Nb Reaction Research Articles

Signature of Incomplete Fusion in the \(\alpha \)-channels of \(^{6}\)Li+\(^{93}\)Nb Reaction

Signature of Incomplete Fusion in the \(\alpha \)-channels of \(^{6}\)Li+\(^{93}\)Nb Reaction

Investigation of RPV samples of the Greifswald NPP with focus on retrospective dosimetry

Reactor pressure vessel (RPV) samples of units 1 and 4 of the Greifswald NPP were investigated with focus on retrospective dosimetry. Specific activities of long-lived radionuclides 63Ni, 93mNb, 94Nb and 99Tc as well as the concentrations of the producing elements were measured. Investigated samples comprise base metal, welding metal and cladding of the RPV. Neutron fluences obtained with the M onte-Carlo codes TRAM O and M CNP were used to calculate specific activities. The gamma-emitter 94Nb appears as a promising candidate due to the large Nb concentration in the cladding of the VVER RPVs. For 93mNb, a very good agreement of measured und calculated activities was found for the RPV cladding samples where 93mNb is primarily produced by the threshold reaction 93Nb(n,n’)93mNb. A strong scatter of the ratios of calculated and experimental activities is observed for 63Ni which is primarily produced by slow neutrons. For 99Tc, a good agreement of calculated and measured activities was found for the majority of the base metal and welding metal samples but not for the cladding samples. Updated reaction cross section data for 62Ni(n,γ) and 92M o(n,γ) lead to a better agreement of calculated and measured activities for 63Ni and 93mNb.

Systematic study of fusion suppression and its dependency on projectile breakup threshold energy

Measurements of the excitation function (EF) of the observed evaporation residues (ERs) populated in the 20Ne + 93Nb reaction at E lab ≈ 91−145 MeV are carried out to explore the systematic of fusion suppression and its dependency on projectile breakup threshold energy, by employing the offline γ-ray detection method. The EF of the observed ERs populated through complete and/or incomplete fusion processes are analysed in the framework of statistical mode code PACE4. The fusion function, derived from the experimentally measured fusion cross section data, is compared with the universal fusion function (UFF) to estimate the degree of fusion incompleteness. Based on the observed results, an empirical formula is proposed to interrelate the degree of fusion suppression and breakup threshold energy of the incident projectile.

Measurement of fast-neutron activation cross section of the 109Ag(n,2n)108mAg reaction and its theoretical calculation of excitation function

The cross section values of the 109Ag(n,2n)108mAg reaction at four neutron energies 13.5, 14.1, 14.4 and 14.8 Me were measured relative to those of the monitor reaction 93Nb(n,2n)92mNb by using the activation technique and using off-line γ-ray spectrometry. Fast neutrons were produced by the T(d,n)4He reaction. The excitation function of this reaction in the neutron energies from the reaction threshold to 20 MeV was obtained based on the nuclear theoretical model program system TALYS-1.95 with the adjusted relevant parameters. The measured results were discussed and compared with the experimental data of literature, and the evaluated data from the evaluated libraries of TENDL-2021 and JEFF-3.1.2, as well as with the theoretical values based on TALYS-1.95.

Measurement of total and partial cross sections of the ^{90}Zr(p,gamma )^{91}Nb reaction with in-beam gamma -ray spectroscopy

The origin of many p-nuclei remains an unsolved problem in nuclear astrophysics. While photo-dissociation reactions in the gamma -process can explain the production of many p-nuclei, some, notably ^{92,94}Mo and ^{96,98}Ru are underproduced in network calculations. The ^{90}Zr(p,gamma )^{91}Nb reaction is part of a possible (p,gamma ) reaction chain for the production of the p-nucleus ^{92}Mo. Available data show a large disagreement between the different reported cross sections measurements for the ^{90}Zr(p,gamma )^{91}Nb reaction. We measured proton capture cross sections with an enriched ^{90}Zr target using in-beam gamma -ray spectroscopy for proton energies between 2.75 MeV and 5.1 MeV. The emitted gamma -rays were detected using the HORUS (High efficiency Observatory for gamma -Ray Unique Spectroscopy) detector array at the University of Cologne, Germany. To account for the possible contribution of the ^{91}Zr(p,n) reaction, an enriched ^{91}Zr was irradiated. We measured production cross sections for the ground and isomeric state of ^{91}Nb as well as partial cross section for up to ten high-energy primary transitions. The results are in good agreement with a former in-beam gamma -ray spectroscopy measurement by Laird et al.. We provide a possible explanation for the discrepancies between our data and other available measurements.

Updates to the AMUR code for R-matrix analyses on heavy nuclei

The AMUR code, that had been initially designed for R-matrix analysis on light nuclei, was updated to perform resonance analyses on heavy nuclei by including approximated theories with experimental corrections such as resolution function. As a feasibility study, we tested these updates by performing a covariance analysis on J-PARC/ANNRI measured data for n+93Nb reactions. In this work we present preliminary results obtained from the fitting procedure including both R-matrix resonance parameters and parameters related to the experimental corrections. We also discuss about physical constraint from the theory for forthcoming in-depth analysis to the measurements.

Application of Machine Learning algorithms for experimental data processing and estimation of 96Mo(n, p)96Nb reaction cross section

In this paper, Machine learning techniques have been employed for preparation and estimation of 96 Mo (n, p) 96Nb reaction data. The experimental data of 96 Mo (n, p) 96Nb reaction available in the EXFOR database was retrieved, analyzed and processed using renormalization and data cleaning techniques. Estimation of the renormalized experimental data with outlier and without outlier, over the entire neutron energy range, was then performed using machine learning regression algorithms of Ordinary Least square, Ridge, Least Absolute Shrinkage and Selection Operator (LASSO) and Support Vector Regressor. The results obtained were then compared and it was observed that the data preparation plays a significant role in data quality.

Non-Boltzmann Effects in Chain Branching and Pathway Branching for Diethyl Ether Oxidation

Low-temperature (LT) engine applications have several potential benefits, including reduced emissions and increased efficiency. Attaining these benefits requires accurate kinetic modeling of LT chain branching, which depends heavily on ketohydroperoxide (KHP) decomposition. For diethyl ether (DEE), a promising biofuel, current estimates of the KHP decomposition rate constant are largely based on empirical fits to data. In this study, we investigate the most important KHP isomer in DEE LT oxidation by applying variable reaction coordinate transition state theory to the main pathway for KHP decomposition: OO bond fission to produce •OH and a keto-alkoxy radical, •OQ′O. We also use ab initio kinetics methods to investigate the decomposition of •OQ′O, where we find dominant branching to acetic acid, with the remaining flux going to CH3C(O)OCHO. Additionally, new time-resolved measurements of DEE and acetic acid concentrations during LT (450–600 K) DEE oxidation are obtained in a laser photolysis flow reactor coupled with multiplexed photoionization mass spectrometry. These new experimental data, along with jet-stirred reactor data in the literature, are compared with the predictions of a recent DEE mechanism (Tran et al. Proc. Comb. Inst. 2019, 37, 511−519) that was modified with the newly calculated ab initio rate constants for KHP and •OQ′O decomposition. The predictions of the modified mechanism are quite poor when compared to the experimental data; this is primarily due to the new KHP ⇄ •OQ′O + •OH rate constant, which is 1–2 orders of magnitude slower than empirical values employed in recent mechanisms. To reconcile the new KHP rate constant and the experimental data, we explore and quantify the possible role of non-Boltzmann (nB) reaction sequences. The nB reactions have a substantial effect on both the overall mechanism reactivity and the •OQ′O branching to acetic acid. We also provide guidance on the proper implementation of nB reactions in kinetic mechanisms.

Laser welding of 6082 aluminum alloy to TC4 titanium alloy via pure niobium as a transition layer

A Ti/Al joint with an Nb transition layer was obtained, where aluminum alloy and Nb sheet partially melted to form the weld and diffusion bonding was formed at Ti/Nb interface. The remaining transition layer Nb acted as a diffusion barrier between TC4 titanium alloy and 6082 aluminum alloy thus successfully prevented the formation of brittle TiAl, TiAl2 and TIAl3 phases. A flat Ti–Nb diffusion zone composed of (Ti, Nb) solid solution was formed at Ti/Nb interface, while a narrow Al–Nb reaction zone was formed at the Nb/Al–FZ (aluminum alloy fusion zone) interface with the main microstructures of NbAl3, Nb2Al and Al-based solid solution. The simulation of welding temperature field and thermal cycle curve by finite element software was conducted to provide theoretical data support for clarifying the formation of the joint and interface reaction mechanism. The mechanical property of the joint was determined by the Al–Nb reaction zone which could be witnessed by observing the fracture location and hardness distribution of the joint. The joint fractured at the Al–Nb reaction zone and adjacent Al–FZ with the maximum tensile strength of 288.97 MPa.

Fabrication of ZnO/nanobentonite as a new efficient adsorbent for rapid elimination of xylenol orange dye

A novel ZnO-nanobentonite (ZnO/NB) nanocomposite was successfully prepared using hexadecyltrimethylammonium bromide (HDTMA) as a surfactant and used as an efficient adsorbent to remove the xylenol orange (XO) from aqueous solutions. The fabricated nanocomposite was fully characterized by FTIR, FESEM, XRD, EDX, and BET measurements. The ZnO33%/NB sample with a high SBET and low total pore volume compared with the nanobentonite clay, based on BET results, indicated an increase in SBET due to the incorporation of ZnO nanoparticles into the layer of nanobentonite. For achieving the optimum condition, the effect of ZnO33%/NB sorbent dosage, initial pH, reaction time, and primary dye concentration, on XO dye elimination was investigated. The result show that the 97% elimination of XO dye occurred at optimum condition (40 mgl/l of dye concentration, pH 2, 15 mg of ZnO33%/NB adsorbent at 30 minutes), and the adsorption capacity and residual XO after treatment at this conditions is 48.5 and 1.2 ppm, respectively. Langmuir models and Freundlich model were used to studying the adsorption isotherms of the elimination process and results authenticated that XO dye adsorption followed the Langmuir model. Also, the recycling experiments showed that ZnO33%/NB adsorbent had more stability and recoverability. High adsorption capacity, simple fabrication method, short reaction time, and supreme reusability of ZnO33%/NB nanocomposite make it an effective sorbent for the elimination of XO dye from wastewaters.

Fabrication of ZnO/nanobentonite as a new efficient adsorbent for rapid elimination of xylenol orange dye

A novel ZnO-nanobentonite (ZnO/NB) nanocomposite was successfully prepared using hexadecyltrimethylammonium bromide (HDTMA) as a surfactant and used as an efficient adsorbent to remove the xylenol orange (XO) from aqueous solutions. The fabricated nanocomposite was fully characterized by FTIR, FESEM, XRD, EDX, and BET measurements. The ZnO33%/NB sample with a high SBET and low total pore volume compared with the nanobentonite clay, based on BET results, indicated an increase in SBET due to the incorporation of ZnO nanoparticles into the layer of nanobentonite. For achieving the optimum condition, the effect of ZnO33%/NB sorbent dosage, initial pH, reaction time, and primary dye concentration, on XO dye elimination was investigated. The result show that the 97% elimination of XO dye occurred at optimum condition (40 mgl/l of dye concentration, pH 2, 15 mg of ZnO33%/NB adsorbent at 30 minutes), and the adsorption capacity and residual XO after treatment at this conditions is 48.5 and 1.2 ppm, respectively. Langmuir models and Freundlich model were used to studying the adsorption isotherms of the elimination process and results authenticated that XO dye adsorption followed the Langmuir model. Also, the recycling experiments showed that ZnO33%/NB adsorbent had more stability and recoverability. High adsorption capacity, simple fabrication method, short reaction time, and supreme reusability of ZnO33%/NB nanocomposite make it an effective sorbent for the elimination of XO dye from wastewaters.

Ground-state and isomeric-state cross-sections for 92Mo(n,α)89Zr and 95Mo(n,p)95Nb reactions in the 13–15 MeV energy region

Abstract The (n,α) and (n,p) cross-sections and their isomeric ratios (σ m /σ g ) were measured at 13–15 MeV for 92Mo and 95Mo by activation and off-line γ-ray spectrometry. The activated Mo samples combined with Al foils were used to obtain the cross-section values and the neutron flux, generated using the 3H(d,n)4He reaction. The cross-sections of the ground states were obtained using the metastable state absolute cross-sections and the residual nuclear decay rule. The excitation functions, total cross-sections, and isomeric ratios for the 92Mo(n,α)89m,gZr and 95Mo(n,p)95m,gNb reactions were calculated using the TALYS-1.95 software. 92Mo(n,α)89m + gZr and 95Mo(n,p)95m + gNb reaction excitation functions were obtained using the EMPIRE-3.2.3 package. These simulation results were compared with the corresponding experimental data and with the evaluated data from the ENDF/B-VIII.0, JEFF-3.3, CENDL-3, and ROSFOND libraries. Only partial agreements were observed.

Benchmark experiment of large-angle scattering reaction cross section of iron at 14 MeV using two shadow bars – Comparison of experimental results with ENDF/B-VIII –

ABSTRACT It is important to perform neutron transport simulations with accurate nuclear data in the neutronics design of a fusion reactor. However, absolute values of large-angle scattering cross sections vary among nuclear data libraries even for well-examined nuclide of iron. Benchmark experiments focusing on large-angle scattering cross sections were thus performed to confirm the correctness of nuclear data libraries. The series benchmark experiments were performed at a DT neutron source facility, OKTAVIAN of Osaka University, Japan, by the unique experimental system established by the authors’ group, which can extract only the contribution of large-angle scattering reactions. This system consists of two shadow bars, target plate (iron), and neutron detector (niobium). Two types of shadow bars were used and four irradiations were conducted for one experiment, so that contribution of room-return neutrons was effectively removed and only large-angle scattering neutrons were extracted from the measured four Nb reaction rates. The obtained experimental results were compared with calculations for five nuclear data libraries including JENDL-4.0, JEFF.-3.3, FENDL-3.1, ENDF/B- VII, and recently released ENDF/B-VIII. It was found from the comparison that ENDF/B-VIII showed the best result, though ENDF/B-VII showed overestimation and others are in large underestimation at 14 MeV.

Stereoselectivity and nonmigratory insertion mechanism of dimethylacetylene dicarboxylate into metallocene‐hydride of Cp2M(L)H [Cp = η5‐C5H5; M = Nb, V; L = CO, P (OMe)3]: A DFT study

The insertion of an alkyne into transition metal–hydrogen bonds is a key elementary step in catalytic polymerization and hydrogenation processes. It was found that a (Z)‐ or (E)‐type alkyenyl complex can be formed through trans/cis stereospecific processes. In this work, the reaction mechanism of Cp2M(L)H [Cp = η5‐C5H5; M = Nb, V; L = CO, P (OMe)3] with dimethylacetylene dicarboxylate (DMAD), and the factors influencing the stereoselectivity have been investigated based on density functional theory calculations. The calculated results show that all of the reactions are exothermic. For L = CO, the Z‐isomer product forms first even at low temperatures because of the low Gibbs free energy barrier (ΔG#). Then the Z‐pro converts to E‐pro, while for L = P (OMe)3, the exclusive product is the E‐isomer. For different metal centers, the reaction mechanisms of the Cp2M(CO)H + DMAD (M = Nb and V) reaction are similar, while their products are different at room temperature. For M = Nb, because the energy barrier of the isomerization from Z‐pro to E‐pro is low and the relative free energies of Z‐pro and E‐pro are almost equal, both Z‐pro and E‐pro can be obtained. While for the Cp2V(CO)H + DMAD reaction, only the Z‐pro can be obtained under mild conditions, E‐pro can be obtained only at high temperatures. For the Cp2M(CO)H+DMAD(M=V and Nb) reactions, the formation of E‐isomer products proceeds via two five‐membered ring transition states. The calculated results provide an reasonable explanation for the experimental results and predict a new insertion reaction.

New measurement of residual cross sections from $${\alpha }{+}^{93}$$Nb reaction: a comparative study of PEQ models and nuclear level densities

An experimental study of the $${\alpha }{+}^{93}$$Nb reaction has been accomplished within 7–12.5 MeV/nucleon energy. A systematic study of the preequilibrium (PEQ) emission of particles over the compound evaporations has been carried out using the model codes—TALYS1.8 and Alice14. The measured cross sections of $$^{96g,95m+g,94m+g,93g}\hbox {Tc}$$, $$^{93m}\hbox {Mo}$$ and $$^{92m,90g}\hbox {Nb}$$ are found to agree with other reported data within the estimated uncertainties and are grossly reproduced by the theoretical calculations. The variation of isomeric cross-sectional ratio (ICR) of $$^{96,95,94}\hbox {Tc}$$ has been examined up to 100 MeV projectile energy. Additionally, a quantitative analysis of the extent of agreement between measured and theoretical data has been performed for different nuclear level densities using F-deviation factor, which is calculated considering those energies for which experimental cross section is known. Comparison of the measured and theoretical results as well as ICR analysis demonstrates the occurrence of PEQ process in the high-energy tail of excitation functions in all channels, where the compound reaction has a negligible effect.

Measurements of the Cross-sections of Produced Short-Lived Nuclei Induced by Neutrons around 14MeV on Isotopes of Tungsten**Supported by the National Natural Science Foundation of China under Grant Nos 11605099 and 11575090.

New experimental cross-section data for the 180W(n,2n)179mW, 186W(n,2n)185mW and 186W(n,p)186Ta reactions at the neutron energies of 13.5 and 14.4 MeV are obtained by the activation technique. The neutron beams are produced by means of the 3H(d,n)4He reaction. The gamma activities of the product nuclei are measured by a high-resolution gamma-ray spectrometer with a coaxial high-purity germanium detector. The neutron fluence is determined using the monitor reaction 93Nb(n,2n)92mNb. The results in the current work are discussed and compared with the measurement results found in the literature. It is shown that these higher accuracy experimental cross-section data around the neutron energy of 14 MeV agree with some previous experimental values from the literature within experimental uncertainties.

Diffusion Bonding of Ti6Al4V and SS 304 with Nb Interlayer

Abstract In this investigation, solid-state indirect diffusion couples (IDCs) were prepared between stainless steel (SS) 304 and Ti6Al4V using a niobium (Nb) interlayer of 200 µm thickness from 850°C to 950°C using uniaxial compressive pressure (∼4 MPa) for 60 min under high vacuum of 10−3 Pa. Microstructural analysis along the Nb|SS-304 interfaces of IDCs processed at 875°C–950°C revealed layer-wise iron–niobium-based intermetallics like Fe2Nb and FeNb + (Nb), apart from these reaction layers IDCs processed at 925°C revealed a (Nb) reaction layer, and IDCs processed at 950°C revealed both (Nb) and γFe + σ reaction layers. IDCs processed at all processing temperatures revealed solid solution behavior along Ti6Al4V|Nb interfaces. Thermodynamic analysis showed that the diffusion mechanism at the Ti6Al4V|Nb interface is quite functionally easier than the diffusion mechanism observed at the Nb|SS-304 interface. Empirical atomic diffusivity (D) characteristics of Nb|SS-304 interface and Ti6Al4V|Nb interfaces are ∼1.957 × 10−14 m2/s and ∼9.197 × 10−14 m2/s, respectively, for the IDCs processed at 950°C. The observed maximum hardness at the Ti6Al4V|Nb interface was ∼300 HV; whereas hardness at the Nb|SS-304 interface is found to be ∼200 HV and ∼650 HV for IDCs processed at 850°C and at 875°C and above, respectively. A maximum strength of ∼372 MPa (tensile) and ∼241 MPa (shear), along with ∼4.5 % ductility, was noticed for the IDCs processed at 875°C. The presence of two reaction layers: FeNb + (Nb) and Fe2Nb at the Nb|SS-304 interfaces improved the strength properties of the IDCs. Strength properties of the IDCs processed at 950°C deteriorated because of the presence of σ phase. Using diffraction studies, hardness property, and fracture behavior, it was established that the IDCs failed because of the propagation of crack, apparently along iron–niobium-based intermetallic reaction layers at Nb|SS-304 interfaces.

Study on the compound nucleus fusion probability PCN in 12C +93Nb reaction at above barrier energies using different degrees-of-freedom

In this work, we extend our earlier study [S. Chopra, Hemdeep, A. Kaur and R. K. Gupta, Phys. Rev. C 93 (2016) 024603] of [Formula: see text] reaction at below- and near- to above-barrier energies for both coplanar ([Formula: see text]) and noncoplanar ([Formula: see text]) degrees-of-freedom. Our main aim is to see the texture of variation of compound nucleus (CN) fusion probability [Formula: see text] at all the experimentally available center-of-mass energies ([Formula: see text]) in the range 41–69[Formula: see text]MeV, using the dynamical cluster-decay model (DCM). In this study, we worked for both degrees-of-freedom, having compact configurations ([Formula: see text]) and including higher multipole deformations (quadrupole to hexadecapole, [Formula: see text]) of nuclei. In the work of above-mentioned reference, for [Formula: see text]Ag[Formula: see text] (weakly fissioning nuclear system), we found a discrepancy in [Formula: see text], i.e., increasing function with increasing [Formula: see text], belongs to superheavy nuclei for the case of [Formula: see text] [see Fig. Fig.4 of [A. Kaur, S. Chopra and R. K. Gupta, Phys. Rev. C 90 (2014) 024619], but this erroneous result moved to correct one after the inclusion of [Formula: see text] (decreasing with increasing [Formula: see text], weakly fissioning class), which encouraged us to check the trend of [Formula: see text] at all available energies. Our evaluation framework shows the noncoplanar configuration, with higher multipole deformations [Formula: see text] included, as the most probable configuration for studying the heavy-ion reactions [S. Chopra, Hemdeep, P. Kaushal and R. K. Gupta, Phys. Rev. C 98 (2018) 041603(R)]. Second, our interest is to check the consistency of experimental data, where the experimentalists have given the data with the mixing of three different experiments for same reaction. In this study, we have found that our results are in good agreement and consistent with only the latest experimental data at five [Formula: see text]’s (=41.097, 47.828, 54.205, 60.051 and 65.454[Formula: see text]MeV), i.e., showing large ([Formula: see text]90%) noncompound nucleus contribution (or equivalently quasi-fission/Incomplete fusion) in the (total) fusion cross-section.

Study of proton induced nuclear reactions on molybdenum: cross section measurements and theoretical calculations

Abstract Excitation functions were measured by the activation method using the stacked-foil technique for the natMo(p,x)93(m+g),94m,g,95m,g,96(m+g),99mTc, 92m,95Nb reactions up to 18 MeV. The experimental results were compared with literature data and theoretical results from EMPIRE-3.2.2 code and TENDL. Special attention was paid to the 100Mo(p,2n)99mTc reaction which is very promising for the production of 99mTc at a cyclotron. In order to optimize the production conditions of some medically important Tc isotopes, the integral yields were estimated based on the measured cross sections.

Measurements of fast neutron capture cross section for 180Hf

The first experimental cross-section data for the 180Hf(n,γ)181Hf reaction have been measured within the neutron energies range of 13.5–14.8 MeV using the activation technique. The fast neutrons were produced by the T(d,n)4He reaction. Induced activities were measured by a high-resolution γ-ray spectrometer with high-purity germanium detector. The neutron fluence was determined by using the monitor reaction 93Nb(n,2n)92mNb. The neutron energies in the measurements were determined beforehand by the method of cross section ratios for the 90Zr(n,2n)89m+gZr and 93Nb(n,2n)92mNb reactions. The experimentally determined cross-section values were compared with the evaluation nuclear data in several major libraries of International Atomic Energy Agency and the theoretically calculated results by using the Talys1.8 code.