Optical Model Calculations Research Articles

Investigation of reaction and α production cross sections with 9Be projectile

In order to investigate the contribution of α production in the reaction cross sections, measurements of elastic scattering and inclusive α particle angular distributions have been carried out with the 9Be projectile on 89Y, 124Sn, 159Tb, 198Pt, and 209Bi targets over a wide angular range at energies near the Coulomb barrier. The measured elastic scattering angular distributions were fitted with optical model calculations, and reaction cross sections were extracted. The same data were also analyzed using both global optical model potentials (Global OMP) and microscopic São Paulo potentials (SPP), to obtain the reaction cross sections. The data available in the literature for 9Be projectile includes the elastic scattering angular distributions, α production cross sections, and complete fusion cross sections on these and other targets at several energies are also utilized for comparative studies. The reaction cross section extracted from the three potentials (Best Fit, Global OMP and SPP) are in reasonable agreement for all the targets except for the energies below the barrier where the results from SPP deviate by 30-50%. Inclusive α particle production cross sections were also extracted by integrating the α particle angular distributions. The present data and data available from literature of reaction and α-particle production cross sections were utilized to make systematic studies. Systematics of reaction and α-particle production cross sections revealed their universal behavior. The ratio of complete fusion (CF), inclusive α cross sections, and their sum (CF+α) to reaction cross sections show that at sub-barrier energies inclusive α dominates and above barrier CF dominates, and cumulative of these two processes almost explains the reaction cross section at all energies over a wide range of target mass. A comparative study of α production with other weakly bound projectiles is also performed and a clear distinction between projectile types is observed, which is found to correlate well with α separation energies of the projectiles.

Deuteron Optical Model Calculations for Elastic and Inelastic Reactions on 14N, 16O, 27Al Target Nuclei

Nuclear reaction cross sections have a key role in nuclear radioisotope production research. It is also an important part of applied fields such as energy production and experimental nuclear studies. It has been the subject of theoretical studies such as elucidating the nuclear structure and preparing and testing nuclear reaction models. It has become a very useful tool, especially for determining nuclear optical model parameters. In this study differential cross sections were calculated for elastic and inelastic scattering of 14-15 MeV energy range deuterons from 14N, 16O and 27Al. Calculation were carried out with TALYS 1.96/2.0 nuclear reaction code. Calculations include determining the deuteron optical model that match the experimental data. The values calculated with theoretical models were compared with experimental data obtained from the literature. While such studies are important for testing nuclear reaction models, they are also important for encouraging the preparation of nuclear reaction codes.

Deterministic sampling approach for the propagation of uncertainties in nuclear reaction models

Uncertainty propagation of model parameters through nuclear reaction models is critical for nuclear data evaluation and other applications. Nuclear reaction models generally contain nonlinear functions of the model parameters, making the process of uncertainty propagation difficult. Usually stochastic approaches like the Monte Carlo method are employed to propagate the uncertainties through nuclear reaction models. The Monte Carlo method does provide proper results, but it takes a lot of computational power and time, which makes the process of uncertainty propagation difficult. Deterministic sampling approaches may provide results with accuracy using less computational time making the process of uncertainty propagation fast. In this study we have explored the use of a deterministic sampling approach called the unscented transform method for the uncertainty propagation in the nuclear reaction models. As a test case we have propagated the uncertainties of correlated optical model parameters through the optical model calculations for total and reaction cross sections of the $n+^{56}\mathrm{Fe}$ reaction. The results obtained using the unscented transform method are then compared with the results of the Monte Carlo method. It has been observed that the unscented transform method provides results practically similar to the Monte Carlo method in less computational time. It is concluded in this study that the unscented transform method can propagate uncertainties effectively through optical model calculations and there should be further investigation of the use of this method for other nuclear reaction models.

Mechanical tuning of defect modes in polymer-based terahertz one-dimensional photonic crystals fabricated by stereolithography

Mechanical tuning of defect modes in a polymer-based one-dimensional photonic crystal was demonstrated for the terahertz (THz) spectral range. A sharp defect mode in the photonic bandgap was achieved by symmetrically enclosing a defect layer with two identical pairs of alternating compact and low-density layers. By adjusting the thickness of the defect layer, the spectral position of the defect mode within the photonic bandgap was easily controlled. Normal incidence transmission spectroscopy in a spectral range from 82 to 125 GHz was used to determine the THz spectral response for different defect layer thicknesses. The transmission data were analyzed using stratified optical layer model calculations. Spectral shift of the center frequency of the narrow transmission peak within a distinct photonic bandgap was observed in the experimental transmission spectra. The shift was achieved by mechanical tuning of the defect layer thickness. A good agreement between the relevant model parameters and the corresponding design parameters was found.

Measurements and parametrization of the 16O(d,d0)16O differential cross section

The differential cross section of the deuteron elastic scattering on oxygen was studied, experimentally, in the energy range of 1.5 – 2.5 MeV, in order for the theoretical study to be accomplished in the energy range 1.9–2.5 MeV for the scattering angles of 130°, 140°, 150°, 160° and 170°.The experiment was performed at the Tandem 5.5 MV Accelerator of the N.C.S.R. “Demokritos” in Athens, Greece. The theoretical study was accomplished in order to extend the pre-existing evaluation, which stopped at 1.98 MeV, up to 2.5 MeV. The used code implements the R-matrix theory along with optical model calculations.

Terahertz anisotropic response of additively manufactured one-dimensional photonic crystals.

A polymer-based, one-dimensional photonic crystal exhibiting anisotropic responses was demonstrated in the terahertz frequency range. The photonic crystal was composed of alternating compact and low-density polymethacrylate layers. The low-density layers consisted of sub-wavelength sized columns, which were slanted 45° with respect to the substrate surface normal to achieve form-birefringence. Normal incidence polarized terahertz transmission measurements were carried out for characterization of the fabricated photonic crystals in the range from 82 to 125 GHz. The experimental data revealed a 2 GHz shift in the center frequency of the photonic bandgap as a function of in-plane orientation, well demonstrating the anisotropic behavior of the fabricated crystal. The transmission data were analyzed using stratified optical layer model calculations. A good agreement was found between the relevant model parameters and the corresponding design parameters.

São Paulo potential version 2 (SPP2) and Brazilian nuclear potential (BNP)

The REGINA code calculates the São Paulo potential version 2 (SPP2) and the Brazilian nuclear potential (BNP). The code also provides nuclear densities obtained from the Dirac-Hartree-Bogoliubov model, which are used to calculate the nuclear potentials. Elastic scattering cross sections are obtained within the context of the optical model, with different options for the real and imaginary parts of the optical potential. In this manuscript, we provide a summary of the theoretical framework and information about the use of the code. Program summaryProgram Title: REGINA.fCPC Library link to program files:https://doi.org/10.17632/vfkkjb8dv7.1Licensing provisions: GPLv3Programming language: Fortran-77Nature of problem: We provide a code to calculate the nuclear potential between two nuclei according to two different models: the São Paulo potential version 2 (SPP2), that includes a dependence on the relative velocity between the nuclei, and the velocity independent Brazilian nuclear potential (BNP). These potentials assume the effective nuclear interactions proposed in [1,2], and are obtained within the double-folding approach with nuclear densities calculated through the Dirac-Hartree-Bogoliubov model [3].Solution method: The code involves two files containing previously calculated results for theoretical neutron and proton distributions and also experimental charge densities obtained from electron scattering experiments. These results are used to obtain matter densities through convolution using Fourier transforms. The Fourier transform method is also employed to obtain the double-folding potentials. Integration of the Schrödinger equation with a complex optical potential is performed using the Cowell method [4,5]. With this, for a given system and energy, we obtain the S-matrix and the elastic scattering cross sections.Additional comments including restrictions and unusual features: The maximum angular momentum supported in the optical model calculations is 2000.

Optical Outcoupling Efficiency in Polymer Light‐Emitting Diodes

AbstractThe electrical properties of polymer‐based light‐emitting diodes (PLEDs) have been extensively studied, resulting in quantitative device models. However, for a complete description of the optoelectronic properties of a PLED, the obtained recombination profiles need to be integrated with an optical model describing the local outcoupling efficiency of the generated light. In this work, combined electrical and optical model calculations are presented, demonstrating that the light‐outcoupling efficiency in PLEDs is governed by the presence of electron traps and the anisotropy factor of optical dipoles. Electron trapping confines the recombination in a region close to cathode, resulting in strong optical trapping in surface plasmon polariton modes. Trap‐filling leads to a voltage‐dependent recombination profile and optical outcoupling efficiency. For a typical electron trap density of ≈1023 m−3, the calculated outcoupling efficiency raises from 5.5% at 2 V to 10.4% at 5 V in case of isotropic emitters. For conjugated polymers such as super yellow poly(p‐phenylene vinylene) with the chains preferentially aligned in the plane of the film, the outcoupling efficiency can reach ≈18% at 5 V. Elimination of electron trapping would allow for a further enhancement up to 24%.

The role of the tightly bound core in the refractive scattering of 17F+12C

The refractive scattering of 17F+12C is analyzed systematically by using the optical model with the cluster folding potentials. First of all, the applicability of the cluster folding approach is validated by analyzing the elastic scattering data of 13C+12C and 12C+12C at 20 A MeV. To perform the optical model calculations of 17F+12C, the less ambiguous optical potentials of 16O+12C and the global optical potential of p+12C are used to give the cluster folding potentials. Apart from the reproduction of the experimental data of the elastic scattering of 17F+12C at 10 A MeV, the Airy patterns are noticeable from about 10 to 40 A MeV. For comparison, the optical model calculations of 17O+12C at the same energies per nucleon are also performed through the cluster folding approach, of which the results are very similar to those of 17F+12C. For both 17F+12C and 17O+12C, the energy dependence of the Airy minima is extracted and compared with that in the case of 16O+12C. It is found that the Airy minima characteristic of 17F+12C is nearly identical with that of 17O+12C and similar to that of 16O+12C, which indicates the strong contributions from the 16O core to the appearance of the nuclear rainbow effects in 17F scattering. At last, the calculated total reaction cross sections are compared with the strong absorption model, which verifies the reasonableness of the present optical model calculations.

Study of the scattering of 15C at energies around the Coulomb barrier

The neutron rich carbon isotope 15C is the only known case of an almost “pure” 2s1/2 single-neutron halo ground state configuration. At collision energies around the Coulomb barrier the reaction dynamics is expected to be dominated by single neutron transfer and breakup. To investigate these effects, we have measured the scattering of 15C with a 208Pb target at 65 MeV at the HIE-ISOLDE facility in CERN (Geneva, Switzerland). The preliminary data demonstrates the presence of a strong long-range absorption pattern in the angular distribution of the elastic cross section. The results are discussed in the framework of Optical Model calculations.

Successful Prediction of Total α-Induced Reaction Cross Sections at Astrophysically Relevant Sub-Coulomb Energies Using a Novel Approach.

The prediction of stellar (γ,α) reaction rates for heavy nuclei is based on the calculation of (α,γ) cross sections at sub-Coulomb energies. These rates are essential for modeling the nucleosynthesis of so-called p nuclei. The standard calculations in the statistical model show a dramatic sensitivity to the chosen α-nucleus potential. The present study explains the reason for this dramatic sensitivity which results from the tail of the imaginary α-nucleus potential in the underlying optical model calculation of the total reaction cross section. As an alternative to the optical model, a simple barrier transmission model is suggested. It is shown that this simple model in combination with a well-chosen α-nucleus potential is able to predict total α-induced reaction cross sections for a wide range of heavy target nuclei above A≳150 with uncertainties below a factor of 2. The new predictions from the simple model do not require any adjustment of parameters to experimental reaction cross sections whereas in previous statistical model calculations all predictions remained very uncertain because the parameters of the α-nucleus potential had to be adjusted to experimental data. The new model allows us to predict the reaction rate of the astrophysically important ^{176}W(α,γ)^{180}Os reaction with reduced uncertainties, leading to a significantly lower reaction rate at low temperatures. The new approach could also be validated for a broad range of target nuclei from A≈60 up to A≳200.

Highly Localized Defect Mode in Polymer-Based THz Photonic Crystals Fabricated Using Stereolithography

A polymer-based one-dimensional photonic crystal with a defect mode was demonstrated for the terahertz frequency range. The photonic crystal was designed to achieve a photonic bandgap centered around 100 GHz with a narrow defect mode at the center frequency. The defect mode allowed a narrow band transmission at the center of photonic bandgap, while the transmitted signal was suppressed in the rest of the bandgap. The photonic crystal incorporated two identical sets of alternating compact and low-density layer pairs symmetrically enclosing a defect layer. The compact layers consisted entirely of polymethacrylate with no intentional internal structures, while the low-density layers were composed of sub-wavelength-sized columns. The columnar structures had a volumetric fraction selected to provide a desired index contrast between the adjacent layers. The photonic crystal samples were fabricated in a single-step stereolithography using a commercial system. THz transmission spectroscopy measurements were carried out to determine the optical response of the sample in a range from 82 to 125 GHz. Stratified optical layer model calculations were used to evaluate the transmission data. A distinct photonic bandgap with a defect mode centered at 99 GHz was observed in the experimental transmission spectra. A good agreement between the relevant model parameters and the corresponding design parameters was found.

Processing conditions using electric discharge and optical characteristics for a short multimode fiber imaging probe

Using a short multimode fiber (SMMF) imaging probe with a diameter of 125μm and a length of 7.4 mm, the full-field optical coherence microscopy (FF OCM) to measure sectional images of in vivo rat brains deeper than 4 mm have been reported (Sato, 2019). However, since the tip of the SMMF was as cut, the process should be studied for smooth insertions into tissues and appropriate contacts to tissues. The SMMF processing conditions using electric discharge and the optical characteristics of the processed SMMF were investigated. Using a high voltage of 12,000 V for discharge duration of 11 s, the fiber tips of SMMF were processed to fabricate a spherical shape with a 77μm curvature radius. The measured imaging conditions approximate the optical model calculations of the parabolic refractive index and the spherical surface. Local blur and distortions in the measured images were identified in detail. Using the processed SMMF with a length of 7.35 mm and a diameter of 125μm, the transmission image of a chicken tendon samples closely corresponded to the image recorded with an optical microscope.

One-dimensional Photonic Crystals Fabricated Using Stereolithographic Single Layer Assembly for the Terahertz Spectral Range

A polymer-based one-dimensional photonic crystal with a photonic bandgap in terahertz frequency range was designed and fabricated through stereolithography and was characterized using THz spectroscopy. The photonic crystal studied here consists of alternating compact and low-density layers. The compact layers were fabricated from fully polymerized polymethacrylate without any intentional internal structure. The low-density layers consist of sub-wavelength sized columns, where the volume density was selected to provide sufficient contrast between the dielectric functions of adjacent layers. The photonic crystal samples were fabricated in a single step using a commercial stereolithography system and polymethacrylate compatible with the system. Transmission spectroscopy in a range from 82 to 125 GHz was used to determine the THz spectral response of the sample. The transmission data were analyzed using stratified optical layer model calculations. A distinct photonic bandgap with a center frequency of 111 GHz was observed in the experimental transmission spectra. Bruggeman effective medium approximation was found to accurately describe the dielectric function of the low-density layers. An excellent agreement between the relevant model parameters and the corresponding design parameters was found, indicating the versatility of the approach for the fabrication of photonic crystals for the THz spectral range.

Alpha particle transmission coefficients from a global optical potential

Statistical model calculations involving a large number of emitted particles can be greatly facilitated by using transmission coefficients in a parametrized form. Thus, the execution and storage of the results of extensive optical model calculations can be avoided. Along these lines, a parametrization of optical model transmission coefficients, involving n, p, 2H, 3He and 4He on many targets, was produced some years ago. In the present work, we question the validity of this technique in the description of low-energy alpha particle evaporation. We propose a new parametrization with an improved low energy behavior.

Comparative study of proton and positive kaon interactions with carbon: hint of new physics like partial restoration of chiral symmetry in nuclei

Concerning the scattering of K+ - mesons on nuclei, the explicit discrepancy between experimental data and optical model calculations is a longstanding problem and none of the conventional medium effect corrections improves significantly the agreement with the data. In this paper the cross sections for the reactions K++12C at incident momenta of the kaon Plab < 800 MeV/c are calculated on the basis of Glauber’s high-energy approximation. The noneikonal corrections, Fermi motion effect and both Pauli and dynamic short-range correlations were incorporated in the Glauber approach for nuclear collisions. The influence of all these corrections on the calculation of the cross sections for the interactions of kaon with nucleus is discussed. The full calculations is compared to available data. The corrections seem to fail in reproducing the experimental data. Our results is compared to optical model calculations. We show that both our model and optical model fails to give a satisfactory description of K+-nuclei cross sections. Different attempts to remove this discrepancy with the in-medium effects taken into account are discussed.

Study of pre-equilibrium contributions in proton spectra of 59Co(n,xp) reaction using TALYS-1.9

In the present study we have calculated the proton spectra of 59Co(n,xp) using TALYS-1.9. TALYS uses all major reaction mechanisms like compound, pre-equilibrium and direct reactions. The contribution from compound nuclear reaction is calculated using optical model calculations. For pre-equilibrium contributions we have used two particle exciton model. The results from the present work suggests the presence of significant pre-equilibrium emission components in the 59Co(n,xp) system within the range of incident projectile energies from 37.5 to 62.7 MeV.

Evaluation of neutron induced reactions on 56Fe with CONRAD

The evaluation of the 56Fe neutron induced reactions is currently ongoing at the CEA-Cadarache using the code CONRAD, with the goal to cover the whole energy range from the Resolved Resonance Region to the continuum and estimate the corresponding uncertainties and covariance matrices. Some first results and issues occurred from this work are presented and discussed here, more specifically on the analysed transmission and capture data in the Resolved Resonance Region, as well as the optical and statistical model calculations in the fast neutron energy range.

Halo Effects in the Low-energy Scattering of \(^{15}\)C with Heavy Targets

The neutron-rich carbon isotope 15C was postulated to be a halo nucleus (Sn = 1215 keV, S2n = 9395 keV) according to different high-energy experiments. If so, it would be the only halo nucleus exhibiting a pure s-wave structure of the ground state. At low collision energies, the effect of this halo structure should manifest as a strong absorption pattern in the angular distribution of the elastic cross section, with a total suppression of the nuclear rainbow due to the large neutron transfer and breakup probabilities, enhanced by the halo configuration. The IS619 experiment, carried out at the HIE-ISOLDE facility at CERN (Switzerland), is the first dynamical study of this nucleus at energies around the Coulomb barrier. It aims to probe the halo structure via the measurement of the elastic cross section on a high-Z 208Pb target. Preliminary results of the elastic cross section are discussed and compared to Optical Model calculations.

Multiband coupling and nuclear softness in optical model calculations for even-even and odd-A actinides

A new dispersive multiband coupled channels optical model with soft-rotator “effective” deformations is proposed to describe nucleon scattering on even-even and odd-A actinides. The impact of the introduction of axial and non-axial dynamical deformations that describe nuclear softness is discussed. Softness and multiband coupling are shown to change compound-nucleus formation cross section by up to ≈ 10% for incident neutron energies below 1 MeV.