M. A. Abdel-Rahman

Effect of sample thickness on the measured mass attenuation coefficients of some compounds and elements for 59.54, 661.6 and 1332.5 keV γ-rays

Abstract Measurements have been made to determine γ-rays attenuation coefficients very accurately by using an extremely narrow-collimated-beam transmission method. The effect of the sample thickness on the measured values of the mass attenuation coefficients (μ/ρ) cm 2 / g of perspex, bakelite, paraffin, Al, Cu, Pb and Hg have been investigated at three different γ-ray energies (59.54, 661.6 and 1332.5 keV). It is seen that for these chosen materials ( μ / ρ ) remains constant in good agreement with the theoretical values up to 3 mean free paths and after that ( μ / ρ ) values for Cu, Pb and Hg decrease with further increase in the absorber thickness. This result may be attributed to the increase in the number of coherent small-angle scattering photons which reach the detector.

Investigation of defects (migration and formation) in metals by positron annihilation lifetime

Abstract In the present work a discussion of the possibilities to study defect in solids is presented. Generally, positron behavior in metals is simpler than in insulators. Migrations and formations of defects (point defects, dislocation) in metals have been studied in detail by using positron annihilation lifetime technique. Samples of Pb, Bi, Al, Mg, Ag, and Cu were deformed to 20% thickness reduction then annealed at different temperature 1 h before quenched (air cooling). In each pair of samples, lifetime spectrum was accumulated, as a function of the annealing temperature and measured at room temperature. For each metal, two stages were observed with a minimum at T=(0.52–0.62)Tm. This seems to be due to the compensation of two different processes; one for recovery and the other for defect formation. This observation of two processes is clear only on the metals have face center cubic structure such as (Al, Pb, Ag and Cu).

Positron Trapping Cross Section and Trapping Efficiency in Plastically Deformed Magnesium

Measurement of positron annihilation lifetime in a pairs of deformed magnesium specimens with deformations of up to 75% are discussed. The lifetime *BAR*τ*BAR* exhibits saturation: for deformations larger than those corresponding to a 15% thickness reduction. The lifetime varies from 231±2 ps for annealed magnesium to 249±2 for dislocation-saturated samples. The trapping cross section and trapping efficiency are calculated.

Estimation of Dislocation Concentration in Plastically Deformed Al-Li Based Alloy by Positron Annihilation.

Measurements of positron annihilation mean lifetime τ have been performed on eight different specimens of Al–Li based alloy plastically deformed at room temperature up to 40% thickness reduction. This measurement shows clearly positron trapping by dislocations. The positron lifetime τ exhibits a saturation for deformations larger than (15%) thickness reduction. The fitted lifetime varies from (183 ±2 ps) for annealed sample to (205 ±2 ps) for the dislocation saturated value. Using a trapping model, the data yield the values of µ= 3.83×10-8 cm3 s-1 for the specific trapping rate and σ= 3.58×10-15 cm2 for the trapping cross section, some what lower than those for plastically deformed Al single crystals. The value obtained for Δτ, the increase in lifetime of positrons trapped at dislocations in plastically deformed Al–Li based alloy sample over annihilation in the annealed sample, is 22 ps. This is about 40% of the lifetime increase for the case of positrons trapped at dislocations in plastically deformed Al single crystals. Dislocation densities at different thickness reduction have been estimated.

Study of recovery in plastically deformed Al-Li-based alloy by positron annihilation

Positron annihilation mean lifetime measurements have been performed on two samples of the commercial alloy [(8090) Al-Li-Cu-Mg-(Zr)]. One sample was deformed (37.5%) at room temperature and subjected to isochronal annealing. The temperature was varied from 300 K to 623 K. The other one was homogenized at 823 K and subjected to isothermal annealing at 873 K. The time of annealing varied from 0 to 12 h in steps of 2 h. Evidence of nonspurious lifetime component, in both cases, have been observed. The results of the plastically deformed samples (*BAR*τ*BAR* = 202±2 ps) are interpreted as trapping of positrons in dislocations and Li-rich zones. On the other hand the results of the homogenized sample (*BAR*τ*BAR* = 183±2 ps) are interpreted as trapping of positrons in Li-rich zones only.

Artificial Ageing Effect on Mechanical, Electrical Properties and Positron Lifetime of Aircraft 2024 Alloy

Heat Treatments for Different Aging Times Were Performed on 2024 Aluminum Alloy. the Effect on the Positron Lifetime, Electrical and Mechanical Properties of the 2024 (Al-Cu-Mg) Alloy Was Studied. Artificial Ageing Was Conducted by Heating at a Constant Rate to a Specific Temperature, Followed by Annealing. the Alloy Was Treated at 192°C for Various Times, Followed by Annealing. Measurements as a Function of Aging Time Were Found to Exhibit Prominent Changes Related to the Formation of Precipitates.

Defect Investigation of Plastically Deformed Al 5454 Wrought Alloy Using PADBS and Electrical Measurements

Positron Annihilation Doppler Broadening Spectroscopy (PADPS) is a nondestructive technique used in materials science. Electrical measurements are one of the oldest techniques also used in materials science. This paper aims to discuss the availability of using both PADPS and electrical measurements as diagnostic techniques to detect defects in a set of plastically deformed 5454 wrought aluminum alloys. The results of the positron annihilation measurements and the electrical measurements were analyzed in terms of the two-state trapping model. This model can be used to investigate both the defect and dislocation densities of the samples under investigation. Results obtained by both nuclear and electrical techniques have been reported.

ELASTIC SCATTERING OF 12C BY 12C AT INTERMEDIATE ENERGIES

Using the double folding model (DF), the real part of the central optical potential for the 12C + 12C system is derived. This potential as well as the single-folding cluster model potential (SFC) are used to calculate the total and differential cross sections for 12C elastically scattered on 12C at three laboratory energies, Elab. = 300, 344.5 and 360 MeV. The calculations are carried out with five sets of nucleon-nucleon (NN) interaction of the integrable Gaussian form and two sets of parameters for the nuclear matter density of the harmonic oscillator form. The transparency of the target nucleus is found to increase as the projectile energy increases. Good fits between the present calculations and the experimental data, as well as with previous calculations, are obtained. The simple methods used here for calculating the real part of the optical potential reduce the potential computing time enormously. The suitable choice of NN interaction as well as nuclear matter densities is important.

Study the Effect of Plastic Deformation in 8006 Al-Alloys by Positron Lifetime Spectroscopy, Vickers Hardness and X-Ray Diffraction

Due to the great effect of defects on the properties of the material including strength, ductility, resistivity and opacity, there are many techniques that are used in defect detecting. Positron annihilation spectroscopy (PAS), Vickers hardness, and X-ray diffraction were used to study the influence of plastic deformation on the properties of 8006 Al-alloy in this work. An increase in the positron lifetime and Vickers hardness with a bit Broadening of XRD peaks was observed with increasing the degree of deformation reflecting a large dislocation density produced by plastic deformation.

Determination of the activation enthalpy for migration of dislocations in plastically deformed 8006 Al-alloy by positron annihilation lifetime technique

The activation enthalpy for migration of dislocations of plastically deformed 8006 Al-alloy was investigated by positron annihilation lifetime technique. Plastic deformation using a hydraulic press produces mainly dislocations and may produce point defects. The type of defect was studied by isochronal annealing which determines the temperature range of recovery of each type. Only one type of defect (dislocations) was observed for the investigated sample and was found to be recovered within the range 455–700 K. Isothermal annealing by slow cooling was performed through this range and used in determination of the activation enthalpy of migration of dislocations which was found to be 0.26 ± 0.01 eV.