Low Projectile Energies Research Articles

Experimental cross sections for electron loss from 0.1 to 1.0 MeV O+ and 0.2-1.5 MeV O2+ and electron capture to 0.05-1.0 MeV O+ and 0.1-1.5 O2+ in SF6

Experimentally determined single and double-electron-capture and single and double projectile stripping cross sections are presented for intermediate and low projectile energies (0.1 – 1.5 MeV) Oq+ (q = 1,2) on SF6 gaseous target. These cross-section data are useful for the simulation of ion–neutral processes in Earth's atmosphere and to improve existing theoretical models.

Low energy ion-solid interactions: a quantitative experimental verification of binary collision approximation simulations

Ultra-low energy ion implantation has become an attractive method for doping of two-dimensional materials and ultra-thin films. The new dynamic Monte Carlo program IMINTDYN based on the binary collision approximation allows a reliable prediction of low energy implantation profiles and target compositional changes, as well as efficient simulation of high energy light ion scattering. To demonstrate the quality of these predictions and simulations, we present a model case experiment where we implanted W ions into tetrahedral amorphous carbon with low (10 keV) and ultra-low (20 eV) ion energies and analyzed the W implantation profiles with high resolution Rutherford backscattering spectrometry (HR-RBS). This experiment is compared with a complete simulation of all aspects of ion-solid-interactions of the experiment using the new IMINTDYN program. A unique novel simulation option, also relevant for implantation into 2D materials, is the inclusion of the vacancy as target species with dynamic vacancy generation and annihilation. Whereas simulations neglecting vacancy formation cannot reproduce the measured implantation profiles, we find excellent agreement between simulated and measured HR-RBS spectra. We also demonstrate the important role of simultaneous weak collisions in the binary collision approximation at low projectile energies.

Effects of semicore electrons on stopping power in helium-irradiated aluminum nanosheets.

The stopping power of energetic He ions traversing an Al film is studied by combining the time-dependent density-functional theory method with molecular dynamics simulations. We investigated the dependence of the semicore electron excitation of the Al film on the projectile's trajectory and its charge state. Our results show that for the off-channeling trajectories the semicore electrons contribute significantly to the stopping power of the Al film as the He+ ion velocity exceeds 1.0 a.u, and in contrast, it is negligible for the channeling trajectories. Most importantly, we found two unexpected effects of semicore electrons on the stopping power in helium-irradiated aluminum nanosheets, i.e., (1) the semicore electrons can contribute to the energy loss for both high and low energy projectiles under the off-channeling trajectory; (2) as the projectile velocity increases from 0.4 a.u. to 2.0 a.u. although semicore electron excitation (including transition in the target, ionization away from the target and transfer to the projectile ion) of the target atom is gradually inhibited, the influence of semicore electrons on valence electron excitation is gradually enhanced. Our finding allows us to gain new insights into the stopping of ions in metals.

Dendrite Formation on the Poly(methyl methacrylate) Surface Reactively Sputtered with a Cesium Ion Beam.

The development of topography plays an important role when low-energy projectiles are used to modify the surface or analyze the properties of various materials. It can be a feature that allows one to create complex structures on the sputtered surface. It can also be a factor that limits depth resolution in ion-based depth profiling methods. In this work, we have studied the evolution of microdendrites on poly(methyl methacrylate) sputtered with a Cs 1 keV ion beam. Detailed analysis of the topography of the sputtered surface shows a sea of pillars with islands of densely packed pillars, which eventually evolve to fully formed dendrites. The development of the dendrites depends on the Cs fluence and temperature. Analysis of the sputtered surface by physicochemical methods shows that the mechanism responsible for the formation of the observed microstructures is reactive ion sputtering. It originates from the chemical reaction between the target material and primary projectile and is combined with mass transport induced by ion sputtering. The importance of chemical reaction for the formation of the described structures is shown directly by comparing the change in the surface morphology under the same dose of a nonreactive 1 keV xenon ion beam.

Study of incomplete fusion reaction dynamics for the system 14N + 169Tm using the forward Recoil Range distribution technique

Studies in the past have demonstrated that complete fusion and incomplete fusion (ICF) dynamics are both significant just above the Coulomb barrier, yet the dynamics of ICF are elusive since they are so complex below 10 MeV/nucleon. In order to investigate low-energy ICF dynamics, we measured the forward recoil range distribution (FRRD) of evaporation residues (ERs) populated in the system 14N + 169Tm at energy ≈5.9 MeV/nucleon. A stack target-catcher activation technique followed by offline-γ-spectroscopy was used to estimate the FRRD of the ERs. In order to investigate a new parameter for describing ICF dynamics, the ICF fraction (F ICF(%)) for the present system was estimated from the range-integrated cross-sections and compared with other systems in the literature. The FRRD and range integrated cross-sections of seven ERs have been estimated experimentally. These cross-section results agree well with the experimental results obtained from the excitation functions. On re-investigation of entrance channel systematics for Q α -value of projectile, mass-asymmetry (μ MA), and Coulomb factor (Z P Z T), it has been found that the Q α -value systematic for 14N is not valid at all projectile energies. The FRRD measurement is one of the direct methods available to probe the complete and ICF contributions in ERs at low projectile energy. It has also been observed that the dynamics of ICF are not only dependent on the parameters of one entrance channel but on multiple entrance channels. We have also introduced the entrance channel parameter zeta (ζ) for the first time in ICF reactions to see the combined effect of mass-asymmetry (μ MA) and Z P Z T, as this parameter is better suited than μ MA and Z P Z T individually and has a linear dependency on F ICF(%).

Numerical Studies on Primary Ionization in TPC

Identification followed by directionality measurement using reconstruction of tracks is very crucial for studying the reaction vertex kinematics. In the field of low-energy nuclear physics, Active-Target Time Projection Chambers (AT-TPCs) can be used to study the nuclear reaction kinematics through tracking of the reaction products which is important for cross-section measurement. Ions produced in primary ionization by any charged particle along their track in the active gas volume of TPC can be utilized for track reconstruction with position-sensitive electron collection system placed inside an electric field. The TPC gas volume acts as the tracker of the reaction products and the target for the reaction with the incoming projectile simultaneously which is advantageous to conventional detector arrays. In this context, the design of the electric field in the drift volume of the TPC is an important criterion for precise tracking as the tracking capability of the TPC is strongly governed by the homogeneity of the electric field. Due to the lesser mobility of positive ions produced in primary ionization, their accumulation in the drift volume can distort the local electric field. In low-energy nuclear physics, this effect may be substantial due to the significant amount of ionization produced by the low-energy projectile and reaction products. Here we report the spatial information of primary space charges produced by cosmic muon and alpha particle obtained with geant4 [1] and Heed [2] simulation packages. We have used photo absorption and ionization physics lists in geant4 for the simulation and compared the results with that of the Heed. The simulation results for the change in pressure of gas volume will be reported. These results can be used for finding the distortion of the electric field due to the space charge in the drift region of the TPC which can be helpful for designing an AT-TPC for low-energy nuclear reaction experiments.

Negative-ion formation by H0/H– projectiles grazing scattering from the MgO(100) surface

A simple theoretical model used to treat the formation of negative ions during ${\mathrm{H}}^{--}/{\mathrm{H}}^{0}$ grazing scattering from the MgO(100) surface is presented. It is revealed that the resonant transfer from projectiles to the conduction band and the detachment of tunneling Coulomb repulsive barrier to the vacuum of the affinity electron of ${\mathrm{H}}^{--}$ ions both play an important role in the electron-loss processes. The negative-ion destruction is dominated by a nearly resonant electron loss in the low projectile energy region of $E\ensuremath{\le}0.7\phantom{\rule{0.16em}{0ex}}\mathrm{keV}$ (velocities $v\ensuremath{\le}0.17\phantom{\rule{0.16em}{0ex}}\mathrm{a}.\phantom{\rule{0.16em}{0ex}}\mathrm{u}.$), whereas the detachment by Coulomb repulsive barrier tunneling during the interaction between projectiles and surface anion sites becomes efficient in the high-energy region of $E\ensuremath{\ge}1.2\phantom{\rule{0.16em}{0ex}}\mathrm{keV}$ ($v\ensuremath{\ge}0.22\phantom{\rule{0.16em}{0ex}}\mathrm{a}.\phantom{\rule{0.16em}{0ex}}\mathrm{u}$). Combined with the valence-band electron capture, our present calculation results of the negative ion yields are in good agreement with the available experimental data in the whole velocity region.

State selective classical electron capture cross sections in Be4+ \u2009+\u2009H(1s) collisions with mimicking quantum effect

We present state-selective electron capture cross sections in collision between Be4+ and ground state hydrogen atom. The n- and nl-selective electron capture cross sections are calculated by a three-body classical trajectory Monte Carlo method (CTMC) and by a classical simulation schema mimicking quantum features of the collision system. The quantum behavior is taken into account with the correction term in the Hamiltonian as was proposed by Kirschbaum and Wilets (Phys Rev A 21:834, 1980). Calculations are carried out in the projectile energy range of 1–1000 keV/amu. We found that our model for Be4+ + H(1s) system remarkably improves the obtained state-selective electron capture cross sections, especially at lower projectile energies. Our results are very close and are in good agreement with the previously obtained quantum–mechanical results. Moreover, our model with simplicity can time efficiently carry out simulations where maybe the quantum mechanical ones become complicated, therefore, our model should be an alternative way to calculate accurate cross sections and maybe can replace the quantum–mechanical methods.

Single and double scattering mechanisms in ionization of helium by electron vortex projectiles

Triple differential cross sections (TDCSs) for electron vortex projectile ionization of helium into the azimuthal plane are calculated using the distorted wave Born approximation. In this collision geometry, the TDCSs at low and intermediate energies exhibit unique qualitative features that can be used to identify single and double scattering mechanisms. In general, our results predict that the ionization dynamics for vortex projectiles are similar to those of their non-vortex counterparts. However, some key differences are observed. For non-vortex projectiles, a double scattering mechanism is required to emit electrons into the azimuthal plane, and this mechanism becomes more important with increasing energy. Our results demonstrate that for vortex projectiles, emission into the azimuthal plane does not require a double scattering mechanism, although this process still significantly influences the shape of the TDCS at higher energies. At low projectile energies, non-vortex ionization proceeds primarily through single binary collisions. The same is generally true for vortex projectiles, although our results indicate that double scattering is also important, even at low energy. Vortex projectiles have an inherent uncertainty in their incident momentum, which causes a broadening of the binary peak at all energies and results in a splitting of the binary peak at higher energies. The results presented here lead to several predictions that can be experimentally tested.

Investigation of α-induced Reaction on Copper Isotopes for Energy Range of 15-50 Mev

The present work was done on alpha induced reaction mechanics on two natural coppers isotopes for the energy range of 15 to 30 Mev were investigated. The reaction channels for the total cross section 63Cu (α, n) 66Ga, 65Cu (α, 2n)67Ga, 63Cu(α, pn) 65Cu and 65Cu(α, n)68Ga were studied. The experimental data of reaction cross section COMPLETE code have been used. The aim study was compared experimental and theoretical reaction cross section both compound and pre-compound reaction and know the property, the reaction mechanism of the projectile particle reacts with target nuclei. The theoretical result was obtained from international atomic energy agency, exchange format data source. We understood the reaction mechanisms and the property of fragment particles during the reaction. Level density parameter and exaction number were varied to become good agreement between the calculated and measured data. In this study different dependency reaction cross section, the projectile energy was observed between the production of 67Ga and 65Zn. In alpha induced reaction with copper isotopes 66Ga, 67Ga, 68Ga and 65Zn are produced. Normally the calculation using a COMPLET code provides good outcome for the reaction cross-section of alpha induced reaction on low projectile energy. During the study of the reaction compound and pre-equilibrium reaction are occurred but direct reaction was almost not expected. Direct reaction is required to very large amount of energy.

Lithium source for focused ion beam implantation and analysis

We present a new Li source for focused ion beam applications. Based on an AuSi eutectic alloy, Li is added as an impurity to minimize effects from degradation when exposed to air. We show the source is stable over the course of an hour and spot sizes ≲10 nm can be achieved. The Li beam can achieve hundreds of nanometer ranges in semiconductors with minimal damage being generated along the path length. The source performance is evaluated through a high-resolution ion beam induced charge collection experiment on an Si-based detector. Further application of the source for ion beam analysis is numerically explored; the example investigated is based on probing a semiconductor heterostructure through a Rutherford backscattering experiment, where the Li beam can reveal information that is inaccessible with either low energy or high energy He projectiles used as probes.

Theoretical study of electron impact single ionization of neon by multicenter three distorted-wave method at low projectile energy: an overall agreement with experiment

Universal theoretical description of electron impact single ionization process for complex atoms and molecules is a long-standing challenge. A perturbative approach named multicenter three distorted wave method (MCTDW) has recently been developed by our group, aiming at calculating (e, 2e) fully differential cross sections for molecular target. In MCTDW method, the incident, scattered and ejected electrons are described by distorted waves using single center expansion technique. The continuum wave functions of the incident and two outgoing electrons are solved in the potential of neutral molecule and ion, respectively. The accuracy and generality of this method has been demonstrated for water molecule as well as simple two-electron atom helium (2018 Phys. Rev. A 98 042710) . Here MCTDW is extended to investigate more complex multi-electron atom neon of electron impact ionization from its 2p orbital at projectile energy of 100 eV and 65 eV. The results are compared with the internormalized experiments reported in the literatures (2013 Phys. Rev. Lett. 110 153202; 2015 Phys. Rev. A. 91 032707). An overall agreement has been achieved with experimental data for different scattering angles and energies, as well as theoretical calculations employing nonperturbative B-spline R-matrix with pseudostates approach.

Stopping and straggling of 60–250-keV backscattered protons on nanometric Pt films

The stopping power and straggling of backscattered protons on nanometric Pt films were measured at low to medium energies (60--250 keV) by using the medium-energy ion scattering technique. The stopping power results are in good agreement with the most recent measurements by Primetzhofer Phys. Rev. B 86, 094102 (2012) and are well described by the free electron gas model at low projectile energies. Nevertheless, the straggling results are strongly underestimated by well-established formulas up to a factor of two. Alternatively, we propose a model for the energy-loss straggling that takes into account the inhomogeneous electron-gas response, based on the electron-loss function of the material, along with bunching effects. This approach yields remarkable agreement with the experimental data, indicating that the observed enhancement in energy-loss straggling is due to bunching effects in an inhomogeneous electron system. Nonlinear effects are of minor importance for the energy-loss straggling.

Positron Scattering from Atoms and Molecules

A review on the positron scattering from atoms and molecules is presented in this article. The focus on positron scattering studies is on the rise due to their presence in various fields and application of cross section data in such environments. Positron scattering is usually investigated using theoretical approaches that are similar to those for electron scattering, being its anti-particle. However, most experimental or theoretical studies are limited to the investigation of electron and positron scattering from inert gases, single electron systems and simple or symmetric molecules. Optical potential and polarized orbital approaches are the widely used methods for investigating positron scattering from atoms. Close coupling approach has also been used for scattering from atoms, but for lighter targets with low energy projectiles. The theoretical approaches have been quite successful in predicting cross sections and agree reasonably well with experimental measurements. The comparison is generally good for electrons for both elastic and inelastic scatterings cross sections, while spin polarization has been critical due to its sensitive perturbing interaction. Positron scattering cross sections show relatively less features than that of electron scattering. The features of positron impact elastic scattering have been consistent with experiment, while total cross section requires significant improvement. For scattering from molecules, utilization of both spherical complex optical potential and R-matrix methods have proved to be efficient in predicting cross sections in their respective energy ranges. The results obtained shows reasonable comparison with most of the existing data, wherever available. In the present article we illustrate these findings with a list of comprehensive references to data sources, albeit not exhaustive.

Gamma-ray emission in alpha-particle reactions with C, Mg, Si, Fe

Cross sections for the strongest γ-ray emission lines produced in α-particle reactions with C, Mg, Si, Fe have been measured in the range E α = 50-90 MeV at the center for protontherapy at the Helmholtz-Zentrum Berlin. Data for more than 60 different γ-ray lines were determined, with particular efforts for lines that are in cross section compilations/evaluations with astrophysical purpose, and where data exist at lower projectile energies. The data are compared with predictions of a modern nuclear reaction code and cross-section curves of the latest evaluation for gamma-ray line emission in accelerated-particle interactions in solar flares.

Disentangling of incomplete fusion dynamics at low energies ≈ 4-6 MeV/A

An experiment has been performed for the measurements of forward recoil range distributions (FRRDs) of evaporation residues (ERs) using 16O beam on the target 148Nd to explore the incomplete fusion (ICF) dynamics at low projectile energy ≈ 4-6 MeV/A. In the present work, FRRDs of ERs 159,158Er(xn), 160g,159Ho(pxn), 157,155Dy(αxn) and 155Tb(αpxn) have been measured. The measured FRRDs of ERs have been compared with their theoretical mean ranges, calculated using code SRIM. These present results obtained from FRRDs measurements show that full and partial linear momentum transfer components are involved. This indicates that the ERs populated through α-emission channels are not only produced via complete fusion, but also through incomplete fusion dynamics. The present analysis indicates that the incomplete fusion contribution increases with projectile energy. This increment in incomplete fusion contribution is due to the increase in breakup probability of projectile 16O into 12C + 4He/ α with projectile energy.

Effect of projectile breakup in the system 19F + 154Sm

An attempt was made to understand the role of various entrance channel parameters on incomplete fusion dynamics by the measurements of excitation functions of evaporation residues populated via complete and incomplete fusion dynamics in the system 19 F + 154 Sm at projectile energy ≈ 4-6 MeV/A. The stacked foil activation technique followed by offline gamma ray spectrometry was employed in these measurements. The measured excitation functions of various evaporation residues populated have been analyzed within the framework of statistical model code PACE-4. It has been observed that the measured excitation functions of xn and pxn emission channels agree well with the theoretical predictions of PACE-4. On the other hand, the measured excitation functions of α-emission channels have been found significantly enhanced over their theoretical predictions. This enhancement may be attributed to the incomplete fusion of the projectile 19 F as the calculations for incomplete fusion are not included in statistical model calculations. The incomplete fusion fraction has been deduced from the present measurements. Further, a systematic study has also been performed, which shows that the incomplete fusion increases significantly with entrance channel mass asymmetry at low projectile energy, differently for different projectiles.

Dissociative multiple ionization of the H2O molecule induced by ion impact: experimental and theoretical results

SynopsisFragment energy spectra of the water molecule impacted by singly charged (SCI) and highly charged (HCI) ions have been measured in crossed beam experiments. Double differential fragmentation cross sections (DDCS) have been determined. Similarities and differences of the measured DDCSs induced by the medium- and low-energy projectiles have been analyzed. Multiple target ionization cross sections have been deduced and they were further analyzed through the results of the CTMC and CDW-EIS models.

Examination of break-up fusion in the O16+Nd148 system through measurements of forward recoil range distributions and angular distributions

The forward recoil range distributions and angular distributions of several evaporation residues produced via complete and incomplete fusion (ICF) dynamics in $^{16}\mathrm{O}+^{148}\mathrm{Nd}$ system at energy $\ensuremath{\approx}6$ MeV/nucleon were measured. The measured forward recoil range distributions of various reaction products show the presence of incomplete fusion components apart from complete fusion. Full and partial linear momentum transfer components of reaction products were found in the interaction of $^{16}\mathrm{O}$ with $^{148}\mathrm{Nd}$. These results were also confirmed by the measurements of angular distributions of evaporation residues. The measured angular distributions of the evaporation residues populated through complete and incomplete fusion channels were found to be distinctly different. The evaporation residues populated via complete fusion channels were trapped in the narrow angular zone as compared to incomplete fusion channels. A systematic study of the dependence of incomplete fusion dynamics on well-known entrance channel parameters shows that the incomplete fusion fraction grows exponentially with mass asymmetry $({\ensuremath{\mu}}_{EC}^{AS})$, Coulomb factor $({Z}_{P}{Z}_{T})$ and $\ensuremath{\alpha}\ensuremath{-}Q$ value of the projectile. The present observations suggest an exponential rise of ICF fraction with entrance channel parameters in contrast with the linear pattern reported in some earlier measurements. Further, the correlation of incomplete fusion fraction with the structure of target (T) was investigated employing four different parameters viz. deformation parameter $({\ensuremath{\beta}}_{2}^{T})$, interaction radius $({R}^{T})$, deformation length $({\ensuremath{\beta}}_{2}^{T}{R}^{T})$ and excess of neutrons ${(N\ensuremath{-}Z)}^{T}$ in the target. In the present study, the ICF fraction was found to rise exponentially with these parameters, independently for different projectiles. The three parameters ${\ensuremath{\beta}}_{2}^{T}, {\ensuremath{\beta}}_{2}^{T}{R}^{T}$, and ${(N\ensuremath{-}Z)}^{T}$ were found more sensitive and effective to investigate the entire picture about the influence of projectile and target deformation along with their relative orientations on incomplete fusion dynamics at low projectile energy. Moreover, the interaction radius of target $({R}^{T})$ is suitable to explain the characteristics of ICF dynamics in the spherical-spherical collisions. These present results show that incomplete fusion dynamics is strongly affected by the structure of projectile along with the target.

Two-center interference effects for single electron capture in fast ion-molecule collisions

Total as well as angular-differential cross sections for single electron capture have been investigated in collision of bare ions ($$H^{+}$$, $$He^{2+}$$ and $$Li^{3+}$$) with hydrogen molecules at intermediate and high collision energies with special emphasis on finding interference effects to be exhibited by angular-differential cross sections. Here, we apply the first-order molecular target continuum distorted-wave approximation. Within the distorted-wave formalism, the one-active-electron model, developed to describe collisions with multi-electronic atomic targets, has been employed for the case of $$H_{2}$$ targets. Here, distortion in the final channel related to the Coulomb continuum state of the active electron in the field of residual molecular target ion is included. The present computed results are compared with the available experimental and other theoretical results. The total cross section is obtained by integrating over the projectile’s scattering angle and averaging over all the molecular orientations. The total capture cross sections for all the projectile ions have fair agreement with the experimental observations particularly at lower projectile energies. We have studied the differential cross sections at $$\theta _{\rho }=90^{\circ }$$, $$\phi _{\rho }=0^{\circ }$$, where $$\theta _{\rho }$$ and $$\phi _{\rho }$$ are the polar and azimuthal angles, respectively, of the molecular axis with respect to the incident direction at different impact energies. The interference between two capture amplitudes associated with two centers in the molecule has been found to be more pronounced at fixed orientation of the molecule.