Resonant Scattering Cross Section Research Articles

Resonant scattering measurement for 11C using thick target in inverse kinematics

The resonant scattering of 10B+p reaction was measured at θ c.m.= 180°, 170°, 160°, 150° and 140° using a 35.93 MeV 10B beam to investigate the spectroscopy of 11C with the thick target inverse kinematic method at RIBRAS facility, IFUSP, São Paulo. Influence of the stopping power uncertainty on the resonant scattering cross section values for 11C in the 10B(p, p)10B reaction is shown. The data measured for the reaction channels p(10B,α) and p(10B,3He) is also presented. Interestingly, the cross sections for the 3He channel are observed upto 2 MeV below the lowest energy measurement available in literature.

Maximum Refractive Index of an Atomic Medium

It is interesting to observe that all optical materials with a positive refractive index have a value of index that is of order unity. Surprisingly, though, a deep understanding of the mechanisms that lead to this universal behavior seems to be lacking. Moreover, this observation is difficult to reconcile with the fact that a single, isolated atom is known to have a giant optical response, as characterized by a resonant scattering cross section that far exceeds its physical size. Here, we theoretically and numerically investigate the evolution of the optical properties of an ensemble of ideal atoms as a function of density, starting from the dilute gas limit, including the effects of multiple scattering and near-field interactions. Interestingly, despite the giant response of an isolated atom, we find that the maximum index does not indefinitely grow with increasing density, but rather reaches a limiting value $n\approx 1.7$. We propose an explanation based upon strong-disorder renormalization group theory, in which the near-field interaction combined with random atomic positions results in an inhomogeneous broadening of atomic resonance frequencies. This mechanism ensures that regardless of the physical atomic density, light at any given frequency only interacts with at most a few near-resonant atoms per cubic wavelength, thus limiting the maximum index attainable. Our work is a promising first step to understand the limits of refractive index from a bottom-up, atomic physics perspective, and also introduces renormalization group as a powerful tool to understand the generally complex problem of multiple scattering of light overall.

Lidar observations of the upper atmospheric nickel layer at Beijing ([formula omitted],[formula omitted

Ni atoms, produced in the Earth's upper atmosphere by meteoric ablation, are challenging to measure by lidar because the Ni atom density is low, the resonance scattering cross section is relatively small, and the transitions occur in the near-UV around 340 nm where absorption by the stratospheric ozone layer starts to become significant. A new Ni lidar has been designed and deployed at Yanqing station (40∘N,116∘E) Beijing, China over the period from 3 April 2019 to 31 December 2019. The combination of a frequency-doubled near-IR laser and narrow bandwidth filters enables stable and continuous operation. From 25 nights of measurements, the Ni peak density ranges from 98 to 460 cm−3 with the peak altitude between 80 and 88 km; the average peak density is 258±115cm−3. The average column abundances of Nickel varied between 1.52×108 and 6.0×108 cm−2 between mid-summer and mid-winter. An experiment was also carried out using the Ni lidar to determine the spectroscopic branching ratios from the excited Ni(3F4) state into 3 lower states; very close agreement with the literature values were obtained.

Resonance cross-section formula for low-energy elastic scattering

A simple analytical formula for partial wave cross section describing low-energy elastic scattering in the presence of a shape resonance located near the elastic threshold is proposed. The formula is based on the extension of the regularized method of analytical continuation in the coupling constant (RAC) recently proposed by Hor\'a\ifmmode \check{c}\else \v{c}\fi{}ek and co-workers. The RAC method provides the complex energies of resonances and virtual states requiring as input information a set of real bound state energies of a perturbed system for which standard highly sophisticated numerical codes may be employed. No scattering calculations are needed. These parameters define the low-energy partial wave resonance scattering cross section. Cross sections are calculated for the $2{s}^{2}\ensuremath{\varepsilon}p\phantom{\rule{0.16em}{0ex}}^{2}P^{0}$ state of beryllium and $3{s}^{2}\ensuremath{\varepsilon}p\phantom{\rule{0.16em}{0ex}}^{2}P^{0}$ of magnesium. The results compare well with recently published data.

Generic singularities of scattering coefficients and a paradox of resonant wave scattering

The paradox of the divergence of the resonant scattering cross section of a cylinder with the permittivity equals minus unity and vanishing radius (R) irradiated by a monochromatic electromagnetic wave is discussed. Within the framework of the exact solution of the Maxwell equations, the divergence at the specified conditions is caused by the overlap of all but one multipolar resonances. It is shown that the paradox is caused by the too straightforward analysis of the expression for the cross section, which has a singularity at this point. To resolve the singularity, one must, first, generalize the problem formulation, taking into account the final linewidth of the incident wave, and then perform the correct sequence of limit transitions. The application of this approach gives rise to the vanishing cross section at the vanishing R. It ruins the expectations to employ such a cylinder as a superscatterer but simultaneously open a door to counterintuitive effects both in far and near field zones related to unusual size dependences of the scattered fields at small but finite R.

Spontaneous Emission and Resonant Scattering in Transition from Type I to Type II Photonic Weyl Systems.

Spontaneous emission and scattering behavior of an emitter or a resonant scatterer strongly depend on the density of states of the surrounding medium. It has been shown that the resonant scattering cross section (RSC) may diverge at the Weyl frequency of a type I Weyl system due to the diminishing density of states. Here we study the spontaneous emission (SE) and RSC in a photonic metacrystal across the critical transition between type I and type II Weyl systems. Theoretical results show that the SE rate of an emitter in a type I Weyl system diminishes to zero at the Weyl frequency. When the system is tuned towards the transition point between type I and type II Weyl point, the dip in the SE spectrum at the Weyl frequency becomes infinitely sharp. The dip vanishes at the critical transition, and transforms into a peak when the system changes into a type II Weyl system. We further show that the resonant scattering cross section also exhibits dramatically different spectral features across the transition. Our study demonstrates the ability to tune SE and RSC through altering the dispersion of the Weyl medium between type I and type II, which provides a fundamentally new route in manipulating light-matter interactions.

Resonant Inelastic X-ray Scattering Amplitudes and Cross Sections in the Algebraic Diagrammatic Construction/Intermediate State Representation (ADC/ISR) Approach.

A scheme has been derived and implemented to gain computational access to the full electronic part of the Kramers-Heisenberg-Dirac (KHD) expression for resonant and nonresonant inelastic scattering amplitudes. Our implementation of this scheme is based on the complex polarization propagator in the algebraic diagrammatic construction (ADC) framework and within its intermediate state representation (ISR). The hierarchy of the second- and third-order ADC/ISR computational schemes known as ADC(2), ADC(2)-x, and ADC(3/2) is considered, and the calculated resonant inelastic X-ray scattering (RIXS) amplitudes and transition strengths for water are in excellent agreement with recent experimental data.

Dynamical Effects in Resonant X-Ray Diffraction.

Using resonant magnetic diffraction at the Ni L_{2,3} edge in a LaNiO_{3} superlattice, we show that dynamical effects beyond the standard kinematic approximation can drastically modify the resonant scattering cross section. In particular, the combination of extinction and refraction convert maxima to minima in the azimuthal-angle dependence of the diffracted intensity, which is commonly used to determine orbital and magnetic structures by resonant x-ray diffraction. We provide a comprehensive theoretical description of these effects by numerically solving Maxwell's equations in three dimensions. The understanding and description of dynamical diffraction enhances the capabilities of resonant x-ray scattering as a probe of electronic ordering phenomena in solids.

Influence of nanocrystalline diamond on resonant properties of gold plasmonic antennas

We report on the influence of a nanocrystalline diamond (NCD) thin film or its segments on optical response of gold plasmonic single and dimer antennas in the visible and near‐infrared. We have simulated optical response of these antennas to the electromagnetic radiation in the wavelength range 500–1500 nm. As the response, we take the localized plasmon resonant wavelength and electric field enhancement around the antennas, localized on the top of NCD films or close to NCD segments. Compared to the antennas on a bare glass substrate, the presence of NCD near the antennas causes a significant red‐shift of the antenna resonant wavelength and slightly decreases the antenna resonant scattering cross section. As for the antenna near‐field, it is more enhanced at the antenna–NCD interface than at the antenna–glass one; however, this field is more confined to the interface.

On the effect of the Coulomb interaction between electrons on the inelastic scattering of light

The Raman scattering by a donor center in a two-dimensional system has been studied theoretically. It has been shown by the example of a donor in a cubic crystal that the inclusion of the electron–electron interaction regardless of its particular form leads to specific polarization dependences of the resonance scattering cross section.

Quantitative spectroscopy on individual wire, slot, bow-tie, rectangular, and square-shaped optical antennas

By using a recently introduced approach combining a focus-modulation technique with a common-path interferometer, we measure quantitatively the extinction, scattering, and absorption cross-section spectra of individual optical antennas. The experimental results on thin-wire antennas, slot antennas, bow-tie antennas, rectangular antennas, and square-shaped antennas resonating at around 1.4 μm wavelength are discussed. We find increased resonant scattering cross sections for the latter four antennas compared to the thin-wire antenna, both in absolute terms and relative to the absorption cross section. The square-shaped antenna's resonant extinction cross section approaches the limit of a coherent point dipole. However, the ratio of the resonant extinction cross section to the geometrical cross section of 38 is largest for the simple thin-wire antenna.

Theory of scattering of electromagnetic waves of the microwave range in a turbid medium

The coefficient of extinction of electromagnetic waves of the microwave range due to their scattering from clusters suspended in an amorphous medium and responsible for turbidity is calculated. Turbidity resembles the case when butter clusters transform water into milk. In the case under investigation, the clusters are conductors (metallic or semiconducting). The extinction coefficient is connected in a familiar way with the cross section of light scattering from an individual cluster. A new formula is derived for the light scattering cross section in the case when damping of oscillations of an electron is due only to spontaneous emission of light quanta. In this case, the resonant scattering cross section for light can be very large. It is shown that this can be observed only in a whisker nanocluster. In addition, the phonon energy on a whisker segment must be higher than the photon energy, which is close to the spacing between the electron energy levels in the cluster.

Plasma screening effects on resonant Compton scattering of photons by excited hydrogenic ions in Lorentzian plasmas

We have carried out calculations to investigate the effects of Lorentzian plasmas on the resonant Compton scattering of photons by the excited state electron of hydrogenic ions using sympletic integration scheme. The resonant scattering cross sections in Lorentizan plasmas between 1s and 2p, 2s and 3p, 2p and 3d states are reported as functions of the spectral index and plasmas parameters. The plasma screening effects are more pronounced with increasing screening strength.

Influence of the laser-induced continuum structure on cross sections of the over threshold scattering of photons on atom

Process of photon scattering on atoms is considered at energy above the ionization threshold. Influence of the resonant structure in the continuum, induced by a laser field due to coupling with the level 41S in helium, on the cross sections of elastic and inelastic scattering of a probe radiation on atom in the meta-stable state 21S is theoretically investigated. In the rotating wave approximation approach dependences of resonant scattering cross sections on the probe and laser radiation characteristics are obtained. The frequency and polarization dependences of the scattering cross sections to the final states of atom 11S, 21S and 41S are calculated.

Total cross sections for dissociative electron attachment to ozone caused by the 2A2 Feshbach resonance

Total resonant cross sections for electron collision with ozone are presented. The results are based on ab initio calculations for the X1A1 target ground state and the 2A2 negative-ion state potential energy surfaces close to the Franck–Condon region. The fixed-nuclei resonance width as a function of collision energy and internuclear distances has been obtained from R-matrix calculations. The nuclear motion has been taken into account employing the Franck–Condon reflection principle. In order to determine the information which is significant for the parametrization of resonant scattering cross sections, the calculations have been carried out at different levels of accuracy. The lifetime of the anionic state with respect to electron detachment was found to be long compared with the fragmentation process. Therefore, the fragmentation probability can be assumed to be equal to 1 and the total cross sections for the formation of the ion can be compared with the experimental cross sections for dissociative electron attachment (DEA). The results confirm the assumption that the prominent structure in the DEA cross sections at 1.3 eV is caused by a metastable 2A2 state of O−3.

Spectrum Shaping of Epithermal Neutron Beam for Accelerator-Based BNCT and Dosimetric Evalution Using a Brain Phantom

Accelerator-based 7Li(p,n)7Be reaction is a favorable way to get neutron source for Boron Neutron Capture Therapy (BNCT). It is widely recognized that epithermal neutrons are more effective than thermal ones in order to treat deep-seated brain tumors with BNCT. For treatment of a deep-seated brain tumor, in addition, it is desirable to use an epithermal neutron beam which has a narrow spectrum concentrated on a specific energy showing good dosimetric properties. With the aim of producing the epithermal neutron beam, various materials for spectrum shaping have been investigated and some dosimetric properties for the beam have been analyzed by using a brain phantom. The neutron source was assumed to be produced from a conventional 2.5 MeV proton accelerator with a thick Li-7 target. All elements with essentially high resonance scattering cross section have been analyzed to determine moderators suitable to spectrum shaping into the useful epithermal neutron beam. Additional uses of Al and, particularly, Ni-60 to the primary moderator, A1F3, were found to be very effective for producing epithermal neutron beams with narrow spectra. The results from dosimetric evaluation indicate that the epithermal neutron beams designed in this study can treat more effectively deep-seated brain tumor.

Effect of the temperature variation of γ-sources on the resonance scattering cross section

The influence of the temperature variation of γ-sources, obtained from neutron capture gamma rays, on the resonance scattering cross section of photons is calculated in detail. The results are used to propose a method for the determination of the temperature of γ-sources from a measurement of scattered intensity ratios from certain scatterers at different temperatures.

Comparison of elastic resonance and elastic recoil detection in the quantification of carbon in SiGeC

The carbon concentrations of chemical vapor deposition grown Si 1− x− y Ge x C y (0.25 < x < 0.37 and 0.01 < y0.12) layers on (100) Si with uniform composition profiles were quantified by two ion analysis techniques. Measurements made with backscattering spectrometry using a 4.295 MeV He 2+ incident ion were compared to compositions predicted by elastic recoil detection (ERD) using a 24 MeV Si 5+ incident ion. To enhance the carbon scattering cross section for the backscattering measurements, the 4.265 MeV 12C(α, α) 12C elastic resonance reaction was used. The carbon concentrations of the films were calculated by integrating the resonant scattering cross section using the energy width of the layer as the limits of integration. The results of this backscattering analysis technique were compared to the predicted carbon concentrations obtained by ERD. It was found that the predictions of these techniques correlated within the uncertainty of each method.

Quantification of carbon in Si 1− x−yGe xC y with uniform profiles

Methods to quantify the carbon concentration of CVD grown Si 1− x−y Ge x C y (0.25 < x < 0.37 and 0.01 < y < 0.12) layers on (100) Si with uniform composition profiles were investigated. Two analysis techniques were used: Rutherford backscattering spectrometry (RBS) using a 4.295 MeV He +2 incident ion and elastic recoil detection (ERD) using a 24 MeV Si +5 incident ion. For the RBS measurements the 12C(α,α) 12C elastic resonance reaction near 4.265 MeV was used to enhance the scattering cross section of carbon. These carbon concentrations were calculated by either integrating the resonant scattering cross section across the energy width of the layer or by using a Lorentzian fit to estimate the area. The backscattering data were additionally analyzed with the program RUMP. These different analysis techniques resulted in a large scatter in the RBS predictions for the carbon concentrations depending on how the resonant cross sectional area was calculated. The appropriateness of each technique was judged by comparing the predicted concentrations to those obtained by ERD. The divergence between the carbon concentration predicted by using the Lorentzian approximation and the ERD values was great enough to deem this method as inappropriate. The values obtained by RUMP were systematically greater than the ERD concentrations, however the percent difference was never more than 20. The predicted carbon concentration that had the closest correlation to ERD was found by integrating an appropriate scattering cross section across the energy width of the layer.

New computer iterative fitting program DVBS for backscattering analysis

A new computer program DVBS for the backscattering (BS) analysis and simulation of the backscattered ions energy spectra was developed. The stimulus was the possibility to calculate the depth concentration profiles from the BS spectra at the specimen interfaces and surfaces to obtain the diffusion coefficients. The program was being developed and improved since December 1989 till 1992, when the last version was finished, and is currently used at IP SAS and LNP JINR. The effects of detector resolution, straggling and non-Rutherford or resonant scattering cross section are included in the program analysis. Using graphics possibilities of a PC computer the program offers a very easy way to handle the data which allows to treat complicated multielement BS spectra and reduce the treatment error down to the theoretical accuracy limit of the method. The great advantage of this program is the possibility to display directly on the screen which part of the spectra corresponds to a given layer of the concentration profile. The interfaces between the layers for a given element in displayed concentration model (or concentration histogram) are linked directly to the corresponding channels in the simultaneously overlapped plots of the theoretically generated and experimentally measured spectra. Thus it is possible to adjust the concentration model on the base of the spectra comparison in a channel region which corresponds to a given layer. With new improved BS techniques, the heavy ions become frequently used. The DVBS can use any type of projectiles from proton to uranium and accepts user's scattering cross section, and stopping powers tabulated in a very simple way. This paper offers the short overview and new aspects and methods of the spectra treatment.