Effect of γ-irradiation on optical and chemical properties of CR-39 polymer

CR-39 polymer samples were irradiated with γ-irradiation up to dose ranging from 500 to 2000 kGy. The virgin and γ-irradiated polymer samples were investigated using UV–visible spectroscopy and Fourier transform infrared (FTIR) spectroscopy. In the present work, the Urbach energy was calculated using the Urbach edge method. Also, the direct and indirect energy band gaps in virgin and γ-irradiated CR-39 polymer samples were calculated. The values of indirect energy band gap were found to be lower than the corresponding values of direct energy band gap. The decrease in the optical energy band gap with increasing γ-irradiation dose was discussed on the basis of γ-irradiation-induced modifications in CR-39 polymer. The correlation between optical energy band gap and the number of carbon atoms in a cluster with modified Tauc's equation was also discussed. The FTIR spectra show considerable changes due to γ-irradiation, indicating that the detector is not chemically stable.     

Influence of γ-irradiation on the optical and electrical properties of Se(0.85) Te(0.15) films

Abstract

Se_(0.85) Te_(0.15) films were prepared by thermal evaporation under vacuum on glass substrate. The optical and electrical properties of as deposited and irradiated Se_(0.85) Te_(0.15) films with different γ-doses are reported.

The optical constants (absorption coefficient (α), extinction coefficient (k), refractive index (n) and dielectric constants (?, ?) of unirradiated and irradiated films were calculated. The value of allowed direct optical energy gap of Se_(0.85) Te_(0.15) films increased from 1.47 eV. to 1.72 eV. with increasing the γ-doses to 2.5 Mrad. The irradiated films have lower resistivity than those as deposited films (unirradiated). The activation energy (ΔE) increases from 0.72 eV. to 0.86 eV. with increasing γ-doses to 2.5 Mrad.     

Effect of 60Co γ-irradiation on structural and optical properties of thin films of Ga10Se80Hg10

Thin films of Ga₁₀Se₈₀Hg₁₀ have been deposited onto a chemically cleaned Al₂O₃ substrates by thermal evaporation technique under vacuum. The investigated thin films are irradiated by ⁶⁰Co γ-rays in the dose range of 50–150 kGy. X-ray diffraction patterns of the investigated thin films confirm the preferred crystallite growth occurs in the tetragonal phase structure. It also shows, the average crystallite size increases after γ-exposure, which indicates the crystallinity of the material increases after γ-irradiation. These results were further supported by surface morphological analysis carried out by scanning electron microscope and atomic force microscope which also shows the crystallinity of the material increases with increasing the γ-irradiation dose. The optical transmission spectra of the thin films at normal incidence were investigated in the spectral range from 190 to 1100 nm. Using the transmission spectra, the optical constants like refractive index (n) and extinction coefficient (k) were calculated based on Swanepoel’s method. The optical band gap (E_g) was also estimated using Tauc’s extrapolation procedure. The optical analysis shows: the value of optical band gap of investigated thin films decreases and the corresponding absorption coefficient increases continuously with increasing dose of γ-irradiation.     

Influence of γ-irradiation on the optical parameters of 4-tricyanovinyl-N,N-diethylaniline thin films

Thin films of 4-tricyanovinyl-N,N-diethylaniline (TCVA) were prepared by thermal evaporation technique. The spectral and the optical parameters have been investigated by using the spectrophotometric measurements of both transmittance and reflectance at normal incidence of light in the wavelength range 200–2500 nm. The effect of γ-irradiation on the optical parameters was investigated. It was observed that the increase in γ-irradiation dose caused an increase in the value of absorption index and a shift in the spectrum towards higher wavelengths. Therefore, the value of the optical band gap has decreased from 1.45 eV for as-deposited film to 1.39 eV for film exposed to γ-ray dose of 150 kGy and Urbach tail increased. On the other hand, the dispersion parameters of TCVA films were increased with the increase of the irradiation dose.     

Effect of silica type and concentrations on the physical properties of EPDM cured by γ -irradiation

This paper reports the results of studies on the thermal and electrical properties of gamma radiation cured composites based on ethylene propylene dieyne rubber (EPDM) reinforced with different concentrations of micro- and nano-silica. The effect of gamma irradiation in the presence of ethylene glycol dimethacrylate (EGDM) as radiation sensitizer on melt flow properties of EPDM was also studied. Thermogravimetric studies of the composites show that the degradation of vulcanizates is controlled mainly by the silica type and its concentration. Increasing the amount of micro- or nano-silica in the vulcanizate decreases the maximum rate of decomposition of the major degradation step compared with that of the unfilled-cured one. The micro- and nano-composites exhibited remarkable heat resistance properties compared with that of the pure EPDM as the filler dispersion of silica inhibited the thermal degradation of the polymeric matrix, which led to the micro and nano-composites showing great improvement in thermal stability. A considerable change in decomposition rate is observed by increasing filler loading from 10 to 39 phr. The dielectric properties of such composites are affected by the silica type and concentration. The dielectric constant and ac-conductivity for all composites were found to increase with increasing silica loading, which is mainly due to the interfacial polarization. The ac-conductivity values of silica/EPDM composites exhibit a strong frequency dependence with both fillers used. The conductance and dielectric constant values have been fitted using a conduction model for all samples.     

The optical properties of MgxZnl-xO thin films

Mg_xZn_1-xO thin films have been prepared on silicon substrates by radio frequency magnetron sputtering at 60℃. The thin films have hexagonal wurtzite single-phase structure and a preferred orientation with the c-axis perpendicular to the substrates. The refractive indices of Mg_xZn_1-xO films are studied at room temperature by spectroscopic ellipsometry over the wavelength range of 400--760\,nm at the incident angle of 70℃. Both absorption coefficients and optical band gaps of Mg_xZn_1-xO films are determined by the transmittance spectra. While Mg content is increasing, the absorption edges of Mg_xZn_1-xO films shift to higher energies and band gaps linearly increase from 3.24.eV at x=0 to 3.90\,eV at x=0.30. These results provide important information for the design and modelling of ZnO/ Mg_xZn_1-xO heterostructure optoelectronic devices.     

Influence of γ-irradiation on the non-isothermal decomposition of calcium-gadolinium oxalate

Thermal decomposition of co-precipitated unirradiated and irradiated Ca-Gd oxalate has been studied by adopting differential thermal analysis (DTA) and thermogravimetric (TG) techniques. The reaction occurs through two stages corresponding to the decomposition of gadolinium oxalate (Gd-Ox) followed by that of calcium oxalate (Ca-Ox). The kinetic parameters for both the stages are calculated by using solid state reaction models and Coats-Redfern's equation. The co-precipitation as well as irradiation alter the DTA peak temperatures and the kinetic parameters of Ca-Ox. The decomposition of Gd-Ox follows the two dimensional Contracting area ( R 2 ) mechanism, while that of Ca-Ox follows the Avrami-Erofeev ( A 2 ) mechanism ( n =2), which are also exhibited by the co-precipitated and irradiated samples. Co-precipitation decreases the energy of activation and the pre-exponential factor of the individual components but the reverse phenomenon takes place upon irradiation of the co-precipitate. The mechanisms underlying the phenomena are explored.     

Influence of alloying elements on structure and some physical properties of quenched Sn–Sb alloy

We study the influence of ternary and quaternary alloying elements (Pb, Cd, Cu or Cu–Pb and Cu–Cd) on structural, electrical, hardness and other mechanical properties of Sn–Sb alloys (using an X-ray diffractometer and optical microscope, the double bridge method, Vickers hardness tester and the dynamic resonance method) to produce the best alloy for bearing applications. Adding Cu or Pb to Sn–Sb alloys improves their bearing properties, such as the mechanical properties (elastic modulus, internal friction, hardness and fracture strain) and thermal conductivity. Also, adding Cu, Pb or Cu–Pb to Sn–Sb alloys makes them excellent in their bearing applications and environmental hazards when compared with the Pb ₈₈Sn ₁₀Cu ₂ alloy for automotive applications (FIAT Normalizzazione) and the lead-based Babbitt bearing alloy.     

Effect of lead on microstructure and some physical properties of Sn–Zn–Cd alloy

The effect of lead on the structure, electrical resistivity, internal friction, elastic modulus and thermal properties of Sn₈₁Zn₉Cd₁₀ ternary alloys have been investigated using different experimental techniques with their analysis. In addition, properties of this alloy were compared with other Sn–Zn or Sn–Zn–Cd alloys and commercial solder alloys. It has a higher electrical resistivity, internal friction and lower elastic modulus when compared with Sn–Zn or Sn–Zn alloys with other additions such as Cd, Bi or In. The Sn₆₁Zn₉Cd₁₀Pb₂₀ alloy has a lower melting point, electrical resistivity and internal friction when compared with the commercial Pb–Sn solder alloy, but it has a similar elastic modulus.     

Influence of Si-N interlayer on the microstructure and magnetic properties of γ′-Fe4N films

The (γ′-Fe₄N/Si-N)_n (n: number of layers) multilayer films and γ′-Fe₄N single layer film synthesized on Si (1 0 0) substrates by direct current magnetron sputtering were annealed at different temperatures. The structures and magnetic properties of as-deposited films and films annealed at different temperatures were characterized using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The results showed that the insertion of Si-N layer had a significant influence on the structures and magnetic properties of γ′-Fe₄N film. Without the addition of Si-N lamination, the iron nitride γ′-Fe₄N tended to transform to α-Fe when annealed at the temperatures over 300 °C. However, the phase transition from γ′-Fe₄N to ?-Fe₃N occurred at annealing temperature of 300 °C for the multilayer films. Furthermore, with increasing annealing temperature up to 400 °C or above, ?-Fe₃N transformed back into γ′-Fe₄N. The magnetic investigations indicated that coercivity of magnetic phase γ′-Fe₄N for as-deposited films decreased from 152 Oe (for single layer) to 57.23 Oe with increasing n up to 30. For the annealed multilayer films, the coercivity values decreased with increasing annealing temperature, except that the film annealed at 300 °C due to the appearance of phase ?-Fe₃N.     

Study on γ-ray exposure buildup factors and fast neutron-shielding properties of some building materials

We have computed γ-ray exposure buildup factors (EBF) of some building materials; glass, marble, flyash, cement, limestone, brick, plaster of paris (POP) and gypsum for energy 0.015–15 MeV up to 40 mfp (mfp, mean free path) penetration depth. Also, the macroscopic effective removal cross-sections (Σ_R) for fast neutron were calculated. We discussed the dependency of EBF values on photon energy, penetration depth and chemical elements. The half-value layer and kinetic energy per unit mass relative to air of building materials were calculated for assessment of shielding effectiveness. Shielding thicknesses for glass, marble, flyash, cement, limestone and gypsum plaster (or Plaster of Paris, POP) were found comparable with ordinary concrete. Among the studied materials limestone and POP showed superior shielding properties for γ-ray and neutron, respectively. Radiation safety inside houses, schools and primary health centers for sheltering and annual dose can be assessed by the determination of shielding parameters of common building materials.     

Structural investigation of bismuth borate glasses under the influence of γ-irradiation through ultrasonic studies

The ultrasonic velocity and attenuation measurements for different compositions of irradiated heavy metal oxide (HMO) borate glasses xBi₂O₃ (1−x) B₂O₃ (where x=0.25, 0.30, 0.35, 0.40, 0.45) has been investigated at room temperature (303 K) using pulse echo overlap method. The elastic moduli, Debye temperature, Poisson's ratio and other acoustical parameters have been obtained from experimental data. Structural changes after irradiation have been investigated by using FTIR spectroscopy and ultrasonic studies. As the changes are strongly dependent on the internal structure of the absorbing substance, in the present investigation ultrasonic velocities before and after γ-irradiation in bismuth borate glasses are measured as a function of composition, from which the structural changes in the network former B₂O₃ and modifier Bi₂O₃ due to irradiation are obtained.     

The influence of growth patterns on the transmission properties of nonabrupt GaAs/AlxGa1−xAs heterojunctions

The influence of growth patterns in the transmission properties of nonabrupt GaAs/Al_xGa_1−xAs heterojunctions is investigated. Five interfacial growth patterns, representative of interfacial alloy variations generated by different growth techniques, are used. It is shown that carrier transmission depends on the type of the aluminum molar fraction variation through the interface. A study of the role of the interface width in carrier transmission is done for each compositional growth profile.     

Studies of some physical properties of PrFe0.7Ni0.3O3 thin films after 200 MeV Ag15+ irradiation

PrFe_0.7Ni_0.3O₃ thin films (thickness ~ 200 nm) were prepared by pulsed laser ablation technique on LaAlO₃ substrate. These films were irradiated with 200?MeV Ag¹⁵⁺ ions at various fluencies, ranging from 1 × 10¹¹ to 1 × 10¹² ions/cm². These irradiated thin films were characterized by using X-ray diffraction, dc conductivity, dc magnetization and atomic force microscopy. These films exhibit orthorhombic structure and retain it even after irradiations. The crystallite size (110–137?nm), micro strain (1.48 × 10^?2–1.75 × 10^?2 line^?2?m^?4) and dislocation density (79.7 × 10¹⁴–53.2 × 10¹⁴ line/m²) vary with ion fluencies. An enhancement in resistivity at certain fluence and then a decrease in its value (0.22175–0.21813?Ω?cm) are seen. A drastic change in observed magnetism after ion irradiation is seen. With ion irradiation, an increase in surface roughness, due to the formation of hillocks and other factors, is observed. Destruction of magnetic domains after irradiation can also be visualized with magnetic force microscopy and is in close agreement with magnetization data. The impact on various physical properties in these thin films after irradiation indicates a distortion in the lattice structure and consequently on single-particle band width caused by stress-induced defects.     

The influence of AlN/GaN superlattice intermediate layer on the properties of GaN grown on Si（111） substrates

AlN/GaN superlattice buffer is inserted between GaN epitaxial layer and Si substrate before epitaxial growth of GaN layer. High-quality and crack-free GaN epitaxial layers can be obtained by inserting AlN/GaN superlattice buffer layer. The influence of AlN/GaN superlattice buffer layer on the properties of GaN films are investigated in this paper. One of the important roles of the superlattice is to release tensile strain between Si substrate and epilayer. Raman spectra show a substantial decrease of in-plane tensile strain in GaN layers by using AlN/GaN superlattice buffer layer. Moreover, TEM cross-sectional images show that the densities of both screw and edge dislocations are significantly reduced. The GaN films grown on Si with the superlattice buffer also have better surface morphology and optical properties.     

Monolithic epitaxy and optoelectronic properties of single-crystalline γ-In2Se3 thin films on mica

The growth of γ-In₂Se₃ thin films on mica by molecular beam epitaxy is studied. Single-crystalline γ-In₂Se₃ is achieved at a relatively low growth temperature. An ultrathin β-In₂Se₃ buffer layer is observed to nucleate and grow through a process of self-organization at initial deposition, which facilitates subsequent monolithic epitaxy of single-crystallineγ-In₂Se₃ at low temperature. Strong room-temperature photoluminescence and moderate optoelectronic response are observed in the achieved γ-In₂Se₃ thin films.     

The influence of the composition of eight-atom Pt–Ir clusters on the magnetic properties

The energetic stability, electronic structure and magnetic properties of Pt_8–nIr_n clusters have been investigated by employing the spin-polarised generalised gradient approximation. The cubic structure is expected to be the effective building block in Ir-rich clusters after optimisation extensively. The average binding energy of all the clusters presents the linear increment trend with iridium atoms, due to the stronger interaction between Ir atoms than Pt atoms. Bader charge analysis shows how tiny charge transfers from iridium to platinum. The atomic moments of Ir are larger than that of Pt, and the Ir-rich clusters show greater moments than the Pt-rich cluster, with the exception of Ir₈ and Ir₇Pt. A unique magnetic property is found in the Pt₄Ir₄ cluster, where two Pt atoms show antiferromagnetic alignment and the other atoms are found to be aligned ferromagnetically.     

The influence of nickel dopant on the microstructure and optical properties of SnO2 nano-powders

The microstructure and optical properties of Ni-doped SnO2 nano-powders are studied in detail. By Ni-doping, not only the grain size reduces, but also the grain shape changes from nano-rods to spherical particles. The crystallization becomes better with annealing temperature increasing. The band gap energy decreases as nickel doping level increases. The sp-d hybridization and alloying effect due to amorphous SnO2-x phase should be responsible for the band gap narrowing effect. Nickel dopant does not change the photoluminescence （PL） peak positions.