摘要:

The energy distributions of both ions and neutral atoms sputtered during ion bombardment of a few polycrystalline metals have been measured. The absolute values of the ionization probabilityP+as a function of the emitted particle velocityvwere obtained. The ionization probability for Be, Cu, Ag and W targets is found to depend exponentially on the particle velocity in accordance with the electron tunneling model. In the case of Pb and Sn the ionization probability shows strong deviation from an exponential dependence at high emission energies.

ISSN:1042-0150    

DOI:10.1080/10420159008213070

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Damage production in (100) InAs by room temperature implantation of N+at 50 keV in the range of 1E15 to 2E17 N+/cm2has been studied by RBS/Channeling. The14N(d, p)15N nuclear reaction was used to check the implanted doses. A quasi saturation of damage at 2E16 N+/cm2was followed by apparent amorphization of the surface at ∼ 1E17 N+/cm2. Channeling measurements at different probe energies have shown that the damage at the highest dose consists of both point and extended defects with small regions of local order still remaining in the matrix.

ISSN:1042-0150    

DOI:10.1080/10420159008213071

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:1042-0150    

DOI:10.1080/10420159008213072

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Niobium films (120 nm thick) deposited by electron-beam evaporation were implanted near 5 K with 100 keV N2ions to maximum fluences of 4 to 7 × 1017N/cm2. STEM diffraction patterns showed a structural phase transformation from the initial Nb lattice with [110] fiber texture (bcc,a0= 0.330 nm) to randomly orientedδ-NbN (fcc,a0= 0.435–0.439 nm), via an intermediate, highly disordered Nb-(interstitial N) structure (bcc, maximuma0= 0.342 nm). Decreases in transition temperatureTcfrom 9 K to a minium of 3 K and rapid linear increases in residual resistivity (ρ10) were observed to fluence of 1.0–1.5 × 1017N/cm2and were attributed to the accumulation of radiation-induced defects. Continued implantation resulted inδ-NbN formation andTcincreases to maximum values of 9–10 K which were achieved at fluences from 3.5 to 5.0 × 1017N/cm2, corresponding to average substoichiometric N/Nb ratios of 0.52–0.75, at which point the phase transformation was complete. Theδ-NbN formation was accompanied by significant lattice reordering and grain growth. At still higher fluencesTcgradually declined to 8–9 K and sharp increases inρ10were observed, possibly due to film sputtering.

ISSN:1042-0150    

DOI:10.1080/10420159008213073

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The experimental measurement of the perturbed angular correlation (PAC) of radiation emitted from probe nuclei implanted in a host lattice is becoming an increasingly important analytical technique. Most recent measurements have involved single crystal samples which are more informative than polycrystal ones, and the perturbing fields have not necessarily been axially symmetric. In these cases the theoretical treatment of the data is necessarily more complex. We have investigated the perturbation function applicable in the case of the hyperfine interaction of probe ions implanted in a host matrix. It is shown that in the general case ofγ–γcorrelations involving static electric quadrupole interactions the perturbation function can always be expressed as a sum of cosine terms, without having to make any assumption about the axial symmetry of the perturbing field or employing the averaging procedure used in the case of polycrystalline hosts. Though many have used this fact, the formal justification for it in this most general case has not been presented before.

ISSN:1042-0150    

DOI:10.1080/10420159008213074

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

According to a molecular dynamics (MD) technique, radiation effects of an amorphous Pd80Si20alloy induced by N ion were simulated in order to study its structural change observed experimentally before and after irradiation. This experimental structural change was well reproduced by the isobaric MD simulation and by a proposed model. Simultaneously, the formation process of radiation-induced damage was investigated in the simulation.

ISSN:1042-0150    

DOI:10.1080/10420159008213075

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Gamma radiolysis of NaNo3, KNO3, Sr(NO3)2and Ba(NO3)2dispersed in sulphate and carbonate matrices has been studied over a wide absorbed dose range. Radiolytic decomposition of the nitrate salt depends on the concentration of the nitrate in admixture as well as the total absorbed dose. G(NO2) values calculated on the basis of electron fraction of the nitrate salt decrease with the increase in the mol% of the nitrate salt. Percent decomposition of Na and K nitrates in sulphate and carbonate admixtures increases with the absorbed dose over a wide concentration range. An admixture of Sr(NO3)2(5 mol.%) with SrSO4and SrCO3exhibited an increase of G(NO2) by 30 and 20-fold respectively. An enhacement of G(NO2) by 25-fold has been observed in case of (5 mol.%) Sr(NO3)2+ BaSo4admixture. G(NO2) values for Ba(NO3)2admixtures with BaSO4, BaCO3and SrSO4have been found to be much larger (16-fold) than that for the pure salt. The additives seem to exhibit sensitizing effect causing enhanced decomposition by the energy transfer process in solid state. A plausible mechanism of energy transfer involving the radical species has been proposed. EPR studies suggest the formation of radicals such as SO4, SO3, SO2, NO2-3, NO2onγ-irradiation. Thermoluminescence (TL) and reflectance spectral studies indicate the possible interaction of defect centres in the matrix with NO3causing enhanced decomposition. The efficiency of energy transfer seems to depend on the nature of the matrix, concentration of nitrate in the admixture and the absorbed dose.

ISSN:1042-0150    

DOI:10.1080/10420159008213076

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Time evolution of non-equilibrium systems, where the probability density is described by a continuum Fokker-Planck (F-P) equation, is a central area of interest in stochastic processes. In this paper, a numerical solution of a two-dimensional (2-D) F-P equation describing the growth of helium-vacancy clusters (HeVCs) in metals under irradiation is given. First, nucleation rates and regions of stability of HeVCs in the appropriate phase space for fission and fusion devices are established. This is accomplished by solving a detailed set of cluster kinetic rate equations. A nodal line analysis is used to map spontaneous and stochastic nucleation regimes in the helium-vacancy (h-v) phase space. Growth trajectories of HeVCs are then used to evaluate the average HeVC size and helium content during the growth phase of HeVCs in typical growth instability regions.

ISSN:1042-0150    

DOI:10.1080/10420159008213077

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor