摘要:

Samples of boron carbide of differenct compostions wre irradiated and observed in a high voltage electron microscope (T.E.M.) at 100 keV, at 300K and 80 K. In spite of the high displacement rates (∼10−3d.p.a./s), the high doses (3 d.p.a.) and the low temperature, no bulk damage was observable in any of these samples either in form of defect clusters on the images or in form of important changes on the the diffraction patterns (phase transformations or Bragg spots broadening). The same observations has been done in samples of β rhomboheral boron and boron oxide irradiated by 800 keV electrons at 300 K and 15K at doses up to 2.3 d.p.a.

ISSN:0033-7579    

DOI:10.1080/00337578508222528

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Human hairs containing a uranium burden were placed in contact with a mica sheet as the recording matrix and irradiated in a thermal neutron flux. The fission fragment tracks penetrating the mica were etched and counted. Calculations have been made to show the losses due to the fission fragment range being less than the diameter of the hair and for the variation of track density with distance from the line of contact between the hair and the mica. Experimental data from 50 μ. diameter hair and those derived by calculation were compared.

ISSN:0033-7579    

DOI:10.1080/00337578508222529

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The mean excitation energy,I, of some solid materials has been studied. An examination for the local-plasma approximation and a discussion about theoretical connections forIbetween solid and gaseous materials have been made. This examination led to the development of a combined model which utilized the local-plasma approximation for inner-shell electrons and the dielectric response function for valence electrons. In the local-plasma approximation, we have used electron density distribution obtained from the Hartree-Fock model with the Wigner-Seitz boundary condition for solid atoms. A Drude-type dielectric function for multi-group valence electrons was applied to the valence band. From first principles, we have calculated the mean excitation energy as varying with the energy of incident electrons. Applying these data to the Bethe stopping power formula, we were able to extend successfully this formula to lower electron energies.

ISSN:0033-7579    

DOI:10.1080/00337578508222530

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Single crystals and polycrystalline samples of hexagonal ferrite BaFe12O19have been irradiated with argon and krypton ions of energies 44 MeV/A and 35 MeV/A respectively and doses ranging from 1013to 1015Ar24+cm−2and from 1012to 1014Kr16+cm−2. Changes in magnetic properties and microstructure have been investigated by saturation magnetization measurements and high resolution electron microscopy. The results lead to the separation of the stopping ion zone from the electronic slowing down region. A crystal to amorphous transformation occurs in the the former when approximately 10−2atom has been displaced per atomic collision. The transition can be explained on the basis of an amorphization process wherein high density defects regions shall be created by the primary ejected ions.

ISSN:0033-7579    

DOI:10.1080/00337578508222531

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Gamma radiation damage in zeolite- 13X is studied with special reference to the Cs+uptake by the zeolite. Prolonged exposure to a 5 kCi60Co-γ source with a dose rate of 4.5 k Gyh−1does not alter the cation exchange capacity of the zeolite. Structural effects consequent to γ-irradiation are examined by the X-ray diffraction, i.r. and surface area measurements. The data support the view of displacement of exchangeable cations as also the framework atoms from their normal locations. EPR measurements suggest the formation of paramagnetic centre in the structure. A 3 % weight loss and release of hydrogen subsequent to γ-irradiation (∼840 h) is attributed to the radiolysis of zeolite water.

ISSN:0033-7579    

DOI:10.1080/00337578508222532

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The optical absorption of LiF crystals implanted with 100 keV magnesium, argon and sodium ions has been investigated in both the visible and vacuum ultraviolet spectral regions. The growth of defect absorption bands has been observed for doses ranging from 1014to 3 × 1017ion cm−2. The V3-, F- and M-bands occur at lower doses. At about 3 × 1016ion cm−2, bands characteristic of the implanted ion appear. These dominate the absorption spectra at higher doses and are attributed to metal colloids. The nature of the colloid band at 4.3 eV (290 nm) in magnesium implanted samples is discussed and is compared with similar bands seen in argon and sodium implanted samples at lower photon energies. A new absorption band which is independent of the type of implanting ion is observed at 8.4 eV (148 nm) at doses of ≧ 1017ion cm−2. Both the colloid and 8.4 eV bands are inhibited in crystals implanted at 77 K.

ISSN:0033-7579    

DOI:10.1080/00337578508222533

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Doubts are expressed concerning the value of energy-based parameters for use in the development of models of radiation action on biological media because they obscure the underlying physical interactions as evidenced by the increasing number of anomalous effects observed at low radiation energies.

ISSN:0033-7579    

DOI:10.1080/00337578508222534

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Observed supralinear dose dependence for the amorphous transformation during irradiation of NiTi is compatible with a cascade overlap model for heavy ion (2.5 MeV Ni+, 6 MeV Ta+++) irradiations. A model based on total defect build-up, however, is necessary to explain the amorphous transition induced by electron irradiation and can also be applied to heavy ion irradiation. The cascade effects in this latter model are manifested by non-uniform defect distribution in the lattice. The defect build-up model requires a high activation energy for interstitial migration which is not incompatible with recent findings. The form of the temperature dependence can also be rationalized using a defect build-up model (amorphous phase transition, heavy-ion irradiation, electron irradiation, NiTi, defect build-up, cascade overlap).

ISSN:0033-7579    

DOI:10.1080/00337578508222535

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The secondary effects caused by the bombardment of solids with medium-energy heavy ions should be sensitive to the specific surface properties of phase transitions. Experimental studies of sputtering, scattering and secondary electron and ion emission have shown that all these effects are influenced both by magnetic and by structural transformations in a number of materials. A common feature is a step-like change at temperatures somewhat lower than the bulk transition temperature. The magnitude of this change is strongly increased under grazing incidence conditions, when the penetration depth of primary ions is restricted to several atomic monolayers.

ISSN:0033-7579    

DOI:10.1080/00337578508222536

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Mirror reflection of charged and neutral particles and γ-quanta on the smooth surface of solids treated. A new type of optics is also discussed.

ISSN:0033-7579    

DOI:10.1080/00337578508222537

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor