Influence of fluorine on radiation-induced charge trapping in the SIMOX buried oxides

Charge trapping in the fluorinated SIMOX buried oxides before and after ionizing radiation has been investigated by means of C-V characteristics. Radiation-induced positive charge trapping which results in negative shift of C-V curves can be restrained by implanting fluorine ions into the SIMOX buried oxides. Pre-radiation charge trapping is suppressed in the fluorinated buried oxides. The fluorine dose and post-implantation anneal time play a very important role in the control of charge trapping.

Improved neutron radiation hardness for Si detectors: Application of low resistivity starting material and or manipulation of N-eff by selective filling of radiation-induced traps at low temperatures

Radiation-induced electrical changes in both space charge region (SCR) of Si detectors and bulk material (BM) have been studied for samples of diodes and resistors made on Si materials with different initial resistivities. The space charge sign inversion fluence (Phi(inv)) has been found to increase linearly with the initial doping concentration (the reciprocal of the resistivity), which gives improved radiation hardness to Si detectors fabricated from low resistivity material. The resistivity of the BM, on the other hand, has been observed to increase with the neutron fluence and approach a saturation value in the order of hundreds k Omega cm at high fluences, independent of the initial resistivity and material type. However, the fluence (Phi(s)), at which the resistivity saturation starts, increases with the initial doping concentrations and the value of Phi(s) is in the same order of that of Phi(inv) for all resistivity samples. Improved radiation hardness can also be achieved by the manipulation of the space charge concentration (N-eff) in SCR, by selective filling and/or freezing at cryogenic temperatures the charge state of radiation-induced traps, to values that will give a much smaller full depletion voltage. Models have been proposed to explain the experimental data.

potential mechanisms involved in resistant phenotype of MCF-7breast carcinoma cells to ionizing radiation induced apoptosis

In the present study, we investigated the mechanisms of apoptosis resistance and the roles of the phosphorylation of BRCA1, p21, the Bax/Bcl-2 protein ratio and cell cycle arrest in IR-induced apoptosis in MCF-7 cells. X-irradiation, in particular at low dose (1 Gy), but not carbon ion irradiation, had a significant antiproliferative effect on the growth of MCF-7 cells. 1 Gy X-irradiation resulted in G1 and G2 phase arrest, but 4 Gy induced a significant G1 block. In contrast, carbon ion irradiation resulted in a significant accumulation in the G2 phase. Concomitant with the phosphorylation of H2AX induced by DNA damage,carbon ion irradiation resulted in an approximately 1.9–2.8-fold increase in the phosphorylation of BRCA1 on serine residue 1524, significantly greater than that detected for X-irradiation. Carbon ion irradiation caused a dramatic increase in p21 expression and drastic decrease in Bax expression compared with X-irradiation. The data implicated that phosphorylation of BRCA1 on serine residue 1524 might,at least partially, induce p21 expression but repress Bax expression. Together, our results suggested that the phosphorylation of BRCA1 at Ser-1524 might contribute to the G2 phase arrest and might be an upstream signal involved in preventing apoptosis signal via upregulation of p21 and downregulation of the Bax/Bcl-2 ratio.

Preparation and physical properties of enhanced radiation induced crosslinking of ethylene-vinyl alcohol copolymer (EVOH)

Preparation and physical properties of ethylene-vinyl alcohol copolymer (EVOH) crosslinked by enhanced radiation have been studied through various methods. It was found that the most effective agent for irradiation-crosslinking was triallyl isocyanurate (TAIC) among four kinds of polyfunctional monomers. Gel content (65.6%) was formed for EVOH-44 (content of ethylene is 44 mol%) at 200 kGy with 5% TAIC, but for EVOH-32 (content of ethylene is 32 mol%), only 37.4% gel content was formed under the same conditions. This result showed that the more the content of ethylene units comprised in EVOH, the easier the chemical bonds could be formed between different molecular chains. Tensile strength and elastic modulus increased after crosslinking at high test temperature and elongation at break decreased at the same time. Hygroscopicity of EVOH showed noticeable decrease after enhancement radiation-crosslinking.

Hydrogel of biodegradable cellulose derivatives. I. Radiation-induced crosslinking of CMC

Radiation crosslinking of carboxymethylcellulose (CMC) with a degree of substitution (DS) from 0.7 to 2.2 was the subject of the current investigation. CMC was irradiated in solid-state and aqueous solutions at various irradiation doses. The DS and the concentration of the aqueous solution had a remarkable affect on the crosslinking of CMC. Irradiation of CMC, even with a high DS, 2.2 in solid state, and a low DS, 0.7 in 10% aqueous solution, resulted in degradation. However, it was found that irradiation of CMC with a relatively high DS, 1.32, led to crosslinking in a 5% aqueous solution, and 20% CMC gave the highest gel fraction. CMC with a DS of 2.2 induced higher crosslinking than that with a DS of 1.32 at lower doses with the same concentration. Hence, it was apparent that a high DS and a high concentration in an aqueous solution were favorable for high crosslinking of CMC. It is assumed that; high radiation crosslinking of CMC was induced by the increased mobility of its molecules in water and by the formation of CMC radicals from the abstraction of H atoms from macromolecules in the intermediate products of water radiolysis. A preliminary biodegradation study confirmed that crosslinked CMC hydrogel can be digested by a cellulase enzyme. (C) 2000 John Wiley & Sons, Inc.

Thermal, mechanical and ionic conductive behaviour of gamma-radiation induced PEO/PVDF(SIN)-LiClO4 polymer electrolyte system

An effort has been made to modify the mechanical behaviour of our previously reported gel-type gamma-radiation crosslinked polyethylene oxide (PEO)-LiClO4 polymer electrolyte. A highly polar and gamma-radiation crosslinkable crystalline polymer, polyvinylidene fluoride (PVDF), was selected to blend with PEO and then subjected to gamma-irradiation in order to make an simultaneous interpenetrating network (SIN), which was used as a polymer host to impart stiffness to the plasticized system. Experimental results have shown that the presence of PVDF in the system, through gamma-radiation induced SIN formation, could not only give a rather high mechanical modulus of 10(7) Pa at ambient temperature, but also maintain the room temperature ionic conductivity at a high level (greater than 10(-4) S/cm). DSC, DMA and conductivity measurement techniques were used to examine the effects of blending, gamma-irradiation and plasticization on the variations of glass transition and melting endotherm, on the appearance of high elastic plateau and on the temperature dependence of ionic conductivity: In addition, it was found that, in contrast with the unplasticized system, the ionic conductivity mechanism of this gel-type electrolyte seems to conform to the Arrhenius model, suggesting that, as a result of the high degree of plasticization, the polymer chains act mainly as the skeleton of the networks or polymer cages to immobilize the liquid electrolyte solution, whereas the ionic species migrate as if they were in a liquid medium. (C) 1997 Elsevier Science Ltd.

Radiation-induced crystallization of polyamide-1010 containing heterogeneous nuclei

Radiation-induced crystallization of polyamide-1010 (PA1010) or nylon-1010 containing heterogeneous nuclei (neodymium oxide, Nd2O3) is discussed in this paper by Wide Angle X-ray Diffraction (WAXD) and Differential Scanning Calorimetry (DSC). The results show that at low dosage the crystallinities of the irradiated specimens increase, while crystallite size (L(hkl)) decreases, indicating that some new crystallites are produced in the course of irradiation. The new centers were brought about in the fold surface of the lamellae. Copyright (C) 1997 Elsevier Science Ltd

Chemiluminescence studies of radiation induced oxidation of various polyethylenes

The chemiluminescence (CL) emission from three kinds of polyethylene, HDPE, LLDPE and LDPE, which had been exposed to 80 kGy dose from Co-60 in both air and nitrogen, has been examined. CL measurement was done under both nitrogen and oxygen atmosphere. The results show that the CL emission from irradiated samples does not result from irradiation itself, but from the oxidation reactions occurring during and after irradiation. Addition of 1 phr of an antioxidant, Irganox 1010, can effectively inhibit the radiation induced oxidation in LLDPE and LDPE. In the case of HDPE, however, it was found that pure HDPE has the best resistance to radiation-induced oxidation of the polymers examined in this work. However, incorporation of Irganox 1010 was found to have not only a stabilizing effect against radiation induced oxidation, but also to promote the oxidation in some cases.

GAMMA-RADIATION INDUCED CROSS-LINKED PEO-LICLO4 SOLID-ELECTROLYTE SYSTEM

Aimed at raising the room temperature ionic conductivity of PEO-based solid polymer electrolyte and considered that the ionic conduction preferentially occurs in the amorphous phase, we lightly crosslinked the high MW PEO through gamma-irradiation and further suppressed the residual crystallinity by plasticizing with propylene carbonate. By incorporating LiClO4 salt to the above described polymer host, the ambient (25 degrees C) ionic conductivity of the electrolyte system could reach as high as 6.8 X 10(-4) S/cm. As the electrolyte was a crosslinked system, it was mechanically self-supportable. Based on the preliminary results of the electrochemical performance of the secondary lithium battery, assembled by using this kind of solid electrolyte and polyaniline as positive electrode, it is realized that the electrolyte thus prepared is of high expectancy.

STUDY ON THE RADIATION-INDUCED COPOLYMERIZATION OF ACRYLAMIDE WITH SODIUM ACRYLATE IN AQUEOUS-SOLUTION

In the present work, the mechanism of radiation-induced copolymerization of acrylamide (AM) with sodium acrylate (AANa) in aqueous solution was studied. A method to protect the copolymerization system from the crosslinking and a carbon-carbon mechanism to form gel in copolymerization reaction have been proposed. The condition to prepare the products with different molecular weight, especially with very high molecular weight were found.

RADIATION-INDUCED PHASE-SEPARATION IN IRRADIATED PTFE

The radiation induced phase separation in PTFE as shown by the observation of separation of its melting curves was investigated in this work. The observed phase separation was found to depend on irradiation temperature and explained as being duo to radiation induced increase in disorder of its crystalline region.

STUDIES ON RADIATION-INDUCED CROSS-LINKING OF POLYISOBUTYLENE

Polyisobutylene can be crosslinked under irradiation as to be expected by either introducing radiation sensitive groups into its macromolecules or blending with a proper radiation crosslinkable polymer.

ESTIMATION OF THE RADIATION-INDUCED DAMAGE IN PTFE BY DEPRESSION OF THE MELTING AND CRYSTALLIZATION TEMPERATURES

The radiation induced depression of the melting and crystallization temperatures of PTFE irradiated at various temperatures followed by heat treatment at 380-degrees-C, and their relationship to structural changes, were investigated. The G(-units) values obtained in this work are different from those of samples which have not undergone heat treatment and seem to be more closely associated with radiation induced branched structures.

STUDY ON GAMMA-RADIATION INDUCED LAMELLAR DAMAGE MECHANISM OF POLY(VINYLIDENE FLUORIDE)

This paper studies gamma-radiation induced lamellar damage mechanism of poly(vinylidene fluoride), using wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), electronic paramagnetic resonance (EPR) and gel fraction determination. We believe that it is ''lamellae core damage'' rather than ''lamellae surface damage'' that results in the decrease of the crystallinity.

RADIATION-INDUCED CRYSTAL DEFECTS IN PTFE

Changes induced in the crystal structure of PTFE by irradiation at different temperatures have been investigated. In the dose and temperature range examined, the density of PTFE was observed to increase continuously with increasing dose due to the radiation-induced increase in crystallinity, while after post-irradiation annealing at 380-degrees-C, the density was observed to increase for samples irradiated at 20-degrees-C, and to begin to decrease after a certain dose for samples irradiated at 150 and 200-degrees-C. On the basis of the observation of radiation-induced separation of the melting peak of PTFE and its stability relative to the change in the rate of heating, the observed decrease in density was explained as being due to the radiation-induced crosslinking and/or branching inhibiting the process of crystallization and existing in the crystalline region as defects.