Recoil-ion Distributions Research Articles

Impact of Nuclear Data Uncertainty in the Modeling of Neutron-Induced Recoil Atom Energy Distributions in Silicon

Recoil ion distributions in silicon and the resulting distribution of the linear energy transfer (LET) are important metrics in microdosimetric studies and in the investigation of neutron-induced single-event effects. A rigorous methodology is presented for quantifying the uncertainty in these metrics due to the underlying uncertainty contributors, including that due to the nuclear data, recoil ion electronic stopping power, and incident neutron spectrum. The methodology uses a Monte Carlo-based approach so that the nonlinear uncertainty propagation is rigorously treated as the response function folded with the full incident neutron spectrum. The uncertainty is captured in the form of both recoil energy and LET-dependent covariance matrices. The uncertainty contributions from the nuclear data are shown to have strong energy-dependent correlations which are comparable in magnitude to that from the uncertainty found in the spectrum characterization for high fidelity reference neutron fields. The uncertainty from the stopping power has the largest magnitude of the largest contributors, but it shows a very strong energy-dependent correlation that translates into a systematic uncertainty that may cancel out in many applications.

Fragmentation of H2O molecules following the interaction with slow, highly charged Ne ions

We measured the energy and angular distribution of fragment ions from collisions of 2–90 keV Neq+ ions (q = 1, 3, 5, 7 and 9) with H2O molecules. A strong dependence on the charge state of the incident ion was observed. The results are interpreted within the framework of a Coulomb explosion model. Deviations from this model in the energy and angular distribution of recoil ions are attributed to post-collision effects by the electric field of the projectile. Absolute cross sections for ion production were measured and found to be consistent with the cross sections calculated using the classical over-barrier model.

Abrupt rise of the longitudinal recoil ion momentum distribution for ionizing collisions.

We report on the experimental observation of an abrupt rise in the longitudinal momentum distribution of recoil ions created in proton helium collision. The details of this structure can be related to electrons traveling with the velocity of the projectile [electron capture to the continuum (ECC)]. The longitudinal as well as the transverse distribution of the recoil ions can be explained as a continuation of the momentum distribution from ions resulting from electron capture illustrating the smooth transition from the capture to bound states of the projectile to the ECC.

Interpretation of momentum distribution of recoil ions from laser-induced nonsequential double ionization by semiclassical rescattering model

Using a semiclassical rescattering model, the momentum distribution of recoil ions from laser-induced nonsequential double ionization is obtained and the result is consistent with the experiment reported recently. We show that the characteristic double-hump structure of the recoil momentum distribution of the ${\mathrm{He}}^{2+}$ ion parallel to the polarization axis is just the consequence of the rescattering dynamic of nonsequential double ionization and the acceleration of the ions in the laser field.

Interpretation of Momentum Distribution of Recoil Ions from Laser Induced Nonsequential Double Ionization

We show that the recently reported momentum distribution of recoil ions from laser induced nonsequential double ionization can be interpreted as a combined effect of interelectron correlation and final state field interaction ("Volkov dressing") of the two outgoing electrons. We also find a cutoff formula for the recoil momentum that gives the maximum momenta observed in the experiments.

Doubly Differential Recoil-Ion Longitudinal Momentum Distributions from Electron DDCS Measurements in Ion-Aton Ionization

We have used the energy and angular distribution of the low energy electron emission to derive the doubly differential final-state longitudinal momentum distributions of the recoil-ions in ion-atom ionization. The complementary nature of the electron spectroscopy and the recoil-ion momentum spectroscopy has been investigated using a formulation based on three body kinematics. The separation of the three-body and binary collision branches of recoil-ion distributions is a novel feature of the present technique.

Ionization dynamics in fast ion-atom collisions. II. Final-state momentum distributions of the ionization products in collisions of He with bare carbon ions

We have used the energy and angular distributions of the low-energy electron emission cross sections from the preceding paper [Lokesh C. Tribedi et al., Phys. Rev. A 58, 3619 (1998)] to derive the doubly differential final-state longitudinal momentum distributions of the electrons, recoil ions, and projectiles in ion-atom ionization for ${\mathrm{C}}^{6+}+\mathrm{H}\mathrm{e}.$ The complementary nature of the electron spectroscopy and the recoil-ion momentum spectroscopy have been investigated using a formulation based on three-body kinematics to explore the ionization dynamics in detail. The influence of the three-body ionization as well as the binary-encounter processes on the recoil-ion (and projectile) longitudinal momentum distributions has been investigated. The separation of the soft- and hard-collision branches of recoil-ion distributions is an important feature of the present technique. The present method also allows one to determine cross sections for very large electron momenta. The single- differential distributions are also derived by numerical integration of the double-differential distributions. The first Born approximation, the continuum distorted wave eikonal initial state, and the classical trajectory Monte Carlo calculations are used to explain the data.

SCORPION: A system for coincidences between recoil and projectile ions at NSC, New Delhi

An on-line facility to measure coincidences between the recoil ions and the scattered projectiles (SCORPION) has been designed, fabricated and commissioned at Nuclear Science Centre (NSC), New Delhi. The facility consists of a four jaw slit assembly, a time of flight (TOF) spectrometer, a parallel plate electrostatic charge analyser and a one dimensional position sensitive parallel plate avalanche counter (PPAC). Details of the design and working principles of various components and the test results obtained for the Si q+-Ar collision system are presented to highlight the performance of the system. A multiple loss of up to four electrons has been observed for 60 MeV Si4+ ions colliding with argon atoms in a single collision condition. Spectra of recoil ions detected in coincidence with a particular charge state of the scattered projectile show a bell shaped distribution as a function of the recoil charge state (r) for the electron loss events. However, the yield of recoil ions drops asr increases for the direct ionization channel. Also for electron loss, the peak of the recoil ion distribution is seen to shift to a higher recoil charge state as the number of lost electrons from the projectile increases.

Xenon recoil-ion charge distributions produced in electron capture and loss collisions of 8 MeV/u Kr

Recoil-ion charge distributions produced in single collisions of 8 MeV/u Kr13+ and Kr32+ projectiles with Xe atoms have been measured using time-of-flight spectroscopy. The post-collision charge states of the projectile ions were determined by magnetic dispersion onto a position sensitive microchannel plate detector. The recoil-ion distributions for ionization accompanied by electron loss from Kr13+ projectiles were bell-shaped with averages that ranged from 7.4 for 1-electron loss to 13.9 for 5-electron loss. The recoil-ion distributions for ionization accompanied by electron capture to Kr32+ projectiles were also bell-shaped, but had much higher average charges that ranged from 20.4 for 1-electron capture to 28.5 for 4-electron capture. The large difference in the average charges produced in the two types of collisions is mainly attributable to charge magnification by Auger decay. A simple model quantitatively explains the variation of the capture-ionization charge distribution width and average charge as a function of the number of captured electrons.

Angular distributions of very low energy recoil ions

We present the first measurements of the angular distribution of recoil ions near 90 ° with respect to the incident projectile direction. Beams of 22.5 and 33 MeV chlorine ions (incident charge states q = 4,5,8) have been used as “hammer” beams incident on Ne atoms. We do not confirm the long standing assumption that these recoil ions are ejected preferentially at angles very near 90 ° with respect to the primary beam direction, although they do have energies typically less than 5 eV. Recoil ions ejected around 90 ° have an energy distribution appreciably wider than those ejected at either larger or smaller angles.

Low energy ion scattering of clean and oxygen-covered Ni(110)

Low energy ion scattering can provide atom location and structural information from a number of different measurements. Low angle scattering can yield information on atom location and surface crystallography from the measurement of the azimuthal angular distribution of scattered particles. Large angle backscattering provides a direct measurement of shadow cone geometry and combined with the angular dependence of the backscattered yield, this large angle scattering event can provide accurate information on the surface structure. Studies of the angular distribution of recoil ions from the surface can also provide information on the site from which the recoil came. These three techniques have been applied to the study of the Ni(110) surface and to oxygen adsorption on that surface. A comparison of the information available from each technique is presented.

Transfer Ionization in Collisions Between Multiply Charged Ions and Atoms at KeV Energies

A crossed-beam coincidence time-of-flight technique has been used to measure the charge-state distribution of recoil ions created by multiply charged projectile ions which capture one or two electrons in single collisions at keV energies. The results of the investigation show the importance of transfer ionization as a contribution to charge-transfer processes: electron capture events were found to cause large shifts in the recoil charge-state distribution toward higher charge states. The dependence of this phenomenon on the charge state of the projectile and the number of transferred electrons was investigated. An overall correlation of the recoil-ion charge states is found with the maximum internal electronic excitation energy available in the collision system. In general, a dependence of the recoil spectra on the projectile kinetic energy has not been observed.