F. H. Abd El-Kader

Electrical properties of gamma-irradiated, pure, and nickel chloride-doped polyvinyl alcohol films

The electrical transport properties, such as direct current (dc) electrical conductivity (σ), dielectric constant (e′), and dc current–time characteristics of unirradiated and γ-irradiated pure and NiCl2-doped PVA were studied in the temperature range of 26–155°C. Quantitative analysis was carried out to determine the thermal activation energy of the conduction process, drift mobility, and carrier concentration. The thermally activated mobility of charge carriers is confirmed from calculations of drift mobility at different γ-doses and temperatures. The results obtained revealed that γ-irradiation enhances the conductivity. The dielectric constant data at different temperatures before and after irradiation can be attributed mainly to the changes in the intra- and intermolecular interactions. The dc conductivity at 30 and 40°C, activation energy in low temperature region I, and proved to be dose-dependent. The obtained data suggests that these materials may have an application in dosimetry.

Electrical and optical studies on γ-irradiated pure and chromium-chloride-doped polyvinyl alcohol

Measurements of optical absorption, electrical conductivity and of the dielectric constant were used to study the changes that occur due to γ-radiolysis of pure and CrCl3-doped polyvinyl alcohol (PVA) thin films. Identification of the structure and assignments of energy bands were derived in terms of ligand field theory. Induced changes in the absorbance at 282 and 222 nm bands in pure and doped PVA samples, respectively, appeared to be dose dependent. The direct-current (d.c.) electrical conductivity of the samples was measured in the temperature range 296–433 K, and the results obtained revealed that γ-irradiation enhances the conductivity. The calculated activation energy in the lower temperature region also proved to be dose dependent. Plots of the dielectric constant, ɛ′, against temperature show an interesting behaviour which depends on the dopant concentrations and exposure to γ-irradiation. The results obtained suggest that these materials may have an application in dosimetry.

Study of thermal currents in CoCl2-doped poly (vinyl alcohol) films irradiated with γ-rays

Abstract Thermally stimulated depolarisation current (TSDC) and time-dependent conduction current of unirradiated and γ-irradiated pure and CoCl 2 -doped PVA films have been measured. Doses in the range 21–75 Mrad were used. The TSDC of pure and doped PVA before and after irradiation revealed a T g relaxation peak. The induced changes in the peak current ( I m ) of the glass relaxation peak are composition and dose dependent. A marked decrease in TSDC corresponding to the main glass relaxation peak is observed with ageing time. The role of γ-irradiation in perturbing the orientation of the dipoles and/or chain segments was inferred from the disappearance of some sub- T g relaxation peaks. The thermally activated mobility of charge carriers is confirmed from calculations of drift mobility at different γ doses and temperatures.

Optical studies of pure and gelatin‐doped poly(vinyl alcohol) films irradiated with fast neutrons

The ultraviolet (UV) and infrared (IR) spectra of pure poly(vinyl alcohol) (PVA) and gelatin–doped PVA films with concentrations (2, 5, 7, 10, and 15 wt %) were studied before and after irradiation with neutron fluences in the range of 105–108 n/cm2. The obtained data revealed that the addition of gelatin and neutron irradiation causes structural variation in the PVA network. The analysis of the UV spectra showed that the increase of dopant concentration above 5 wt % gelatin makes the sample less resistant to a degradation effect caused by neutron irradiation. It was also found that the intensity of the band at 210 nm increases by increasing dopant concentration. Careful examination of the infrared spectra indicated that the induced percent crystallinity of the sample containing 5 wt % gelatin has more stability than the other doped samples. Neutron irradiation also results in the appearance of new absorption bands and irregular change in the absorbance of some IR bands.

Synthesis and characterization of PVK/AgNPs nanocomposites prepared by laser ablation

Nanocomposites of Poly (n-vinylcarbazole) PVK/Ag nanoparticles were prepared by laser ablation of a silver plate in aqueous solution of chlorobenzene. The influences of laser parameters such as; time of irradiation, source power and wavelength (photon energy) on structural, morphological and optical properties have been investigated using X-ray diffraction (XRD), Transmission electron microscopy (TEM), Ultraviolet-visible (UV-Vis) and Photoluminescence (PL). A correlation between the investigated properties has been discussed. XRD, TEM and PL indicated that the complexation between AgNPs and PVK in the composite system is possible. Only the reflection peak at 2θ=38° of AgNPs appeared in the composite nanoparticles while the other reflection peaks were destroyed. The nanoparticles shape and size distribution were evaluated from TEM images. TEM analysis revealed a lower average particle size at long laser irradiation time 40min and short laser wavelength 532nm together with high laser power 570mW. From UV-Visible spectra the values of absorption coefficient, absorption edge and energy tail were calculated. The reduction of band tail value with increasing the laser ablation parameters confirms the decrease of the disorder in such composite system. The PL and UV-Vis. spectra confirm that nanocomposite samples showed quantum confinement effect.

Electrical studies on PVA-PE copolymer

The electrical transport properties including electrical conductivity (σ), dielectrical constant (ϵ′), thermally stimulated depolarization current (TSDC), and pyroelectric coefficient (P) of a poly(vinyl alcohol)-polyethylene (PVA-PE) copolymer were studied in the temperature range 296–433 K. Two stages of behavior have been observed with activation energies 1.49 and 0.05 eV. Discussion of conduction mechanism was carried out in terms of relevant theories. The existence of a relaxation peak in ϵ′ versus T relation has been analyzed taking into consideration space charge effects and dipole orientation phenomena. The TSDC spectra showed two peaks with differing intensity and position independent of field intensity. Pyroelectric current data provide further support to space charge effects.

Changes in the structure of poly (vinyl alcohol)-CrCl3 composites irradiated by low level fast neutron doses

Cast thin films of the composites PVA-CrCl3 were prepared. The absorption spectra, X-ray diffraction, hardness number and dielectric constant were measured before and after irradiation by neutrons in the fluence range of 3.4 × 105 to 1.68 × 108 n/cm2. The Racah constant was calculated to be 600 cm-1 which is about 65% of the free ion value. A pronounced band characterizing the carbonyl group has developed at 220 nm by irradiation. The degree of crystallinity is enhanced with the increase of neutron fluence. The position of the glass transition and α-relaxation temperatures were dependent on neutron fluence and doping content.

A study on the kinetic energy release in metastable transitions gererated by electron impact and field ionization

Abstract A conventional EI-FI ion source, characterized by the fact that the ions are generated in the same place in both techniques, was used to investigate the kinetic energy released in metastable transitions. No appreciable difference was found between TEI and TFI values for the same transition occurring in the second field-free region of the reversed Nier-Johnson Varian-MAT DF mass spectrometer. This result implied that both Fl ions of low internal energy and EI ions of somewhat higher internal energy pass over the same potential surface during decomposition, and that the T value is independent of the excess vibrational energy present in the transition state. The influence of the El ion source temperature and the field anode temperature was also investigated. The T values were shown to be temperature dependent in some cases.

Influence of the nitrogen content on the optical properties of CNx films.

Polycrystalline carbon nitride thin films were prepared by electrolysis of methanol-urea solution at different concentrations of urea to methanol and applied voltage 800 volts for 10h. Grazing incidence X-ray diffraction (GIXRD) revealed that the crystalline structure of carbon nitride films at moderate nitrogen content changed from amorphous phase to polycrystalline α-C(3)N(4), and β-C(3)N(4) phases. The optical transmission analysis of the films revealed that the band gap value for indirect allowed transitions increased with increasing nitrogen content, while the associated phonon energy value showed the opposite behavior. The refractive index and the extinction coefficient of the samples deposited with different concentrations were determined as a function of wavelength. The refractive index decreases with increasing both nitrogen content and crystallinity. The refractive index dispersion for the investigated samples is discussed in terms of the single oscillator model and oscillator parameters.

Comparative study on the kinetic energy release observed by high voltage and sector voltage scan techniques

Abstract A careful study has been carried out to compare the kinetic energy released in some metastable transitions occurring in the first and second field-free regions of the reversed Nier-Johnson double focusing mass spectrometer. No detectable difference in kinetic energy released was observed in some cases. In other cases, the kinetic energy released, calculated from the HV scan technique, is somewhat higher than that in the ESA scan method. In some cases the differences in kinetic energies released may be attributed to shorter observation times, whilst variation of T with ion decomposition time is indicative of the existence of ions having different internal energies.