L-Shell Ionization in Proton and Alpha Particle Collisions with Argon

We report results of coupled-state calculations of argon L-shell ionization by proton and alpha particle collisions in the 100 to 500 kev/amu energy range. Our target-centered basis includes up through f-states. We have explored the angular momentum convergence and ability of our pseudostates to describe the ionization continuum by comparing to the Born calculations of Choi; excellent agreement is obtained. In the Born we have shown the effect of using different independent-particle target potentials; these effects are large, particularly at low energy. We propose a modification of the Hartree-Fock potential that leaves all the wavefunctions and the bound orbital energies unaltered, but that lowers the continuum by an amount that brings the L-shell ionization potentials roughly into agreement with experiment. Our coupled-states calculations show deviations from the 1st Born approximation, and are in fair agreement with experiment. A complete comparison to experiment will require the calculation of the charge transfer channel contribution to the vacancy production.     

Product yields for the photofission of ~(232)Th,~(234,238)U,~(237)Np,and ~(239,240,242)Pu actinides at various incident photon energies

Photofission fragments mass yield for~(232)Th,~(234;238) U,~(237) Np, and~(239;240;242) Pu isotopes are investigated.The calculations are done using a developed approach based on Gorodisskiy's phenomenological formalism. The Gorodisskiy's method is developed to be applied for the neutron-induced fission. Here we revised it for application to photofission. The effect of emitted neutron prior to fission on the fission fragment mass yields has also been studied. The peak-to-valley ratio is extracted for the240 Pu isotope as a function of energy. Obtained results of the present formalism are compared with the available experimental data. Satisfactory agreement is achieved between the results of present approach and the experimental data.     

Electromagnetic field effects on nucleon transverse momentum for heavy ion collisions around 100A MeV

With taking electromagnetic field into account for the transport model of Boltzmann-Uehling-Uhlenbeck,electromagnetic effects are studied for ~(208)Pb +~(208)Pb collisions around 100A MeV. Electromagnetic field evolution during the collisions was estimated. It was found that the electric field has an obvious effect on the transverse momentum(p_T) spectra of nucleons during heavy ion collisions, and leads to different minimum position for the peak of p_T spectra of nucleons versus beam energy when the electric field is switched on. For the magnetic field, it affects the z-axis direction distributions of nucleons for central heavy ion collisions at lower energy.     

Spatial and energy distributions of the fragments resulting from the dissociation of swift molecular ions in solids

We have simulated the spatial evolution and energy loss of the fragments that result when swift molecular ions dissociate inside solid targets. In our calculations we have considered that these fragments undergo the following interactions: Coulomb repulsion (among like charged particles), stopping and wake forces (due to electronic excitations induced in the target), and nuclear scattering (with the target nuclei). We study the case of silicon targets irradiated with boron molecular or atomic ions; our results show that the main differences in the energy and spatial distributions of molecular fragments or atomic ions appear at shallow regions, and these tend to disappear at deeper depths.     

Neutron-γ Emission Competition in Spontaneous Fission of ^2S2Cf

宏观-微观模型预言，在Z=108存在强的质子形变壳，而相应的中子壳位于N=162，预计^270Hs是一“双幻数”形变核。因此，实验上合成^270Hs，进而研究其核结构将很有意义。然而超重核合成截面很低，在pb（10^-12barn）数量级，因而难度大。为了能成功的合成超重核，选择最佳弹靶组合和轰击能量至关重要。本工作将提出合成超重核^270Hs的最佳反应。     

Nuclear dynamics in multinucleon transfer reactions near Coulomb barrier energies

The mechanism of multinucleon transfer reactions has been investigated within the dinuclear system model, in which the sequential nucleon transfer is described by solving a set of microscopically derived master equations. The transfer dynamics in the reaction of~(136)Xe+~(208)Pb near Coulomb barrier energies is thoroughly analyzed. It is found that the total kinetic energies of primary fragments are dissipated from the relative motion energy of two touching nuclei and exhibit a symmetric distribution along the fragment mass. The angular distribution of the projectile-like fragments moves forward with increasing beam energy. However, the target-like fragments exhibit an opposite trend. The shell effect is pronounced due to the fragment yields in multinucleon transfer reactions.     

Foreign atom location by channeling in a helium irradiated Al-Mn alloy

The results of channeling experiments on single crystals are not in all cases comparable to analytical calculations with the continuum model, in which the interactions with the individual atoms surrounding the channel are smoothed out. For interpretation of angular scans it is necessary to simulate the channeling process in a Monte Carlo program on the basis of the binary collision model. Such a program which yields the energy and flux distributions of the channeled ions by calculating their collisions with the nearest target atoms in the momentum approximation was described earlier.With this program, irradiation induced interstitial-impurity complexes in a dilute Al-0.09 at.% Mn alloy are analysed on the basis of 〈111〉 and 〈110〉 symmetrical and — for the first time published — asymmetrical angular scans measured by Swanson et al. Here, He⁺ ions backscattered from the Mn atoms are assumed to be displaced in a 〈100〉, 〈110〉 or 〈111〉 direction from a normal lattice site. Displacements of this kind would occur in mixed dumbbells, where an impurity atom and a self-interstitial atom share one lattice site. The best fit to the experimental data has been obtained assuming the impurity atom to be displaced 0.14 nm in 〈100〉 direction. A 〈111〉 mixed dumbbell with a displacement of 0.22–0.27 nm might be possible, too. The evaluation needs the value of the stopping power in channel direction the knowledge of which is inaccurate. It will be shown that the results are not sensitive to the angular dependence of this stopping power.     

Propagation characteristics of microwaves in dusty plasmas with multi-collisions

In this study, we consider three main collisions in dusty plasmas and investigate the effects of dust grains on the propagation of electromagnetic(EM) waves through uniform, unmagnetized and weakly ionized dusty plasma. The Drude model is improved to describe the dielectric property of dusty plasmas, which accounts for collisions including electron–molecule, electron–ion, and electron–dust particles. Based on the improved Drude model, the propagation characteristics of microwaves in dusty plasmas have been numerically calculated and studied.The results show that the propagation characteristics of microwaves through dusty plasmas are different from those through normal plasmas. The effects of dust density and size are mainly studied. Numerical results indicate that the momentum transfer between electrons and dust grains makes more energy loss. The dust density and dust size have a similar influence on EM wave propagation, resulting in less transmission and more absorption.     

Validation of nuclear reaction models of 180 MeV proton-induced fragmentation of Al

Kinetic energy, angular distribution, and isobaric cross section data for A = 7-25 fragments formed in p + ²⁷Al reaction at bombarding energy of 180 MeV are compared with the calculations of the Binary Cascade Model (BIC), the Cascade Exciton Model (CEM), JQMD/PHITS, as well as the Statistical Model with Final State Interaction (SMFSI). For completeness, the kinetic energy spectra of light particles (n, p, α) formed in p + ²⁷Al reaction at bombarding energy of 156 MeV are also presented. A general agreement between the data and predictions of these models is found. However, disagreement with the data for the yields of light-mass fragments as well as near-target fragments is also found and discussed. The importance of this comparative study to simulation and analysis of radiation effects on microscopic electrical components operating in space is also discussed.     

An investigation of the role of spectroscopic factors in the breakup reaction of ~(11)Be

The experimental elastic cross section data of the projectile11 Be on target12 C at 49.3 Me V/nucleon energy is analysed. The calculations for the elastic scattering are performed by the phenomenological optical model. The different optical potentials to include breakup effects into the calculations, which are neutron+12C, neutron+10Be and10Be+12C, are described with the aid of the global potentials for neutron interactions and fitted to experimental data for the core and target interaction. Also, the first analysis of the optical model for10 Be on target12 C at 39.1 Me V is done for building the interaction potential of the core and the target for11 Be. For investigating the effects of the spectroscopic factors, obtained factors from the direct capture process using the nuclear level density are compared with the previous cross section and spectroscopic factor results. Obtained results for the elastic cross section reproduce the experimental data very well and show the requirement of including spectroscopic properties such as, spectroscopic factors and density of the excited states, to explain this elastic cross section data.     

Effects of target fragmentation on evaluation of LET spectra from space radiation in low-earth orbit (LEO) environment: impact on SEU predictions

Recent improvements in the radiation transport code HZETRN/BRYNTRN and galactic cosmic ray environmental model have provided an opportunity to investigate the effects of target fragmentation on estimates of single event upset (SEU) rates for spacecraft memory devices. Since target fragments are mostly of very low energy, an SEU prediction model has been derived in terms of particle energy rather than linear energy transfer (LET) to account for nonlinear relationship between range and energy. Predictions are made for SEU rates observed on two Shuttle flights, each at low and high inclination orbit. Corrections due to track structure effects are made for both high energy ions with track structure larger than device sensitive volume and for low energy ions with dense track where charge recombination is important. Results indicate contributions from target fragments are relatively important at large shield depths (or any thick structure material) and at low inclination orbit. Consequently, a more consistent set of predictions for upset rates observed in these two flights is reached when compared to an earlier analysis with CREME model. It is also observed that the errors produced by assuming linear relationship in range and energy in the earlier analysis have fortuitously canceled out the errors for not considering target fragmentation and track structure effects.     

Exotic break-up modes in heavy ion reactions up to Fermi energies

We discussed recent studies, within the framework of transport theories, on heavy ion reactions between charge asymmetric systems, from low up to Fermi energies. We concentrated on the analysis of ternary breakup events of dynamical origin occurring in semi-central reactions, where the formation of excited systems in various conditions of shape, excitation energy and spin is observed. At beam energies around 20 A Me V, we showed how this fragmentation mode emerges from the combined action of surface(neck) instabilities and angular momentum effects, leading to the observation of three aligned massive fragments in the exit channel. At Fermi energies, a transition towards a prompt emission of small fragments from the neck region with larger relative velocity with respect to projectile and target remnants is observed. We also focus on isospin sensitive observables, aiming at extracting information on the density dependence of the isovector part of the nuclear effective interaction and of the nuclear symmetry energy.     

Simulation of momentum flux ratios in the cascade in the sputtering of Mo---Mo

Momentum flux ratios ⁹²Mo/¹⁰⁰Mo towards the surface and the bulk through marker planes have been studied by a static Monte Carlo simulation program for an isotopic mixture ⁹²Mo_0.5¹⁰⁰Mo_0.5 bombarded with 5 keV Xe ions. The calculations show that the momentum flux ratios in the cascade deviate far from one at different surface depths. The calculations also show that the zero-fluence isotopic ratio in the near-normal direction and its difference between small and large polar emission angles are positive.     

Anisotropic ion emission in the fragmentation of small molecules by highly charged ion impact

In this work, we present double differential ion emission yields measured by the method of fragment ion spectroscopy for collisions of N⁶⁺ and O⁷⁺ ions with water and methane molecules at ∼30 keV impact energies. The angular distribution of the fragment ions shows expected post-collision and nucleus-nucleus binary collision effects with the indication of an interplay between Coulomb explosion and binary collision mechanisms. We have found significant differences in the fragmentation patterns of methane for the two projectiles, which may be a signature of strong, resonant capture channels. For triple capture, an unexpected angular distribution has been found for water, which may be attributed to orientation sensitivity of some of the capture channels. Such processes can be highly important for radiation therapy and astrophysics.     

Head-on collision between single- and multi-soliton heavy ion acoustic waves in multi-ion plasmas

Head-on collisions among the single-and multi-soliton’s heavy ion acoustic waves (HIAWs) of multi-ion plasma are studied. The plasma consists of adiabatic positively charged inertial heavy ions, Boltzmann energy distributed light ions and kappa energy distributed electrons. The extended poincaré-Lighthill-Kuo (ePLK) method is applied for the derivation of two-sided Korteweg–de Vries (KdV) equations (KdVEs). The KdV single-soliton solutions (KdVSSs) are determined using the hyperbolic secant method and the KdV multi-soliton solutions (KdVMSs) are obtained using the Hirota method. The effects of superthermality of electrons, temperature ratios of electron to light ion and heavy ion to electron, and the density ratio of electron to heavy ion on phase shifts are investigated for the head-on collisions between two-soliton HIAWs. The effects of plasma parameters on angular frequency, phase speed, production of multi-soliton structures, and the head-on collisions among single-, double-, triple-, quadruple-, and quintuplesolitons are also studied.     

Angular distributions of high energy protons channeled in long (10, 10) single-wall carbon nanotubes

In this work we study the angular distributions of 1 GeV protons channeled in long (10, 10) single-wall carbon nanotubes. The nanotube length, L, is varied between 10 and 100 μm. The angular distributions of channeled protons are obtained using the numerical solution of the proton equations of motion in the transverse plane and the Monte Carlo method. The effects of proton energy loss and scattering angle dispersion caused by its collisions with the nanotube electrons are taken into account. Analysis shows that for L < 30 μm, the transverse structure of the nanotube could be deduced from the angular distribution. For L ? 40 μm, the angular distribution contains the concentric circular ridges whose number increases and the average distance between them decreases when L increases. A possible application of the obtained results for characterization of carbon nanotubes is discussed.     

Neutron Transport Benchmark Calculations, (I)

Five benchmark problems were selected as standards for the evaluation of calculations on neutron penetration. For three of these problems there were available reliable experimental results obtained in absolute intensities of the neutron angular spectrum in graphite and in water and of the neutron reaction rate in a two-dimensional water shield. The two remaining problems were based on PALLAS transport calculations in graphite and in water in plane geometry. For the first three problems, comparisons were made between the results of PALLAS calculations using ENDF/B-I cross sections and those obtained by experiment. It is concluded that the PALLAS calculations result in fairly good agreement with experiment, except at certain spatial meshes in two-dimensional geometry, due to ray effect. Comparisons are also made of the angular flux spectrum in graphite between calculations using ENDF/B-I and B-III data, as well of the scalar flux spectrum in water between those by PALLAS and by ANISN codes.     

Tables for plane-wave Born-approximation calculations of K- and L-shell ionization by protons

Tables are presented in universal form for the calculation of plane-wave Born cross sections for proton-impact ionization of the K-shell and of individual L-subshells. The reason for these new calculations was twofold: First, these tables cover a wider range of proton energies and target binding energies than the original tables of Khandelwal et al., so that corrections for increased binding energy, Coulomb deflection etc. can be taken into account. Second, the table values have been calculated with the exact physical limits of integration given by energy and momentum conservation. This leads to lower cross-section values than in the original tables for low proton energies.