Strong Absorption Model Research Articles

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.

Total reaction cross sections of neutron-rich light nuclei measured by the COMBAS fragment-separator

Preliminary results of measurements of the total reaction cross sections σR for nuclei 4He, 6He, 8He, 7Li, 8Li, 9Li, 1Li, 11Be, 9Be, 10Be, 11Be, 12Be, 8B, 10B, 11B and 12B nuclei at energy range (10-50) A MeV with 28Si target is presented. The secondary beams of light nuclei were produced by bombardment of the 15N (50 A MeV) primary beam on Be target and separated by COMBAS fragment-separator. In dispersive focal plane a horizontal slit defined the momentum acceptance as 1% and a wedge degrader of 600 μm Al was installed. The Bρ of the second section of the fragment-separator was adjusted for measurements in energy range (10-45) A MeV. The strong absorption model reproduces the A-dependence of ψR, but not the detailed structure. We are comparing our experimental data with predictions of microscopic (dashed line) and strong absorption model, Glauber multiple scattering theory and preliminary results are obtained.

Total reaction cross sections of neutron-rich light nuclei measured by the COMBAS fragment-separator

Preliminary results of measurements of the total reaction cross sections σ R for nuclei 4 He, 6 He, 8 He, 7 Li, 8 Li, 9 Li, 11 Li, 7 Be, 9 Be, 10 Be, 11 Be, 12 Be, 8 B, 10 B, 11 B and 12 B nuclei at energy range (10-50) AMeV with 28 Si target is presented. The secondary beams of light nuclei were produced by bombardment of the 15N (50 AMeV) primary beam on Be target and separated by COMBAS fragment- separator. In dispersive focal plane a horizontal slit defined the momentum acceptance as 1% and a wedge degrader of 600 µm Al was installed. The B ρ of the second section of the fragment-separator was adjusted for measurements in energy range (10-45) AMeV. The strong absorption model reproduces the A-dependence of σ R , but not the detailed structure. We are comparing our experimental data with predictions of microscopic (dashed line) and strong absorption model, Glauber multiple scattering theory and preliminary results are obtained.

Strong absorption model with antisymmetric S-matrix

We present a strong absorption model with an [Formula: see text]-matrix in a new form of an antisymmetrized Fermi distribution for describing diffraction patterns of neutron–nucleus scattering at intermediate energies. The proposed antisymmetric [Formula: see text]-matrix has a form close to the conventional one and allows to obtain exact analytical expressions for the damping factor that determines the elastic scattering amplitude and the total cross-sections for interaction, reactions and elastic scattering. The use of an antisymmetrized Fermi function instead of the usual Fermi function in successful strong absorption models basically does not notably affect the calculated nucleon–nucleus elastic scattering differential cross-sections in the intermediate energy region.

A study of the nucleus-nucleus total reaction cross section of stable systems at intermediate energies: An application to 12C

A semi-microscopic analytical expression of the nucleus-nucleus total reaction cross section (σR) was proposed based on the strong absorption model. It is suitable for stable nuclei at intermediate energies. The matter density distributions of nuclei and the nucleon-nucleon total cross section were both considered. Particularly, the Fermi motion effect of the nucleons in a nucleus was also taken into account. The parametrization of σR was applied to the colliding systems including 12C. The experimental data at energies from 30 to 1000 MeV/nucleon were well reproduced, according to which an approach of deriving σR without adjustable parameters was developed. The necessity of considering the Fermi motion effect in the parametrization was discussed.

Strong Absorption model for the studying of Pion-Nuclei Elastic Scattering

Strong Absorption model for the studying of Pion-Nuclei Elastic Scattering

Regge pole analysis of elastic scattering of α particles by even isotopes of Ni target nuclei at incident energies above Coulomb barrier

Regge pole model is adopted to account for the angular distribution at backward angles for a set of elastic scattering processes of incident [Formula: see text]-particles by different isotopes of nickel ions, [Formula: see text]Ni, at different laboratory energies above Coulomb barrier. The reproduction of cross-sections at backward angles is preceded by an attempt to fit the experimental data at forward angles of the scattering. Three-parameter McIntyre model which is based on concept of strong absorption parametrization of the scattering matrix elements, has been employed to analyze and reproduce the experimental data of angular distribution of different elastic scattering reactions at forward angles. The three parameters extracted from McIntyre model analysis are employed as fixed entries in the fitting process of the full angle-range of angular distribution where another four free parameters are employed using the Regge pole model. Diffractive features observed in the angular distributions are studied. The Fresnel-type diffraction pattern is found dominant for all investigated elastic scatterings where Coulomb interaction is strong. The interaction radius of elastic scattering is found decreasing and the total cross-section increasing when the incident projectile energy increases. Moreover, the interaction radius and total reaction cross-section are found increasing with the increase in the size of target ion. Such diffractive behavior is consistent with the prescriptions of strong absorption model (SAM). Furthermore, the explanation of the diffractive features of studied elastic scattering reactions is model-independent. The Regge pole analysis reveals the existence of a pole which has its location, width, amplitude and phase angle exhibiting a common peak at energy of 24.1[Formula: see text]MeV with oscillatory behaviour at energies around this peak energy, for all elastic scattering of alpha particle on isotopes of Ni targets except that of [Formula: see text]Ni target which exhibits extra peaks for energy larger than 24.1[Formula: see text]MeV. We believe that the presence of poles is responsible for the oscillatory structure of the backward cross-sections. The variation of Regge pole parameters with both incident energy and size of target nucleus is illustrated.

A Study of The Alpha – Nucleus Scattering

Angular distribution data for the elastic scattering of 1.37 GeV alpha particles from several nuclei are analyzed in terms of the three parameter strong absorption model of Frahn and Venter. The fits are quite satisfactory over practically the entire angular range and the best fit parameters are obtained. These are used for the study of the inelastic scattering of alpha particles leading to the collective states in nuclei. A reasonably good fit is obtained without any adjustment of the parameters suggesting thereby the success of the strong absorption model. Deformation parameters are extracted for the collective states in nuclei.
 Asiat. Soc. Bangladesh, Sci. 40(2): 249-258, December 2014

Comprehensive analysis of fusion data well above the barrier

We report on the comprehensive systematics of nearly 400 fusion-evaporation and/or fusion-fission cross-section data for a very large variety of systems over an energy range $\ensuremath{\sim}3A$ to $155A$ MeV. Scaled by the reaction cross section and expressed as a function of the center-of-mass energy per nucleon, the fusion cross section displays a universal behavior. Within experimental errors, this behavior does not depend on system mass, mass asymmetry, or system isospin. The deduced homographic functional dependence for complete and summed complete and incomplete fusion excitation functions is derived from basic strong absorption model formulas for reaction cross sections and allows us to draw the main properties of these functions. The limiting energy for the complete fusion and the main characteristics (onset, maximum, and extinction) of the incomplete fusion excitation functions are determined. The complete fusion reaction process disappears around 6.5 MeV/nucleon and the incomplete one disappears at about 13 MeV/nucleon in the center-of-mass frame. The regularity in fusion data is particularly obvious for the evaporation-residue subset of the data ensemble. Adding the fusion-fission data component does not alter the general data trend but somewhat obscures it owing to the larger uncertainty and/or possible normalization problems.

A STUDY OF SCATTERING OF ALPHA PARTICLES FROM NUCLEI

The angular distribution data for the elastic scattering of 100–172.5 MeV isoscalar alpha particles from several nuclei between 16 O and 208 Pb are studied within the framework of the strong absorption model due to Frahn and Venter. The best fit parameter values of the nuclear interaction are determined. These are then used to analyze the inelastic scattering of alpha particles leading to the excitation of the 2+ and 3- collective states in the target nuclei and the corresponding deformation parameters are extracted. A reasonably good account of both elastic and inelastic scattering is given by the same set of parameter values derived from the analyses of the elastic scattering.

Reaction and proton-removal cross sections ofLi6,Be7,B10,C9,10,11,N12,O13,15, andNe17on Si at 15 to 53 MeV/nucleon

Excitation functions for total reaction cross sections, $\sigma_R$, were measured for the light, mainly proton-rich nuclei $^6$Li, $^7$Be, $^{10}$B, $^{9,10,11}$C, $^{12}$N, $^{13,15}$O, and $^{17}$Ne incident on a Si telescope at energies between 15 and 53 MeV/nucleon. The telescope served as target, energy degrader and detector. Proton-removal cross sections, $\sigma_{2p}$ for $^{17}$Ne and $\sigma_p$ for most of the other projectiles, were also measured. The strong absorption model reproduces the $A$-dependence of $\sigma_R$, but not the detailed structure. Glauber multiple scattering theory and the JLM folding model provided improved descriptions of the measured $\sigma_R$ values. $rms$ radii, extracted from the measured $\sigma_R$ using the optical limit of Glauber theory, are in good agreement with those obtained from high energy data. One-proton removal reactions are described using an extended Glauber model, incorporating second order noneikonal corrections, realistic single particle densities, and spectroscopic factors from shell model calculations.

George Wells Farwell

George Wells Farwell

STRONG ABSORPTION MODEL STUDIES OF PION-NUCLEUS SCATTERING AROUND THE Δ RESONANCE

Angular distribution data on the elastic scattering of pions are studied on several nuclei around the Δ resonance in terms of the three-parameter strong absorption model of Frahn and Venter. The parameters thus obtained are used in the analyses of inelastic scattering of pions leading to the lowest as well as higher lying 2+ and 3- states, and the corresponding deformation parameters are extracted.

A Study of Semi-Classical Processes in the Elastic Scattering of 32 S by 64 Ni and 58 Ni by 27 Al

In order to determine the extent of the presence of semi-classical phenomena such as Fresnel and Fraunhofer patterns etc., we have analyzed the elastic scattering of 32S by 64Ni and 58Ni by 27Al using the McIntyre parametrization at several energies. The theoretical approach can reasonably account for the general pattern of the data, thus allowing us to extract the parameters pertinent to these semi-classical processes. The scattering of 58Ni by 27Al at 220, 185, 170, 160 and 155 MeV laboratory energies, exhibits features expected from the strong absorption model (SAM). However, the features of the scattering of 32S by 64Ni at 150, 108, 98, 93, 91, 88 and 82 MeV laboratory energies have significant deviation from the expected pattern of SAM.

Improved nearside-farside method for elastic scattering amplitudes

A simple technique is described, that provides improved nearside-farside (NF) decompositions of elastic scattering amplitudes. The technique, involving the resummation of a Legendre partial wave series, reduces the importance of unphysical contributions to NF subamplitudes, which can arise in more conventional NF decompositions. Applications are made to a strong absorption model and to a $^{16}$O + $^{12}$C optical potential at $E_{\text{lab}} = 132$ MeV.

GENERALIZED DIFFRACTION MODEL STUDY OF INTERMEDIATE ENERGY PROTON-NUCLEUS SCATTERING

The three-parameter strong absorption model of Frahn and Venter is used to study elastic scattering of intermediate energy protons from several nuclei between 12 C and 208 Pb and the best-fit parameters are obtained and their systematics are discussed. The inelastic scattering of protons is then studied and the deformation parameters are extracted. A reasonably good account of both elastic and inelastic scattering is given by the same set of parameter values.

Diffractive scattering in the Ericson model for the S matrix

The elastic scattering of spinless charged particles on nuclei is considered within the strong-absorption model proposed by Ericson for the S matrix in the angular-momentum representation. Our analytic method for summing partial-wave amplitudes, which is based on a generalization of the Abel-Plana formula, makes it possible to take into account the contributions from the possible singularities of the S matrix in the right-hand half-plane of the complex-valued variable l. The uniform asymptotic behavior obtained in the present study for the scattering amplitude offers a fresh view on the origin of the diffraction patterns in the angular distributions of elastically scattered heavy particles. Special attention is given to Coulomb-nuclear interference (in particular, to refraction phenomena) in the case of scattering into the classically allowed region (illuminated region) and the classically forbidden region (shadow region). In contrast to other analytic results, our solutions to the diffraction problem within the Ericson model do not give grounds whatsoever to draw profound analogies either with Fresnel diffraction in optics or with the phenomenon of rainbow scattering in classical mechanics.

Unified optical-model approach to low-energy antiproton annihilation on nuclei and to antiprotonic atoms

A successful unified description of p ̄ nuclear interactions near E=0 is achieved using a p ̄ optical potential within a folding model, V opt ∼ v ̄ ∗ρ , where a p ̄ p potential v ̄ is folded with the nuclear density ρ. The potential v ̄ fits very well the measured p ̄ p -annihilation cross sections at low energies ( p L<200 MeV /c) and the 1s and 2p spin-averaged level shifts and widths for the p ̄ H atom. The density-folded optical potential V opt reproduces satisfactorily the strong-interaction level shifts and widths over the entire periodic table, for A>10, as well as the few low-energy p ̄ -annihilation cross sections measured on Ne. Both v ̄ and V opt are found to be highly absorptive, which leads to a saturation of reaction cross sections in hydrogen and on nuclei. Predictions are made for p ̄ -annihilation cross sections over the entire periodic table at these very low energies and the systematics of the calculated cross sections as function of A, Z and E is discussed and explained in terms of a Coulomb-modified strong-absorption model. Finally, optical potentials which fit simultaneously low-energy p ̄ − 4 He observables for E<0 as well as for E>0 are used to assess the reliability of extracting Coulomb modified p ̄ nuclear scattering lengths directly from the data. The relationship between different kinds of scattering lengths is discussed and previously published systematics of the p ̄ nuclear scattering lengths is updated.

Backangle anomaly in scattering of [formula omitted] -particles from [formula omitted] Si at low energies

In order to resolve the differences in the literature on the existence of quasi-molecular states in the α - 28 Si system, excitation functions were measured for the scattering of α -particles from 28 Si in the incident energy range E lab =3 –7.8 MeV. An angular distribution measurement was carried out in the angular range θ lab =30° –174.5 ° for every potential resonance observed in the excitation functions. Data was analysed using a Regge-pole formalism by coherently adding specific resonances to an underlying diffraction term calculated by a strong absorption model. Furthermore, the usual compound elastic contribution was incoherently added to the direct interaction part of the cross section. The 6.8 MeV resonance was confirmed with J=3 and some evidence was observed for a J=1 resonance around 6.0 MeV.

Structures in the12C(16O,12C(02+)→3α)16Oreaction in the regionEc.m.=15to 34 MeV

A study of the ${}^{12}\mathrm{C}{(}^{16}\mathrm{O}{,}^{12}\mathrm{C}{(0}_{2}^{+}){)}^{16}\mathrm{O}$ reaction over the energy interval ${E}_{\mathrm{c}.\mathrm{m}.}=15--34 \mathrm{MeV}$ has been performed. A simple reaction model based on the strong absorption model with the coherent addition of a single partial wave has reproduced the main features of the excitation function. The model further suggests that two broad structures around 24 and 26.5 MeV arise from the low resolution observation of two or more overlapping peaks. With the possible exception of two $J=12$ enhancements at 23.4 and 24.2 MeV, none of the structures have been definitively identified as resonances.