摘要:

Trapping of ion-irradiation induced defects has been studied in Na-implanted polycrystalline Fe, Ni, and Mo. The samples were implanted at room temperature with 250-keV23Na+ions to a fluence of 1.5 × 1017cm−2. The Na concentration distributions were characterized using nuclear reaction via the resonant reaction23Na(p, σ)24Mg. The trapping and detrapping of Na-implantation and proton-irradiation induced defects were observed via their decoration with hydrogen. The H distributions were measured with the nuclear resonance reaction1H(15N, ασ)12C. The formation of defect-hydrogen complexes is interpreted by vacancy migration to Na followed by trapping of H from the bulk. To elucidate the mechanisms, the Na-doped samples were also post-irradiated with 100-keV protons and 6.4-MeV15N2+ions, and isochronally annealed at 300-970 K.

ISSN:1042-0150    

DOI:10.1080/10420159108220757

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A novel method to determine the widths of the distributions of implanted atoms and of atomic defects from resistivity measurements is described for implantation of H, D, and He in thin films of Au and W at 5 K and energies from 0·25 to 3 keV. The widths obtained for He in W are in agreement with experimental data from field ion microscopy but deviate from results of Monte Carlo simulations (“TRIM”-code). Furthermore the resistivity contribution per implanted atom are derived, giving ρH. D= 1.7 ± 0.5 and ρHe= 3.3 ± 0.8 μΩ/u.c. in gold and ρH.D= 1.6 ± 0.2 and ρHe= 7.6 ± 0.6 μωm/u.c. in tungsten. The number of defects produced per implanted ion are determined from resistivity damage rate measurements. Calculations shows that the threhold energy for atomic displacement and the displacement function under low energy light ion irradiation agree reasonably with respective values derived from electron irradiation.

ISSN:1042-0150    

DOI:10.1080/10420159108220758

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Amorphous carbon films have been irradiated with Cl-ions with energies between 1 and 40 MeV, and the electrical conductivity of the material has been measured as a function of the ion dose. The room temperature conductivity is increased by nearly three orders of magnitude and saturates at a dose of about 1015cm−2. The rate of conductivity changevsthe ion energy can be explained by an ion track model. The temperature dependence of the conductivity between 100 and 300 K at low doses is in accordance with variable range hopping with a temperature exponent of 1/2. Hopping sites are assumed to be graphite rings or microcrystallites. At higher doses the variable range hopping is replaced by a metallic conductivity with a linear dependence on the temperature similar to that of polycrystalline graphite. This is probably due to the formation of complete percolation paths through the material by interconnection of the graphite regions. Estimates of the size of the crystallites, the hopping activation energy, and the cross section for producing crystallites in the material have been extracted.

ISSN:1042-0150    

DOI:10.1080/10420159108220759

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Radiation effects induced in thallium-based superconducting copper oxides Tl2Ba2CaCu2O8and Tl2Ba2Ca2Cu3O10irradiated by 5.8 GeV-Xe ions—have been investigated by high resolution electron microscopy (HREM). Two main points should be more particularly outlined: the inhomogeneous character of the irradiation induced-defects regions without amorphization. A significant difference in the radiation sensitivity of the two compounds is also observed in agreement with the electron transport properties modifications. The results are compared with those previously reported for YBa2Cu3O7-δsamples irradiated by 3.5 GeV-Xe ions and 5.3 GeV-Pb ions.

ISSN:1042-0150    

DOI:10.1080/10420159108220760

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Helium clustering in alpha irradiated copper has been investigated by positron annihilation spectroscopy. Pure copper samples have been homogeneously helium implanted using a cyclotron, yielding helium concentrations of 100 appm and 400 appm. Post-implantation positron lifetime and Doppler broadened annihilation lineshape measurements have been carried out on these Cu samples as a function of isochronal annealing temperature. An annealing stage observed in the isochronal annealing curveviz., a marked reduction in the resolved lifetime τ2and an increase of its intensityI2, is explained as due to the formation of helium bubble embryos. At higher annealing temperatures, τ2corresponding to helium bubbles increases and saturates while its intensityI2decreases, indicating an increase in the size of the bubble with a concomitant decrease in the bubble concentration. This stage is interpreted to be the bubble growth stage. From an analysis of positron lifetime parameters in the growth stage, helium stom density, bubble size and bubble concentration have been deduced at various annealing temperatures. The bubble characteristics are found to be affected by the helium dose. The present results on direct helium implanted Cu are compared with those of our earlier study onn-irradiatedCu-B, where helium was introduced using10B(n, α)7Li reaction.

ISSN:1042-0150    

DOI:10.1080/10420159108220761

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Anomalous transient tail diffusion is interpreted as being associated with the equilibration of the metastable state formed by the implantation process. During annealing, the sample approaches the thermodynamic equilibrium via quasi-chemical reactions involving radiation defects. The corresponding set of reaction-diffusion equations can be solved giving the space and time evolution of the defect profiles as well as their electrical activity. To exemplify the approach, the tail diffusion of the boron implants with peak concentrations transcending the solubility limit will be discussed in detail. Finally, a simple explanation will be given of the influence of lattice damage on boron diffusion due to pre- or post-implantation of silicon and boron atoms, respectively.

ISSN:1042-0150    

DOI:10.1080/10420159108220762

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A technique is developed which addresses the problem of irradiation assisted stress corrosion cracking of stainless steels in light water reactors using high energy protons to induce grain boundary segregation. These results represent the first grain boundary segregation measurements in bulk produced by proton irradiation of stainless steel. The technique allows the study of grain boundary composition with negligible sample activation, short irradiation time, rapid sample turnaround and at minimal cost. Scanning Auger electron microscopy is used to obtain grain boundary composition measurements of irradiated and unirradiated samples of ultra high purity (UHP) type 304L stainless steel and UHP type 304L steels with the additions of phosphorus (UHP + P) and sulphur (UHP + S). Results show that irradiation of all three alloys causes significant Ni segregation to the grain boundary and Cr and Fe away from it. Irradiation of the UHP + P alloy also results in segregation of P at the grain boundary from 5.3 to 8.7 at %, over 80 times the bulk value. No radiation-induced grain boundary segregation of S was measured in the UHP + S alloy. Results also indicate that the presence of P or S may enhance radiation-induced segregation of major alloying elements at the boundary. Comparison of irradiated and unirradiated regions of the UHP + P alloy indicate that while a prior thermal treatment segregates P to the grain boundary to 5.3 at %, the major element concentrations at the grain boundary are completely different from those under irradiation.

ISSN:1042-0150    

DOI:10.1080/10420159108220763

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

For a natural single crystal of zircon, ZrSiO4, from Sri Lanka, exhibiting zonation in U and Th contents, the hardness and elastic modulus have been determined as a function of α-decay dose using a mechanical properties microprobe (MPM). The zones vary in thickness from one to hundreds of micrometers, and have uranium and thorium concentrations such that the α-decay dose varies between 2 × 1015and 1 × 1016α-decay events/mg (0.15 to 0.65 dpa, displacement per atom). The transition from the crystalline to the aperiodic metamict state occurs over this dose range. For a traverse of 75 indent pairs across layers sampling a large portion of the crystalline-to-metamict transition (3.7 × 1015to 9.7 × 1015α-decay events/mg) both the hardness and elastic modulus decrease linearly with increasing α-decay dose. The radiation-induced softening follows a behavior similar to other radiation-induced changes, that is with the expansion of the unit cell parameters there is a decrease in density, birefringence, hardness and bulk modulus.

ISSN:1042-0150    

DOI:10.1080/10420159108220764

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor