摘要:

A computer simulation is carried out of the motion of high-energy electrons and positrons in the continuum string potential of single crystal axes with the given Miller indices, using the Molière model. Characteristic trajectories of various types are obtained which correspond to properly channeled or quasichanneled particles. Angular distributions of particles at the exit from a crystal are analyzed as well as their radiation spectra.

ISSN:0033-7579    

DOI:10.1080/00337578408206080

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A general method is presented for obtaining approximate solutions for the steady-state diffusion flux of point defects to a sink in the presence of other competing sinks. The solutions and approximations hold for cases in which the reactions between various point-defect species, e.g. between vacancies and interstitials, are negligible. As an example, the growth or shrinkage of a dislocation loop in a thin plate during continuous generation of diffusing vacancies and interstitials is dealt with, a situation which can experimentally be realized in high-voltage electron microscopes.

ISSN:0033-7579    

DOI:10.1080/00337578408206081

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

We derive an approximate expression for the steady-state vacancy and interstitial fluxes into a circular dislocation loop in a thin foil during continuous production of mobile vacancies and interstitials. It is assumed that vacancy-interstitial recombination is the dominant process by which vacancies and interstitials are lost.

ISSN:0033-7579    

DOI:10.1080/00337578408206082

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The chemical states of35S in solutions of thermal neutron irradiated (TNI) chloride samples have been investigated using (a) chemical precipitation techniques after sample dissolution in the presence or absence of inactive carriers in the forms of S2-, SO32-, SO42-and S2O3−2, and (b) anion exchange separation. The second method has been used to study variations in the composition of TNI chloride solutions as a function of the time interval between sample dissolution and addition of the solution to the ion exchange column. The results point towards the following conclusions: (i) dissolution of TNI chloride in water or 0.3 M NaOH in the absence of any inactive sulfur-anion carrier yields primarily35SO32-and not35SO42-and35S2-as was thought earlier; (ii) about 20% of the35S in solution is present initially as elemental sulfur; (iii) the composition of the solution varies markedly with time; (iv) in the presence of carrier sulfur anions at the time of dissolution different35S-species are formed; and (v) chemical precipitation techniques do not give a true indication of the species present in solution.

ISSN:0033-7579    

DOI:10.1080/00337578408206083

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The deposition profiles that form around precipitates undergoing energetic transmutation reactions can be used to study the effects of helium, hydrogen and lithium on microstructural development during neutron irradiation. A completely general derivation has been performed to determine the deposition profile concentrations for any transmutation reaction and precipitate/matrix combination. Calculations of the deposition profiles were performed for the10B(n, α)7Li reaction and selected precipitate/matrix stopping power ratios. With increasing ratio the deposition profiles become more uniform but the reaction products are deposited over larger volumes leading to lower concentrations in the matrix.

ISSN:0033-7579    

DOI:10.1080/00337578408206084

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The ion surface scattering near 180° scattering angle is investigated, based on the two-atom scattering model. The importance of the shadowing effect and the focusing effect on the intensity of large-angle backscattering is discussed in detail.

ISSN:0033-7579    

DOI:10.1080/00337578408206085

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A “hydrodynamic” model of displacement-spike evolution is proposed. At moderate recoil energies when the mean free path for atomic collisions is about interatomic distance, the shockwave formation is assumed to be the main mechanism of energy dissipation. It was shown that for recoil energies less than 1.5–3 keV the problem may be reduced to the problem of shock-wave propagation in an ideal gas with an initial opposite pressure. Some possible applications of the model are discussed, including calculations of threshold displacement energy and damage function, space distribution of radiation defects, and phase transitions in the displacement spike.

ISSN:0033-7579    

DOI:10.1080/00337578408206086

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

With the help of the binary collisions model the glancing scattering of 10 MeV protons by a system of ten tungsten crystals is investigated. The dependence of the total reflection coefficient and the angular spread of reflected protons on the number of crystal reflectors is calculated.

ISSN:0033-7579    

DOI:10.1080/00337578408206087

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

190 keV H ions are implanted with doses ranging from 1 × 1015to 1.4 × 1018cm−2into pure amorphous silicon layers prepared by 2 MeV Silicon irradiation of crystalline silicon. Depth profiles of the changed complex refractive index (n+ik) are determined from high-resolution reflection and transmission measurements across bevelled surfaces. The increase of the reflectivity of annealed amorphous silicon (a-Si) resulting from collision induced Si bonding defects is used to determine the nuclear stopping power depth profile. A nuclear energy density of 3.1 eV per Si atom has to be deposited by the H projectiles in order to transform the relaxed structure ofa-Si into the state of saturated disorder which is characteristic for irradiation amorphized silicon (ia-Si). On account of the saturated damage in pre-amorphized ia-Si targets the observed reduction of n and k is associated with the implanted H concentrationcH. Projected range, range straggling, and skewness are evaluated from the optically determined range distribution. The comparison of calculated high-dose concentration profiles with corresponding optical depth profiles yields the optical constants as well as the atomic H and Si densities as functions ofCHup to 66 at. %. A model for the incorporation of the implanted H atoms into the amorphous bonding network accounts for the removal of Si bonding defects and for the formation of H2bubbles. A corresponding analysis of theK(CH) curve yields a density of 4 × 1021Si bonding defects per cm3inia-Si. In accordance with the experimental results the permittivity ε1is calculated in dependence on CH by mixing the optical polarizabilities of Si-H bonds, H2molecules, Si bonding defects, and partially distorted Si-Si bonds.

ISSN:0033-7579    

DOI:10.1080/00337578408206088

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Dose-response curves have been obtained for the gamma-irradiation of some amino acids and pyrimidines in dry powder form. In all cases these curves display second-order effects which are very marked in the case of the amino acids. Monte Carlo simulations have been carried out for various possible models and it has been shown that for some of the compounds, a model postulating two different kinds of trapping sites gives the best fit to the experimental curves.

ISSN:0033-7579    

DOI:10.1080/00337578408206089

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor