Γ-ray Irradiation Dose Research Articles

60Co γ irradiation effects on the current–voltage ( I– V) characteristics of Al/SiO 2/p-Si (MIS) Schottky diodes

It is well known that the exposure of any semiconductor surfaces to the 60Co γ-ray irradiation causes electrically active defects. To investigate the effect of γ-ray irradiation dose on the electrical characteristics of metal–insulator–semiconductor (MIS) Schottky diodes, the fabricated devices were exposed to γ radiation at a dose of 2.12 kGy/h. The total dose range was from 0 to 450 kGy at room temperature. The density of interface states N ss as a function of E ss− E v, the values of series resistance R s and the bias dependence of the effective barrier height Φ e for each dose were obtained from the forward bias I– V characteristics. Experimental results show that the γ-irradiation gives rise to an increase in the zero bias barrier height Φ BO, as the ideality factor n, R s and N ss decreases with increasing radiation dose.

Effects of secondary electrons emitted from surroundings on defect formation in silica glass under γ-ray irradiation

We have investigated the effects of secondary electrons and photons emitted from surrounding materials on defect formation in silica glass under γ-ray irradiation. SiO2 (silica) glass plates and those sandwiched in a pair of various material disks (carbon, stainless steel or lead) were irradiated by γ-ray, and the optical absorption spectra (UV–vis spectra) of the silica glass plates before and after the irradiation were examined. UV–vis spectra of the glass plates after the irradiation showed three absorption bands peaked around 2eV, 4eV and 5.8eV being assigned to color centers relate metal impurities (Al and Ge) and oxygen-deficient centers like E′ center, respectively. All three bands were found to grow with γ-ray irradiation dose and saturated at higher doses, and absorbance of the bands at the saturation for the sandwiched glass plates was higher than that for the bare glass plate. Moreover, the saturated absorbance was higher for the glass plate sandwiched with heavier materials. Employing Monte Carlo N-Particle (MCNP) code for the simulation of the photon–electron transport process, enhanced energy deposition and numbers of secondary electrons and photons emitted from sandwiching material disks to a silica glass plate were calculated. The higher deposition energy correlates well to the higher saturated absorbance, indicating that the secondary electrons and photons emitted from the disks clearly enhanced the defect formation in the sandwiched silica glass plates. This suggests the existence of the dose effect above a critical does, i.e. the irradiation with higher dose will result in higher saturated absorbance.

Modeling Equilibrium Moisture Content of γ-Ray Irradiated Rough Rice

Experimental studies show that gamma irradiation dose affects the values of equilibrium moisture content of grain at the same relative humidity and temperature of ambient. Values of the equilibrium moisture content decreased with increasing dose of γ-ray irradiation during both adsorption and desorption. Factor of irradiation dose was included in three widely used models for equilibrium moisture content; the parameters in the models were estimations from experimental data. Based on the correlation coefficient, mean relative error, and standard error of moisture, the modified Chung-Pfost equation and the modified Henderson equation were found to fit the desorption and adsorption isotherms for rough rice in the range of experimental conditions studied.

Experimental study on lung cancer-targeted oncostatin M gene therapy induced by ionizing radiation

To improve the efficacy and selectivity of gene therapy for lung cancer through inducing oncostatin M (OSM) gene expression by radiation via the early growth response gene-1 (Egr-1) promoter. The radio-inducible OSM gene was constructed by insertion of Egr-1 promoter into upstream of the OSM gene. The expression of OSM in lung adenocarcinoma cell line A549 which was transfected with pEO and exposed to different doses of γ-ray irradiation was analyzed, and the relative survival fraction of cells and cell survival curve were observed. To examine the efficacy of this pEO gene therapy in vivo, the tumor supression effects were investigated in 40 nude mice bearing lung tumors. Expression of OSM gene in A549 cells transfected with pEO plasmids was markedly upregulated in a radiation dose-dependent manner. A gene therapy experiment in vitro showed that pEO transfected A549 cells became highly sensitive to ionizing radiation. pEO transfected tumors regressed significantly after a combination therapy with irradiation in all mice (n=10), and three tumors disappeared in 3 weeks without any side effect. The results indicate that tumor targeted expression of OSM gene under the control of a radio-inducible promoter represents a novel strategy for safe and effective gene therapy for lung cancer and might be widely applied in the future.

γ-Ray Irradiation Practical Conditions for Low Molecular Weight Chitosan Material Production

ABSTRACTThe present work focuses on the γ-ray irradiation doses and conditions (dry solid state, solid state dispersing in 0.5–2 % aqueous H2O2 solution, solid state dispersing in 1% aqueous acetic acid, and 2% aqueous K2S2O8) to determine the level that the molecular weight of chitosan is lowered significantly without changing its primary structure. Molecular weight of chitosan (105-106 Dalton) is reduced approximately 50% under the γ-ray dose of 20 kGy in the dry solid state. The decrease in molecular weight is enhanced up to 80% when chitosan is suspended in 0.5–2 % aqueous H2O2 solution during γ-ray irradiation. In either condition, the backbone structure of the irradiated product is maintained with little change in the terminal chain. In the cases of (i) chitosan suspended in 2% aqueous K2S2O8 and (ii) chitosan in 1% aqueous acetic acid, chitosans lose their primary structures and physical properties.

Variation of the absorption spectra and optical energy gap with γ-ray irradiation and heat treatment in SbNbO 4 films deposited on MgO and quartz substrates

The effects of both γ-rays irradiation and annealing temperature on the optical absorption spectra of SbNbO 4 films deposited on MgO or quartz substrates in the spectral range 190–800 nm were studied. The dose of γ-ray irradiation was varied up to 100 kGy and the annealing temperature was varied up to 900 °C. The transmittance and the reflectance were measured and hence the absorption coefficient was estimated. Annealing and γ-rays irradiation changed the general level of absorption in the treated films. A number of bands show a continuous shift in position and decrease in intensity with increasing γ-dose. The allowed optical transitions were found to be indirect transitions, hence values of the allowed indirect optical energy gap was calculated as a function of γ-dose and heat annealing temperature. The results can be discussed on the basis of γ-irradiation-induced defects in the film and on the film microstructure. The optical parameters of SbNbO 4 films are affected by the kind of substrate. The effect is more pronounced in case of films deposited on quartz substrates.

Effects of gamma-ray irradiation on the microstructural and luminescent properties of radio-frequency magnetron-sputtered GaN thin films

The microstructural and luminescent properties of sputtered GaN thin films preiiradiated and γ-ray irradiated were systematically investigated. Analytical results revealed that the increasing doses of γ rays could enhance the occurrence of more nitrogen vacancies, which not only created a prominent deep level luminescence but also destroyed the crystallinity of GaN thin films. For low dose of γ-ray irradiation [≦4 Mrad (GaN)], evidence showed that by raising the irradiation dose, more associated Ga–H complexes would be effectively promoted, yielding an enhanced yellow band emission. However, for high dose of γ-ray irradiation [>4 Mrad (GaN)], further higher doses of γ rays could lead to the dissociation of Ga–H complexes in GaN samples, resulting in a repressed yellow band emission. From both the Fourier transform infrared spectroscopy and yellow band emission results, it is strongly suggested that Ga–H complexes in the vicinity of N most probably act as the origin of yellow band emission in GaN material.

γ-Ray Irradiation Effect on the Intersubband Transition in Ingaas/Aigaas Multiple Quantum Wells

AbstractIntersubband transitions in n-type InGaAs/AlGaAs multiple quantum wells were studied as a function of 1.0 to 5.0 MRad γ-ray irradiation dose using the optical absorption technique. The spectra were recorded at both 295 and 77K. The results show that the total integrated area of the intersubband transition is decreased as the irradiation dose is increased. This could be explained as follows: The secondary electrons generated from the γ-ray irradiation cause lattice damages where traps and point defects are created. Some of the electrons in the quantum wells are trapped by these defects causing the two dimensional electron gas (2DEG) density to decrease. The reduction of the 2DEG density thus leads to the reduction of the total integrated area of the intersubband transitions.

Influence of 60Co γ-Ray irradiation on the morphology of crystalline polyethylene studied by high-resolution solid-state 13C NMR

The relationship and influence of varying 60Co γ-ray irradiation doses, in the range 0.77–5.2 MGy, on the morphology of polyethylene have been investigated using high-resolution solid-state 13C nuclear magnetic resonance analyses through variation of different phase components, T1c, T2c relaxation parameters, and line width. The cross-linking in the irradiated polyethylene takes place mainly in the non-crystalline regions. However, distortion and damage to the folded chain of the crystal lattice are observed in the crystalline regions. For the interfacial phase, both cross-linking and distortion could occur. As a result, part of the crystalline component transformed into a non-crystalline one. It was also found that the orthorhombic crystalline lattice transformed into a monoclinic one within the crystalline phase in polyethylene under higher doses of irradiation.

Adaptive response induced by low dose ionizing radiation in human cervical carcinoma cells

Adaptive response induced by low dose γ-ray irradiation in human cervical carcinoma cells was examined. Cells were exposured to low dose of γ-ray (1 cGy) followed by high doses of γ-ray irradiation (0, 1, 2, 3, 5, 7 and 9 Gy for clonogenic assay or 1.5 Gy for micronucleus assay) with various time intervals. Survival fractions of cells in both low dose-irradiated and unirradiated groups were analyzed by clonogenic assay. Survival fractions of low dose-irradiated cells was higher than that of control group irradiated only with high dose γ-ray. The increase in cell survival was maximum when low and high dose irradiation time interval was 4 hr. Frequencies of micronuclei which is an indicative of chromosome aberration were also enumerated in both low dose-irradiated and unirradiated groups. In consistent with the result obtained from survival fractions analyzed by clonogenic assay, maximum reduction in frequencies of micronuclei was observed when low dose radiation was given 4 hr prior to high dose irradiation. These results demonstrate that low dose γ-ray irradiation induced adaptive response to subsequent high dose γ-ray irradiation in human cervical carcinoma cells. Our data suggest that one of the possible mechanisms of adaptive response induced by low dose radiation is the increase in repair of DNA double strand breaks in low dose radiation-adapted cells.

Effect of Gamma Irradiation on Superconductivity of Pb-Doped Bi2Sr2CaCu2Oy Crystals

Bi2.4-x Pbx Sr2CaCu2Oy crystals with x=0.05, 0.1 and 0.2 were irradiated with 60Co γ-rays of 0.6 MR/h up to a dose of 64.8 MR at room temperature. For all the irradiated samples with x=0.05, 0.1, the superconducting transition temperature T c increased after γ-ray irradiation, while the T c of irradiated samples with x=0.2 increased at lower doses, and then decreased at 64.8 MR. X-ray photomission spectroscopy results reveal that higher oxidation states of Bi and Cu occurred in the sample irradiated with 64.8 MR. The dependence of T c on γ-ray irradiation dose can be explained in terms of the change of valence state of Bi and Cu.

Effects of high energy radiation on group III–V compound semiconductors

The determination of the properties of compound semiconductors exposed to radiation from the environment is relevant because this exposure triggers optically induced degradation mechanisms which introduce strong non-radiative recombination centers. Two different III–V compound materials were studied: indium phosphide and indium gallium arsenide, both with interesting properties and well suited to optoelectronic applications. A highly doped InP:Sn (3 × 10 18 cm −3) substrate was exposed in different experiments to high energy electrons (3.8 MeV) and γ-rays (0–3.8 MeV) and annealed at room temperature and 473 K. Photoluminescence (PL) analyses showed a significant effect of radiation as well as of heat treatments on InP properties. Thick (3 μm) In 0.4Ga 0.6As epitaxial layers grown on a multistage strain-relief buffer system produced on GaAs substrates were exposed to the same irradiation doses employed for InP. It was expected these layers would not perform well after irradiation since they were grown on mismatched substrates. Nevertheless PL measurements indicated that In x Ga 1−x As was not affected by the γ-ray irradiation doses employed in this work, while it was quite sensitive to electron irradiation although almost complete recovery was possible after heat treatment.

Effect of γ-ray irradiation on the electrical conductivity of β-PbF 2

Effect of γ-ray irradiation on polycrystalline β-PbF 2 was investigated by X-ray, Raman scattering and electrical conductivity. With an increase in the dose of γ-ray irradiation, the half line width of Raman peak increased, suggesting the formation of Frenkel defects. On the other hand, the electrical conductivity decreased with an increase in the irradiation dose. The motion of the formed interstitial F - ions is presumed to be hindered by unidentified defects formed simultaneously by the irradiation.

State of radon in crystalline polymers

The state of radon in crystalline polymers, polyethylene and polypropylene, has been studied by methods of macro- and microauto-radiography. Radon-222 was introduced into the samples by diffusion from the gas phase at various temperatures and time intervals. Effects on the state of radon of such factors as density and polymer crystallinity, extent of macromolecular chain branching, spherulite radius, content of different admixtures, γ-ray photon irradiation dose or irradiation with accelerated electrons, etc., were investigated. In pure polymers, radon was found to be in an atomically dispersed state. Radon forms thermally stable accumulations at the surface as well as in the bulk of the material due to admixtures, gas bubbles and crazes. The probable effect of radon's tendency to form accumulations on the kinetics of its diffusion in crystalline polymers is discussed.

Studies on bound water in poly(vinyl alcohol). Hydrogel by DSC and FT-NMR

The phase transition of water bound in poly(vinyl alcohol)(PVA) hydrogel was measured by differential scanning calorimetry. The cross-link density calculated from the swelling ratio of PVA hydrogel ranged from 3 × 10 −5 to 1 × 10 −3 according to the total dose of 60Co γ-ray irradiation. From the enthalpy of melting, it was found that water in PVA gel can be classified into at least three groups; ca. 1–1.5 mol non-freezing water, 5–6 mol freezing bound water, and the rest free water, corresponding to each hydroxyl group of PVA. The characteristic properties of polymer hydrogel were attributed to the large number of molecules of freezing bound water in the network. The amount of free water depended markedly upon cross-link density; however, it was not apparent in PVA gel with cross-link density >2.0 × 10 −4. The decreases in the nuclear magnetic resonance relaxation times of water and PVA were related to the cross-link density and were found to level off at a cross-link density 2.0 × 10 −4.

Deep level defects in gamma-ray irradiated ge doped with pb or sn

Abstract Deep level transient spectroscopy has been used to investigate the electrical properties of deep defect states in γ-ray irradiated Ge doped with the isoelectronic elements Pb or Sn. Three deep levels are observed in the irradiated Pb-doped Ge (Ev +0.28 eV, Ec −0.33 eV, Ec −0.39 eV) and two deep levels observed in the Sn-doped Ge (Ev + 0.19 eV, Ec −0.15 eV). For the same γ-ray irradiation doses, Ge crystals grown from graphite crucibles and doped with Pb or Sn shows about two-thirds the total density of deep level defects observed in undoped Ge grown from synthetic quartz crucibles. All of the defect states observed were removed by a 1 hour, 250°C thermal anneal, and all but the Ec −0.39 eV state in the Pb-doped material were neutralized by exposure to a low pressure atomic hydrogen plasma.

Infrared reflection studies of γ-ray irradiated NaNO2

The infrared reflectances of virgin and γ-ray irradiated NaNO2 have been determined from the reflection spectra which have been investigated as functions of temperature (ranging from RT to 180 °C) and crystallographic orientation, and γ-ray irradiation dose (4×107 and 3×108 röntgen.) over a frequency region between 700 and 2000 cm−1. Using the Kramers-Kronig dispersion relation, we have obtained the dielectric function and oscillator parameters from the reflection spectra. These constants are used to explain the ferroelectric properties of NaNO2. In addition the observed differences between the reflection spectra of virgin and those of γ-ray irradiated NaNO2 are explained using a broken-bond model.