Reduce Radiation Damage Research Articles

Cell structure properties during in situ creep experiments in the H.V.E.M.

The behaviour of the dislocation substructure during the steady stage regime of creep, as well as its contribution to the creep rate, are poorly known. In particular, the stability of the subboundaries has been questioned recently, on the basis of experimental observations |1||2| and theoretical estimates |1||3|. In situ deformation experiments in the high voltage electron microscope are well adapted to the direct observation of this behaviour. We report here recent results on dislocation and subboundary properties during stationary creep of an aluminium polycristal at 200°C.During a macroscopic creep test at 200°C, a cell substructure is developed with an average cell size of a few microns. Microsamples are cut out of these specimens |4| with the same tensile axis, and then further deformed in the microscope at the same temperature and stain rate. At 1 MeV, one or a few cells can be observed in the foil thickness |5|. Low electron fluxes and an image intensifier were used to reduce radiation damage effects.

Detection efficiency and estimation of the performance of high voltage STEM

One of the problems which are met in conventional transmission electron microscopy (CTEM) at high voltages is the reduction of the sensitivity of photographic films for high energy electron beams, resulting in the necessity of using high beam current. This cancels out an advantage of high voltage electron microscopy which is otherwise expected from the reduction of the inelastic scattering in the specimen, that is the reduced radiation damage of the specimen during observations. However, it is expected that the efficiency of the detector of scanning transmission electron microscopy (STEM) can be superior to that of CTEM, since the divergence of the electron beam in the detecting material does not affect the quality of the image. In addition to observation with less radiation damage, high voltage STEM with high detection efficiency is very attractive for observations of weak contrast objects since the enhancement of the contrast (which is an important advantage of STEM) is easily realized electrically.

Molecular image of copper phthalocyanine

SUMMARYThe structure of copper phthalocyanine has been studied by high resolution transmission electron microscopy (TEM). To reduce radiation damage, the technique of minimal beam exposure has been used together with X‐ray film for recording the image. This resulted in very noisy micrographs but optical averaging clearly revealed the molecular shape of the copper phthalocyanine, and also showed that a slight discrepancy exists between the averaged image, and the model structure which had been assumed to be isomorphous with platinum phthalocyanine.

Nitrogen centers in GaP produced by hot implantation

Backscattering yields of 1.5 MeV−He + ions and low temperature photoluminescence (PL) spectra were measured in GaP crystals implanted with 200 keV−N + ions as functions of ion-dose, temperature during implantation and annealing temperature after implantation. Backscattering results indicate that hot implantation at 500°C greatly reduces radiation damage. The PL intensities of NN lines become maximum in the sample implanted with N + ions of 3 × 10 14cm −2 at 500°C, and annealed at 1000°C for 1 hr with aluminum glass. The PL intensity is comparable to that of the nitrogen-doped sample during liquid phase epitaxy which is widely accepted as the best method of introducing nitrogen into GaP crystals. In the case of 500°C—hot implantation, the radiation damage produced during implantation is annealed out at 700 ~ 800°C and the implanted nitrogen substitutes for the phosphorous sites after annealing at 900 ~ 1000°C. Some kinds of defects or strains remain around the NN centers even in implanted samples with a maximum PL efficiency. These defects or strains don't seem to reduce the PL efficiency. In the case of room temperature implantation, PL efficiency decreases to one-hundredth or one-thousandth due to the formation of the non-crystalline state compared with hot implantation.

A Mechanism for Reduced Radiation Damage

AbstractIn highly anisotropic targets, radiation damage due to electron irradiation can be drastically reduced as electron energy increases. A theoretical study of this effect is made, and some experimental evidences of this effect are cited.

A possible mechanism for reduced radiation damage by relativistic charged particles, e.g. in electron microscopy

Contrary to the common belief that radiation damage varies slowly as the energy of the incident particle becomes relativistic, the authors argue that a strong energy dependence may occur, provided that the target material has very strong directional properties. In the case of a material with extremely strong directional properties, the damage may decrease as much as the inverse of the square of the energy. This effect arises from a general feature of the primary collision of the projectile with an atom, i.e. that the cross-section differential with respect to angle has a very strong energy dependence even at relativistic energies. Thus, the Rutherford differential cross-section, which gives a reasonable description of both elastic and inelastic processes over some important kinematic regions, decreases as the inverse of the square of the energy. The correlation between the energy dependence and directional properties of the target has been studied in the context of a simple model of radiation damage.

Image intensification and the electron microscopy of radiation sensitive polymers

The role of image intensification in the electron microscopy of radiation sensitive polymers is analysed. It is shown that image intensification cannot improve the quality of the usual internal recording with electron image plates. The chief advantage of image intensification is the reduced radiation damage to the specimen during focusing and alignment. For bright-field microscopy, unaided focusing imparts an electron dose to the specimen which is approximately 9 times larger than the dose sustained during the subsequent recording. Image intensification reduces the radiation damage during focusing to an insignificant fraction of the unavoidable radiation damage which occurs during the exposure of the plate and improves the picture quality correspondingly. In the darkfield case the chief advantage of the image intensifier is the greatly improved yield of useful pictures rather than improved quality. Optimum working conditions, including optimum voltage, for radiation sensitive specimens are calculated. Experimental results on polyethylene single crystals confirm the analysis.

Anomalous effects of dimethyl sulfoxide on the response of the mouse lens and cornea to x-irradiation: "protection" of lens and "sensitization" of cornea.

Radiation effects on the eye are of considerable interest from both radiobiologic and radiotherapeutic points of view. They have been the subject of many experimental and clinical investigations. A number of workers (e.g., 1-3) have shown that relatively small doses of ionizing radiation to the lens can cause posterior lenticular opacities. Relatively large, repeated exposures result in late corneal lesions (4). In clinical situations irradiation of the eye is avoided, if possible, by appropriate direction of the beam and by use of shields. Elaborate technics for shielding the eye during irradiation of the periorbital region with high-energy electrons have been reported (5, 6). In many instances, however, all scattered radiation cannot be prevented from entering the eye. Much work has been done on chemical protection of the lens against effects of ionizing radiation. Cysteine administered intravenously is an effective protector against radiation cataract (7), but when given by subconjunctival injection exerts only a moderately protective influence (8). Other substances, e.g., glutathione, are also somewhat effective in reducing radiation damage to the lens when given by intravenous injection (8). To our knowledge, no substance administered topically to the eye has been reported to protect the lens from radiation damage. Local lenticular protection, as opposed to systemic protection, would have the inherent advantage of reducing radiation damage to the lens while not affording concomitant protection to nearby tissue (e.g., periorbital tumors). In addition, protection by topical administration would be far simpler than the complex shielding technics otherwise required. Three properties of dimethyl sulfoxide (DMSO) suggested its possible use in topical application for protection of the lens from the damaging effects of ionizing radiation. First, it passes easily through biological membranes and even through intact skin (9, 10). Second, DMSO has been shown to be a radioprotective substance at levels of the animal (ll), the cell (12), and the molecule (13). Third, it can act as a penetrant carrier for other organic molecules (14), perhaps for a protector such as 13mercaptoethylamine (MEA).

Selenoamino Acids as Radiation Protectors in Vitro

The role of sulfhydryl compounds in reducing radiation damage to biological systems has been extensively studied. These compounds are known to react by mechanisms including free radical scavenger, repair of damage sites, and capacity to form mixed disulfides (1-3). We determined the specific influence of sulfhydryl compounds in reducing radiation damage to amino acids of cytochrome c, hemoglobin, and ovalbumin in solutions under anaerobic conditions (1). Results show that the sulfhydryl compounds offer considerable protection to the radiolabile amino acids such as histidine, methionine, phenylalanine, and cystine. Electron paramagnetic resonance studies on solid amino acids, peptides, and proteins indicate that radiation-induced unpaired electrons finally localize on sulfur atoms (4-8). Gordy and Miyagawa (4) suggested that unpaired electrons can migrate through certain segments of polypeptide chains of protein. Furthermore, Henriksen et al. (7, 8) showed an intermolecular transfer of unpaired electrons from protein molecules to sulfur protectors. Collectively, this evidence suggests that the ideal radiation protector is a molecule that can release and accept electrons and hydrogen atoms easily without itself becoming dissociated. If this is the case, selenoamino acids would be a better protector than analogous sulfur amino acids. This is because the ionization potential and bond energy of selenium compounds are smaller than that of sulfur compounds (9), and also selenium has more metallic character than sulfur (10). The biological function of selenium as a trace nutrient can be ascribed to the oxidation-reduction properties of compounds like selenoamino acids and selenoproteins (11, 12). Lipid antioxidant properties of selenoamino acids and selenoproteins have been described (11-14). Other mechanisms, especially free radical scavengers and repair of damage sites, are probably of great importance in its biological function. Selenium analogs of 2-aminoethylisothiouronium. HBr (AET) and related compounds have been synthesized, and the selenium analog of cysteamine has been shown to have a radiation-protective effect in mice (15). The purpose of this research is to test the effects and mechanisms of selenoamino

The effect of chronological and physiological aging of onion seeds on the frequency of spontaneous and x-ray induced chromosome aberrations

Both chronological and “physiological” aging of onion seeds increases the frequency of both spontaneous and X-ray induced chromosome aberrations. Both types of aging result in increased sensitivity to X-rays. In general the factors which reduce radiation damage in seeds also promote longer life. This correlation may be of value in studies on aging.

Prevention by cysteamine of radical formation in bovine serum albumin by gamma-rays.

CYSTEAMINE is one of the most effective substances for the protection of animals against ionizing radiations, and in vitro has been shown to reduce radiation damage of macromolecules by energy transfer in solid polymethylmethacrylate1, by capture of OH˙ radicals for serum albumin in dilute solution2, and by hydrogen transfer to an organic radical for polymers in aqueous solution3,4. Gordy and Miyagawa5 have found that the electron spin resonance spectrum of the protein zein is altered in magnitude and character if cysteamine is present, and have ascribed this to the combination of cysteamine with the protein by a disulphide exchange reaction. Earlier experiments1 led us to believe that an energy-transfer process is a more probable mechanism of protection, and to test this hypothesis we studied the effect of cysteamine on the electron spin resonance spectrum of bovine serum albumin irradiated with cobalt-60 γ-rays at room temperature and at 77° K. (dose, 5 Mrads, dose-rate = 750 krads/hr.). The mixture of 90 per cent bovine serum albumin +10 per cent cysteamine was produced by freeze-drying a solution. Although bovine serum albumin contains 17 disulphide groups per molecule, none of these reacts with cysteamine under isoelectric conditions because they are sterically inaccessible6,7 and the possibility of protection by disulphide exchange is therefore excluded (human serum albumin combines with cysteamine at the isoelectric point because one disulphide bond is reactive7).

Effect of AET on sodium, potassium and esterases of the alimentary tract of irradiated mice

A study was made of the effect of S,2-aminoethylisothiuronium bromide hydrobromide (AET) on the changes in sodium and potassium concentrations in the walls and contents of the gastrointestinal tracts of mice exposed to 1500 r. Mice were given AET and were then irradiated. At intervals thereafter, portions of the gastrointestinal tract and its contents were analyzed for sodium and potassium in a flame spectrophotometer. In mice given AET before exposure to 1500 r, the following radiation-induced abnormalities were completely or partially corrected: decrease in potassium and increase in sodium in the wall of the small intestine; decrease in potassium in the colon wall; and increase in sodium and potassium in the contents of the stomach, small intestine and colon. Extracts from the walls of the small intestines of AET-treated or nontreated, irradiated mice were analyzed chemically for esterase activity. In AET-treated, irradiated mice, complete recovery of esterase activity was observed by day 7 after 900 r, and partial recovery occurred after 1500 r. Since AET reduces radiation damage and thereby allows recovery, the beneficial effects of the compound on the correction of electrolyte imbalance and esterase activity are ascribed to recovery of the tissues of the gastrointestinal tract.