Collisions Of Projectiles Research Articles

R-matrix calculations for elastic electron and positron scattering from pyrazine: effect of the polarization description

We present R-matrix calculations of electron and positron low energy scattering from the highly polarizable pyrazine molecule. We compare integral and differential elastic cross sections with experimental results and assess the quality of the models used for describing collisions of either projectile. Static-exchange-plus-polarization models give a good description of electron scattering (including that of shape resonances), whereas both the integral and small-angle differential cross sections are underestimated for positron collisions for the same models. We discuss whether the absence of a permanent dipole moment improves the comparison with experiment for this molecule, as well as future calculations that may improve the description of polarization effects and thus positron scattering.Graphical abstract

Calculation of energy loss in antiproton collisions with many-electron systems using Ehrenfest's theorem

Energy loss in collisions of charged projectiles with many-electron systems can be dealt with in time-dependent density functional theory by invoking Ehrenfest's theorem for the time evolution of expectation values of observables. We derive an exact expression for the evaluation of energy loss for systems described in a target reference frame, which is a functional of the electron density. Using an approximation scheme, we then apply the expression to antiproton-atom collisions at intermediate and high energies within the framework of the basis generator method. The calculations are performed within the semiclassical approximation for the nuclear motion, and a straight-line trajectory is employed. The energy loss is evaluated from an expectation value of the time derivative of the time-dependent projectile potential, and it avoids the problem of identifying the excited and ionized many-electron contributions in the many-electron wave function. There is also no need to invoke the independent-event model, since the calculations are performed within the framework of the independent-electron mean-field model. Detailed comparisons are provided for net ionization and total energy loss of antiprotons colliding with hydrogen, helium, neon, carbon, nitrogen, and oxygen. Reasonable agreement is found with the results from one-electron and two-electron calculations for atomic hydrogen and helium, and with experiment in the latter case. For the $\overline{p}\text{\ensuremath{-}}\mathrm{Ne}$ system at intermediate collision energies, we find discrepancies with previous work that included only single-electron transitions. The sequence of results for C, N, O, and Ne allows one to paint a consistent picture that awaits experimental verification.

Electron-loss-to-continuum cusp in collisions of U89+ with N2 and Xe

We study the electron-loss-to-continuum (ELC) cusp experimentally and theoretically by comparing the ionization of U$^{89+}$ projectiles in collisions with N$_2$ and Xe targets, at a beam energy of 75.91 MeV/u. The coincidence measurement between the singly ionized projectile and the energy of the emitted electron is used to compare the shape of the ELC cusp at weak and strong perturbations. A significant energy shift for the centroid of the electron cusp is observed for the heavy target of Xe as compared to the light target of N$_2$. Our results provide a stringent test for fully relativistic calculations of double-differential cross sections performed in the first-order approximation and in the continuum-distorted-wave approach.

Eccentric loading effects by projectile collision into fracture behavior of 3-point bending crack specimen

Eccentric loading effects by projectile collision into fracture behavior of 3-point bending crack specimen

The Adhesive Response of Regolith to Low-Energy Disturbances in Microgravity

Abstract Small, airless bodies are covered by a layer of regolith composed of particles ranging from μm-size dust to cm-size pebbles that evolve under conditions very different than those on Earth. Flight-based microgravity experiments investigating low-velocity collisions of cm-size projectiles into regolith have revealed that certain impact events result in a mass transfer from the target regolith onto the surface of the projectile. The key parameters that produce these events need to be characterized to understand the mechanical behavior of granular media, which is composed of the surfaces of small bodies. We carried out flight and ground-based research campaigns designed to investigate these mass transfer events. The goals of our experimental campaigns were (1) to identify projectile energy thresholds that influence mass transfer outcomes in low-energy collision events between cm-size projectiles and μm-size regolith, (2) to determine whether these mass transfer events required a microgravity environment to be observed, and (3) to determine whether the rebound portion of these collision events could be replicated in a laboratory drop tower environment. We found that (1) mass transfer events occurred for projectile rebound accelerations <7.8 m/s2 and we were unable to identify a corresponding impact velocity threshold, (2) mass transfer events require a microgravity environment, and (3) ourdrop tower experiments were able to produce mass transfer events. However, drop tower experiments do not exactly reproduce the free-particle impacts and rebound of the long-duration microgravity experiments and yielded systematically lower amounts of the overall mass transferred.

PHENIX Results on Production in p+Al, p+Au and 3He+Au Collisions

Results are presented of measurements of the modification in p+Au, d+Au and 3He+Au collisions at forward and backward rapidity by the PHENIX experiment. The rapidity, transverse momentum and collision centrality dependence of the modifications are presented, and compared between the three light projectile collision systems. The modification for p+Al is found to be small. For p+Au it is depends strongly on collision centrality at forward rapidity. In both cases models describe the data well. The modifications for d+Au and 3He+Au are very similar to those for p+Au, although there is a hint of slightly increased suppression for 3He+Au over p+Au at backward rapidity.

Selection of projectiles for producing trans-uranium nuclei in transfer reactions within the improved dinuclear system model

The multi-nucleon transfer process is a promising approach for producing neutron-rich heavy nuclei. Its favorable projectile-target combinations play a key role in experiments. As an important theoretical approach to investigate the multi-nucleon transfer process, the dinuclear system (DNS) model is improved and shown in detail. Based on the degree of freedom of the deformation of the improved DNS model, a method of calculating the excitation energies of the primary fragments is proposed, and a remarkable improvement in describing the experimental data is noted. To produce trans-uranium nuclei, the collisions of 48Ca, 136Xe, and 238U projectiles with the 238U target are investigated within the improved DNS model. Based on the potential energy surface, the influence of the projectiles on the probabilities of transferring neutrons and protons from the projectiles to the target are studied. One behavior found is that the transfer probabilities strongly depend on the projectiles in the neutron stripping process, while a relatively weak projectile dependence is seen in the proton transferring process. The 136Xe and 238U projectiles show great advantages of cross sections for producing neutron-rich trans-uranium nuclei, although the fission probabilities are large.

Hypersonic impact flash characteristics of a long-rod projectile collision with a thin plate target

Impact flash occurs when objects collide at supersonic speeds and can be used for real-time damage assessment when weapons rely on kinetic energy to destroy targets. However, the mechanism of impact flash remains unclear. A series of impact flash experiments of flat-head long-rod projectiles impacting thin target plates were performed with a two-stage light gas gun. The impact flash spectra for 6061 aluminum at 1.3–3.2 km/s collision speeds were recorded with a high-speed camera, a photoelectric sensor, and a time-resolved spectrometer. The intensity of the impact flash exhibited a pulse characteristic with time. The intensity (I) increased with impact velocity (V0) according to I∝V0n , where n = 4.41 for V0 > 2 km/s. However, for V0 < 2 km/s, n = 2.21, and the intense flash duration is an order of magnitude less than that of higher V0. When V0 > 2 km/s, a continuous spectrum (thermal radiation background) was observed and increased in intensity with V0. However, for V0 < 2 km/s, only atomic line spectra were detected. There was no aluminum spectral lines for V0 < 2 km/s, which indicated that it had not been vaporized. The initial intense flash was emission from excited and ionized ambient gases near the impact surface, and had little relationship with shock temperature rise, indicating a new mechanism of impact flash.

Electron capture and loss of O+ projectile in collision with water near the Bragg Peak Energies

The combined experimental and theoretical works of the study of the absolute single and double electron loss (stripping) and single and double electron capture cross sections for 0.2–1.2 MeV O+ projectiles colliding with water molecule are presented. In order to mimic the experimental observation we performed three, four and five-body classical trajectory Monte Carlo calculations. In our model the O+ projectile is either one, (two or three) particle(s) depending on the model used (3, 4 or 5 body model, respectively) and the water target is taken into account as two virtual particles. We found that the calculated cross sections are in agreement with the present experimental data. Moreover, the similarity of the present data with an isoelectronic system, the methane molecule allows us to draw a common curve through both data sets.

Systematic Study of Neutron-Rich Rare Isotope Production in Peripheral Heavy-Ion Collisions at Beam Energies 15–25 MeV/nucleon

The production cross sections of projectile-like fragments from collisions of 86Kr projectiles with 64,58Ni and 124,112Sn targets at 15 and 25 MeV/nucleon are studied systematically with emphasis on the neutron-rich isotopes. Our recent experimental data are compared with calculations for the above collisions employing a hybrid approach. The dynamical stage of the projectile-target interaction was described with either the phenomenological deep-inelastic transfer (DIT) model or with the the microscopic constrained molecular dynamics model (CoMD). Subsequently, for the de-excitation of the projectile-like fragments, the statistical multifragmentation model (SMM) or the binary-decay code GEMINI were employed. An overall good agreement with the experimental results was obtained. We point out that our current understanding of the reaction mechanism at beam energies below the Fermi energy suggests that such nuclear reactions, involving peripheral nucleon exchange, can be exploited as a novel route to access extremely neutron-rich rare isotopes toward the r-process path and the hard-to-reach neutron drip-line. For this purpose, we believe that the use of re-accelerated neutron-rich radioactive beams may offer unique and exciting opportunities toward unexplored regions of the nuclear landscape.

Fully differential cross sections for ionization of by ion impact: classical and quantum effects

Single ionization of molecular ions by impact of bare ions is theoretically studied. Fully differential cross sections are calculated by employing the prior version of the continuum distorted wave-eikonal initial state model within an independent electron approximation. It is shown in this work that, under certain conditions there can exist a competition between classical and quantum mechanisms in the ionization reaction that gives rise to the suppression of characteristic classical structures, namely the binary and recoil peaks, from the ionization angular spectra. The existence of destructive quantum interferences due to the coherent emission of electrons from the neighbourhood of both molecular centres may be held as the responsible for the suppression of these classical signatures. Different behaviours are observed depending on whether the ground (gerade) or the first excited (ungerade) states of the target are analysed. Different values of the projectile nuclear charge and collision geometries are considered when calculating FDCS.

Hyperelastic modelling of yarn structures for dynamic applications

Dry fabrics comprised of high performance polymeric fibers have been widely used as protection layers in structures submitted to high velocity impacts (HVI). Their outstanding impact energy dissipation ability combined with an high strength-to-weight ratio make them a preferable choice in different applications such as bullet vests or blade containment systems over standard materials. Among the different approaches adopted to study these structures numerical methods assume a central role. Thanks to their reduced costs and the related possibility of evaluating the effects of single phenomena, they are often used to predict the structure ballistic limits or to study the physical events which occur during the penetration. Among the different strategies adopted to model a fabric, mesoscopic models have been largely adopted by different authors. These models assume the yarns as a continuum body while the fabric geometry is explicitly described. Nowadays yarn material models are universally assumed to be linear elastic and orthotropic. This modelling approach mostly focuses on the longitudinal behaviour of the yarn, however fiber-scale analyses and experimental results shows the importance of three-dimensional stress state on the ballistic limit. In order to obtain a three-dimensional description of the yarn strain state during the impact, a novel hyperelastic model for yarn structures here is developed. In a first step, fiber-level preliminary analyses have been performed to obtain the effective behaviour of these structure under the projectile collision. In the second step, the hyperelastic model has been implemented and identified thanks to microscopic elementary tests. Finally, a continuum model of the yarn have been performed. First results show the relevance of the hyperelastic model compared to the fiber-level observation and enhance the limit of the classical linear elastic material model.

Origins of collectivity in small systems

We review recent developments in the theoretical description and understanding of multi-particle correlation measurements in collisions of small projectiles (p/d/3He) with heavy nuclei (Au, Pb) as well as proton+proton collisions. We focus on whether the physical processes responsible for the observed long range rapidity correlations and their azimuthal structure are the same in small systems as in heavy ion collisions. In the latter they are interpreted as generated by the initial spatial geometry being transformed into momentum correlations by strong final state interactions. However, explicit calculations show that also initial state momentum correlations are present and could contribute to observables in small systems. If strong final state interactions are present in small systems, recent developments show that results are sensitive to the shape of the proton and its fluctuations.

Cumulative Pion Production via Successive Collisions in Nuclear Medium

Production of pions in proton-nucleus (p+A) reactions outside of a kinematical boundary of proton-nucleon collisions, the so-called cumulative effect, is studied. The kinematical restrictions on pions emitted in backward direction in the target rest frame are analyzed. It is shown that cumulative pion production requires a presence of massive baryonic resonances that are produced during successive collisions of projectile with nuclear nucleons. After each successive collision the mass of created resonance may increase and, simultaneously, its longitudinal velocity decreases. Simulations within Ultra relativistic Quantum Molecular Dynamics model reveals that successive collisions of baryonic resonances with nuclear nucleons plays the dominant role in cumulative pion production in p+A reactions.

Two-stage light-gas magnetoplasma accelerator for hypervelocity impact simulation

The development of macroparticles acceleration methods for high-speed impact simulation in a laboratory is an actual problem due to increasing of space flights duration and necessity of providing adequate spacecraft protection against micrometeoroid and space debris impacts. This paper presents results of experimental study of a two-stage light- gas magnetoplasma launcher for acceleration of a macroparticle, in which a coaxial plasma accelerator creates a shock wave in a high-pressure channel filled with light gas. Graphite and steel spheres with diameter of 2.5-4 mm were used as a projectile and were accelerated to the speed of 0.8-4.8 km/s. A launching of particle occurred in vacuum. For projectile velocity control the speed measuring method was developed. The error of this metod does not exceed 5%. The process of projectile flight from the barrel and the process of a particle collision with a target were registered by use of high-speed camera. The results of projectile collision with elements of meteoroid shielding are presented. In order to increase the projectile velocity, the high-pressure channel should be filled with hydrogen. However, we used helium in our experiments for safety reasons. Therefore, we can expect that the range of mass and velocity of the accelerated particles can be extended by use of hydrogen as an accelerating gas.

Using mobile applications for learning: Effects of simulation design, visual-motor integration, and spatial ability on high school students’ conceptual understanding

The purpose of this study was to investigate the effects of simulation design, visual-motor integration, and spatial ability on students’ conceptual understandings of projectile motion and collision. We developed three simulations including two mobile applications (app) and a computer simulation. One app (TA) employed the multi-touch feature for virtual manipulation, the other (TAG) implemented the multi-touch and tilt features, while the computer simulation (CS) was performed using a mouse. 211 10th graders were assigned to the three simulation groups. The results indicated that on the items of basic concepts, the CS and TA groups performed significantly better than the TAG group, whereas for the advanced concepts, the TA and TAG groups scored significantly higher than the CS group. Also, high visual-motor integration students did significantly better on the advanced concepts than low visual-motor integration students. Additionally, the interaction effect between simulation design and spatial ability showed that the two apps had a similar effect on students with different levels of spatial ability. The results suggest that mobile apps could narrow the performance gap between students with different levels of spatial ability, but effective interactions with the multi-touch interface of apps may require new skills such as visual-motor integration.

Consequences of high-xproton size fluctuations in small collision systems atsNN=200GeV

Recent measurements of jet production rates at large transverse momentum ($p_T$) in the collisions of small projectiles with large nuclei at RHIC and the LHC indicate that they have an unexpected relationship with estimates of the collision centrality. One compelling interpretation of the data is that it captures an $x_p$-dependent decrease in the average interaction strength of the nucleon in the projectile undergoing a hard scattering. A weakly interacting or "shrinking" nucleon in the projectile strikes fewer nucleons in the nucleus, resulting in a particular pattern of centrality-dependent modifications to high-$p_T$ processes. We describe a simple one-parameter geometric implementation of this picture within a modified Monte Carlo Glauber model tuned to $d$$+$Au jet data, and explore two of its major consequences. First, the model predicts a particular projectile-species dependence to the centrality dependence at high-$x_p$, opposite to that expected from an energy loss effect. Second, we find that some of the large centrality dependence observed for forward di-hadron production in $d$$+$Au collisions at RHIC may arise from the physics of the "shrinking" projectile nucleon, in addition to impact parameter-dependent shadowing or saturation effects at low nuclear-$x$. We conclude that analogous measurements in recently collected $p$$+$Au and $^3$He$+$Au collision data at RHIC can provide a unique test of these predictions.

Single charge exchange between hydrogen-like projectiles and hydrogen atom: the post version of the BDW-4B approximation

The post version of the four-body Born distorted wave method (BDW-4B) is applied to calculate the total cross section for single electron exchange in the collision of hydrogen-like projectiles with hydrogen atom. The post form of transition amplitude is obtained in terms of two-dimensional real integrals which can be computed numerically. This second-order theory which satisfies the correct boundary conditions is used for the collision of with hydrogen atoms at intermediate and high impact energies. The validity of our results is assessed in comparison with available experimental data and other theories.

Double K-shell ionization of Kr induced by swift Xe54+ ions

SynopsisKα satellite and hypersatellite lines of Kr induced by 52-, 94-, 146-, and 197-MeV/u Xe54+ ions were measured. Experimental values were compared with theoretical ones obtained within the independent electron model (IEM) employing single electron probabilities calculated with the semi-classical approach (SCA). This comparison suggests that first order perturbation approximation is consistent well with the experimental result at 197-MeV/u projectile collision while breaks down for the lower energies.

Performance‐Based Probabilistic Capacity Models and Fragility Estimates for RC Columns Subject to Vehicle Collision

AbstractWith the increasing population and the demand associated with it, the infrastructure and transportation facilities have increased rapidly over the years. The progress has been accompanied by an increasing number of vehicle collisions with structures. This type of collision might lead to the damage and sometimes collapse of the structures. In reinforced concrete (RC) structures, columns are usually the most vulnerable members exposed to collisions. However, the existing design guidelines and provisions for protection of these members against collision of vehicles are not adequate. In particular, the desired behavior and the associated performance levels of a structure during a vehicle collision are not defined. Therefore, there is a need to assess the vulnerability of structures against such collisions. This article develops performance‐based probabilistic models for the dynamic shear force capacity of RC columns in bridges and buildings. A framework is also developed to estimate the fragility of the RC columns subject to vehicle collision. The developed probabilistic dynamic shear force capacity models can be used for a performance‐based design of structures such as buildings and bridges. The developed framework can be used to estimate the adequacy of a structure to sustain a collision event and make recommendations for repair and retrofit. Proposed approach can be applied to study similar cases of collision such as ship collision to bridge piers, projectile collision into concrete walls and develop adequate models.