Integral Cross Section Values Research Articles

Quantum Dynamics Studies of the Li + Na2 (V = 0, j = 0) → Na + NaLi Reaction on a New Neural Network Potential Energy Surface.

The ultracold reaction offers a unique opportunity to elucidate the intricate microscopic mechanism of chemical reactions, and the Na2Li system serves as a pivotal reaction system in the investigation of ultracold reactions. In this work, a high-precision potential energy surface (PES) of the Na2Li system is constructed based on high-level ab initio energy points and the neural network (NN) method, and a proper asymptotic functional form is adopted for the long-range interaction, which is suitable for the study of cold or ultracold collisions. Based on the new NN PES, the dynamics of the Li + Na2 (v = 0, j = 0) → Na + NaLi reaction are studied in the collision energy range of 10-7 to 80 cm-1. In the high collision energy range of 8 to 80 cm-1, the dynamics of the reaction is studied using the time-dependent wave packet method and the statistical quantum mechanical (SQM) method. Comparing the results of the two methods, it is found that the SQM method provides a rough description of the product ro-vibrational state distribution but overestimates the integral cross-section values. With the decrease of collision energy, the reaction differential cross section gradually changes from forward-backward symmetric scattering to predominant forward scattering. In the low collision energy range from 10-7 to 8 cm-1, the SQM method is used to study the reaction dynamics, and the rate constant in the Wigner threshold region is estimated to be 2.87 × 10-10 cm3/s.

Gaussian Process Regression for State-to-State Integral Cross Sections: The Case of the O + O2 Collision Dissociation Reactions.

Research on hypersonic vehicles has become increasingly important worldwide in recent years. However, accurately simulating the dynamics of the nonequilibrium high-temperature reactions that are in the hypersonic flow around the vehicles presents a significant challenge as a large number of states and transitions are accessible even for the smallest atom-diatom reaction systems. It is quite difficult, sometimes even impossible, to exhaustively investigate all relevant combinations or determine high-dimensional analytical representations for the state-to-state reaction probabilities. In this study, we used Gaussian process regression (GPR) to fit a model based on only 807 QCT data for training. The confidence interval of the GPR prediction and the Kullback-Leibler (KL) divergence were used to help minimize the sampling amount of data for fitting the converged GPR model. The model aims to predict the state-to-state integral cross section (ICS) of the O + O2 → 3O dissociation reaction under random initial conditions (Et, v, j). In total, it took almost a month to obtain this converged GPR model, but it took only a few seconds to predict the ICS value for any initial condition. For 330 initial conditions not included in the training set, the mean-square error (MSE) between the QCT-calculated ICSs and the GPR-predicted ones is only 0.08 Å2 and the R2 is 0.9986, indicating that the GPR model can replace the direct expensive QCT calculation with high accuracy. Finally, we calculated the equilibrium dissociation rate coefficients based on the StS ICS values predicted by the GPR model, and the results were in good agreement with available experimental and theoretical results. Thus, this study provides an effective and accurate approach to the extensive direct state-to-state reaction dynamic calculations.

Understanding heavy-ion fusion cross section data using novel artificial intelligence approaches

We modeled an unprecedentedly large dataset of complete fusion cross section data using a novel artificial intelligence approach. Our analysis aims especially to unveil, in a data-driven way, nuclear structure effects on the fusion between heavy ions and to suggest a universal formula capable to describe all previously available data. The study focused on light-to-mediummass nuclei, where incomplete fusion phenomena are more difficult to occur and less likely to contaminate the data. The method used to derive the models exploits a state-of-the-art hybridization of genetic programming and artificial neural networks and is capable to derive an analytical expression that serves to predict integrated cross section values. For the first time, we analyzed a comprehensive set of nuclear variables, including quantities related to the nuclear structure of projectile and target. In this manuscript, we describe the derivation of two computationally simple models that can satisfactorily describe, with a reduced number of variables and only a few parameters, a large variety of lightto- intermediate-mass collision systems in an energy domain ranging approximately from the Coulomb barrier to the oncet of multi-fragmentation phenomena. The underlying methods are particularly innovative and are of potential use for a broad domain of applications in the nuclear field.

Understanding Heavy-ion Fusion Cross Section Data Using Novel Artificial Intelligence Approaches

An unprecedentedly extensive dataset of complete fusion cross section data is modeled via a novel artificial intelligence approach. The analysis was focused on light-to-medium-mass nuclei, where fission-like phenomena are more difficult to occur. The method used to derive the models exploits a state-of-the-art hybridization of genetic programming and artificial neural networks and is capable to derive, in a data-driven way, an analytical expression that serves to predict integrated cross section values. We analyzed a comprehensive set of nuclear variables, including quantities related to the nuclear structure of projectile and target. In this paper, we describe the derivation of two computationally simple models that can satisfactorily describe, with a reduced number of variables and only a few parameters, a large variety of light-to-intermediate-mass collision systems in an energy domain ranging approximately from the Coulomb barrier to the oncet of multi-fragmentation phenomena. The underlying methods are of potential use for a broad domain of applications in the nuclear field.

Coupled three-dimensional quantum mechanical wave packet study of proton transfer in H2+ + He collisions on accurate abinitio two-state diabatic potential energy surfaces.

We have carried out fully close-coupled three dimensional quantum mechanical wave packet dynamical calculations for the reaction He+H2+→HeH++H on the ground electronic adiabatic potential energy surface and on the lowest two electronic states of newly constructed abinitio calculated diabatic potential energy surfaces for the system [Naskar et al., J. Phys. Chem. A 127, 3832 (2023)]. With the reactant diatom (H2+) in its roto-vibrational ground state (v = 0, j = 0), the calculations have been carried out in hyperspherical coordinates to obtain the reaction attributes. Convergence profiles of the reaction probability with respect to the total angular momentum quantum number at different collision energies are presented for the title reaction. State-to-state as well as initial state selected integral reaction cross sections are calculated from the fully converged reaction probabilities over a range of collision energies. The integral cross section values computed using the two-state diabatic potential energy surfaces are significantly lower than those obtained using the ground electronic state adiabatic potential energy surface and are in much better agreement with the available experimental results than the latter for total energy greater than 1.1eV. Therefore, it becomes clear that it is important to include the nonadiabatic coupling terms for a quantitative prediction of the dynamical observables.

Dynamics studies of O+ + D2 reaction using the time-dependent wave packet method

Based on the potential energy surface (PES) reported by Li et al. (Phys. Chem. Chem. Phys. 20, 1039 (2018)), the initial state dynamics calculation of O+ + D2 (v = 0, j = 0) reaction was conducted using the time-dependent wave packet method with a second order split operator. Dynamics properties such as reaction probability, integral cross section, differential cross section, and distribution of products were calculated and compared with available experimental and theoretical results. The present integral cross section values were in good agreement with experimental results. In addition, the differential cross section indicates that the mechanism of the complex-formation reaction plays a dominant role during the reaction.

Non-adiabatic state-to-state dynamic studies of Na(3p) + H2(v = 1, 2, 3; j = 0) → NaH + H reactions

Abstract The time-dependent wave packet method is used to study non-adiabatic state-to-state Na(3p) + H2(v = 1, 2, 3, j = 0) → NaH + H reactions, which are sub-processes in the formation of NaH from the collision between Na(3p) and H2. Integral cross section values of the Na(3p) + H2(v) → NaH + H reaction increase significantly when H2 is excited to the v = 2 or v = 3 states. Products from the Na(3p) + H2(v) → NaH + H reaction with three different initial vibrational states all prefer to form in vibrationally cold but rotationally hot states. Regarding the vibrational state distribution of the product from Na(3p) + H2(v > 0) → NaH + H, our theoretical results are consistent with experimental results.

Interference effects in the electron and positron scattering from molecules at intermediate and high energies

The independent atom model representation (IAM) in combination with the additivity rule (AR) is customary accepted as a good approximation to describe electron and positron scattering processes with polyatomic molecules at intermediate and high energies (typically above 100eV). Within this approach, interference terms are not properly evaluated and are usually ignored in the cross section calculations. However, through a numerical solution of the Lippmann–Schwinger equation for three dimensional multicentre potentials we here demonstrate how interference terms can affect to the calculated differential and integral cross section values even at such relatively high energies. Practical corrections to the AR approach for both differential and integral electron and positron scattering cross section calculations from molecules are also proposed.

Quantum dynamics on S(1D) + H2 reaction: effect of orientation and rotation

Time-dependent quantum mechanical wave packet calculations have been carried out to study the effect of orientation and rotation of the hydrogen molecule on the reaction S (1D) + H2(X1 Σ + )(v = 0, j = 0–3) → SH(X2 Π) + H(2S) using the double many-body expansion (DMBE)/complete basis set (CBS) potential energy surface (PES) by Song and Varandas [J. Chem. Phys. 130, 134317 (2009)]. Reaction probability and integral cross section values were calculated over a range of collision energy values. The cross section values are compared with the experimental values as well as with the other quantum mechanical results. Our calculation shows that reaction probability values strongly depend on the orientation and rotation of the hydrogen molecule. It was also found that rotational excitation of H2 molecule significantly enhances integral reaction cross section values contrary to earlier reported quasi-classical trajectory calculation results.

Recent integral cross section validation measurements at the ASP facility

This work presents new integral data measured at the ASP 14MeV neutron irradiation facility at Aldermaston in the UK, which has recently become available for fusion-related work through the CCFE materials programme. Measurements of reaction products from activation experiments using elemental foils were carried out using gamma spectrometry in a high efficiency, high-purity germanium (HPGe) detector and associated digital signal processing hardware. Following irradiation and rapid extraction to the measurement cell, gamma emissions were acquired with both energy and time bins.Integral cross section and half-life data have been derived from these measurements. Selected integral cross section values are presented from the measurement campaigns. Details of the data processing approach and outputs generated are highlighted for measurement of the 186W(n,2n)185mW reaction—a selected short-lived reaction resulting from W foil irradiations; C/E results are reported along with the associated uncertainties and compared using the SAFEPAQ-II tool against existing available data.

Integrated cross sections for excitation of nuclear isomers by inelastic photon scattering at giant resonance

In the view of the evidences arising from our experimental and theoretical studies, the long-standing picture of a two-humped excitation function for photoexcitation of isomers cannot be confirmed. Whereas the first maximum (at the photoneutron threshold) of the cross section of nuclear photon scattering can be attributed to inelastic (compound) scattering, the second large peak at about giant dipole resonance is mostly due to the elastic (direct) process. A second large peak or increase reported to appear in isomer production has been shown to be practically vanishing. On realizing such a situation, calculated estimates have been given for saturated integral cross section values for isomer activation, based on photoabsorption cross sections taken from the usual Lorentzian parametrization up to the photoneutron threshold. Results compare reasonably well to available experimental data acquired by gamma-ray spectrometry in a large set of stable nuclides having long-lived isomeric states.

Measurement of the Fourth O−H Overtone Absorption Cross Section in Acetic Acid Using Cavity Ring-Down Spectroscopy

We report the absolute absorption cross sections of the fourth vibrational O-H (5ν(OH)) overtone in acetic acid using cavity ring-down spectroscopy. For compounds that undergo photodissociation via overtone excitation, such intensity information is required to calculate atmospheric photolysis rates. The fourth vibrational overtone of acetic acid is insufficiently energetic to effect dissociation, but measurement of its cross section provides a model for other overtone transitions that can affect atmospheric photochemistry. Though gas-phase acetic acid exists in equilibrium with its dimer, this work shows that only the monomeric species contributes to the acetic acid overtone spectrum. The absorption of acetic acid monomer peaks at ∼615 nm and has a peak cross section of 1.84 × 10(-24) cm(2)·molecule(-1). Between 612 and 620 nm, the integrated cross section for the acetic acid monomer is (5.23 ± 0.73) × 10(-24) cm(2)·nm·molecule(-1) or (1.38 ± 0.19) × 10(-22) cm(2)·molecule(-1)·cm(-1). This is commensurate with the integrated cross section values for the fourth O-H overtone of other species. Theoretical calculations show that there is sufficient energy for hydrogen to transition between the two oxygen atoms, which results in an overtone-induced conformational change.

QUASI-CLASSICAL TRAJECTORY STUDY OF THE REACTIONS N(2D) WITH H2, D2, AND HD

Quasi-classical trajectory (QCT) calculations are carried out for the title reactions on the potential energy surface (PES) of Ho et al.1 Our calculated integral cross-section values have been compared with the recent two quantum mechanics (QM) ones: they are close to those of one QM calculation in the high collision energy range, but they approach to another one in the low collision energy range. The product rotational alignments 〈P2 (J' ⋅ K)〉 have also been calculated.

Enhanced oscillator strengths and optical parameters of doped ZnS bulk and nanophosphors

We synthesize and investigate the oscillator-strength (OS), dipole-moment (DM), and integrated cross-section values (ICSVs) of singly (Mn) and doubly (Mn and Co or Ni) doped samples of ZnS bulk and nanophosphors. The oscillator-strength values (OSVs) are found to enhance by three orders of magnitude when Co or Ni dopant is incorporated in ZnS:Mn bulk phosphors, which strongly suggests that a quencher dopant triggered an energy-transfer process in the host ZnS material. Nevertheless, although these quencher dopants were previously considered to kill the luminescence from the host material, we used these dopants in ZnS:Mn to create an additional pathway for the relaxation of the carrier, and to initiate the energy-transfer mechanism. On the other hand, a four orders of magnitude enhancement in the OSVs was observed on incorporating the quencher dopants in ZnS:Mn nanophosphors, which is attributed to the fact that our nanosamples are related to a strong-confinement case while the quencher dopant played a significant role in the variation of OSVs. Moreover, the analysis of OSVs showed that excitonic/defect level emission from ZnS host is due to a weak electric dipole transition (WEDT), while a magnetic dipole transition (MDT) dominates in the case of ZnS:Mn nanophosphors. Based on the present investigations, we clearly obtained an origin of excitonic- and impurity-related emission from the doped ZnS bulk and nanophosphor samples, which were almost vague in the previous studies of other researchers.

Mechanism of the 15N(p, α) 12C reaction at Ep=9.09–43.7 MeV

The spectroscopic-factor amplitudes for the triton-cluster transfer are used in distorted wave born approximation (DWBA) analyses for the first six 12C states, up to E x =17.76 MeV, in the reaction 15N(p, α) for E p=9.09–43.7 MeV. Agreements are obtained for most 12C states between the theoretically predicted spectroscopic factors ( S) and both of experimental and theoretical forward integrated cross-section values (at E p∼43.7 MeV) and their sequence states with the same nuclear parameters. The theoretical spectroscopic factors failed to predict the transition strengths for the two 12C states at 7.6542 and 17.76 MeV, while the DWBA predictions failed to reproduce the strengths of the three 12C states at 7.6542, 14.083 and 17.76 MeV. This is probably, in the first case, due to the inclusion of other direct mechanisms and (or) to the multi-step processes in their mechanism, while for the second case, it is may be due to either the angular momentum mismatching effect or the choice of the optical parameters. The agreement between theoretical and experimental data for the first six investigated 12C states indicate the success of the Cohen–Kurath wave-functions itself and their accuracy. They also indicate the success of the model of calculations of spectroscopic factors.

Energy deposition model for low-energy electrons (10–10 000 eV) in air

An energy deposition model for electrons in air that can be useful in microdosimetric applications is presented in this study. The model is based on a Monte Carlo simulation of the single electron scattering processes that can take place with the molecular constituents of the air in the energy range 10–10 000 eV. The input parameters for this procedure have been the electron scattering cross sections, both differential and integral. These parameters were calculated using a model potential method which describes the electron scattering with the molecular constituent of air. The reliability of the calculated integral cross section values has been evaluated by comparison with direct total electron scattering cross-section measurements performed by us in a transmission beam experiment. Experimental energy loss spectra for electrons in air have been used as probability distribution functions to define the electron energy loss in single collision events. The resulting model has been applied to simulate the electron transport through a gas cell containing air at different pressures and the results have been compared with those observed in the experiments. Finally, as an example of its applicability to dosimetric issues, the energy deposition of 10 000 eV by means of successive collisions in a free air chamber has been simulated.

Fourier Transform Spectroscopy of the O2 Herzberg Bands: II. Band Oscillator Strengths and Transition Moments

From absorption spectra obtained at high resolution by coupling a Fourier transform spectrometer to a long-path multiple reflection cell [A. Jenouvrier, M.-F. Mérienne, B. Coquart, M. Carleer, S. Fally, A. C. Vandaele, C. Hermans, and R. Colin, J. Mol. Spectrosc. 198, 136–162 (1999)] the intensities of the O2 Herzberg bands (A3Σ+u–X3Σ−g, c1Σ−u–X3Σ−g, A′3Δu–X3Σ−g) have been studied at ambient temperature. The integrated cross section values are given for the lines of the (v′–0) bands in the A3Σ+u–X3Σ−g, c1Σ−u–X3Σ−g, and A′3Δu–X3Σ−g transitions with v′ = 0–11, v′ = 2–19, and v′ = 2–12, respectively. The band oscillator strengths have been deduced and transition moments have been calculated. The total absorption values in the region of the Herzberg bands together with the photoabsorption values determined previously above the dissociation limit can be modeled by a single curve, in agreement with the continuity relationship of the cross sections through the dissociation limit.

Electron scattering in chlorine dioxide

Cross-sections are reported for total integral and backward scattering of electrons from chlorine dioxide (OClO) for energies in the range 20-500 meV. The measurements were made in transmission experiments using a synchrotron radiation photoionization apparatus with an energy resolution in the incident electron beam of ~1.0 meV (FWHM). Integral and backward scattering cross-sections are reported. The present integral cross-section values are a correction to those reported in an earlier publication (Gulley et al 1998a J. Phys. B: At. Mol. Opt. Phys. 31 5197) which have been found to be too low due to the presence of an impurity in the original OClO samples. The absolute accuracy of the integral cross-sections is limited by experimental difficulties with respect to strong rotationally inelastic forward scattering due to the dipolar nature of the target molecules. Backward scattering data provide good evidence that dissociative attachment occurs through p-wave attachment. Comparison is made with predictions of the first Born pure dipole approximation for both total and backward scattering with excellent agreement above 100 meV with integral scattering data, but showing a significant underestimate for backward scattering cross-sections. Behaviour at energies below 100 meV represents competition between inelastic scattering and attachment and is not well understood.

Measurement of angular distribution of M shell fluorescent X-rays excited by 5·95 keV photons in thorium

The differential cross-sections for the emission of M shell fluorescent X-rays from Th by 5·95 keV photons at eight angles ranging from 50° to 120° have been measured. The differential cross-section is found to decrease with increase in the emission angle showing anisotropic spatial distribution of M shell fluorescent X-rays. The present results contradict the predictions of the calculations of Cooper and Zare [1] that the atomic inner shell vacancy states produced in photoionization are not aligned but confirm those of Fluggeet al [2] and Scofield [3] that the vacancy states withJ > 1/2 are aligned. The integral M shell fluorescent emission cross sections have been determined from the measured angular distribution coefficients and compared with theoretical integral cross-sections calculated by using theoretical values of M subshell photoionization cross-sections, fluorescence yields and coster kronig transition probabilities available in literature. The experimental and theoretical values of integral crosssections show a reasonable agreement.

Comment on "Resonant excitation of the reaction 180Tam( gamma, gamma ')180Ta"

We point out that the large integral cross section values reported for the $^{180}\mathrm{Ta}^{\mathit{m}}$(\ensuremath{\gamma},\ensuremath{\gamma}'${)}^{180}$Ta reaction by Collins et al. correspond to transition strengths exceeding the recommended upper limits. The small overall cross section ratio of the aforementioned and the $^{115}\mathrm{In}$(\ensuremath{\gamma},\ensuremath{\gamma}'${)}^{115}$${\mathrm{In}}^{\mathit{m}}$ reactions is shown to be an indirect piece of evidence against the enormous integral cross sections. Collins et al. used the $^{87}\mathrm{Sr}$(\ensuremath{\gamma},\ensuremath{\gamma}'${)}^{87}$${\mathrm{Sr}}^{\mathit{m}}$ reaction to verify their calculated photon flux, but did not identify the observed activation levels. We identify four photoactivation levels of $^{87}\mathrm{Sr}$ at 1228.42 keV, 5/${2}^{+}$, 1770.46 keV, 5/${2}^{+}$, 1919.9 keV, 7/${2}^{+}$, 2706.5 keV, 9/${2}^{+}$, and deduce the existence of (at least) a further one around 2.6 MeV. These new data suggest that the calculated photon flux used by Collins et al. should be rechecked.