Angular Distributions Of Emitted Particles Research Articles

Mechanisms of molecular emission from phenylalanine monolayer deposited on free-standing graphene bombarded by C60 projectiles

The Molecular Dynamics (MD) computer simulations are used to gain insight into the mechanism of molecular ejection from a monolayer of phenylalanine (C9H11NO2) molecules deposited on free-standing two-layer graphene. The system is bombarded with C60 projectiles with different kinetic energy and angle of incidence. Mass spectra, sputtering yields, and angular distributions of emitted particles are recorded in two bombardment geometries, in which the projectile hits the sample from above and below.The sputtering yields increase with the primary kinetic energy. There is an optimal angle of incidence for each kinetic energy, leading to the most effective molecular emission. The value of this angle increases with kinetic energy. The interplay between the area energized by the impinging projectile, the energy back-reflection, and molecular fragmentation determines the shape of the yield dependence on the angle of incidence. The bombardment geometry has little effect on the efficiency of molecular emission. Generally, organic molecules are emitted by interaction with the projectile and/or a graphene substrate. The main factor affecting the relative contribution of each of these interactions is whether graphene is punctured. The implications of current results for the potential use of graphene supports in Secondary Ion Mass Spectrometry are discussed.

Пространственное распределение каналируемых ионов и пробеги изотопов водорода в кристаллическом кремнии и вольфраме

Ranges of H and D ions in crystalline Si and W were calculated. It is shown, that as the energy of ions increases the depth distribution of ranges splits into two components: one is connected with near-surface scattering, and the other one characterizes channeled particles. A new phenomenon was observed – a stable spatial structure of the channeled part of the beam forms after the beam passes a short distance. As the ions slow down they start to transition into adjacent channels. The spatial structure of channeled ions falls apart near the stopping point of the particles. An experiment which would connect the obtained spatial distribution with angular distribution of emitted particles is proposed.

POLYMERS CONTAINING Cu NANOPARTICLES IRRADIATED BY LASER TO ENHANCE THE ION ACCELERATION

<p>Target Normal Sheath Acceleration method was employed at PALS to accelerate ions from laser-generated plasma at intensities above 10<sup>15 </sup>W/cm<sup>2</sup>. Laser parameters, irradiation conditions and target geometry and composition control the plasma properties and the electric field driving the ion acceleration. Cu nanoparticles deposited on the polymer promote resonant absorption effects increasing the plasma electron density and enhancing the proton acceleration. Protons can be accelerated in forward direction at kinetic energies up to about 3.5 MeV. The optimal target thickness, the maximum acceleration energy and the angular distribution of emitted particles have been measured using ion collectors, X-ray CCD streak camera, SiC detectors and Thomson Parabola Spectrometer.</p>

Comparisons of hadrontherapy-relevant data to nuclear interaction codes in the Geant4 toolkit

Comparisons between experimental data, INCL and other nuclear models available in the Geant4 toolkit are presented. The data used for the comparisons come from a fragmentation experiment realised at GANIL facility. The main purpose of this experiment was to measure production rates and angular distributions of emitted particles from the collision of a 95.A MeV 12C beam and thick PMMA (plastic) targets. The latest version of the Intra Nuclear Cascade of Liege code extended to nucleus-nucleus collisions for ion beam therapy application will be described. This code as well as JQMD and the Geant4 binary cascade has been compared with these hadrontherapy-oriented experimental data. The results from the comparisons exhibit an overall qualitative agreement between the models and the experimental data. However, at a quantitative level, it has been shown that none of this three models manage to reproduce precisely all the data. The nucleus-nucleus extension of INCL, which is not predictive enough for ion beam therapy application yet, has nevertheless proven to be competitive with other nuclear collisions codes.

Measurement of Charged-Particle Emission Double-Differential Cross Section of Fluorine for 14.2MeV Neutrons

We carried out detailed measurement of the double-differential cross sections of fluorine for the emissions of protons, deuterons, tritons, and α-particles with 14.2MeV incident neutrons. An improved charged-particle spectrometer with a pencil DT-neutron beam furnished at the FNS facility of the Japan Atomic Energy Agency enabled us to obtain precise data with a fine energy resolution over a wide energy range and an angular range from 15 to 150°. The present experiment is the first simultaneous measurement of the four different kinds of charged particles and provides useful data to establish a nuclear reaction model of fluorine as well as to confirm previous experimental data. Angular-differential cross sections for several discrete peaks corresponding to excited states of residual nuclei were extracted to discuss the reaction mechanism of charged-particle emission. The obtained data suggest that the charged-particle emission reaction of fluorine has a complicated mechanism in which there are contributions from the direct reaction, pre-equilibrium, and equilibrium processes. The obtained data were compared with the nuclear data evaluated in JENDL-3.3 and ENDF/B-VII.0. The results show large differences in the energy and angular distributions of emitted particles and the charged-particle production cross sections between the measured and evaluated data.

Calculation of Neutron Nuclear Data on Rubidium and Strontium Isotopes for JENDL-4

Neutron nuclear data on 85,86,87Rb and 84,86,87,88,89,90Sr have been calculated for the evaluated nuclear data library JENDL-4 in the energy region from 10 keV to 20MeV. Simultaneously calculated are the total, elastic, and inelastic scattering, (n,γ), (n, p), (n, d), (n, t), (n,3He), (n,α), (n, np), (n, nd), (n, nα), (n, 2n), (n, 3n) reaction cross sections, angular distributions of emitted particles, and energy distributions of emitted particles and γ-rays. The statistical model was applied to calculate these quantities. Coupledchannel optical model parameters were used for neutrons. Preequilibrium and direct-reaction processes were taken into account in addition to the compound process. The present calculations are consistent with available experimental data. The calculated results are compiled into JENDL-4.

Calculation of Neutron Nuclear Data on Selenium Isotopes for JENDL-4

Neutron nuclear data on 74,76,77,78,79,80,82Se have been calculated for the evaluated nuclear data library JENDL-4. Simultaneously calculated are the total, elastic and inelastic scattering, (n, γ), (n, p), (n, d), (n, t), (n, 3He), (n, α), (n, np), (n, nd), (n, nα), (n, 2n), (n, 3n) reaction cross sections, angular distributions of emitted particles, and energy distributions of emitted particles and γ-rays. The statistical model was applied to calculate these quantities. Coupled-channel optical model parameters were used for neutrons. Preequilibrium and direct-reaction processes were taken into account in addition to the compound process. The present calculations are consistent with available experimental data. The calculated results are compiled into JENDL-4.

Considerations on the determining factors of the angular distribution of emitted particles in laser ablation

Simulations of particles which are emitted in laser ablation have been performed by the method of Direct Simulation Monte Carlo to investigate the deposition profiles of the emitted particles. The influences of the temperature, pressure and stream velocity of the initial evaporated layer formed during laser ablation process on the profile of the deposited film have been examined. It is found that the temperature gives a minor influence on the deposition profile, whereas the stream velocity and the pressure of the initial evaporated layer have a greater impact on the deposition profile. The energy in the direction of surface normal ( E ⊥) and that in the parallel direction of the surface ( E ||) are shown to increase and decrease, respectively after the laser irradiation due to collisions between the emitted particles, and this trend is magnified as the pressure increases. As a consequence, the stream velocity in the direction of surface normal increases with the increase in the pressure. A mechanism of the phenomenon that a metal with a lower sublimation energy shows a broader angular distribution of emitted particles is presented. It is suggested that low density of evaporated layer of a metal with a low sublimation energy at its melting point decreases the number of collisions in the layer, leading to the low stream velocity in the direction of surface normal, which results in the broader deposition profile of the emitted particles.

Calculation of Neutron Nuclear Data on Rubidium and Strontium Isotopes for JENDL-4

Neutron nuclear data on 85,86,87Rb and 84,86,87,88,89,90Sr have been calculated for the evaluated nuclear data library JENDL-4 in the energy region from 10 keV to 20MeV. Simultaneously calculated are the total, elastic, and inelastic scattering, (n,γ), (n, p), (n, d), (n, t), (n,3He), (n,α), (n, np), (n, nd), (n, nα), (n, 2n), (n, 3n) reaction cross sections, angular distributions of emitted particles, and energy distributions of emitted particles and γ-rays. The statistical model was applied to calculate these quantities. Coupledchannel optical model parameters were used for neutrons. Preequilibrium and direct-reaction processes were taken into account in addition to the compound process. The present calculations are consistent with available experimental data. The calculated results are compiled into JENDL-4.

Calculation of Neutron Nuclear Data on Molybdenum Isotopes for JENDL-4

Neutron nuclear data on 92,94,95,96,97,98,99,100 Mo have been calculated for the evaluated nuclear data library JENDL-4. Simultaneously calculated are the total, elastic and inelastic scattering, (n, p), (n, d), (n, t), (n, 3He), (n, α), (n, np), (n, nd), (n; nα), (n, 2n), (n, 3n) reaction cross sections, the angular distributions of emitted particles, and the energy distributions of emitted particles and γrays. The statistical model was applied to calculate these quantities. Coupled-channel optical model parameters were used for neutrons. Preequilibrium and direct-reaction processes were taken into account in addition to the compound process. The present calculations are almost consistent with available experimental data. The calculated results are compiled into JENDL-4.

Calculation of Neutron Nuclear Data on Molybdenum Isotopes for JENDL-4

Neutron nuclear data on 92,94,95,96,97,98,99,100 Mo have been calculated for the evaluated nuclear data library JENDL-4. Simultaneously calculated are the total, elastic and inelastic scattering, (n, p), (n, d), (n, t), (n, 3He), (n, α), (n, np), (n, nd), (n; nα), (n, 2n), (n, 3n) reaction cross sections, the angular distributions of emitted particles, and the energy distributions of emitted particles and γrays. The statistical model was applied to calculate these quantities. Coupled-channel optical model parameters were used for neutrons. Preequilibrium and direct-reaction processes were taken into account in addition to the compound process. The present calculations are almost consistent with available experimental data. The calculated results are compiled into JENDL-4.

Angular dependence of the redeposition rates during SiO2 etching in a CF4 plasma

The angular dependence of the redeposition rates during SiO2 etching in a CF4 plasma was studied using three types of Faraday cages located in a transformer coupled plasma etcher. The SiO2 substrates were fixed on sample holder slopes that have different angles to the cathode. The substrate was subjected to one of three processes depending on the design of the Faraday cage, i.e., redeposition of sputtered particles from the SiO2 bottom surface (case I), substrate etching by incident ions (case II), or simultaneous etching and redeposition (case III). Both the redeposition and the etch rates were measured by changing the substrate–surface angle and the self-bias voltage in the range of −100 to −800 V. The redeposition-only rates (case I) at −450 and −800 V closely followed the quadratic curve of the angle whereas the rates at −100 V followed the cubic curve, indicating different mechanisms of the bottom SiO2 etching depending on the energy regimes. The steep increase of the redeposition rate with the angle was attributed to three factors: the substrate–bottom distance, the angular distribution of emitted particles from the bottom surface, and the particle incident angle on the substrate surface. The etch-only rate curves (case II) closely followed the cosine of the surface angle. The etch-rate curve changed into a reverse-S shape when the substrate was subjected to simultaneous etching and redeposition (case III). The net etch rate for case III decreased drastically above 60°, showing a negative value, i.e., a net redeposition, beyond 75°. The drastic decrease in the net etch rate coincided with the steep increase in the redeposition rate, implying the significant effect of redeposition.

Simultaneous Calculation of Reflection, Physical Sputtering and Secondary Electron Emission from a Metal Surface due to Impact of Low-Energy Ions

A computer simulation code which treats elastic and inelastic collision processes of low-energy ions in solids is presented. In the code, the direct excitation of electrons by a penetrating ion and recoiling atoms is simulated using the Monte Carlo technique, in addition to the simulation of elastic collisions of the moving particles with solid atoms. Electron cascades of the excited electrons and collision cascades of the recoil atoms are also taken into account, and as a result, the code allows us to simulate ion-solid interactions such as ion reflection, physical sputtering and secondary electron emission from the solids. This code is applied to calculations of the energy and angular distributions of emitted particles and the total particle yields of aluminum by impact of ions with the atomic numbers Z1 of 1 to 17 and energies Ei of 10 eV to 10 keV at normal incidence. The calculated sputtering yield and ion reflection coefficient are in reasonable agreement with empirical formulae which have been recently presented. The calculated electron yield shows the clear dependence on Z1 and Ei, but the Ei-dependence is different from that of the electronic stopping power at such low impact energies. The energy and angular distributions of emitted particles indicate the similarities of the secondary electron emission and the physical sputtering, as observed in recent experiments.

Various Phenomena on PSI. Fundamental Processes Related to PSI. Physical Sputtering and Secondary Electron Emission.

This paper describes the similarities and differences between physical sputtering and secondary electron emission from solids under ion bombardment. Emphasis is placed on the energy and angular distributions of emitted particles and particle emission statistics, as well as on total particle yield. The sputtering yield and secondary electron yield are strongly related to the nuclear stopping power and electronic stopping power of the solids for incident ions, respectively, whereas the energy distributions of sputtered atoms and secondary electrons are less influenced by these ions. Due to “collision cascade” and “electron cascade” before these atoms and electrons escape from the surface, both the energy distributions are similar to each other. However, the angular distribution of sputtered atoms shows under- and over-cosine distribution for low-energy and high-energy ions, respectively, whereas the angular distribution of secondary electrons is close to the cosine distribution, which results from the isotropic momentum distribution of secondary electrons inside the solids. For both, the statistical distribution for emission probabilities deviates from the Poission distribution in most cases.

Entrance channel effects in fusion-evaporation processes

The effect of shape equilibration on particle emission in fusion reactions is thoroughly studied. Following a detailed evaluation of the various time scales a microscopic dynamical picture of the fusion path is coupled to a statistical decay probability at different time steps. It is shown that excitation energy and deformation of the compound system are influencing the emission pattern of charged particles and Giant Dipole photons. A quantitative analysis is performed for a 164Yb compound system formed via O + Sm (mass asymmetric) and Ni + Mo (mass symmetric) channels at various excitation energies. In the mass-symmetric case interesting effects are revealed on spectra and angular distributions of emitted particles, particularly for α's, protons and Giant Dipole photons. Experiments are suggested to directly measure these “pre-equilibrium” contributions leading to new information on very exotic hyperdeformed nuclear systems.

Angular distributions of emitted particles by laser ablation of silver at 355 nm

to 8 J/cm2. The distribution is strongly peaked in the forward direction corresponding to cospθ, where p varies from 5 to 12 for the largest beam spot, but is less peaked for the smallest beam spots. The total collected yield of ablated atoms is about 2×1015 Ag atoms per pulse for the highest pulse energies.

Particle-hole state densities with linear momentum and angular distributions in preequilibrium reactions.

We present two methods for the calculation of state densities with linear momentum. The first is exact, convoluting single-particle and hole densities in momentum space, and can be used for nuclear excitations with small numbers of particles and holes. The second, based on statistical arguments, is applicable for excitations of many particles and holes and leads to state densities with a Gaussian linear-momentum dependence. Together, these two techniques allow state densities with linear momentum to be determined for any particle-hole excitation. The relationship between linear- and angular-momentum state densities is discussed, and we show how the familiar Gaussian angular-momentum distribution of states can be obtained from state densities with linear momentum. We argue that these state densities provide the most elegant and straightforward means for obtaining angular distributions in semiclassical preequilibrium theories, avoiding inconsistencies inherent in the commonly adopted procedure of using a nucleon-nucleon scattering kernel. In our approach the angular distribution of preequilibrium particles emitted from a two-particle--one-hole state is identical to that found by Kikuchi and Kawai. Angular distributions from more complex particle-hole states do, however, differ from a convolution of Kikuchi-Kawai scattering kernels, since we do not make a leading-particle approximation. As an illustrative example to the use of the Gaussian form of state densities with linear momentum, we calculate the angular distributions of emitted particles in the preequilibrium reaction $^{165}\mathrm{Ho}$(\ensuremath{\alpha},p), ${\mathit{E}}_{\mathrm{\ensuremath{\alpha}}}$=109 MeV. Our calculations account for the experimental angular distributions well, even at large backward angles where many semiclassical approaches fail.

Relativistic Vlasov equation and heavy-ion collisions

A relativistic Vlasov equation was derived from the mean field theory (MFT) of the Walecka model by using nonequilibrium Green function techniques. The Vlasov equation was then used to investigate the collisions of 16O + 16O at intermediate energies. From studying the transverse momentum distribution, we have found that the transverse momentum transfer involves a cancellation between large attractive and repulsive components. For intermediate- and high-energy heavy-ion collisions, the transverse momentum transfer is essentially determined by the interaction with the vector meson. We have calculated the angular distributions of the emitted particles during heavy-ion collisions and found a forward peak, which is not sensitive to the impact parameter and incident energy. Introducing the nonlinear self-interaction of the scalar meson, we have also studied the sensitivities of the magnitude of the transverse momentum and angular distribution of emitted particles to the nucleon effective mass and the nuclear compressibility at saturation density.

The average angular distribution of emitted particles in multi-step compound processes

A simple model for the differential cross section that describes the angular distribution of emitted particles in heavy-ion induced multi-step compound reactions, is constructed. It is suggested that a careful analysis of the deviations of the experimental data from the pure Hauser-Feshbach behaviour may shed light on the physical nature of the pre-compound, heavy-ion configuration.

Angular distributions in a unified model of preequilibrium and equilibrium neutron emission

An alternative mathematical formulation is presented for the generalized master equation of the exciton model, introduced by Mantzouranis et al. to describe preequilibrium effects in angular distributions of emitted particles in nuclear reactions. The exciton model proposed in this paper includes internal transitions with $\ensuremath{\Delta}n=2, 0, \ensuremath{-}2$, and describes both the preequilibrium and the stages of the reaction process. A simple, but exact formula is given to calculate mean lifetimes of exciton states and their Legendre coefficients, from which double differential cross sections can be easily calculated. The mathematical improvements of the generalized exciton model greatly facilitate a systematical comparison with experimental data. In this paper the neutron inelastic scattering data for 34 elements measured by Hermsdorf et al. at 14.6 MeV were used for such intercomparison. The results show underestimation of angular distributions at backward angles. However, a good overall fit of all angular distributions is obtained by adjustment of only two global parameters. It is concluded that further study with regard to the physics of the model is required. Some local variations in the angular distribution coefficients as a function of the mass number might be ascribed to level-density effects. Although it appeared that the presently adopted formulas and parameters in exciton model calculations are not adequate to give detailed predictions of the energy and angular distributions, meaningful improvements were obtained by variation of final-state parameters. Finally, some attention was devoted to the unification of the exciton and Hauser-Feshbach models. By introducing a proper definition of equilibrium emission it is shown that consistent results are obtained for neutron emission spectra calculated with the two models.NUCLEAR REACTIONS Be, C, Na, Mg, Al, Si, P, S, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Se, Br, Zr, Nb, Cd, In, Sn, Sb, I, Ta, W, Au, Hg, Pb, Bi ($n, \mathrm{nx}$), $E=14.6$ MeV; calculated $\ensuremath{\sigma}$ (${E}_{n}, \ensuremath{\theta}$), Legendre coefficients. Generalized exciton model, preequilibrium and analysis, Hauser-Fesh-bach model.