A study of the radiation degradation of styrene/alkane and α-methylstyrene/alkane copolymers

The effects of copolymer composition and microstructure on the radiation chemistry of styrene/alkane and alpha-methylstyrene/alkane copolymers have been studied. The primary radical species formed on radiolysis of the copolymers at 77 K, and identified by ESR spectroscopy, are the same as those formed during radiolysis of the homopolymers. The yields of radicals for the copolymer are as predicted assuming that the cross-section is proportional to the electron density of each component; however, there is some evidence of radical migration to aromatic groups at 77 K. Changes in molecular structure on irradiation were detected by using C-13 NMR spectroscopy. Evidence of the consumption of terminal double bonds, and chain scission in alpha-methylstyrene/alkane copolymers was found. Measurements of viscosity supported the mechanism of cross-linking predominating in styrene/alkane copolymers, while in alpha-methylstyrene/alkane copolymers chain scission was the major result of irradiation. (C) 2003 Society of Chemical Industry.

Measurements of environmental background radiation in the surrounding area of a coal-fired power plant

Certain materials used and produced in a wide range of non-nuclear industries contain enhanced activity concentrations of natural radionuclides. In particular, electricity production from coal is one of the major sources of increased exposure to man from enhanced naturally occurring materials. Over the past decades there has been some discussion about the elevated natural background radiation in the area near coal-fired power plants due to high uranium and thorium content present in coal. This work describes the methodology developed to assess the radiological impact due to natural radiation background increasing levels, potentially originated by a coal-fired power plant’s operation. Gamma radiation measurements have been done with two different instruments: a scintillometer (SPP2 NF, Saphymo) and a gamma ray spectrometer with energy discrimination (Falcon 5000, Canberra). A total of 40 relevant sampling points were established at locations within 20 km from the power plant: 15 urban and 25 suburban measured stations. The highest values were measured at the sampling points near to the power plant and those located in the area within the 6 and 20 km from the stacks. This may be explained by the presence of a huge coal pile (1.3 million tons) located near the stacks contributing to the dispersion of unburned coal and, on the other hand, the height of the stacks (225 m) which may influence ash’s dispersion up to a distance of 20 km. In situ gamma radiation measurements with energy discrimination identified natural emitting nuclides as well as their decay products (212Pb, 214Pb, 226Ra 232Th, 228Ac, 234Th 234Pa, 235U, etc.). This work has been primarily done to in order to assess the impact of a coal-fired power plant operation on the background radiation level in the surrounding area. According to the results, an increase or at least an influence has been identified both qualitatively and quantitatively.

Gamma 60Co DL50/30 of Biomphalaria glabrata (Say, 1818)

The variation of resistance to 60Co gamma-rays of Biomphalaria glabrata was studied. A population of 480 mollusks was observed during 30 days - distributed in 8 groups of snails isolated and 8 groups of snails in colonies - after exposure (30 snails per group per dose) to increasing doses of gamma radiation. Doses of 10, 20, 40, 60, 80, 160, 320 and 640 Gy from a Gamma-cell 60Co irradiator, were applied to the test groups and two groups control (non-irradiated) of snails - isolated and colony - were kept apart. After have been exposed, the snails were drew back to the aquaria where they were maintained before. The survival was estimated on a daily score of the alive animals in each group-dose, starting after the irradiation exposure day. As a result, the survival self-fertilization forms (DL50/30 = 218.2 Gy) was found greater than in cross-fecundation forms. These data point to a low radio-resistance on the cross-fertilization forms - the sexual reproductive form - which is most found in nature. The lower radio-resistance of the cross-fertilization forms suggests the presence of some sex-linked hormonal factor related to this phenomenon.

Aflatoxins detoxification by gamma irradiation

[Excerpt] Mycotoxins are secondary toxic metabolites of filamentous fungi. Aflatoxins (AFs) are produced to Aspergillus species such as A. flavus and A. parasiticus. These fungi are ubiquitous in nature and usually found on agricultural commodities. Therefore, AFs are encountered in many important foodstuff, including wheat, rice, maize, peanuts, sorghum, pearl millet, spices, oilseeds, tree nuts and milk. Due to the high toxicity of AFs, many methods have been studied to reduce or eliminate these mycotoxins from food and feed. Gamma irradiation is one technology that has been investigated with promising results. The aims of this study were (I) to study the effect of gamma radiation on aflatoxin B1, aflatoxin B2, aflatoxin G1 and aflatoxin G2 (II) to evaluate the effect of the presence of water on AFs degradation during the irradiation process; and (IV) to evaluate the cytotoxicity of radiolytic products formed. (...)

Very-High-Energy gamma rays from a Distant Quasar: How Transparent Is the Universe?

The atmospheric Cherenkov gamma-ray telescope MAGIC, designed for a low-energy threshold, has detected very-high-energy gamma rays from a giant flare of the distant Quasi-Stellar Radio Source (in short: radio quasar) 3C 279, at a distance of more than 5 billion light-years (a redshift of 0.536). No quasar has been observed previously in very-high-energy gamma radiation, and this is also the most distant object detected emitting gamma rays above 50 gigaelectron volts. Because high-energy gamma rays may be stopped by interacting with the diffuse background light in the universe, the observations by MAGIC imply a low amount for such light, consistent with that known from galaxy counts.

Effect of gamma irradiation on the behavioral properties of crotoxin

Crotoxin has been detoxified with gamma radiation in order to improve crotalic antiserum production. Nevertheless, present knowledge of the biological characteristics of irradiated crotoxin is insufficient to propose it as an immunizing agent. Crotoxin is known to increase the emotional state of rats and to decrease their exploratory behavior (Moreira EG, Nascimento N, Rosa GJM, Rogero JR and Vassilieff VS (1996) Brazilian Journal of Medical and Biological Research, 29: 629-632). Therefore, we decided 1) to evaluate the effects of crotoxin in the social interaction test, which has been widely used for the evaluation of anxiogenic drugs, and 2) to determine if irradiated crotoxin induces behavioral alterations similar to those of crotoxin in the social interaction, open-field and hole-board tests. Male Wistar rats (180-220 g) were used. Crotoxin (100, 250, and 500 µg/kg) was injected intraperitoneally 2 h before the social interaction test. Similarly, irradiated crotoxin (2000 Gy gamma radiation from a 60Co source) was administered at the doses of 100, 250, and 500 µg/kg for the hole-board test, and at the doses of 1000 and 2500 µg/kg for the open-field and social interaction tests. ANOVA complemented with the Dunnett test was used for statistical analysis (P<0.05). Crotoxin decreased the social interaction time (s) at the doses of 100, 250 and 500 µg/kg (means ± SEM) from 51.6 ± 4.4 to 32.6 ± 3.7, 28.0 ± 3.6 and 31.6 ± 4.4, respectively. Irradiated crotoxin did not induce behavioral alterations. These results indicate that 1) crotoxin may be an anxiogenic compound, and 2) in contrast to crotoxin, irradiated crotoxin was unable to induce behavioral alterations, which makes it a promising compound for the production of crotalic antiserum

Long-term correlation of the electrocorticogram as a bioindicator of brain exposure to ionizing radiation

Understanding the effects of radiation and its possible influence on the nervous system are of great clinical interest. However, there have been few electrophysiological studies on brain activity after exposure to ionizing radiation (IR). A new methodological approach regarding the assessment of the possible effects of IR on brain activity is the use of linear and nonlinear mathematical methods in the analysis of complex time series, such as brain oscillations measured using the electrocorticogram (ECoG). The objective of this study was to use linear and nonlinear mathematical methods as biomarkers of gamma radiation regarding cortical electrical activity. Adult Wistar rats were divided into 3 groups: 1 control and 2 irradiated groups, evaluated at 24 h (IR24) and 90 days (IR90) after exposure to 18 Gy of gamma radiation from a cobalt-60 radiotherapy source. The ECoG was analyzed using power spectrum methods for the calculation of the power of delta, theta, alpha and beta rhythms and by means of the α-exponent of the detrended fluctuation analysis (DFA). Using both mathematical methods it was possible to identify changes in the ECoG, and to identify significant changes in the pattern of the recording at 24 h after irradiation. Some of these changes were persistent at 90 days after exposure to IR. In particular, the theta wave using the two methods showed higher sensitivity than other waves, suggesting that it is a possible biomarker of exposure to IR.

Radiation-induced changes in the export of photoassimilated carbon /|nBarry Jess Shelp. -- 260 0 St. Catharines, [Ont. : s. n.],

Low levels of ionizing radiation induce two translocation responses in soybean: a reduction in photoassimilate export from leaves and a change in the distribution pattern of exported photoassimilate within the plant. In this investigation these responses have been further studied specifically to ascertain the site of radiation damage and to better understand the physiological responses observed. Experimentally the primary data was obtained from studies in which a mature trifoliate leaf of a young soybean plant (Glycine ~ L. cultivar Harosoy '63) is isolated in a closed transparent chamber and allowed to photoassimilate 14C02 for 15 minutes. This is followed by an additional 45 ~_il'1;ute period before the plant is sectl.o ne d an d 14 C-ra dl' oactl.v.l ty d eterml. ne d'l n a 11 parts. Such 14c data provides one with the magnitude and distribution pattern of translocation. Further analyses were conducted to determine the relative levels of the major photosynthetic products using the techniques of paper chromatography and autoradiography. Since differences between control and irradiated P 1 ants were not 0 b serve d l' n t h e par tl't"lo nlng 0 f 14 C between the 80% ethanol-soluble and -insoluble fractions 14 or in the relative amounts of C-products of photosynthesis, the reduction in export in irradiated plants is not likely due to reduced availability of translocatable materials. Data presented in this thesis shows that photoassimilate export was not affected by gamma radiation until a threshold dose between 2.0 and 3.0 krads was reached. It was also observed that radiation-induced damage to the export process was capable of recovery in a period of 1 to 2 hours provided high light intensity was supplied. In contrast, the distribution pattern was shown to be extremely radiosensitive with a low threshold dose between .25 and .49 krads. Although this process was also capable of recovery,lt" occurred much earlier and was followed by a secondary effect which lasted at least for the duration of the experiments. The data presented in this thesis is interpreted to suggest that the sites of radiation action for the two translocation responses are different. In regards to photoassimilate export, the site of action of ionizing radiation is the leaf, quite possibly the process of photophosphorylation which may provide energy directly for phloem loading and for membrane integrity of the phloem tissue* In regards to the pattern of distribution of exported photoassimilate, the site is likely the apical sink, possibly the result of changes of levels of endogenous hormones. By the selection of radiation exposure dose and time post-irradiation, it is possible to affect independently these two processes suggesting that each may be regulated independent of the other and involves a distinct site.

pH effects on the complexation, miscibility and radiation-induced crosslinking in poly(acrylic acid)-poly (vinyl alcohol) blends

The effect of pH on the complexation of poly(acrylic acid) with poly(vinyl alcohol) in aqueous solution, the miscibility of these polymers in the solid state and the possibility for crosslinking the blends using gamma radiation has been studied. It is demonstrated that the complexation ability of poly(vinyl alcohol) with respect to poly(acrylic acid) is relatively low in comparison with some other synthetic non-ionic polymers. The precipitation of interpolymer complexes was observed below the critical pH of complexation (pH(crit1)), which characterizes the transition between a compact hydrophobic polycomplex and an extended hydrophilic interpolymer associate. Films prepared by casting from aqueous solutions at different pH values exhibited a transition from miscibility to immiscibility at a certain critical pH, pH(crit2), above which hydrogen bonding is prevented. It is shown here that gamma radiation crosslinking of solid blends is efficient and only results in the formation of hydrogel films for blends prepared between pH(crit1), and pH(crit2). The yield of the gel fraction and the swelling properties of the films depended on the absorbed radiation dose and the polymer ratio.

Short-term effects of gamma ray bursts on Earth

The aim of the present work is to study the potential short-term atmospheric and biospheric influence of Gamma Ray Bursts on the Earth. We focus in the ultraviolet flash at planet`s surface, which occurs as a result of the retransmission of the gamma radiation through the atmosphere. This would be the only important short-term effect on life. We mostly consider Archean and Proterozoic eons, and for completeness we also comment on the Phanerozoic. Therefore, in our study we consider atmospheres with oxygen levels ranging from 10(-5) to 1 of the present atmospheric level, representing different moments in the oxygen rise history. Ecological consequences and some strategies to estimate their importance are outlined.

MRI study of radiation effect on Fricke gel solutions

The quality control optimization of medical processes that use ionizing radiation in the treatment of diseases like cancer is a key element for patient safety and success of treatment. The major medical application of radiation is radiotherapy, i.e. the delivery of dose levels to well-defined target tissues of a patient with the purpose of eliminating a disease. The need of an accurate tumour-edge definition with the purpose of preserving healthy surrounding tissue demands rigorous radiation treatment planning. Dosimetric methods are used for dose distribution mapping region of interest to assure that the prescribed dose and the irradiated region are correct. The Fricke gel (FXG) is the main dosimeter that supplies visualization of the three-dimensional (3D) dose distribution. In this work the dosimetric characteristics of the modified Fricke dosimeter produced at the Radiation Metrology Centre of the Institute of Energetic and Nuclear Research (IPEN) such as gel concentration dose response dependence, xylenol orange addition influence, dose response between 5 and 50Gy and signal stability were evaluated by magnetic resonance imaging (MRI). Using the same gel solution, breast simulators (phantoms) were shaped and absorbed dose distributions were imaged by MRI at the Nuclear Resonance Laboratory of the Physics Institute of Sao Paulo University. (C) 2007 Elsevier Ltd. All rights reserved.

Thermoluminescence properties of natural zoisite mineral under gamma-irradiations and high temperature annealing

Natural silicate mineral of zoisite, Ca(2)Al(3)(SiO(4))(Si(2)O(7))O(OH), has been investigated concerning gamma-radiation, UV-radiation and high temperature annealing effects on thermoluminescence (TL). X-ray diffraction (XRD) measurement confirmed zoisite structure and X-ray fluorescence (XRF) analysis revealed besides Si, Al and Ca that are the main crystal components, other oxides of Fe, Mg, Cr, Na, K, Sr, Ti, Ba and Mn which are present in more than 0.05 wt%. The TL glow curve of natural sample contains (130-150), (340-370) and (435-475)degrees C peaks. Their shapes indicated a possibility that they are result of composition of two or more peaks strongly superposed, a fact confirmed by deconvolution method. Once pre-annealed at 600 degrees C for 1 h, the shape of the glow curves change and the zoisite acquires high sensitivity. Several peaks between 100 and 400 degrees C appear superposed, and the high temperature peak around 435 degrees C cannot be seen. The ultraviolet radiation, on the other hand, produces one TL peak around 130 degrees C and the second one around 200 degrees C and no more. (C) 2010 Elsevier B.V. All rights reserved.

Bond Strength of Dental Adhesive Systems Irradiated with Ionizing Radiation

Purpose: The aim of the present paper was to determine the effect of different types of ionizing radiation on the bond strength of three different dentin adhesive systems. Materials and Methods: One hundred twenty specimens of 60 human teeth (protocol number: 032/2007) sectioned mesiodistally were divided into 3 groups according to the adhesives systems used: SB (Adper Single Bond Plus), CB (Clearfil SE Bond) and AP (Adper Prompt Self-Etch). The adhesives were applied on dentin and photo-activated using LED (Lec 1000, MMoptics, 1000 mW/cm(2)). Customized elastomer molds (0.5 mm thickness) with three orifices of 1.2 mm diameter were placed onto the bonding areas and filled with composite resin (Filtek Z-250), which was photo-activated for 20 s. Each group was subdivided into 4 Subgroups for application of the different types of ionizing radiation: ultraviolet radiation (UV), diagnostic x-ray radiation (DX), therapeutic x-ray radiation (TX) and without irradiation (control group, CG). Microshear tests were carried out (Instron, model 4411), and afterwards the modes of failure were evaluated by optical and scanning electron microscope and classified using 5 scores: adhesive failure, mixed failures with 3 significance levels, and cohesive failure. The results of the shear bond strength test were submitted to ANOVA with Tukey`s test and Dunnett`s test, and the data from the failure pattern evaluation were analyzed with the Mann Whitney test (p = 0.05). Results: No change in bond strength of CB and AP was observed after application of the different radiation types, only SB showed increase in bond strength after UV (p = 0.0267) irradiation. The UV also changed the failure patterns of SB (p = 0.0001). Conclusion: The radio-induced changes did not cause degradation of the restorations, which means that they can be exposed to these types of ionizing radiation without weakening the bond strength.

FT-IR spectroscopy assessment of aesthetic dental materials irradiated with low-dose therapeutic ionizing radiation

The aim of the present study was to evaluate the effects of low-dose therapeutic ionizing radiation on different aesthetic dental materials. Forty five specimens (n = 45) of three different aesthetic restorative materials were prepared and randomly divided into five groups: G1 (control group); G2, G3, G4, G5 experimental groups irradiated respectively with 0.25, 0.50, 0.75, and 1.00 Gy of gamma radiation by the (60)Co teletherapy machine. Chemical analyses were performed using a FT-IR Nicolet 520 spectrophotometer with reflectance diffuse technique. Even a minimal exposition at ionizing radiation in therapeutic doses can provide chemical changes on light-cured composite resins. The three studied restorative materials showed changes after exposure at gamma radiation, however the increase of the radiation dose did not contribute to an increase in this effect.

Co-60 gamma irradiation prevents Bothrops jararacussu venom neurotoxicity and myotoxicity in isolated mouse neuromuscular junction

The ability of gamma radiation from Co-60 (2000 Gy) to attenuate the toxic effects of Bothrops jararacussu venom was investigated on mouse neuromuscular preparations in vitro. A comparative study between the effects of native and irradiated venoms was performed on both phrenic-diaphragm (PD) and extensor digitorum longus (EDL) preparations by means of myographic, biochemical and morphological techniques. Native venom (10 and 20 mug/ml) induced a concentration-dependent paralysis of both directly and indirectly evoked contractions on PD preparations. At 20 mug/ml, it also caused a pronounced myotoxic effect on the EDL muscle preparation that was characterized by an increase of creatine kinase release and by several morphological changes of this preparation. By contrast, irradiated venom, even at concentrations as high as 40 mug/ml, induced neither paralyzing nor myotoxic effects. It was concluded that Co-60 gamma radiation is able to abolish both the paralyzing and the myotoxic effects of B. jararacussu venom on the mouse neuromuscular junction. These findings support the hypothesis that gamma radiation could be an important toot to improve antisera production by reducing toxicity while preserving immunogenicity. (C) 2002 Elsevier B.V. Ltd. All rights reserved.