Post-irradiation Degradation Research Articles

Post-irradiation degradation of radio-oxidized natural rubber latex films induced by 60Co gamma rays

The present work involves the post-irradiation aging of radio-oxidized natural rubber latex (NRL) films irradiated by 60Co gamma rays. The NRL films underwent the two consecutive processes: irradiation oxidation in air with a dose of 0.1 kGy h−1 (pre-irradiation phase) and radiolysis in argon with a dose of 10 kGy h−1 (post-irradiation phase). The changes of oxygen-containing groups in radio-oxidized NRL films were subsequently analyzed by FTIR (ATR method), XPS, and Raman spectroscopy. Analysis of the EPR spectra of free radicals and macroscope properties (including mechanical and thermodynamic properties) were also carried out. Pre-irradiation of NRL films in air resulted in the rapid formation of various carbonyl and unsaturated carbonyl products related to aliphatic esters, ketones, and carboxylic acids. These were followed by the decomposition of the oxygen-containing functional groups in the post-irradiation phase. In particular, the formation of an enol tautomer of a β-diketone functionality was observed. The increase and decrease of free radicals by EPR analysis were closely related to the crosslinking and degradation of the NRL network structures induced by irradiation. Further analysis indicated that the variations in macroscopic properties of NRL films were attributed to the secondary reactions of free radicals. Mechanistic routes for these irradiation aging processes are proposed and discussed.

Protective effects in radiation modification of elastomers

Saturated character of ethylene/octene thermoplastic elastomers demands an application of nonconventional methods of crosslinking connections between chains of molecules. These are organic peroxides, usually in the presence of coagents or an application of ionizing radiation. Several approaches (radiation, peroxide, peroxide/plus radiation and radiation/plus peroxide) were applied in crosslinking of elastomere Engage 8200. Attention was directed to the protection effects by aromatic peroxides and by photo- and thermostabilizers on radiolysis of elastomers. Role of dose of radiation, dose rate of radiation as well as the role of composition of elastomere on the radiation yield of hydrogen and absorbtion of oxygen was investigated. DRS method was used to follow postirradiation degradation. Influence of crosslinking methods on properties of elastomers is described. Results were interpreted from the point of view of protective actions of aromatic compounds.

The influence of stabilisers on resistance to gamma radiation for epoxy based polymeric composite material

In certain applications plastic materials are getting irradiated while in end use. High energy irradiation leads to the auto-oxidation and degradation. The primary approach for stabilization against post irradiation degradation is to use appropriate stabilisers. In this research work, an experimental analysis of the effect of dose rate of gamma irradiation on epoxy resin based samples prepared by using combinations of primary and secondary stabilisers is presented. The chemistry, reaction mechanisms and morphology changes are studied and its effect on mechanical properties is observed. The results show an improvement of mechanical strength as dose increases, indicating cross-linking over oxidative degradation.

The Enhanced Role of Shallow-Trench Isolation in Ionizing Radiation Damage of 65 nm RF-CMOS on SOI

The mechanism for ionizing radiation damage in multi-finger SOI CMOS devices is presented for the first time. We analyzed the effects of shallow-trench isolation on ionizing radiation response of 65 nm Silicon-On-Insulator (SOI) CMOS technology. The radiation response of the CMOS devices was investigated using 63 MeV protons and 10 keV X-rays. The implications of proton irradiation and X-ray irradiation on the dc and RF performance of these devices are presented. The cut-off frequency is degraded due to post-irradiation degradation of device transconductance. Even though there is charge-accumulation in the buried-oxide, there is minimal impact on the front-gate characteristics of the partially-depleted SOI devices in this 65 nm CMOS technology. The implications of parasitic conduction along the STI on device design constraints, particularly for varying device width and number of gate fingers, are discussed in the context of high performance RF CMOS technology. These results suggest that body-contacting schemes which eliminate sidewalls (e.g., H-body, T-body) will provide the necessary total-dose radiation tolerance for multi-finger analog and RF devices, without additional hardening techniques.

Impact of Proton Irradiation on the RF Performance of 65 nm SOI CMOS Technology

The effects of 63 MeV proton irradiation on 65 nm Silicon-On-Insulator (SOI) CMOS technology are presented for the first time. The radiation response of the CMOS devices was investigated up to an equivalent total gamma dose of 4.1 Mrad (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). We analyze the implications of proton irradiation on RF performance of these devices. The cut-off frequency is degraded due to post-irradiation degradation of device transconductance. High-frequency measurements show that the input and output matching conditions are not affected, up to a cumulative dose of 4.1 Mrad. The implications of proton irradiation on device design constraints, particularly device width and number of gate fingers, are discussed in the context of high performance RF CMOS technology. These results suggest that multi-finger CMOS devices with higher finger width are better-suited for the development of total-dose radiation tolerant analog and RF circuits without additional radiation hardening.

Radiation effect on the mechanical stability and biodegradability of CPP/Bionolle blend

Blends of polypropylene-co-ethylene (CPP) and polybutylene succinate (Bionolle) with polypropylene grafted maleic anhydride (Modic) as a compatibilizer were prepared by melt blending. Irradiation of the resultant polyblend was carried out using an electron beam in air. It was noted that the Modic compatibilizer also appears to act as a protective agent toward radiation degradation. The occurrence of crosslinking in the polyblend was observed, mainly contributed by Bionolle. However the whole process over all blend composition ranges was dominated by degradation. During indoor storage, the mechanical stability of irradiated polyblends was found to be fairly good, particularly compatibilized Bionolle and CPP/Bionolle (27/75). On the other hand, the sample buried in soil showed a drastic reduction in the over all mechanical properties. The extent of biodegradability as estimated from the weight loss increased with increasing Bionolle content. A synergistic effect on the weight loss was shown by compatibilized Bionolle and CPP/Bionolle (25/75). Additionally, even if the sample was no longer strong due to postirradiation degradation, the biodegradability of the polyblend was not much improved. Using a curve fit model the time for complete weight loss was found to be approximately 14, 8, 7, and 12 months for unirradiated and irradiated Bionolle, compatibilized Bionolle, CPP/Bionolle (25/75) and (50/50), respectively.

Dose rate and total dose dependence of low frequency noise performance, I-V curves and sidegating for GaAs MESFETs

Total dose and dose rate performance of GaAs MESFET devices of various geometries and sidegating structures at various distances and orientations are presented. Parameters measured include low frequency noise, I-V curves and sidegating. The GaAs MESFET devices tested are shown to be useful to a total dose greater than 500 Mrad(GaAs). The observed reduction in drain current for a given bias point versus total dose is believed to be due to the sinking gate effect. The post irradiation degradation of 1/f noise performance shows a Lorentzian component which grows continuously with total dose to 1 Grad(GaAs). The during irradiation noise performance exhibits a dose rate dependent Lorentzian component. This component has been named selfgating dose rate noise. The sidegating effect exhibits a dose rate dependent degradation which decreases with increasing distance at low dose rates and saturates at a dose rate of approximately 150 krad(GaAs)/hour. The dose rate dependent sidegating effect is reduced with accumulated total dose.

Discussion

The post-irradiation storage stability of ethylene-propylene copolymer (CP) irradiated with γ-ray at irradiation doses of 3 and 5 Mrad has been studied. The effectiveness of an antioxidant, two hindered amine light stabilizers and a nucleating agent in stabilizing ethylene-propylene copolymer against post-irradiation oxidative degradation, at various concentrations is compared with that of the control sample. The variation in melt index (MI), yellowness index (YI) and mechanical properties of stabilized CP was followed with respect to post-irradiation time. It is found that the HALS used for this study, do not contribute much towards the post-irradiation mechanical stability and result in higher discolouration, whereas the antioxidant and nucleating agent show a very good retention in the mechanical properties and less yellowing in the post-irradiation storage period.

The enhanced stability of the cross-linked hylan structure to hydroxyl (OH) radicals compared with the uncross-linked hyaluronan

A comparison has been made of the relative stabilities of hyaluronan and hylan to degradation by OH radicals produced by γ-irradiation of aqueous solutions in N 2O, when G (yield per 100 eV) for OH radicals is 5.6 and H atoms 0.6. Using low angle light scattering and viscometric methods, the change in molecular weight of the polysaccharides was measured with increasing dose. From the yield/dose curves (expressed as breaks per molecule), the initial G value for hyaluronan degradation is ∼ 4. A further slow post-irradiation decrease in molecular weight is observed, which can be brought to completion by incubating the solutions for 1 h at 60°C. Thereafter, the G value for degradation is ∼ 6. A similar post-irradiation degradation was found for hylan. A technique using tetranitromethane (TNM) has been used to distinguish between two types of radicals formed on the hyaluronan backbone. Radicals of the 1-hydroxy-2-alkoxy type (C-2, C-4, C-2 and C3 of the glucuronic acid) would induce strand breakage by alkoxy elimination. For the equivalent alkoxy radical at C6 of the acetamido monosaccharide, ring opening would occur with formation of a hemi-acetal, leading also to strand breakage. The C-2 and C-3 radicals would eliminate water rather than produce breaks by β-alkoxy elimination. Thus three out of the initially formed radicals would produce breaks by β-alkoxy formation. These can be stabilised with TNM and distinguished. It is concluded that these are the radicals involved in the post-irradiation thermal degradation process. Comparison of hylan and hyaluronan is, therefore, most valid when this post-irradiation process has been completed. Therefore, all G values for degradation were measured after incubation for 1 h at 60°. This investigation establishes the greater stability of hylan ( G degradation = 2) compared to hylan ( G degradation = 6). Therefore, in an environment such as supplementation of an inflammed joint where OH radicals are released, hylan is able to retain its integrity as a viscoelastic macromolecule three times better than hyaluronan. Its potential as a viscosupplementation material, or as an inflammatory drug release matrix inserted within the joint is, therefore, greater than non-cross-linked hyaluronan.

Post-irradiation degradation of polypropylene

We present the mechanical changes (elongation at break, tensile strength, modulus of elasticity) and electrical changes (volume and surface resistivity, tgΔ, ∈, breakdown voltage) ofisotactic polypropylene (PP) due to γ-radiation. Ageing of PP was achieved in air by using a137Cs γ-source with 400 Ci activity; the dose rate was of 8·104 rad/h, and the integrated doses ranged from 2 to 160 Mrad. Severe deterioration of mechanical properties was observed. The changes of electrical properties were not as significant as those of mechanical characteristics. These variations are caused by the increase in density of crosslinking chain-scission and by oxidative processes. The rate of extent of degradations has been evaluated by the growth of the hyydroxy and carbonylbands in the IR spectrum By using FTIR mapping, we have also investigated the degradation of PP which had been irradiated in air 15 years ago. We determined the contour lines of FTIR absorption bands of carbonyl groups at different regions of the cross-section of an irradiated sample. Dust particles of irradiated brittle PP were also studied. The FTIR showed that the carbonyl band is broad, indicating a mixtures of many different functional groups (ester, acid, ketone, lactones). We determined also the gel content at different irradiation doses.

Radiation degradation of polypropylene

Post-irradiation degradation of isotactic polypropylene irradiated by Co 60-γ-ray has been followed for 12 months. Effects of irradiation doses (10–100 kGy) up on the change of the structure and mechanical properties as well as flowability of this polymer has been studied. Carbonyl index increases with increasing post-irradiation time. The rate of which was much higher for doses above 50 kGy. Tensile strength declines with time and those samples irradiated above 50 kGy become quite brittle, just after irradiation. Results reveal that post-irradiation degradation of polypropylene irradiated by γ-ray occurs via chain scission mechanism.

Post-irradiation degradation of polypropylene: Comparison of hindered aromatic phenole and amine as gamma-stabilizer—I

Post-irradiation stability of 60Co-γ-ray irradiated isotactic PP has been studied at 25 and 50 kGy. The effectiveness of 2,6-di-tert-butyl-p-cresol (BHT) and polymerized 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ) at various concentrations is compared. The variation of crystallinity, carbonyl and hydroxyl index, mechanical properties, of stabilized and unstabilized PP was followed for 6 months after irradiation. Although the percentage of crystallinity of the unstabilized samples increased upon irradiation, but for all stabilized ones not only the initial value was retained but remained constant and lower to that of the unstabilized samples during storage. Tensile strength and bend strength was also retained. The extent of chain scission has been followed by measuring the change in apparent viscosity (μ a) and flowability parameters, ( K) and ( n), using power law equation. Although both types of stabilizers were highly effective, the amine type imparts more stability at a longer time after irradiation as the corresponding nitroxyl and hydroxyl amine groups are formed.

Distribution of nuclease attack sites and complexity of DNA in the products of post-irradiation degradation of rat thymus chromatin.

The distribution of nuclease attack sites in chromatin has been studied on the basis of the quantitative relationship of the single- and double-stranded fragments of various lengths in the products of post-irradiation degradation of chromatin (PDN). It has been shown that in irradiated thymocytes internucleosome degradation of chromatin occurs and the products of the enzymic digestion of chromatin derive from randomly distributed genome areas accumulate. Analysis of the reassociation curves has not shown any differences in the complexity of the PDN fractions and total DNA.

Role of exonucleases V and VIII in adenosine 5'-triphosphate- and deoxynucleotide triphosphate-dependent strand break repair in toluenized Escherichia coli cells treated with X-rays

The repair of X-ray-induced strand breaks was studied in permeabilized Escherichia coli recBC cells deficient for the adenosine 5'-triphosphate (ATP)-dependent exonuclease V and in recBC sbcA cells that possess the ATP-independent exonuclease VIII. It is shown that repair induced by additon of ATP does not take place in recBC and recBC sbcB cells and is limited in recBC sbcA cells. ATP-dependent repair is nevertheless observable if together with ATP a mixture of deoxynucleotide monophosphates is supplied to the cells. These data fit with the assumption that in wild-type cells ATP-dependent repair involves exonuclease V-induced deoxyribonucleic acid degradation and rephosphorylation of the degradation products which are reused for deoxyribonucleic acid polymerase I-dependent break closure. Repair in the presence of deoxynucleotide triphosphates rejoins a similar fraction of breaks in all strains tested irrespective of the amount of postirradiation degradation resulting from exonuclease V and exonuclease VIII activities. Thus, exonuclease V is dispensable for deoxynucleotide triphosphate-dependent repair, i.e., does not "clean" the ends of breaks produced by X-irradiation. ATP- and deoxynucleotide triphosphate-dependent repair are not additive and seem to repair the same population of deoxyribonucleic acid molecules damaged by X-irradiation.

Post-irradiation Degradation and Strand Breaks in DNA; the Sequence of Events inE. Coli

Post-irradiation Degradation and Strand Breaks in DNA; the Sequence of Events in<i>E. Coli</i>

Induction of protein synthesis in Escherichia coli following UV-or γ-irradiation, mitomycin C treatment or tif expression

The rate of synthesis of total cellular proteins has been studied by pulse labelling cells at various periods after irradiation with UV or gamma-rays, after treatment with mitomycin C (MMC) or after expression of the temperature sensitive mutation tif. Subsequent gel electrophoresis and autoradiography reveals changes in the rate of synthesis of several proteins. The most striking change is in a protein of molecular weight 40,000, protein X, which has been previously most extensively studied in cells treated with nalidixic acid (Gudas, 1976). Synthesis of large quantities of protein X is induced by UV, gamma-rays, MMC treatment or tif expression in rec+ but not recA cells. A feature of recA cells is that they break down their DNA excessively after irradiation or MMC treatment. However, if protein synthesis following irradiation is prohibited by chloramphenicol, post-irradiation degradation becomes excessive in recA+ cells. This inverse relationship between DNA degradation and new protein synthesis consistent with the hypothesis that an induced protein such as X is responsible for controlling DNA degradation following irradiation. Protein X is not induced in a lexB mutant following MMC treatment. In this respect the lexB mutant behaves like lexA and recA mutants in that the ability to induce protein X can be correlated with excessive DNA degradation. Studies on the induction of proteins in inf, tif and tif sfi mutants fail to reveal any correlation between induction of protein X and either the induction of prophage lambda or septation.

Action of Hydrogen Peroxide on Degradation of DNA after Irradiation inEscherichia Coli

Hydrogen peroxide (H2O2), which produces breaks in cellular DNA, has not hitherto been shown to cause degradation of DNA. In this investigation it is shown that if transcription is blocked with rifampin, treatment with H2O2 causes degradation of DNA to nearly the same extent as does gamma-radiation. Further, if cells are given a treatment with H2O2 and incubated for 50 min, the amount of degradation in a second treatment is markedly less. This is attributed to the induction of the inhibitor of post-irradiation degradation of DNA (prd) by the first treatment. There is thus a double action of H2O2: first, to induce inhibition, and second, to cause degradation of DNA to begin in non-induced cells. The genetic dependence of induction by H2O2 mimics that of ionizing radiation. Accordingly, the induction process does not occur in recA- and lex- cells, because they are not inducible and is absent in recB- cells because they lack exonuclease V, the major component of prd. Potassium iodide (KI), an OH radical scavenger, negates the action of peroxide on DNA. The results obtained in this study suggest a possible theory for the evolution of radiation response systems

Post-irradiation Degradation of DNA in Electron and Neutron-irradiatedE. ColiB/r; the Effect of the Radiation Sensitizer Metronidazole

Post-irradiation Degradation of DNA in Electron and Neutron-irradiated<i>E. Coli</i>B/r; the Effect of the Radiation Sensitizer Metronidazole

A Strain of Escherichia coli with Minimum Postirradiation Degradation Properties

A strain of Escherichia coli has been isolated which possesses minimum postirradiation degradation properties. Starting with E. coli ${\rm B}_{{\rm s}-1}$, mutational selection procedures were used to select for cells which do not degrade their DNA. Our strain (PHH1) does not degrade its DNA when exposed to 20 krad or less. It has a high survival capacity, even greater than E. coli B/r. This strain has an OER of about 3.0. The insensitivity of this cell to radiation-induced degradation suggests that it is a prime candidate for the study of relative sensitivities of the molecular apparatus of cells to ionizing radiation.

Formation and repair of γ-ray induced thymine damage in Micrococcus radiodurans

A reductive assay for the identification and determination of the major radiolysis products of thymine and its derivatives has been developed. Radiolysis products of the 6-(hydroxy or hydroperoxy)-5,6-dihydrothymine type ( t † ) are reductively cleaved with NaBH 4 and a four-carbon alcohol is released containing the thyminemethyl substituent. If thymine derivatives carrying a radioactive label in the methyl group are used as starting materials for the radiolysis, the amount of the four-carbon fragments produced by the treatment with NaBH 4 (mostly 2-methylglycerol after irradiation in air) can be determined by radioactivity measurements and is a measure of the extent of thymine radiolysis. The formation and repair of thymine base damage was investigated in Micrococcus radiodurans after exposure to γ -rays with the help of the reductive assay. The radiolysis products of thymine were determined in the cytoplasm and the culture medium after their release from the DNA during post-irradiation incubation. It is estimated that t † is formed in the DNA of M. radiodurans with an efficiency of about 1.2 × 10 −6 /rad, 10 6 daltons for irradiation in air and 10 −6 /rad, 10 6 daltons for irradiation in nitrogen. Damaged residues are released from the DNA of irradiated M. radiodurans into cytoplasm and medium during post-irradiation incubation in a biphasic, selective process. On the average, about 300 undamaged thymine residues are removed from the DNA per damaged residue during 240 minutes post-irradiation repair after irradiation in air. The first phase of removal (0 to 30 min at 37°C) and post-irradiation degradation may be part of the same process. Selectivity of product removal may be due to product clustering. Degradation is assumed to start at nearby radiation induced breaks. After a temporary halt, a second phase of product removal is observed (60 to 200 min).