A.M.A. El-Sayed

Natural radioactivity of basement younger granite rocks from the eastern desert

Abstract The present work deals with a study of natural radioactivity of various samples of granite rocks from the Umm Gidri area located in North Eastern Desert. In this area, about 300 km apart from El-Minia, some geological investigations were carried out. Several samples of the basement rocks (of the Precambrian Age) 5 m subsurface were obtained from different locations. Suitable samples were prepared for natural gamma ray measurements using a 5 × 5 in. NaI(Tl) scintillation spectrometer. Qualitative analysis of natural gamma radiations from the present samples have revealed the presence of the radioisotopes: 40K, 214Bi, 208Tl and 228Ac in meaningful concentrations. These results are thought to correlate with the findings of a recent trace element geological assay done at the same area, and it would be of help in monitoring and assessing the national background radiation levels.

Positron annihilation studies of some charge transfer molecular complexes

Abstract Positron annihilation lifetimes were measured for some solid charge transfer (CT) molecular complexes of quinoline compounds (2,6-dimethylquinoline, 6-methoxyquinoline, quinoline, 6-methylquinoline, 3-bromoquinoline and 2-chloro-4-methylquinoline) as electron donor and picric acid as an electron acceptor. The infrared spectra (IR) of the solid complexes clearly indicated the formation of the hydrogen-bonding CT-complexes. The annihilation spectra were analyzed into two lifetime components using PATFIT program. The values of the average and bulk lifetimes divide the complexes into two groups according to the non-bonding ionization potential of the donor (electron donating power) and the molecular weight of the complexes. Also, it is found that the ionization potential of the donors and molecular weight of the complexes have a conspicuous effect on the average and bulk lifetime values. The bulk lifetime values of the complexes are consistent with the formation of stable hydrogen-bonding CT-complexes as inferred from the IR-spectral data.

Microstructure analysis of the effect of SRF carbon black on butyl rubber (IIR) by positron annihilation lifetime spectroscopy

Abstract The positron annihilation lifetime technique (PAL) has been applied to investigate the behaviour of the free volume (size and concentration) in butyl rubber (IIR) as a function of the concentration of semi-reinforcing furnace (SRF) carbon black. An attempt is to establish a correlation between the macroscopic mechanical and electrical properties of rubber and the microscopic properties of the free volume holes. The dependence of the size and the fraction of free volume in rubber on the concentration of SRF carbon black has been discussed on the basis of the free volume model.

Effect of temperature on γ-irradiated poly(vinyl alcohol) studied by positron annihilation

Abstract Positron lifetime measurements were performed on pure poly(vinyl alcohol) (PVA) and on PVA treated with 10% Na(acac) after gamma irradiation. Three components could be resolved in each spectrum; the long-lived component (τ 3 ) and the probability of its formation ( I 3 ) have been studied as a function of temperature from 20 to 150°C. The observed shift in the glass transition temperature ( T g ) to lower values is attributed to the increase in the electrical conductivity σ. The average free volume as a function of temperature can be extracted from the value for the long-lived component. Also, values of the thermal expansion coefficients (α) for pure and treated PVA are deduced. These values confirm the increase in the electrical conductivity in PVA due to γ-irradiation.

Free volume hole distributions of polymers via the positron lifetime technique

Abstract The positron annihilation lifetime (PAL) technique has been applied to measure the free volume hole distribution in an epoxy resin ( T g = 70°C) and in poly(vinyl alcohol) (PVA) ( T g = 80°C) at temperatures below and above T g . The PAL spectra were analyzed to continuous lifetime distributions, using the CONTIN program. The hole volume distributions were determined from the results of the ortho -positronium ( o -Ps) lifetime distributions. At 50°C, the free volume hole radii of PVA are distributed between 1·98 and 2·4 A with a maximum at 2·18 A, while for epoxy, at 40°C, they peak at 2·4 A inside the 2·18–2·6 A interval. The distributions are shifted to a larger radius as the temperature increases. The free volumes were found to range between 32 and 75 A 3 for PVA and between 50 and 325 A 3 for epoxy.

Attenuation of atomic-field bremsstrahlung from 204Tl and 99Tc in a thick target

Abstract Attenuation of the atomic-field bremsstrahlung, which is known as the external bremsstrahlung (EB), excited by 204 Tl and 99 Tc β-emitters in Al, Cu, Cd and Pb targets has been studied. The β stopper technique is employed to measure the integral intensities above 100 keV energy in different absorber thicknesses. The calculated values were obtained from the bremsstrahlung spectra recorded with different targets and the tabulated values of attenuation coefficients for mono-energetic gamma rays. A good agreement between the calculated and experimental results is obtained. It supports the correctness of the procedure used to obtain the attenuation of EB in metallic targets.

Target thickness dependence of build-up bremsstrahlung accompanying β decay of 99Tc and 204Tl

Abstract The build-up of external bremsstrahlung (EB) intensity as a function of target thickness was studied. The conventional β stopper technique is employed. Targets of Al, Cu, Cd and Pb were used to investigate the build-up of EB by low and medium end point energies of 99 Tc and 204 Tl β emitters, respectively. The experimental values show good agreement with the calculated ones in the entire range of target thickness in all cases for both β emitters.

Dose effect in gamma-irradiated polyethylene studied by positron annihilation lifetime technique

Abstract Commercial high-density polyethylene (HDPE) samples were irradiated by λ-rays with doses ranging from 10 to 200 kGy. Positron annihilation lifetime measurements were performed to study the effect of λ-radiation on the structure of polyethylene. The lifetime π 3 , associated with the pick-off process, in which the positron in o-Ps annihilates an electron from the surrounding material, and its intensity I 3 are measured as a function of λ-dose. It can be concluded that the effect of λ-radiation on polyethylene results in intensive formation of new bonds or crosslinking at doses ranging from 10 to 100 kGy. Saturation of I 3 for the irradiated HDPE at doses ranging from 100 to 200 kGy may indicate the achievement of a structural stability.

Dose effect in gamma irradiated polyethylene studied by the positron annihilation lifetime technique

Abstract Commercial high density polyethylene samples have been irradiated by gamma rays with doses ranging from 10 to 200 KGy. Positron annihilation lifetime measurements have been performed to study the effect of gamma radiation on the structure of polyethylene. The lifetime, τ 3 , associated with the pick-off process, in which the positron in o -Ps annihilates with an electron from the surrounding material, and its intensity, I 3 , are measured as a function of gamma dose. It can be concluded that the effect of gamma irradiation on polyethylene results in intensive formation of new bonds or cross-linking from 10 to around 100 KGy. Saturation of I 3 from 100 to 200 KGy may indicate the achievement of structural stability.