FTIR and DSC studies on gamma irradiated P(VdF-HFP) fluoropolymers applied to dosimetry

Radiation effects on semicrystalline poly(fluorovinylidene-co-hexafluoropropylene) copolymer [P(VdF-HFP)] induced by high-energy irradiation were investigated. Films with 150 μm thickness were irradiated with gamma doses ranging from 1.0 kGy to 3.0 MGy. Fourier transform infrared (FTIR) spectroscopy was used to follow the radio-induction of new molecular bonds. Differential scanning calorimetry (DSC) was employed to study the crystalline degradation of the irradiated samples. P(VdF-HFP) copolymers have fluorinated monomers [-CF₂-CF-CF₃-] randomly added to the [-CH₂-CF₂-] main chain of PVdF homopolymer. In this case, the [-CF₃-] molecular bonds are branched to the main chain. There is an increasing interest about the effect of high gamma radiation dose on the P(VdF-HFP) radiolysis, once it could enhance some of their already known interesting properties such as biomedical applications and electrostrictive transducers/actuators. FTIR spectroscopic data revealed two optical absorption bands at 1730 and 1754 cm⁻¹ whose intensities are unambiguously related to gamma delivered dose ranging from 0.0 to 1000 kGy. Fading analysis has demonstrated no loss of signal until 11 months after irradiation. DSC and XRD data revealed a continuous decrease in both the melting latent heat and crystalline dimensions for doses ranging from 250 to 3000 kGy. Because of the low fading and the linear behavior with respect to delivered gamma doses of the absorption band at 1754 cm⁻¹, P(VdF-HFP) copolymers are good candidates for being explored for high gamma dose dosimetry application.     

Use of poly(methyl methacrylate) in radioactive waste management: I. Radiation stability and degradation

In this study, in order to understand the possible use of PMMA in radioactive waste management as a solidifying agent, radiation stability of the PMMA was studied by gamma irradiations at two different dose rates of 1485 and 82.8 Gy/h. The total dose of irradiation was up to 523 kGy. Degradation nature was tested by studying the changes in mechanical and thermal properties with rate and total dose of irradiation. Ultimate tensile strength and toughness first increased and then decreased with total irradiation dose. Half value dose (HVD) for elongation was 148 kGy and it was 178 kGy for tensile strength at the dose rate of 1485 Gy/h. Half value dose was found from the extrapolation of experimental data as 228 kGy for elongation and 205 kGy for tensile strength at the dose rate of 82.8 Gy/h. The FTIR spectral analysis showed depolymerization degradation of polymer with irradiation. It was concluded from experimental results that PMMA can be used for embedding radioactive wastes.     

Effect of 1.25 MeV gamma irradiation in α-phased PVDF

The radiation induced changes taking place in α-phased poly(vinylidene fluoride) (PVDF) films exposed to gamma rays were investigated in correlation with the applied doses. Samples were irradiated in vacuum at room temperature by a 1.25 MeV Co⁶⁰ source with the doses in the range of 0–300 kGy. Optical and chemical properties of the irradiated as well as un-irradiated PVDF films were studied using UV–visible and FTIR techniques. Gamma irradiation was found to induce changes vary depending on the radiation dose.     

Effect of irradiation dose on plastic deformation of vacuum hot pressed ultra high molecular weight polyethylene

Ultra high molecular weight polyethylene is a type of semi-crystalline polymer which is widely used in artificial joints. Degradation of it’s mechanical properties under irradiation is an important aspect for its applications. In this study, molded and ram extruded material were gamma irradiated in vacuum at doses of 50 kGy, 100 kGy and 150 kGy and its uniaxial tensile properties were investigated at room temperature. The results showed that the tensile modulus, true ultimate stress and true ultimate strain were reduced as the dose increased. There was no significant difference of the true yield strain between non-crosslinked and crosslinked material, but the true yield stress of non-crosslinked material was significantly higher than the crosslinked material. The curvature of the true stress-true strain curve after yielding did not exhibit a significant relationship as a function of dose. However, both molded and ram extruded material showed a significant exponent relationship with dose.     

Co-60 gamma radiation assisted diffusion of iodine in polypropylene

Thin films of polypropylene having dimensions 50 mm × 15 mm × 350 μm were immersed in 1 N iodine solution and then irradiated with Co-60 gamma radiation for the periods of 48, 96 and 144 h at the doses varying from 14.4 to 43.2 kGy. The films were also kept immersed in iodine solution for similar periods but without irradiation. Furthermore, the films were also directly-irradiated with Co-60 gamma radiation for similar periods and doses. The radiation-iodinated, plain-iodinated and directly-irradiated samples were characterized by using various techniques such as weight gain EDS, SEM, FTIR, UV–visible spectroscopy, contact angle and XRD. Weight gain, EDS and SEM collectively reveal that gamma irradiation enhances iodine intake in polypropylene. FTIR, EDS and contact angle measurements indicate that presence of iodine during irradiation resists radiation induced carbonylation of polypropylene. FTIR also shows presence of HOI (Hypoiodous acid) species instead of expected C–I bonds. UV–visible analysis unambiguously shows that presence of iodine enhances radiation induced band gap reduction process of polypropylene. XRD indicates that iodine decreases the crystallinity of polypropylene.     

Effect of Li3+ irradiation on the transport properties of La0.7Pb0.3MnO3 type CMR material

We report the low temperature (below the metal–insulator transition temperature T_im) resistivity and magnetoresistance (MR) behavior of 50 MeV Li³⁺ beam irradiated La_0.7Pb_0.3MnO₃ for three different fluences. Ion beam irradiation causes a decrease of T_im leading to the increase of insulating regime. Resistivity data of the unirradiated as well as irradiated samples fitted well with an equation of the form ρ = ρ₀ + ρ_2.5T^2.5 which indicates predominant contribution from the electron–magnon interaction (second term). The temperature dependent MR data of samples irradiated with different ion fluences follow the simple relation [MR = a + b/(T + C)] showing appreciable effect of radiation on the parameters a, b and C. The physical significance of the radiation effect on these parameters is not yet very clear.     

Doping of 6H–SiC pn structures by proton irradiation

The influence of proton irradiation on current–voltage characteristics, N_d − N_a values and parameters of deep centres in 6H–SiC pn structures grown by sublimation epitaxy has been studied. The irradiation was carried out with 8 MeV protons in the range of doses from 10¹⁴ to 10¹⁶ cm⁻². Irradiation with a dose of 3.6 × 10¹⁴ cm⁻² leaves the voltage drop at high forward currents (10 A/cm²) practically unchanged. For higher irradiation dose of 1.8 × 10¹⁵ cm⁻², the forward voltage drop and the degree of compensation in the samples increased ; partial annealing of the radiation defects and partial recovery of the electrical parameters occurred after annealing at T∼400–800 K. Irradiation with a dose of 5.4 × 10¹⁵ cm⁻² resulted in very high resistance in forward biased pn structures which remained high even after heating to 500°C. It is suggested that proton irradiation causes decreasing of the lifetime and formation of an i- or an additional p-layer.     

Effect of gamma irradiation on a polymer electrolyte: Variation in crystallinity, viscosity and ion-conductivity with dose

PEO(1 − x)NH₄ClO₄(x) samples with x = 0.18 are irradiated with gamma doses varying up to 50 kGy. DSC and XRD studies indicate, in general, a decrease in crystallinity with dose. Measurement of viscosity of aqueous solutions of the irradiated samples at the same concentration, shows that there is overall chain scission on irradiation, though there is evidence of some cross-linking also at higher doses. This is corroborated by FTIR measurements. The ion-conductivity shows a strong increase for irradiation dose 35 kGy. This suggests that there is a possibility of improving polymer electrolyte properties on gamma irradiation.     

Hydrogen-induced disproportionation characteristics of Zr(1 − x)Hf(x)Co(x = 0, 0.1, 0.2 and 0.3) alloys

Doping hafnium to partially substitute zirconium in ZrCo is a promising strategy to improve the ability to resist hydrogen-induced disproportionation. Herein, Zr(1 ? x)Hf(x)Co(x = 0,0.1,0.2, and 0.3) alloys were fabricated by arc melting and the effect of hafnium substitution ratio and temperature on their hydrogen-induced disproportionation was studied. Additionally, the disproportionated products were characterized by XRD, DSC and TDS. Results showed that disproportionation rate and the extent of disproportionation decreased with hafnium substitution ratio increasing from 0 to 30% and increased with temperature increasing from 400 °C to 550 °C. It was exciting that Zr0.7Hf0.3Co alloy had much better ability of anti-disproportionation than ZrCo in hydrogen pressure of about 200 kPa when temperature increasing from 400 °C to 550 °C, which was practical for tritium application.     

Improving the properties of poly(ethylene-co-vinyl acetate)/clay composite by using electron beam irradiation

Effect of electron beam irradiation on the thermal and mechanical properties of poly(ethylene-co-vinyl acetate) (EVA)/clay composites prepared by blending using solvent method has been investigated. The results show that the tensile strength increased continuously with increasing electron beam (EB) irradiation dose up to 200 kGy, thereafter decreased with further increase in dose, similarly increased with increasing the clay percentage until 50%, then decreases with further increase in clay percentage. Alternatively, elongation at break decreased continuously with increasing irradiation dose and clay percentage in the prepared composite. Conversely hardness increased continuously with increasing both clay percentage and irradiation doses. The thermogravimetric analysis revealed that thermal stability of the EVA/clay composites improved with increasing dose. The improvement in the mechanical and thermal properties is attributed to the formation of radiation-induced crosslinking as evidenced by the gel-content results. The adsorption capacity of EVA/clay composite for acid red 37 dye was 63.6 (mg/g) at adsorption conditions of: EVA/clay 50:50 (wt.%); dye concentration: 300 mg/l; sample dose: 0.05 g/25.00 ml; initial pH 7.0; temperature: 30 °C and equilibrium time: 8 h.     

Comparison of neutron and gamma irradiation effects on KU1 fused silica monitored by electron paramagnetic resonance

Electron paramagnetic resonance (EPR) studies have been carried out on KU1 fused silica irradiated with neutrons at fluences 10²¹ and 10²² n/m², and gamma-ray doses up to 12 MGy. The effects of post-irradiation thermal annealing treatments, up to 850 °C, have also been investigated. Paramagnetic oxygen-related defects (POR and NBOHC) and E′-type defects have been identified and their concentration has been measured as a function of neutron fluence, gamma dose and post-irradiation annealing temperature. It is found that neutrons at the highest fluence generate a much higher concentration of defects (mainly E′ and POR, both at concentrations about 5 × 10¹⁸ spins/cm³) than gamma irradiations at the highest dose (mainly E′ at a concentration about 4 × 10¹⁷ spins/cm³). Moreover, for gamma-irradiated samples a lower treatment temperature (about 400 °C) is required to annihilate most of the observed defects than for neutron-irradiated ones (about 600 °C).     

Engineering evolution of the FAST machine

FAST (Fusion Advanced Studies Torus) is a proposal for a Satellite Facility which can contribute the rapid exploitation of ITER and prepare ITER and DEMO regimes of operation, as well as exploit innovative plasma facing component systems for DEMO. FAST is a compact (Ro = 1.82 m, a = 0.64 m, triangularity δ = 0.4) and cost effective machine able to investigate, with integration capability, non linear dynamics effects of alpha particle behaviour in burning plasmas. FAST operates in high performance H-mode (B_T up to 8.5 T; I_P up to 8 MA), as well as in advanced tokamak mode (I_P = 3 MA), and in full non inductive current mode (I_P = 2 MA). Helium gas at 30 K is used for cooling the resistive copper magnets. This allows for a pulse duration up to 170 s at 3 MA/3.5 T. The vacuum vessel (VV), segmented into 20-degree modules, is capable to accommodate a 40 MW RF power system. The machine has been designed to house a 10 MW Negative Neutral Beam Injection (NNBI) system. Tungsten (W) or liquid lithium (L-Li) have been chosen as the divertor plate materials, and argon or neon as the impurities to be injected for mitigating the thermal loads.     

Y(BD4)3, an efficient store of deuterium,and impact of isotope effects on its thermal decomposition

Y(BD₄)₃, which stores as much as 16.6 wt.% and 252 kg/m³ D, has been synthesized via high-energy disk milling. The thermal decomposition of Y(BD₄)₃ has been investigated using thermogravimetric and calorimetric analyses combined with the spectroscopic evolved gas analysis. Two major endothermic events corresponding to thermal decomposition could be distinguished in the DSC profile up to 400 °C at ca. 231 and 285 °C, preceded by a phase transition (at ca. 198 °C) from the low-temperature Pa-3 form to a high-temperature polymorph of Y(BD₄)₃ (F-43c). The high-temperature phase forming at the onset of thermal decomposition may be prepared quantitatively by heating of the low-temperature phase to ca. 216 °C followed by rapid quenching.Effects of isotope H→D substitution on various properties of yttrium borohydride have been analyzed. Y(BD₄)₃ constitutes a very efficient low-temperature source of deuterium gas on the laboratory scale.     

Experimental studies on single-phase flow and heat transfer in a narrow rectangular channel

The state-of-the-art studies on single-phase flow and hear transfer in narrow rectangular channels shows some difference in terms of the agreement with the conventional theory. To further make clear this issue, the experimental studies on single-phase flow and heat transfer in a narrow rectangular channel with deioned water as test fluid was carried out. The narrow rectangular channel had the following dimensions: depth (e) = 2 mm, aspect ratio (e/b) = 0.05, length to diameter ratio (L/D_h) = 300, and mean wall relative roughness (?/D_h) = 8.3 × 10^?4. The experiments were performed with the channel oriented uprightly. The parameters that were varied during the experiments included the mass flow rate, inlet temperature and heat flux.Based on the measured temperatures, mass flow rates, pressure drops and heat fluxes, the isothermal and non-isothermal friction factors and the local and mean Nusselt numbers have been calculated. The correlations for the isothermal friction factors and the mean Nusselt numbers have been developed, and have a satisfactory agreement with the conventional theory. Based on the property ratio method, the correlations for non-isothermal friction factors have been proposed, but the new exponent (m) for modifying variable-property effect need to be developed.     

Effects of BF2+ implantation on the strain-relaxation of pseudomorphic metastable Ge0.06Si0.94 alloy layers

Metastable pseudomorphic Ge_0.06Si_0.94 alloy layers grown by molecular beam epitaxy (MBE) on Si (1 0 0) substrates were implanted at room temperature by 70 keV BF₂⁺ ions with three different doses of 3 × 10¹³, 1 × 10¹⁴, and 2.5 × 10¹⁴ cm⁻². The implanted samples were subsequently annealed at 800°C and 900°C for 30 min in a vacuum tube furnace. Observed by MeV ⁴He channeling spectrometry, the sample implanted at a dose of 2.5 × 10¹⁴ BF₂⁺ cm⁻² is amorphized from surface to a depth of about 90 nm among all as-implanted samples. Crystalline degradation and strain-relaxation of post-annealed Ge_0.06Si_0.94 samples become pronounced as the dose increases. Only the samples implanted at 3 × 10¹³ cm⁻² do not visibly degrade nor relax during anneal at 800°C . In the leakage current measurements, no serious leakage is found in most of the samples except for one which is annealed at 800°C for 30 min after implantation to a dose of 2.5 × 10¹⁴ cm⁻². It is concluded that such a low dose of 3 × 10¹³ BF₂⁺ cm⁻² can be doped by implantation to conserve intrinsic strain of the pseudomorphic GeSi, while for high dose regime to meet the strain-relaxation, annealing at high temperatures over 900°C is necessary to prevent serious leakages from occuring near relaxed GeSi/Si interfaces.     

A simple way to analyze infrared reflectivity spectra of p-type Hg0.78Cd0.22Te implanted in various conditions

Different ion-implanted p-type Hg_0.78Cd_0.22Te samples were analyzed by infrared reflectivity in the 2–20 μm wavelength range. We show how to derive some characteristic values of the free carriers induced by ion implantation from simple models of the implanted samples. For low energy implantations (Al (320 keV)) an excess of electrons with concentration n⁺ ≈ 5 × 10¹⁷ cm⁻³ for doses 10¹² and 10¹⁴ ions cm⁻² is observed between the surface and the projected range R_p of the ions, in agreement with the well-known change of type of the free carriers induced by the ion implantation in this kind of samples. High energy α particle (0.8 and 2 MeV, 10¹⁴ ions cm⁻²) implantations lead to a pronounced inhomogeneous concentration of free electrons with n⁺ ≈ 9.2 × 10¹⁶ cm⁻³ between the surface and R_p where a negligible amount of defects due to the nuclear energy loss is formed, and n⁺ ≈ 1.6 × 10¹⁷ cm⁻³ between R_p and R_p + ΔR_p, ΔR_p being the longitudinal straggling, where the defect production rate through the nuclear energy loss mechanism is maximum.     

The lower hybrid current drive system for steady-state operation of the Vulcan tokamak conceptual design

The steady-state current drive system for the Vulcan tokamak concept has been designed, taking into account requirements of high field, small size, and high operational wall temperature (B₀ = 7 T, R₀ = 1.2 m, T_wall > 800 K). This lower hybrid current drive system allows steady-state operation by utilizing high field side launch, high RF source frequency (8 GHz), and dedicated current drive ports. An iterative MHD and current drive solver is used to determine the ideal launching spectra and location to assure strong single pass absorption. It is found that with nominal Vulcan operational parameters (n_e ≈ 4 × 10²⁰ m^?3, T_e ≈ 2.8 keV, I_p = 1.7 MA, P_LHCD = 19.8 MW) bootstrap currents of ～70% and lower hybrid current drive efficiencies of 1.16 × 10¹⁹ A W m^?2 could be achieved. The optimized solution yielded advanced tokamak profiles with q values on-axis above 2. A conceptual design of the system is presented, which takes into account space, power, cooling, and launched spectrum requirements. The system is found to be compatible with the vacuum vessel design and requires cooling power of <1 MW per waveguide bundle.     

Gamma irradiation induced damage creation on the cation distribution,structural and magnetic properties in Ni–Zn ferrite

Ferrite of system, namely Ni_1?xZn_xFe₂O₄ with x = (0.0, 0.2, 0.4, 0.6, 0.8, 1.0), have been prepared by solid state reaction to investigate the effect of gamma rays irradiations using Co⁶⁰ source on the cation distribution, structural and magnetic properties. The unirradiated and irradiated samples were then subjected to characterization techniques such as X-ray diffraction, magnetization and AC susceptibility. The results of these characterizations are found to be different for irradiated from that of the pristine sample. The modifications in respect of irradiated samples are explained in terms of the ion-induced disorder. The important result of γ-irradiation on the cation distribution, structural and magnetic properties is the change of ratio Fe²⁺/Fe³⁺. Possible reasons on the results are proposed.     

Effective atomic and electron numbers of some steels at different energies

The effective atomic numbers (Z_eff) and effective electron density (N_e) for three different steels have been determined via the mass attenuation coefficients (μ/ρ). The mass attenuation coefficients have been calculated at the photon energy range of 1 keV–1 GeV and measured at the photon energies of 662, 1173 and 1332 keV. The measurement has been performed using a gamma spectrometer that contains a NaI(Tl) detector connected to Multi-Channel-Analyzer (MCA). The measured results of effective atomic numbers (Z_eff) and effective electron density (N_e) were found to be in good agreement with the calculations.     

Theoretical critical angels of ion channeling in carbon nanotubes

We have developed a mass- and charge-dependent equation to predict theoretical critical angles for ion channeling in carbon nanotubes. We focus M (ion mass) effects how to reduce Ze (ion nucleus charge) effects on Ψ_C (critical angles). As an instance, we give theoretical critical angels of He, Ne, Ar, Kr, Xe and Rn ion channeling in carbon nanotubes. We find that for (10, 10) single-wall carbon nanotubes, Ψ_C(He) ≈ Ψ_C(Ne) ≈ Ψ_C(Ar) ≈ Ψ_C(Kr) ≈ Ψ_C(Xe) ≈ Ψ_C(Rn) ≈ 23.3 (keV/E)^1/2 deg. This is because (Z/M)^1/2 ≈ 0.66 [amu]^?1/2.