Wave Eikonal Initial State Approximation Research Articles

Radiobiological effectiveness of iodouracil and the influence of atomic giant resonance

Hadron therapy combined with nanotechnology has been proposed as an elegant alternative for cancer treatment. Internal amplification of electron emission causing radiobiological effectiveness in nanoinserted biomolecules is of prime importance and has been measured here for the iodouracil molecule. Our experiment involves the measurement of angle and energy resolved double differential cross section (DDCS) of electron emission from iodouraciil and uracil (and also water) in collisions with fast ${\mathrm{C}}^{6+}$ ions. The electron emission from iodouracil is substantially enhanced over that from uracil or water. The enhancement is much larger than the state-of-the-art model for Coulomb ionization based on the continuum distorted wave-eikonal initial state (CDW-EIS) approximation. The electron sensitizing factor ($\ensuremath{\approx}2.4$) is in excellent agreement with the strand-breaking sensitizing factor ($\ensuremath{\approx}2.0$) for metal nanoparticle embedded in a DNA. The enhancement is explained in terms of collective excitation of strongly correlated 4d electrons, known as atomic giant dipole resonance (GDR) in I atoms. The GDR contribution to the enhancement is derived, which is in excellent agreement with recent theoretical prediction, thereby providing conclusive experimental evidence of the crucial role of collective excitation in radio sensitization.

Ionization of pyrimidine molecule induced by proton

SynopsisIn the present study will be investigated the ionization of isolated pyrimidine molecules induced by ions. The total and differential cross section have been computed with a quantum mechanical method within the continuum distorted wave-eikonal initial state (CDW-EIS) approximation. A comparison with the available data is presented.

Electron emission induced by Helium ions on water molecule

SynopsisThis study focuses on the electron emission induced by He ions on water molecule. In this context, the ionization and the electron capture processes will be investigated using a quantum mechanical description within the continuum distorted wave-eikonal initial state (CDW-EIS) approximation.

Absolute total cross sections of multiple electron processes for molecules of biological interest by fast proton impact

SynopsisWe present the study of multiple electron processes produced by impact of proton beams on molecular targets from intermediate to high projectile impact energies. Transition probabilities and absolute cross sections were determined by using the Continuum Distorted Wave-Eikonal Initial State approximation. Results were compared with previous calculations and also with recent experimental data.

Electron emission cross sections for collisions of heavy ions with atomic targets

A theoretical study of the double-differential cross sections (DDCS) for ejection of electron from hydrogen atom in ground state by the impact of $$\hbox {C}^{6+}$$ ion with energy values 1 and 2.5 MeV/amu is presented. For the final state, we use a continuum distorted wave that contains the product of two Coulomb distortions due to the projectile–electron and target–electron Coulombic interactions for which it is called the two-Coulomb-wave (2CW) model. In this paper, the energy and angular distributions of DDCS for electron emission from atomic hydrogen have been investigated. The ejected electrons are influenced by the combined fields of the target and the projectile ion. Comprehensive comparisons are made between the three-Coulomb-wave model (Jana et al. in Eur Phys J D 66:243, 2012) and the present 2CW model. The emitted electron, the incident projectile ion and the residual ion are considered to be in the same plane. It is found that the two-centre effect has a major influence on the observed forward–backward angular asymmetry in the angular distribution of electron emission spectra. The region of the binary encounter peak is analysed in detail. The present computed results have been compared with the available experimental results as well as other theoretical calculations based on the first Born approximation and the continuum distorted wave eikonal initial state approximation. Moreover, the present computed results are in better agreement with the available experimental data for electron emission cross sections.

Single- and multiple-electron processes in water molecules colliding with proton beams

Single- and multiple-electron removal processes (ionization, capture and transfer-ionization) from water molecules by the impact of protons have been studied. A prior version of the three-body continuum distorted wave-eikonal initial state (3B-CDW-EIS) approximation within the independent electron approximation is used to calculate transition probabilities as a function of the impact parameter and consequently pure and net absolute cross sections for the collisions under consideration. A unitarization procedure is employed to avoid possible overestimation of the 3B-CDW-EIS single-particle impact parameter probabilities at intermediate collision energies. Multiple-electron transitions are determined using a statistical multinomial distribution. A critical analysis of the validity of this type of distribution for describing pure single-electron processes is presented. The results are compared with other theoretical calculations and available experimental data at impact energies from 50 keV to 5 MeV. New physical insights into the reactions studied are introduced.

Reprint of: Ionization probabilities of Ne, Ar, Kr, and Xe by proton impact for different initial states and impact energies

In this contribution we present ab initio results for ionization total cross sections, probabilities at zero impact parameter, and impact parameter moments of order +1 and −1 of Ne, Ar, Kr, and Xe by proton impact in an extended energy range from 100 keV up to 10 MeV. The calculations were performed by using the continuum distorted wave eikonal initial state approximation (CDW-EIS) for energies up to 1 MeV, and using the first Born approximation for larger energies. The convergence of the CDW-EIS to the first Born above 1 MeV is clear in the present results. Our inner-shell ionization cross sections are compared with the available experimental data and with the ECPSSR results. We also include in this contribution the values of the ionization probabilities at the origin, and the impact parameter dependence. These values have been employed in multiple ionization calculations showing very good description of the experimental data. Tables of the ionization probabilities are presented, disaggregated for the different initial bound states, considering all the shells for Ne and Ar, the M-N shells of Kr and the N-O shells of Xe.

Ionization probabilities of Ne, Ar, Kr, and Xe by proton impact for different initial states and impact energies

In this contribution we present ab initio results for ionization total cross sections, probabilities at zero impact parameter, and impact parameter moments of order +1 and −1 of Ne, Ar, Kr, and Xe by proton impact in an extended energy range from 100keV up to 10MeV. The calculations were performed by using the continuum distorted wave eikonal initial state approximation (CDW-EIS) for energies up to 1MeV, and using the first Born approximation for larger energies. The convergence of the CDW-EIS to the first Born above 1MeV is clear in the present results. Our inner-shell ionization cross sections are compared with the available experimental data and with the ECPSSR results. We also include in this contribution the values of the ionization probabilities at the origin, and the impact parameter dependence. These values have been employed in multiple ionization calculations showing very good description of the experimental data. Tables of the ionization probabilities are presented, disaggregated for the different initial bound states, considering all the shells for Ne and Ar, the M-N shells of Kr and the N-O shells of Xe.

Multiple electron processes from H2O by He2+ and Li3+ impact

SynopsisWe employ the Continuum Distorted Wave-Eikonal Initial State approximation for He2+ and Li3+ ions impacting on water vapor targets to study multiple electron removal processes at the intermediate to high projectile energy range. Transition probabilities and absolute cross sections for pure ionization, capture and transfer-ionization channels were calculated. Results are compared with previous calculations and recent experimental data.

Proton impact fragmentation of water molecules

SynopsisThe Continuum Distorted Wave-Eikonal Initial State approximation for impact of H+ on H2O molecules is used to calculate absolute cross sections for multiple electron removal processes at intermediate and high collision energies. Resulting fragmentation patterns are also matter of study. Results are compared with previous calculations and available experimental data.

Total Ionization Cross Sections in Particle and Antiparticle Collisions with Rare Gases

In this contribution we analyze the total ionization cross sections by impact of electrons, positrons, protons and antiprotons in Ne, Ar, Kr and Xe. We compare theoretical results using the continuum distorted wave eikonal initial state approximation with a detailed compilation of the available experimental data for the four projectiles in each target. The charge and mass effects, and the convergence at intermediate energies are discussed, which are important issues for antiparticle normalization. We remark the influence of the post-collisional Auger-like electron emission, which is decisive to describe the total ionization of Kr and Xe at impact velocities above9 a.u.

Differential electron emission in the ionization of Ne and Xe atoms under fast bare carbon ion impact

Measurement of the energy and angular distributions of the double differential cross section (DDCS) of electron emission from Ne and Xe atoms in collision with 5 MeV u−1 bare carbon ions is reported. This study aimed to investigate the electron emission processes in the case of multi-electronic systems. In general, several clear differences between the electron emission spectra of Ne and Xe are found, which indicate the influence of the increasing number of electrons. For instance, the sharp peak due to the binary nature of collision is almost absent in the case of Xe, unlike Ne, which could be understood due to the increasing contribution from the strongly bound inner shell (such as ) electrons for the Xe atom. The forward–backward angular asymmetry has also been derived from the angular distributions. For Xe, the qualitative behaviour of the asymmetry parameter is seen to be quite different since it reveals structures due to Auger contributions. It is, in general, different and much lower than that for Ne, which shows the smooth behaviour that one finds for other lighter atoms like He. The single differential and total cross sections are also derived. The theoretical calculations based on the prior form of the continuum distorted wave-eikonal initial state (CDW-EIS) approximation have been provided for both the targets. Overall, it gives a very good agreement with the energy and the angular distributions of DDCS for Ne. For Xe, the agreement is not as good as for Ne. We also provide a detailed discussion on the DDCS obtained from different sub-shell ionization, estimated in this framework.

The dependence of the forward-backward asymmetry parameter on the molecular orientation in angular distributions of emitted electrons in the H2 ionisation induced by bare ion impact

We have studied the angular distributions of electron emission in collisions of bare ions with H2 oriented target using molecular wave functions calculated with the Schwinger variational iteractive method within the Continuum Distorted Wave-Eikonal Initial State approximation (CDW-EIS-SVIM). By calculating the forward-backward asymmetry parameter for different molecular orientations we show that this parameter depend not only on the perturbation strength, Sp = Zp/vp, where Zp and vp are respectively the projectile charge and velocity (two-centre effect) and on the outgoing electron velocity, but may also depend on how the molecule is aligned with respect to the projectile incident axis. Doubly differential cross sections (DDCS) for fixed in space molecular target were calculated. The asymmetry parameter was compared with both experimental and theoretical orientation averaged results.

Effectiveness of projectile screening in single and multiple ionization of Ne by B2+

Pure multiple ionization cross sections of Ne by B${}^{2+}$ projectiles have been measured in the energy range of 0.75 to 4.0 MeV and calculated using the continuum distorted wave-eikonal initial state approximation. The experiment and calculations show that the ionization cross sections by B${}^{2+}$, principally for the production of highly charged recoils, is strongly enhanced when compared to the bare projectile with the same charge state, He${}^{2+}$, at the same velocities.

CDW-EIS calculations for multiple ionization of Ne, Ar, Kr and Xe by the impact of H+ and He+, including post-collisional electron emission

We present theoretical single to quintuple ionization cross sections for Ne, Ar, Kr and Xe bombarded by H+ and He+. Post-collisional contributions due to Auger-like processes are taken into account using recent photoionization data. The present continuum distorted wave-eikonal initial state (CDW-EIS) and first Born approximation results are compared with the experimental data available in the energy range of 50–10 000 keV amu−1 for H+ on Ne and Ar, and 50–1000 keV amu−1 for the other cases. In general, the combination of the CDW-EIS with the post-collisional branching ratios describes well the multiple ionization data above 300 keV amu−1, showing a clear tendency to coalesce with the first Born approximation at high energies. The surprising result of this work is the good performance of the first Born approximation which describes rather well the experimental data of double and triple ionization, even in the intermediate energy range (50–300 keV amu−1), where direct ionization is the dominant contribution.

Review of theories on double electron capture in fast ion-atom collisions

This work reviews quantum-mechanical four-body distorted wave theories for double electron capture in collisions between fast heavy multiply charged ions and heliumlike atomic systems. The widely used distorted wave methods of the first- and second-order in the pertinent perturbation series expansions are compared with each other. This tests the presumed importance of double continuum intermediate states of two electrons. Further, the relative performance is evaluated of the second-order theories with and without the eikonalization of the two-electron Coulomb wave functions for double continuum intermediate states. This checks the correctness and usefulness of the eikonalized Coulomb waves when two electrons participate actively to the transition from the initial to the final state of the entire system. We also analyze the significance of the contributions from excited heliumlike states especially in comparison between theory and measurement. The overall goal of the present study is to determine how much of the unprecedented experience gained over several decades in studying high-energy theories of pure three-body charge exchange could be exported directly to four-body double-electron capture without much of additional and essential eleaborations, besides the naturally increased computational demand. In particular, we address the unexpected breakdown of the continuum distorted wave eikonal initial state approximation and the anticipated success of continuum distorted wave theory for double charge exchange in ion-atom collisions at high impact energies.

Angular and energy differential electron emission cross sections in collisions between antiprotons and helium atoms

We present theoretical singly- and doubly-differential ionization cross sections in collisions between antiprotons and helium atoms at 50 and 100 keV impact energies. The calculations were performed within the frame work of the continuum distorted wave eikonal initial state approximation and a three-body classical trajectory Monte Carlo method. We find clear evidence for the formation of the anti-cusp in the differential distributions.

Double differential distributions of electron emission in ion–atom and electron–atom collisions using an electron spectrometer

We study electron emission from atoms and molecules in collisions with fast electrons and heavy ions (C 6+). The soft collision electrons (SE), two center electron emission (TCEE), the binary encounter (BE) events and the KLL Auger lines along with the elastically scattered peaks (in electron collisions) are studied using a hemispherical electrostatic electron analyzer. The details of the measurements along with description of the spectrometer and data acquisition system are given. The angular distributions of the low energy (few eV) electrons in soft collisions and the binary encounter electrons at keV energies are compared with quantum mechanical models based on the first Born (B1) and the continuum distorted wave-Eikonal initial state approximation (CDW-EIS).

New approach on molecular ionization by ion impact: the CDW-EIS-SVIM model

We have extended the continuum distorted wave eikonal initial state approximation for single ionization of atoms by ion impact to the molecular case where a model potential for the molecular target is introduced. The continuum wavefunctions of the ejected electrons are then calculated in the static-exchange potential field generated by the residual molecular ion. The Schwinger variational iterative method was used in the calculation of these continuum wavefunctions. We apply this model to the single ionization of the hydrogen molecule (H2) by different bare projectiles. Doubly differential cross sections are calculated and compared with available experimental data for intermediate impact energies.

Single electron capture in ion–atom collisions involving multielectronic targets

The generalized continuum distorted wave-eikonal initial state (GCDW-EIS) approximation is employed to study single electron capture by impact of protons on Ne and Ar targets. We analyze the contributions to the total cross sections coming from the different target shells. Present results are compared with theoretical calculations obtained using the previous CDW-EIS formulation and to experimental data in order to show the importance of the description of the bound and continuum target states in the entry and exit channels, respectively.