摘要:

The migration of defects, leading to eventual reaction, is analyzed on the basis of diffusion theory and compared with chemical rate theory. A diffusional treatment is carried out in detail and in special cases of particular interest. Correlations between interstitials and vacancies, typical of metals following electron irradiation, are examined. Trapping by impurities and dislocations, thermal conversion, and high temperature bombardment are also treated. In each case, formulations are developed along both one- and three-dimensional diffusion models. These alternative results are compared with experiments, particularly annealing in copper irradiated by electrons at low temperature. The results support the conclusion that the defect which migrates in Stage I diffuses in three dimensions.

ISSN:0033-7579    

DOI:10.1080/00337577008235611

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Point defect characteristics, including configuration and relaxation energies of vacancies and interstitials, migration energies of vacancies, and binding energies of divacancies, are determined by computer simulation using models representing copper and α-iron. The sensitivity of these characteristics to small variations in the range of the interatomic potential is studied using potentials of the Morse type modified to include third or fourth neighbors. Vacancy relaxation energies were found to increase and migration energies decrease with increased range. Divacancy binding energies were generally insensitive to range, but were appreciably higher than found with first and second neighbor potentials. The energies of interstitial configurations varied markedly with range, but retained their relative order with one minor exception. The lowest energy configuration for copper was the (100) split, in agreement with previous work. The lowest energy configurations for α-iron, however, were the crowdions, rather than the (110) split configuration found in previous work using shallower second neighbor potentials. The significance of arbitrary potential cutoffs and small discontinuities is discussed.

ISSN:0033-7579    

DOI:10.1080/00337577008235612

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Dielectric plastics were irradiated with high energy neutrons to investigate their usefulness as flux detectors. Shields thick to heavy particles and of varying composition were placed in front of the plastics to test their effectiveness as radiators. Track producing particles resulted from (n,4He) reactions and from recoils of light nuclei. Elements possessing high (n,4He) cross sections were chosen as shields along with other heavy elements chosen to screen the surface of the plastic from all external track-producing particles. Carbon and aluminum satisfied the first condition while gold and lead satisfied the second.

ISSN:0033-7579    

DOI:10.1080/00337577008235613

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Each of the nine passive dosimetry packets worn by the crew of Apollo VIII contained two 190 μ layers of Lexan polycarbonate plastic. The plastics served as threshold type, heavy charged particle track detectors. Upon recovery the detectors were fmt sensitized using the recently discovered photo-oxidation technique, and then etched to reveal tracks of particles whose restricted energy loss rate exceeded 2 × 102MeV cm2/g. A flight average of about 1 tr/cm2was observed. In tracing tracks through from one layer to the next it is possible to say whether a particle stops in the plastic, the sense and direction of travel, and in many cases make estimates ofzto ± 1 unit of charge. All the particles observed had a charge in excess of 10, 30 per cent came to rest in the plastic. The measurements demonstrate that plastic track detectors can be conveniently and easily utilized in accurately monitoring the astronauts' high LET radiation exposure on extended space missions lasting up to several years.

ISSN:0033-7579    

DOI:10.1080/00337577008235614

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

A new method is presented for the sensitization of plastic track detectors. It has been found effective for cellulosics, polycarbonates, and polyesters. Most of the reported data deals with Lexan.

ISSN:0033-7579    

DOI:10.1080/00337577008235615

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The sputtering efficiency (i.e. the ratio of reflected to incident energy) has been measured for graphite, aluminum, silicon, copper, silver, tantalum, and lead with 30–75 keV He+, C+, Ne+, Ar+, Cu+, Kr+, Xe+, and Pb+ions at perpendicular incidence. The measured efficiencies range from 0.5 per cent (He+→ Si) to 7 per cent (Ne+→ Pb). In accordance with theory, the results for heavier projectiles may be represented as a function of the ratio of target-to-projectile massesM2/M1only. The results are either energy independent or they decrease with increasing energy, the energy dependence being more pronounced the lighter the targets and projectile.

ISSN:0033-7579    

DOI:10.1080/00337577008235616

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Measurements of transversal relaxation times in the two-pulse Electron Spin Echo method. of radicals trapped in α- and γ-irradiated frozen solution of H2SO4and in methyl alcohol yields information on spatial distribution of trapped radicals. The results testify to the essential influence of the LET of radiation on the nature of spatial radical distribution and can be explained on the basis of the spur-and-track model. Average distances between radicals in tracks and spurs, and the number of radicals in spurs were calculated from relaxation data.

ISSN:0033-7579    

DOI:10.1080/00337577008235617

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

High resistivity single crystals ofp-type silicon have been implanted at room temperature in the (110) direction with 400 keV P-31 and P-32 ions, using total doses of 1013and 1015ions/cm2.

ISSN:0033-7579    

DOI:10.1080/00337577008235618

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Niobium samples were neutron-irradiated at reactor ambient temperatures (approximately 50 °C for polycrystals and 90°C for single crystals) to doses from 4 × 1015to 8 × 1018neutrons/cm2(E> 1 MeV). The density and size distribution of radiation-produced defect clusters, observed by transmission electron microscopy, were measured in polycrystalline niobium over a range of doses from 2 × 1017to 4.4 × 10l8neutrons/cm2. The TEM results were correlated with yield stress measurements as a function of dose. The radiation hardening was analyzed on the basis of a planar dispersed barrier model. It was found that the observed increases in yield stress at low doses were consistent with the measured density and size distribution of the defect clusters, with a cluster strength of (0.5–0.8) Gb2(G, shear modulus; b, Burgers vector). This corresponds to strong barrier hardening. At doses above about 1018neutrons/cm2, the hardening rate decreased sharply; this apparent saturation is discussed in terms of the coarsening of defect clusters, dislocation channeling, and the effect of interstitial impurities.

ISSN:0033-7579    

DOI:10.1080/00337577008235619

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The degradation of polyethylene and polyoxymethylene crystals in the high voltage electron microscope was determined from 100–1000 kV. As in previous work at lower electron energies, the dose needed to change the initial crystalline diffraction patterns into amorphous ring patterns was measured. It was found that the dose required to destroy the crystal order increases by a factor of about three in going from 100 to 1000 kV. The result agrees roughly with the theoretically predicted ionization rate, assuming that the damage rate is proportional to the ionization rate.

ISSN:0033-7579    

DOI:10.1080/00337577008235620

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor