sensitivity of fracture density identification. The accurate calculation range of fracture density using the new method has been extended from 5% to 10% under the condition that the tagged proppant concentration is 0.2%. Meanwhile, whereas water salinity significantly impacts capture cross-section variation, the effects of porosity, lithology, and fluid type on capture cross-section variation are negligible. A simulated fracturing example demonstrates the method’s applicability in various measurement environments. The results show that fracture density and height are consistent with the model settings after correcting for water salinity, and the fracture density calculation error is less than 3%. Therefore, our evaluation method for fracture density corrected for the neutron self-shielding effect improves response sensitivity and fracture density calculation accuracy.

Charge Carrier Capture by Prominent Defect Centers in 4H-SiC

The knowledge of capture properties of electrically active defects is of primary importance as it helps to understand which deep states are effective in controlling the excess free carriers’ lifetime. Combining DLTS capture experiments with thermal emission measurements enables an overall thermodynamic description of deep states, thus making it possible to characterize recombination centers in semiconductor-based devices. In the present study, junction DLTS capture rate measurements were employed to extract the true capture cross-sections (inversely proportional to the carrier lifetime) and capture energy barriers for the main lifetime limiting defects in 4H-SiC (silicon carbide). A peculiar forward bias dependence of the capture parameters was observed for the shallow boron (B) hole trap. Capture rate measurements on the deep boron (D-center) trap also evidenced the presence of two capture mechanisms, thus allowing discrimination of D1 and D2 deep states within the D-center DLTS peak. The results were combined with activation energies and apparent capture cross-sections to obtain the free energy (ΔG) of electronic activation for the analysed deep states.

State-selective electron capture in Ar16++H(1s) collisions for charge-exchange recombination spectroscopy

Abstract State-selective electron capture in collisions of Ar16+ ions with ground-state hydrogen atoms has been modeled using the two-center wave-packet convergent close-coupling approach. The partially stripped He-like projectile ion is represented using a model potential. Experimental measurements are not available for this collision system and to date, only the classical trajectory Monte Carlo (CTMC) method has been applied to calculate cross sections. The calculated total electron-capture cross section (TECS) is in good agreement with the previous CTMC results at the low energies but slightly larger at higher energies. This is likely because, in this work, we account for capture into highly excited states, which contribute significantly to the TECS at the intermediate energies. The n-resolved electron-capture cross sections have also been presented for capture into states with n = 6 − 19 , where n is the final-state principal quantum number. The most important of these are the cross sections for capture into the n = 14 − 17 states, which are used in charge-exchange recombination spectroscopy techniques. For these cross sections, a significant difference is observed between the present and previously published data. The cross sections differ by an order of magnitude in the 10−60 keV u−1 energy range. The agreement between the calculations is observed at the energies above 70 keV u−1. The n ℓ -resolved electron-capture cross sections have also been presented at 15, 60, 100 and 200 keV u−1 projectile energies, where ℓ is the final-state angular momentum quantum number.

Prediction of Shockley–Read–Hall lifetimes in strained layer superlattices for mid-wave and long-wave infrared photodetectors

We have calculated carrier nonradiative recombination lifetimes limited by Shockley–Read–Hall (SRH) centers in strained layer superlattices (SLSs) for mid-wave and long-wave infrared applications. The capture rate of an electron (hole) in the SLS's conduction (valence) band by the defect level is dominated by a multi-phonon process, which is orders-of-magnitude more efficient than the radiative process. Long-range polar coupling between electrons and optical phonons can account for the observed SRH lifetimes in a variety of SLSs reported in the literature. The capture rate depends on temperature rather weakly, consistent with experimental observations. The efficient capture is caused by the comparable electronic difference and lattice relaxation energy, Ect∼Sℏω, with S and ℏω being the Huang–Rhys factor and optical photon energy in the SLSs. A weaker polar coupling would give rise to a smaller capture cross section, which, for InAs/InAsSb SLSs, can be achieved by increasing Sb in the alloy region.

Charged Particles Capture Cross-section by a Weakly Charged Schwarzschild Black Hole

We study the capture cross-section of charged particles by a weakly charged Schwarzschild black hole. The dependence of the maximum impact parameter for capture on the particle’s energy is investigated numerically for different values of the electromagnetic coupling strength between the particle and the black hole. The capture cross-section is then calculated. We show that the capture cross-section is independent of the electromagnetic coupling for ultra-relativistic particles. The astrophysical implications of our results are discussed.

Shedding Light on the Origin of ^{204}Pb, the Heaviest s-Process-Only Isotope in the Solar System.

Asymptotic giant branch stars are responsible for the production of most of the heavy isotopes beyond Sr observed in the solar system. Among them, isotopes shielded from the r-process contribution by their stable isobars are defined as s-only nuclei. For a long time the abundance of ^{204}Pb, the heaviest s-only isotope, has been a topic of debate because state-of-the-art stellar models appeared to systematically underestimate its solar abundance. Besides the impact of uncertainties from stellar models and galactic chemical evolution simulations, this discrepancy was further obscured by rather divergent theoretical estimates for the neutron capture cross section of its radioactive precursor in the neutron-capture flow, ^{204}Tl (t_{1/2}=3.78 yr), and by the lack of experimental data on this reaction. We present the first ever neutron capture measurement on ^{204}Tl, conducted at the CERN neutron time-of-flight facility n_TOF, employing a sample of only 9mg of ^{204}Tl produced at the Institute Laue Langevin high flux reactor. By complementing our new results with semiempirical calculations we obtained, at the s-process temperatures of kT≈8 keV and kT≈30 keV, Maxwellian-averaged cross sections (MACS) of 580(168)mb and 260(90)mb, respectively. These figures are about 3% lower and 20% higher than the corresponding values widely used in astrophysical calculations, which were based only on theoretical calculations. By using the new ^{204}Tl MACS, the uncertainty arising from the ^{204}Tl(n,γ) cross section on the s-process abundance of ^{204}Pb has been reduced from ∼30% down to +8%/-6%, and the s-process calculations are in agreement with the latest solar system abundance of ^{204}Pb reported by K. Lodders in 2021.

Recombination lifetimes and mechanisms of In0.75Ga0.25As and In0.53Ga0.47As as a function of doping density

The minority carrier lifetimes in InGaAs ternary alloys are investigated both experimentally and theoretically. Two groups of InGaAs/InP photodetector samples are designed for experiments, one with In0.75Ga0.25As and the other with In0.53Ga0.47As as the absorption layers. The lifetimes are obtained to be about 100–200 ns in In0.75Ga0.25As and 600 ns-1 µs in In0.53Ga0.47As by microwave photoconductivity decay technique. The calculated lifetimes are also found to be consistent with the experimental ones. Besides, for both InGaAs materials, the Shockley-Read-Hall (SRH), radiative and Auger recombination mechanisms are identified in calculations to be the dominant mechanisms at low, intermediate and high doping densities at room temperature, respectively. Furthermore, the effects of density, capture cross-sections and energy levels (Ets) of recombination centers, and bandgaps (Egs) on the SRH lifetimes are determined and compared for the two InGaAs materials. For an n-type material, when Et is near the mid-bandgap (Eg/2), the SRH lifetime is only inversely proportional to the product of the density and the capture cross-section of the recombination centers. When Et is not near the mid-bandgap, the magnitude of Eg also plays an important role in the SRH lifetime. By increasing the In-content from 53 % in In0.53Ga0.47As to 75 % in In0.75Ga0.25As, where the bandgap narrows from 0.75 to 0.52 eV, the SRH lifetime in In0.75Ga0.25As is shortened by a factor of about 1–42 for Et < Eg/2 and 1–65 for Et > Eg/2 within the bandgap, respectively.

Comprehensive investigation of material properties and operational parameters for enhancing performance and stability of FASnI3-based perovskite solar cells

Recent advancements in the efficiency of lead-based halide perovskite solar cells (PSCs), exceeding 25%, have raised concerns about their toxicity and suitability for mass commercialization. As a result, tin-based PSCs have emerged as attractive alternatives. Among diverse types of tin-based PSCs, organic–inorganic metal halide materials, particularly FASnI3 stands out for high efficiency, remarkable stability, low-cost, and straightforward solution-based fabrication process. In this work, we modelled the performance of FASnI3 PSCs with four different hole transporting materials (Spiro-OMeTAD, Cu2O, CuI, and CuSCN) using SCAPS-1D program. Compared to the initial structure of Ag/Spiro-OMeTAD/FASnI3/TiO2/FTO, analysis on current–voltage and quantum efficiency characteristics identified Cu2O as an ideal hole transport material. Optimizing device output involved exploring the thickness of the FASnI3 layer, defect density states, light reflection/transmission at the back and front metal contacts, effects of metal work function, and operational temperature. Maximum performance and high stability have been achieved, where an open-circuit voltage of 1.16 V, and a high short-circuit current density of 31.70 mA/cm2 were obtained. Further study on charge carriers capture cross-section demonstrated a PCE of 32.47% and FF of 88.53% at a selected capture cross-section of electrons and holes of 1022 cm2. This work aims to guide researchers for building and manufacturing perovskite solar cells that are more stable with moderate thickness, more effective, and economically feasible.

Prompt gamma activation analysis for boron determination in the tens of milligram range at the HOTNES facility

Boron is an elective element for the Prompt Gamma Activation Analysis (PGAA), due to its exceptionally large neutron capture cross section. This technique, usually performed in nuclear reactors with neutron fluxes as high as 108 cm−2 s−1, can determine quantities of boron as low as tens of nanograms. Some applications, such as the industry of neutron shielding materials, would better benefit from a less sensitive but more portable and accessible boron PGAA, which could be established at construction or fabrication sites. For these purposes ENEA and INFN jointly setup a compact PGAA based on a 0.5 cm3 Cadmium–Zinc–Telluride gamma spectrometer and the HOTNES thermal neutron source. Relying on a series of borated resins with known composition and on comprehensive experimental and Monte Carlo evaluations, this technique features a detection limit in the order of few milligrams in terms of boron mass. As the facility consists simply on a lab-scale neutron source and a polyethylene block with well-established geometry, this simplified PGAA system is suited to be replicated or transported to construction or fabrication sites for QA/QC purposes on borated construction materials for the nuclear sector.

Observation of temperature-dependent capture cross section for main deep-levels in β-Ga2O3

Direct observation of the capture cross section is challenging due to the need for extremely short filling pulses in the two-gate Deep-Level Transient Spectroscopy (DLTS). Simple estimation of the cross section can be done from DLTS and admittance spectroscopy data but it is not feasible to distinguish temperature dependence of pre-exponential and exponential parts of the emission rate equation with sufficient precision conducting a single experiment. This paper presents experimental data of deep levels in β-Ga2O3 that has been gathered by our group since 2017. Based on the gathered data, we propose a derivation of apparent activation energy (Eam) and capture cross section (σnm) assuming the temperature dependent capture via the multiphonon emission model, which resulted in a strong correlation between Eam and σnm according to the Meyer–Neldel rule, which allowed us to estimate low- and high-temperature capture coefficients C0 and C1 as well as capture barrier Eb. It also has been shown that without considering the temperature dependence of capture cross section, the experimental values of σn are overestimated by 1–3 orders of magnitude. A careful consideration of the data also allows to be more certain identifying deep levels by their “fingerprints” (Ea and σn) considering two additional parameters (EMN and σ00) and to verify the density functional theory computation of deep-level recombination properties.