摘要:

Samples of nominally pure single crystal KCI were irradiated by H, H2, He, C and N positive ions in the energy range 0–2 MeV. The growth of F-type centers was recorded as a function of ion fluence. Depth profiles of damage by H and He ions were constructed, and it was found that the damage profile does not follow the stopping power as a function of penetration depth in the target. Determinations of damage track radii, based on the data, were done, and found to be on the order of 10 Å. Comparisons of defect production by H2with H at the same fluences of nuclei and the same energy per mass showed at low energies more defects by H than by H2, the difference attributable to track overlap.

ISSN:0033-7579    

DOI:10.1080/00337578008210010

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A model of electron induced sputtering of alkali halides is described. It is assumed that fast neutral particles are emitted when H-centres, taking part in the focused replacement sequence, cross the surface. When the focused replacement sequence is terminated at a certain distance from the surface, the H-centre may diffuse to the surface, giving rise to thermal particles.

ISSN:0033-7579    

DOI:10.1080/00337578008210011

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Cascades of atomic collisions created by high energy particles as a result of irradiation of solids by them are considered. The solution of the problem is based on the investigation of the Boltzmann stationary kinetic equation for moving atoms. For this equation a model scattering indicatrix is constructed with an arbitrary form of the potential of interaction of moving atoms with lattice atoms. The choice of the model scattering indicatrix of atoms is determined by the normalization, the average energy loss in a single collision and by the deviation of the energy losses really occurring in the collision from the mean value, as well as by the initial kinetic-equation for moving atoms. The energy distribution of moving atoms for arbitrary interatomic interaction potentials has been obtained using the constructed model scattering indicatrix. On the basis of the theory constructed a cascade is calculated with an interatomic interaction potential in the form of the Thomas-Fermi potential and the power potential.

ISSN:0033-7579    

DOI:10.1080/00337578008210012

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Measurements have been made using thermal desorption spectrometry of the entrance probability η of He+ions incident on a W(100) surface at energies 8 eV to 5000 eV. For energies above 250 eV, η for normal incidence, ηn, is within 20 of unity, while for “random” incidence ηn= 0.6 ± 0.1. Below 250 eV, both decrease and become equal forE≤ 25 eV. At 25 eV, η = 0.2 and at 8 eV, η ≈ 0.01.

ISSN:0033-7579    

DOI:10.1080/00337578008210013

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The formation of ethers in radiolysis of methane, ethane, and propane in the presence of either methanol or ethanol was studied in the gas-phase using a conventional approach based on analysis of the stable products. A mechanism is established to be ionic and probably involves condensations of ions originating from alkanes with alcohols, solvation of ionic complexes by alocohols, and finally supersession of ethers by alcohols in equilibrium exchanges. For want of mass spectrometric data the identity of ionic precursors remains speculative, although there is strong evidence that C2H5+ions are not involved. In propane another ionic mechanism contributes to the formation of C2H5O-n-C3H7; in this case the ionic precursor originates from the alcohol rather than from the alkane.

ISSN:0033-7579    

DOI:10.1080/00337578008210014

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Using a double-spike, mass spectrometric technique, we have measured the absolute isotopic composition of Ca sputtered from several Ca minerals by normally incident, low energy, nitrogen beams (130 keV N+and 100 keV N+2). The precision in the40Ca/44Ca ratio is 0.05% for samples as small as 10−7g, corresponding to a resolution of possible mass dependent isotope fractionation effects of ∼0.01% per unit mass difference. In general, the material sputtered first was isotopically light by up to 2% in the isotopic ratio40Ca/44Ca when compared with the measured isotopic composition of the target; as the bombardment progressed, the isotopic composition became less light and approached the initial composition of the target. We have demonstrated that, after prolonged bombardment, a surface layer develops on the target with a distinctly heavy isotopic composition; the thickness of the layer is a significant fraction of the range of the bombarding ions. Angular distributions of the sputtered material show that, throughout the bombardment, the material ejected back along the beam direction was isotopically light relative to the material ejected at oblique angles; the difference in the isotopic ratio40Ca/44Ca over the angular range was ∼ 1.5%. This fractionation with angle of ejection persisted even when a quasi-steady state was reached after heavy bombardment, when the isotopic composition of the material averaged over angle had become essentially indistinguishable from that of the pristine target. These results indicate that sputtering produces isotope fractionation and that there is a marked angular dependence in the effects. This suggests that solar wind sputtering of the lunar surface may contribute to the isotopic and elemental enrichments observed for the surface layers of soil grains.

ISSN:0033-7579    

DOI:10.1080/00337578008210015

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A Monte-Carlo-program has been used to study the channelling process in NbC-single crystals implanted with C-ions at 830°C. The dechannelling yields measured in the ⟨110⟩-direction separately for the Nb- and the C-sublattice are compared to calculated results. In the calculation two defect models (statistically displaced C-atoms and stacking faults) were applied and the characteristic parameters for these models were varied in order to reproduce the behavior of the experimental spectra. The best agreement was obtained by assuming a defect structure consisting of stacking faults with a Burger's vector ofa/6 [112] and a stacking fault length of 7 nm. The analyzing ion beam energy was varied in the cal- culation and the expected energy independence of the dechannelling yield for stacking faults was found which lies in reasonable agreement with the experimental values.

ISSN:0033-7579    

DOI:10.1080/00337578008210016

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Photographic measurements, using a precession camera, were made of the diffuse X-ray scattering from zircons (ZrSiO4) subjected to natural radiation damage. The diffuse scattering was concentrated near the zircon reciprocal-lattice positions only and the intensity contours could approximately be described by spheres. However in fairly severely damaged samples there were significant deviations from circularity of the diffuse intensity contours in the (hk0)reciprocal-lattice planes but not in the (0kl) planes. Positron annihilation lifetime spectra were obtained for lightly damaged zircon and were satisfactorily fitted by three lifetime components. Annealing and ionizing radiation produced changes in the intensities of the longer-lived components of the positron lifetime spectra. These changes appeared mainly to derive from bleaching and re-coloring of electron- or trapped hole-centers associated with displaced ions rather than those associated with impurity ions.

ISSN:0033-7579    

DOI:10.1080/00337578008210017

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Measurements of the depth profiles of disorder and the depth integrated disorder produced in Si at 40 K or 300 K by low energy (15 keV-60 keV) ions of a range of masses from the light (N+and P+), intermediate (Ar+and As+) to heavy (In+, Sb+, As+2, Bi and Sb+2) were made using Rutherford scattering-dechannelling techniques.

ISSN:0033-7579    

DOI:10.1080/00337578008210018

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The models of random media used at present in describing polycrystal scatteringcannot explain some experimental facts, such as the double-scattering peak in the energy spectra of reflected ions. Two models of simulation of ion interactions with polycrystals are proposed here, namely 1) the model of random filling of the coordinative spheres in which the polycrystal is represented by a set of singlecrystal coordinative spheres with arbitrary positions of atoms and the distances between atom may sometimes be smaller than those in single crystal, a fact that can be treated as the presence of an imbedded atom; 2) the model of arbitrary selection of the bombarded face in which the surface and incidence planes are selected randomly for each ion (or of a group of ions). In both models, the atoms are free, the Born-Mayer potential is used, and thermal vibrations of atom are included. A good agreement with experimental results has been obtained in both methods.

ISSN:0033-7579    

DOI:10.1080/00337578008210019

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor