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1.
The long-standing problem of the lacking signature of a Barkas effect in the stopping of swift heavy ions under channeling conditions has been analyzed theoretically. The stopping model provides explicit dependences on impact parameter and allows for projectile screening and higher-order Z(1) corrections. The analysis differentiates between principal target shells. A distinct Barkas correction is found in accordance with standard theory. It is less pronounced for channeled than for random stopping because of the dominance of outer target shells. Varying contributions from different target shells to the stopping force may give rise to an inversion of the commonly observed variation with ion energy and charge state of the Barkas correction. 相似文献
2.
We have measured projectile and target X-ray cross sections for F + Si, S, Ar and Kr collisions at projectile energies from 1 to 25 MeV. The experiments were performed under single collision conditions using a differentially pumped gas target. X-rays were measured by a Si(Li) detector and a proportional counter. The experimental cross sections are compared to predictions of theoretical models for direct and quasi-molecular ionization. Effects of multiple ionization that influence theK-shell fluorescence yields were examined using experimental information from line energy shifts and intensity ratios. 相似文献
3.
Fast atoms with keV energies are scattered under a grazing angle of incidence from a clean and flat LiF(001) surface. For scattering along low index azimuthal directions within the surface plane ("axial surface channeling") we observe pronounced peak structures in the angular distributions for scattered projectiles that are attributed to "supernumerary rainbows." This phenomenon can be understood in the framework of quantum scattering only and is observed here up to projectile energies of 20 keV. We demonstrate that the interaction potential and, in particular, its corrugation for fast atomic projectiles at surfaces can be derived with a high accuracy. 相似文献
4.
《Solid State Communications》1987,63(4):307-310
The combined channeling backscattering and channeling nuclear reaction analysis of the α-LiIO3 monocrystal in an electrostatic field has been performed by proton beam at different energies to identify the behaviour of Li and I ions in the crystal. The thickness of the crystal was about 2 mm and has been cut perpendicular to C-direction. The channeling parameters like half angular width and minimum yield of 〈001〉 axial channeling have been measured precisely and the channeling behaviour of different ions in the crystal has been observed and measured quantitatively first time. The ionic d.c. conductivity can be calculated from the surface peak of the aligned channeling spectrum directly. 相似文献
5.
P. Sigmund A. Schinner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):201-209
Collisional electronic energy-loss straggling has been treated theoretically on the basis of the binary theory of electronic
stopping. In view of the absence of a Bloch correction in straggling the range of validity of the theory includes both the
classical and the Born regime. The theory incorporates Barkas effect and projectile screening. Shell correction and electron
bunching are added on. In the absence of shell corrections the Barkas effect has a dominating influence on straggling, but
much of this is wiped out when the shell correction is included. Weak projectile screening tends to noticeably reduce collisional
straggling. Sizable bunching effects are found in particular for heavy ions. Comparisons are made with selected results of
the experimental and theoretical literature.
Received 24 September 2002 / Received in final form 1st December 2002 Published online 4 February 2003 相似文献
6.
Spectra and angular distributions have been measured for the light particles emitted from the reactions induced by 36 MeV 6Li and 7Li ions on targets of 12C, 13C and 27Al. Some measurements were also performed at beam energies of 28 and 32 MeV. The spectra are dominated by broad peaks centered at energies corresponding to the beam velocity, a characteristic of projectile breakup. A simple breakup model roughly reproduces the shapes of the measured spectra and angular distributions. The total cross sections observed for projectile breakup average about 600 mb and are almost as large as the fusion cross sections. The 7Li breakup yields are somewhat larger than those for 6Li, the same trend that was previously observed for the Li-induced fusion cross sections on C. As a result the measured total reaction cross sections induced by 7Li ions are about 200 mb larger than those of 6Li on the same targets. This difference is not predicted by conventional optical model calculations. 相似文献
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9.
Feasibility of an electron-based crystalline undulator 总被引:3,自引:0,他引:3
The feasibility to generate powerful monochromatic radiation of the undulator type in the gamma region of the spectrum by means of planar channeling of ultrarelativistic electrons in a periodically bent crystal is proven. It is shown that to overcome the restriction due to the smallness of the dechanneling length, an electron-based crystalline undulator must operate in the regime of higher beam energies than a positron-based one does. A numerical analysis is performed for a 50 GeV electron channeling in Si along the (111) crystallographic planes. 相似文献
10.
Yu. E. Penionzhkevich Yu. G. Sobolev V. V. Samarin M. A. Naumenko 《Physics of Atomic Nuclei》2017,80(5):928-941
The energy dependence of the total cross sections for the 6He + Si and 9Li + Si reactions was measured at beam energies between 5 and 20 MeV per nucleon. The results agree with experimental data published for the 6He + Si reaction. New data are obtained for the 9Li + Si reaction in the vicinity of a local enhancement of the total cross section. A theoretical analysis of the possible reasons behind the appearance of this peculiarity in the case of collisions of 6He and 9Li nuclei with silicon target nuclei is performed. In particular, the enhancement may owe its origin to the effect of loosely bound projectile nucleons. 相似文献
11.
Yu. A. Belkova Ya. A. Teplova 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(2):248-250
Experimental data on the energy loss of light H, Li, B, and N ions in methane and H and N ions in benzene vapor have been
presented for the range of ion energies from 0.01 to 0.6 MeV/nucleon. It has been shown that the energy loss in the compounds
does not follow the addition rule for small ion energies, which indicates the necessity of taking into account the chemical
bonds of the molecular targets. The deviation from the addition rule has been experimentally found to increase with the nuclear
charge of the projectile ion. 相似文献
12.
Neutral Ne atoms with keV energies are scattered under channeling conditions, i.e., at a glancing angle of incidence, from a LiF(001) surface. By means of a time-of-flight method with a pulsed neutral beam, energy distributions for scattered projectiles are obtained. We find for this specific system that the small energy transferred to the crystal lattice during channeling via binary collisions with large impact parameters dominates the dissipation of projectile energy, whereas all other excitations of the solid can be brought to a negligible level. 相似文献
13.
In this paper, the channeling behavior of deuterons in the energy of 1400 keV along the <100> channel of Si was studied by the simulation of the channeling Rutherford spectrum in the backscattering geometry. The simulation was done by taking three considerations into account: (i) a minimum random component of the beam which enters the sample because of the scattering ions from the surface, (ii) the dechanneling starts at the greater penetration depths and (iii) the dechanneling follows a Gompertz type sigmoidal function with the two parameters which present the dechanneling rate and range, respectively. The Levenberg–Marquardt algorithm was used to set the best characteristic channeling parameters, the penetration depth at which the dechanneling starts, the energy loss and the dechanneling rate and range. The energy dependence of the ratio of channeling to random energy loss of deuterons in the energy range 1–2 MeV is investigated by comparing the determined value with the ones obtained in the other references. 相似文献
14.
《Nuclear Physics A》1995,588(1):c91-c97
We show that a large number of neutrons are expected to be transferred from the projectile to the target if a neutron rich unstable nucleus with a neutron skin is used as the projectile in heavy-ion collisions at energies about twice the Coulomb barrier. We then show that though the neutron halo enhances the fusion cross section through the size effect, the additional effect due to the molecular bond formation is not significant in the fusion between 11Li and 9Li at energies near and below the Coulomb barrier. 相似文献
15.
Yu. E. Penionzhkevich 《Physics of Atomic Nuclei》2009,72(10):1617-1628
Excitation functions are measured for complete-fusion and transfer reactions induced by the interaction of 6He and 6Li with 206Pb, 209Bi, and Pt. Data obtained for fusion reactions induced by 6He ions deviate from the predictions of the statistical model of compound-nucleus decay at projectile energies in the vicinity
of the Coulomb barrier height. A strong enhancement of cross sections for fusion reactions induced by the interaction of 6He with target nuclei is observed. The cross sections for reactions of cluster transfer, neutron transfer from 6He, and deuteron transfer from 6Li at deep-subbarrier energies are also found to be enhanced. These results are discussed from the point of view of the effect
of the cluster structure of nuclei on the interaction probability at energies in the vicinity of the Coulomb barrier height. 相似文献
16.
The electron-stimulated desorption of Li+ ions from lithium layers adsorbed on the tantalum surface coated with a silicon film has been investigated. The measurements are performed using a static magnetic mass spectrometer equipped with an electric field-retarding energy analyzer. The threshold of the electron-stimulated desorption of lithium ions is close to the ionization energy of the Li 1s level. The secondary thresholds are observed at energies of about 130 and 150 eV. The threshold at an energy of 130 eV is approximately 30 eV higher than the ionization energy of the Si 2p level and can be associated with the double ionization. The threshold at 150 eV can be caused by the ionization of the Si 2s level. It is demonstrated that the yield of Li+ ions does not correlate with the silicon amount in near-the-surface region of the tantalum ribbon and drastically increases at high annealing temperatures. The dependence of the current of Li+ desorption on the lithium concentration upon annealing of the tantalum ribbon at T>1800 K exhibits two maxima. The ions desorbed by electrons with energies higher than 130 and 150 eV make the largest contribution to the current of lithium ions after the annealing. The yield of lithium ions upon ionization of the Li 1s level at an energy of 55 eV is considerably lesser, but it is observed at higher concentrations of deposited lithium. The results obtained can be interpreted in the framework of the Auger-stimulated desorption model with allowance made for relaxation of the local surface field. 相似文献
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18.
K. A. Kuterbekov A. M. Kabyshev I. Tleulessova G. A. Almanov A. M. Mukhambetzhan Yu. E. Penionzhkevich N. K. Skobelev Yu. G. Sobolev S. M. Lukyanov T. N. Nurakhmetov E. T. Abseitov B. M. Sadykov 《Physics of Atomic Nuclei》2014,77(5):581-586
The results of a joint analysis of experimental data (angular distributions for scattering and total reaction cross sections) are presented for the case of the interaction of 6,7Li ions with 28Si nuclei at energies between 7.5 and 32 MeV. The respective calculations were performed on the basis of a deformed potential of the optical model by using the SPI-GENOA code. The energy dependences of the parameters of the macroscopic optical model and the total cross section for the (6,7Li+28Si) reactions were obtained over the energy interval from 7.5 to 32 MeV. The calculated angular distributions and total reaction cross sections are in good agreement with experimental data. 相似文献
19.
Experimental results on the multiplicity distributions of various particles produced in the interactions of 7Li with emulsion nuclei at a momentum of 3 GeV/c per projectile nucleon are reported. A comparison with data on collisions induced by other nuclei at a nearly identical momentum per nucleon is presented in order to reveal the dependence on the projectile mass. The internal structure of 7Li is explored by studying the projectile fragment. The mean multiplicity of shower particles, 〈n s〉, induced by 7Li is found to be less than that in the case of 6Li projectiles. The angular distributions of target fragments and relativistic charged secondaries are investigated. No shock-wave phenomena are observed. Forward-to-backward ratios are calculated for each case. The probability distributions for relativistic secondaries produced per unit rapidity are studied in detail, along with the rapidity densities and their dependence on the projectile and the target mass. A comparison of the angular spectra of shower particles produced in central and peripheral collisions supports the limiting-fragmentation hypothesis. The collisions in question seem to become more central with increasing shower-particle multiplicity. 相似文献
20.
K. Dettmann 《Zeitschrift für Physik A Hadrons and Nuclei》1975,272(3):227-235
The electronic energy loss of MeV-protons in crystals is investigated in the Hartree-Fock approximation for the core electrons of the target. It turns out that each core electron can be regarded as stopping the proton independent of all other electrons without restriction by the Pauli principle. For the channeling stopping power the impact parameter dependent energy loss of a proton moving rectilinearly past a crystal ion is calculated in first Born approximation. Low excitations of the core electrons lead to a long range impact parameter dependence, whereas high excitations contribute to the energy loss proportional to the electron density sampled along the proton trajectory. The results are applied to 4 MeV proton channeling along the main channels of Si using Clementi wave functions for the core electrons and a free electron approximation for the valence electrons. The comparison with the experimental results of Clarket al. yields good agreement. In the high velocity limit a reduction of the channeling stopping power to 0.64(0.83) of the random value is predicted for Si(C). 相似文献