Irradiation effect on dielectric properties and electrical conductivity of Au/SiO2/n-Si (MOS) structures

The Au/SiO₂/n-Si (MOS) structures were exposed to beta-ray irradiation to a total dose of 30 kGy at room temperature. Irradiation effect on dielectric properties of MOS structures were investigated using capacitance−voltage (C−V) and conductance−voltage (G/ω−V) characteristics. The C−V and G/ω−V measurements carried out in the frequency range from 1 kHz to 10 MHz and at various radiation doses, while the dc voltage was swept from positive bias to negative bias for MOS structures. The dielectric constant (ε′), dielectric loss (ε″), loss factor (tan δ) and ac electrical conductivity (σ_ac) were calculated from the C−V and G/ω−V measurements and plotted as a function of frequency at various radiation doses. A decrease in the ε′ and ε″ were observed when the irradiation dose increased. The decrease in the ε′ and ε″ of irradiated MOS structures in magnitude is explained on the basis of Maxwell−Wagner interfacial polarization. Also, the σ_ac is found to decrease with increasing radiation dose. In addition, the values of the tan δ decrease with increasing radiation dose and give a peak. From the experimental results, it is confirmed that the peak of loss tangent is due to the interaction between majority carriers and interface states which induced by radiation.     

Effect of swift heavy ion irradiation on the surface morphology of highly c-axis oriented LSMO thin films grown by pulsed laser deposition

A detailed investigation of the surface morphology of the pristine and swift heavy ion (SHI) irradiated La_0.7Sr_0.3MnO₃ (LSMO) thin film using atomic force microscope (AFM) is presented. Highly c-axis oriented LSMO thin films were grown on LaAlO₃ (1 0 0) (LAO) substrates by the pulsed laser deposition (PLD) technique. The films were annealed at 800 °C for 12 h in air (pristine films) and subsequently, irradiated with SHI of oxygen and silver. The incident fluence was varied from 1 × 10¹² to 1 × 10¹⁴ ions/cm² and 1 × 10¹¹ to 1 × 10¹² ions/cm² for oxygen and silver ions, respectively. X-ray diffraction (XRD) studies reveal that the irradiated films are strained. From the AFM images, various details pertaining to the surface morphology such as rms roughness (σ), the surface rms roughness averaged over an infinite large image (σ_∞), fractal dimension (D_F) and the lateral coherence length (ξ) were estimated using the length dependent variance measurements. In case of irradiated films, the surface morphology shows drastic modifications, which is dependent on the nature of ions and the incident fluence. However, the surface is found to remain self-affine in each case. In case of oxygen ion irradiated films both, σ_∞ and D_F are observed to increase with fluence up to a dose value of 1 × 10¹³ ions/cm². With further increase in dose value both σ_∞ and D_F decreases. In case of silver ion irradiated films, σ_∞ and D_F decrease with increase in fluence value in the range studied.     

Coherent pair production by energetic gamma rays incident on quasicrystals

We develop a Born-approximation theory of coherent pair production (CPP) of electrons by energetic gamma rays incident on an icosahedral quasicrystal, described by a schematic model (K model) that includes phonon and phason disorder. Our main result is a formula for the cross-section dσ_cpp/dε₊ for CPP, differential with respect to the positron energy ε₊ and of order α² in the fine-structure constant α ≈ 1/137, but which is otherwise exact. We discuss results of numerical calculations of dσ_cpp/dε₊ versus y = ε₊/k for gamma rays of energies k = 20 MeV, 200 MeV, and 3 GeV, incident on icosahedral Al-Mn-Si, described as a special case of the K model (vertex model). This consists in placing an Mn atom at each vertex of the relevant Ammann tiles. Our calculations include CPP of types A and B. Both types exhibit vertical intensity drops at irregularly distributed y-values, many of these drops being so large that they should be observable experimentally. They are analogous to the large intensity drops exhibited by coherent bremsstrahlung in quasicrystals. We predict that CPP drops also occur for realistic models of i-Al-Mn-Si at the same y-values as for the vertex model, but whose magnitudes may differ from those predicted by this model.     

Characteristics of the electron-emission defects introduced in Si-SiO2 structures by MeV electron irradiation

Defects induced by high-energy electrons in Si-SiO₂ structure have been studied by the optically stimulated electron emission (OSEE) method. Si-SiO₂ structures with oxide thickness of 100 nm are irradiated with 23 MeV electrons for different durations. It is shown that most of the defects created by electron irradiation at the interface and in the oxide bulk are vacancies like E′-centers. Most of the photoemission activity changes are observed during low doses electron irradiation. Some uncharged defects like diamagnetic oxygen-deficient centers are also observed, together with E′-centers.     

Effects of γ-ray irradiation on the C-V and G/ω-V characteristics of Al/SiO2/p-Si (MIS) structures

The effect of the ⁶⁰C_o (γ-ray) exposure on the electrical characteristics of Al/SiO₂/p-Si (MIS) structures has been investigated using capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements. The MIS structures were stressed with a bias of 0 V during ⁶⁰C_oγ-sources irradiation with the total dose range from 0 to 25 kGy. The C-V and G/ω-V characteristics were measured at 500 kHz and room temperature before and after ⁶⁰C_oγ-ray irradiation. The results indicated that γ-irradiation caused an increase in the barrier height Φ_B, interface states N_ss and depletion layer width W_D obtained from reverse bias C-V measurements. The series resistance R_s profile for various radiation doses was obtained from forward and reverse bias C-V and G/ω-V measurements. Both C-V and G/ω-V characteristics indicate that the total dose radiation hardness of MIS structures may be limited by the decisive properties of the SiO₂/Si interface to radiation-induced damage. After γ-irradiation, the decrease in capacitance of MIS structure results in the increase in the semiconductor depletion width.     

Determination of mass attenuation coefficients, effective atomic and electron numbers for Cr, Fe and Ni alloys at different energies

The total mass attenuation coefficients (μ_m), for Cr, Fe, Ni and Fe_xNi_1−x (x = 0.8, 0.7, 0.6, 0.5, 0.4, 0.3 and 0.2), Fe_xCr_yNi_1−(x+y) (x = 0.7, y = 0.1; x = 0.5, y = 0.2; x = 0.4, y = 0.3; x = 0.3, y = 0.3; x = 0.2, y = 0.2 and x = 0.1, y = 0.2) and Ni_xCr_1−x (x = 0.8, 0.6, 0.5, 0.4 and 0.2) alloys were measured at 22.1, 25.0, 59.5 and 88.0 keV photon energies. The samples were irradiated with 10 mCi Cd-109 and 100 mCi Am-241 radioactive point source using transmission arrangement. The γ- and X-rays were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. Total atomic and electronic cross-sections (σ_t and σ_e), effective atomic and electron numbers (Z_eff and N_eff) were determined experimentally and theoretically using the obtained mass attenuation coefficients for investigated 3d alloys. The theoretical mass attenuation coefficients of each alloy were estimated using mixture rule. The experimental values were compared with the calculated values for all samples.     

Irradiation damage of uridine molecules with MeV heavy ions

In order to study the mechanism of the nucleotide directly damaged by energetic heavy ions, the residual ratio of uridine molecules after irradiation was measured by means of High Performance Liquid Chromatography (HPLC). The experimental results show that the irradiation damage probability depends on the electronic energy loss rate (S_e) of incident ions: first it increases quickly with S_e, then becomes stable when S_e reaches 800 eV/nm. The contribution of the nuclear collisions can be neglected compared with that of the electronic process. This is not only because that the nuclear energy loss rate (S_n) is much smaller than S_e for MeV heavy ions, but also because the energy deposition through the electronic process is more efficient in damaging molecules than through the nuclear process.     

Radiation-induced degradation of galactomannan polysaccharides

In this study, guar gum, tara gum and locust bean gum were irradiated in a gamma cell in the solid state. The change in their molecular weights were determined by size exclusion chromatography analysis and the change in their viscosity values with change of temperature and irradiation dose were determined. Chain scission yield, G(s), and degradation rate values were calculated. The calculated G(s) values is 1.09 ± 0.16, 1.07 ± 0.06, 0.85 ± 0.10 for GG, TG and LBG, respectively. The effect of mannose-galactose ratio and initial molecular weight of these gums on the degradation behavior were discussed.     

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.     

Effect of swift heavy ion irradiation on nanocrystalline CaS:Bi phosphors: Structural, optical and luminescence studies

Luminescence studies of CaS:Bi nanocrystalline phosphors synthesized by wet chemical co-precipitation method and irradiated with swift heavy ions (i.e. O⁷⁺-ion with 100 MeV and Ag¹⁵⁺-ion with 200 MeV) have been carried out. The samples have been irradiated at different ion fluences in the range 1 × 10¹²-1 × 10¹³ ions/cm². The average grain size of the samples before irradiation was estimated as 35 nm using line broadening of XRD (X-ray diffraction) peaks and TEM (transmission electron microscope) studies. Our results suggest a good structural stability of CaS:Bi against swift heavy ion irradiation. The blue emission band of CaS:Bi³⁺ nanophosphor at 401 nm is from the transition ³P₁ → ¹S₀ of the Bi³⁺. We have observed a decrease in lattice constant (a) and increase of optical energy band gap after ion irradiation. We presume this change due to grain fragmentation by dense electronic excitation induced by swift heavy ion. We have studied the optical and luminescent behavior of the samples by changing the ion energy and also by changing dopant concentration from 0.01 mol% to 0.10 mol%. It has been examined that ion irradiation enhanced the luminescence of the samples.     

Role of trace elements in somatic embryogenesis - A PIXE study

Proton induced X-ray emission was used to study the trace elemental profiles of embryogenic and non-embryogenic callus of an important cash crop of India - Plantago ovata. Somatic embryogenesis, a well-known process for plant regeneration and crop improvement is modulated by various factors such as ionizing radiation and micro nutrients in the growth media. The present work reports the trace element variation in normal and irradiated callus tissue of P. ovata. Embryogenic and non-embryogenic callus tissues were exposed to gamma rays from a ⁶⁰Co gamma source. The absorbed dose ranged from 10 to 100 Gy. Subsequent experiments showed significant dose dependent alterations in K, Ca, Mn, Fe, Ni, Cu, Zn, Br, Sr in both the embryogenic and non-embryogenic callus. The precise involvement of these elements has been discussed in light of somatic embryogenesis of the selected medicinal plant.     

8 MeV electron irradiation effect on the dielectric and optical properties of iminodiacetic acid doped ferroelectric triglycine sulphate crystals

Single crystal of iminodiacetic acid (5 mol%) doped Tri Glycine Sulphate (IDATGS) was grown by slow evaporation from its aqueous solution at constant temperature, using solution growth method. The dielectric constant (ε′) and pyroelectric current (I_P) were measured over the temperature range of 30-60 °C in the ferroelectric direction. The measured values of ε′ and I_P were found to be smaller compared to pure triglycine sulphate (TGS) crystal parameters. But increased transition temperature was observed for doped crystals. Curie Weiss constants C_P and C_f in the paraelectric and ferroelectric phases were also determined. The doped crystal was irradiated with graded dosages from 5 to 80 kGy of electron beam from 8 MeV Microtron at room temperature and radiation effects on optical and dielectric properties were studied. The UV-Vis absorption spectrum indicates that the UV lower cutoff shifts towards the higher wavelength region (red shift) and the optical band gap is found to be decreasing with the increase of electron dose. It is also observed that the electron irradiation effects in pure and doped TGS were found to be long lasting. The dielectric study shows that there is a gradual reduction in dielectric constant at T_C and shifting of Curie temperature towards lower temperature region with the increase in electron radiation dose. The material figures of merit were found increased after the crystal was irradiated. Induced changes in the physical and optical properties due to irradiation may help one to tailor the device quality and characteristics.     

Solar parameters of induced WO3-coated glass

WO₃ films were prepared by sol-gel deposition process on Corning 2947, microscope slide substrates. The effects of irradiation on the solar parameters of WO₃ films were investigated between ∼1 and 21 kGy absorbed dose by Co-60 radioisotope. Three characteristic optical density bands explained the causes of color due to the absorption of sunlight at induced color centers of the transition elements such as W, Fe and Zr after the gamma irradiation. These bands lead to variations on the solar control in terms of shading coefficient. The absorbed dose plays a key role in the improvement of the shading coefficient dramatically, hence the solar parameters changed considerably depending on the induced color centers of the transition elements and the variations of the grains and the void sizes of the film. The results of the solar parameters of irradiated WO₃ films were compared with the unirradiated WO₃ films and uncoated corning in the solar range.     

Effect of 200 MeV Ag ion irradiation on structural and electrical transport properties of Fe3O4 thin films

Thin films of Fe₃O₄ have been deposited on single crystal MgO(1 0 0) and Si(1 0 0) substrates using pulsed laser deposition. Films grown on MgO substrate are epitaxial with c-axis orientation whereas, films on Si substrate are highly 〈1 1 1〉 oriented. Film thicknesses are 150 nm. These films have been irradiated with 200 MeV Ag ions. We study the effect of the irradiation on structural and electrical transport properties of these films. The fluence value of irradiation has been varied in the range of 5 × 10¹⁰ ions/cm² to 1 × 10¹² ions/cm². We compare the irradiation induced modifications on various physical properties between the c-axis oriented epitaxial film and non epitaxial but 〈1 1 1〉 oriented film. The pristine film on Si substrate shows Verwey transition (T_V) close to 125 K, which is higher than generally observed in single crystals (121 K). After the irradiation with the 5 × 10¹⁰ ions/cm² fluence value, T_V shifts to 122 K, closer to the single crystal value. However, with the higher fluence (1 × 10¹² ions/cm²) irradiation, T_V again shifts to 125 K.     

Measurement of thermal neutron cross-sections and resonance integrals for Hf(n,γ)Hf and Hf(n,γ)Hf reactions at the Pohang neutron facility

The thermal-neutron cross-sections and the resonance integrals for the ¹⁷⁹Hf(n,γ)^180mHf and the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reactions have been measured by the activation method. The high purity Hf and Au metallic foils within and without a Cd shield case were irradiated in a neutron field of the Pohang neutron facility. The gamma-ray spectra from the activated foils were measured with a calibrated p-type high-purity Ge detector.In the experimental procedure, the thermal neutron cross-sections, σ₀, and resonance integrals, I₀, for the ¹⁷⁹Hf(n,γ)^180mHf and the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reactions have been determined relative to the reference values of the ¹⁹⁷Au(n,γ)¹⁹⁸Au reaction, with σ₀ = 98.65 ± 0.09 barn and I₀ = 1550 ± 28 barn. In order to improve the accuracy of the experimental results, the interfering reactions and necessary correction factors were taken into account in the determinations. The obtained thermal neutron cross-sections and resonance integrals were σ₀ = 0.424 ± 0.018 barn and I₀ = 6.35 ± 0.45 barn for the ¹⁷⁹Hf(n,γ)^180mHf reaction, and σ₀ = 12.87 ± 0.52 barn and I₀ = 32.91 ± 2.38 barn for the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reaction. The present results are in good agreement with recent measurements.     

Positron annihilation on the surfaces of SiO2 films thermally grown on single crystal of Cz-Si

Two-detector coincidence system and mono-energetic slow positron beam has been applied to measure the Doppler broadening spectra for single crystals of SiO₂, SiO₂ films with different thickness thermally grown on single crystal of Cz-Si, and single crystal of Si without oxide film. Oxygen is recognized as a peak at about 11.85 × 10⁻³m₀c on the ratio curves. The S parameters decrease with the increase of positron implantation energy for the single crystal of SiO₂ and Si without oxide film. However, for the thermally grown SiO₂-Si sample, the S parameters in near surface of the sample increase with positron implantation energy. It is due to the formation of silicon oxide at the surface, which lead to lower S value. S and W parameters vary with positron implantation depth indicate that the SiO₂-Si system consist of a surface layer, a SiO₂ layer, a SiO₂-Si interface layer and a semi-infinite Si substrate.     

Photon interaction and energy absorption in glass: A transparent gamma ray shield

The effective atomic number, Z_eff, the effective electron density, N_e,eff, and the energy dependence, ED, have been calculated at photon energies from 1 keV to 1 GeV for CaO-SrO-B₂O₃, PbO-B₂O₃, Bi₂O₃-B₂O₃, and PbO-Bi₂O₃-B₂O₃ glasses with potential applications as gamma ray shielding materials. For medium-Z glasses, Z_eff is about constant and equal to the mean atomic number in a wide energy range, typically 0.3 < E < 4 MeV, where Compton scattering is the main photon interaction process. In contrast, for high-Z glasses there is no energy region where Compton scattering is truly dominating. Heavy-metal oxide glasses containing PbO and/or Bi₂O₃ are promising gamma ray shielding materials due to their high effective atomic number and strong absorption of gamma rays. They compare well with concrete and other standard shielding materials and have the additional advantage of being transparent to visible light. The single-valued effective atomic number calculated by XMuDat is approximately valid at low energies where photoelectric absorption is dominating.     

Rheological study of polypropylene irradiated with polyfunctional monomers

The aim of this paper is to investigate the rheological properties of polypropylene (PP) modified by ionization radiation (gamma rays) in the presence of two different monomers. The samples were mixed in a twin-screw extruder with ethylene glycol dimethacrylate (EGDMA) or trimethylolpropane trimethacrylate (TMPTMA) with concentration in the range of 0.5-5.0 mmol. After that, they were irradiated with 20 kGy dose of gamma radiation. The structural modification of polypropylene was analyzed in the melt state by measuring melt flow rate (MFR), η* (complex viscosity) and G′ (storage modulus) in the angular frequency range of 10⁻¹ to 3 × 10² rad s⁻¹. From the oscillatory rheology data, one could obtain the values of η₀ (zero shear viscosity) that would be related to the molar mass. All results were discussed with respect to the crosslinking and degradation process that occur in the post-reactor treatment to produce controlled rheology polypropylene.The resulting polymeric materials were submitted the cytotoxicity in vitro test by neutral red uptake methodology with NCTC L 929 cell line from American Type Culture Collection bank. All modified PP samples presented no cytotoxicity.     

Gamma irradiation of PolyEthyleneTerephthalate and PolyEthyleneNaphthalate

The effect of gamma irradiation in air is investigated in two thermoplastic polyesters (PET and PEN), in order to evaluate the influence of aromatic density and the role of oxygen on radiation resistance. EPR measurements were carried out to detect radical stability against oxygen permeation and to provide radical characterization. Viscometric data reveal a different behaviour between films and thick samples. Positron annihilation spectra show a decrease of ortho-positronium intensity, which is more marked in film samples. ortho-positronium lifetime does not depend on the radiation dose.