No abstract available

[en] The barium titanate BaTiO3 is a material of great technological interest due to their dielectric properties. The functionality of this mixed oxide is mainly determined by its structure. Different synthesis methods have been used to improve the electrical response of BaTiO3. In this work BaTiO3 powders were synthesized using the polymeric precursor method, Pechini, obtaining the compound at 650< C, with uniform nanometric particle size (∼ 20nm). The nature of the synthesized powders was analyzed using X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results indicate that the crystalline phase present in the sample treated at 650< C is cubic and at 1100< C is tetragonal, with a relation c/a . 1.007. The samples sinterized at 1100< C showed a ferroelectric-paraelectric transition at a temperature of T . 123oC. The ceramic powders of barium titanate tetragonal, pressed and densified, was electrical characterizing with curves current-voltage (I-V) at different temperatures. Additionally, we measured the change in electrical resistance versus temperature (R-T) and we tested the behavior thermistor (PTCR) of the material for different pressures. Also the electric response of the material with the variation of the frequency, for different temperatures, was measured. (Author).

[en] The use of ionizing radiation sources and radioisotopes in Argentina takes place at more than 1700 facilities, which operate in Nuclear Medicine, in telecobaltherapy, in Industry, in Biochemistry, and in research. All of these centers have one or more professional trained in the specific field of radioprotection and they have been authorized by the Nuclear Regulatory Authority. At the School of Pharmacy and Biochemistry of the Buenos Aires University, Argentina, we consider of great interest to teach radioisotopes methodology at different levels, to harmonize the use of these methodologies with environmental preservation and to provide education and training on radioprotection. Currently, the school offers five different courses in all of which the radioprotection is one of the most important subjects: 1) Course on Methodology of Radioisotopes for students at the undergraduate level, in the Biochemistry Career (140 hrs). Since 1960, more than 6000 students have passed their examinations. 2) Course on Methodology of Radioisotopes for post-Graduates in Biochemistry, Biology, Chemists or other related disciplines. 3) Course for Graduates in Medicine. Since 1962, the School delivers every year these two courses. Their syllabus (212 hrs) dedicates a 50% of the time schedule to subjects related to radioprotection aspects. More than 1800 professional have passed their examinations, many of them from different Latin American countries. 4) Up-date on Methodology of Radioisotopes (100 hrs) a course delivered since 1992 for professionals wishing to up-date their knowledge. 5) Course for Technicians in Nuclear Medicine (more than 200 hrs). At present, this course is the basic level of the Technicians in Nuclear Medicine Career. At the present paper it will be presented statistics regarding the different courses and the experience that has been gathered for the last 40 years organizing courses and carrying out research activity on radiobiology, radioimmunoanalysis, radioreceptors and radiopharmacy. (Author) 7 refs

[en] The radical anions of 5-bromo- and 5-iodouracil produced by the reaction of e/sub aq/^- with the halouracils have been observed in nanosecond pulse radiolysis experiments by their optical absorption at 330 nm. They decay with half-periods of 7.0 +- 0.5 and 1.7 +- 0.3 ns. These short lifetimes contrast with the much longer periods observed for the electron adducts to 5-chloro- and 5-fluorouracil (4.9 and > 15 μs). The uracilyl radical produced by halide elimination from the radical anions has an extinction coefficient not greater than 150 M^-1cm^-1 at 330 nm and no appreciable absorption at wavelengths longer than 310 nm but reacts with 5-bromouracil to form an addition product which has a broad absorption at 365 nm. The rate constant for this latter reaction, (2.66 +- 0.09) x 10⁸ M^-1s^-1, provides a reference against which to compare the rates of competing reactions. The absolute rate constant for abstraction of hydrogen from tert-butyl alcohol by uracilyl radical has been determined to be (2.3 +- 0.2) x 10⁷M^-1s^-1. It is clear that uracilyl radical reacts very rapidly by both addition and abstraction processes, reflecting the sigma character of this radical. 6 figures

[en] The photodestruction of purine free base used as a model for the purine bases in DNA has been studied in order to better understand the effect of UV light on these molecules. Photodestruction yields have been determined in glassy aqueous solutions at 77 K and at room temperature at different pH's. The yield decreases in the order of 0.04, 0.01, 0.001 in 8 M NaOH, 8 M NaClO₄ and 6 M H₃PO₄, respectively, while at room temperature the highest destruction yield is 0.005 for the unbuffered neutral solution. These yields have been determined by measuring the initial decrease in the purine absorption maximum as a function of irradiation time. During the illumination stable photoproducts, as well as reactive intermediates, such as trapped electrons, radical anions and cations, are formed and have been characterized from their absorption spectra. The addition of triplet quenchers and an electron scavenger resulted in a decrease in the yield, implying the participation of the purine triplet state and a radical anion in the reactions leading to the photodestruction of purine. (author)

[en] Short communications only

[en] On-going and recently completed studies of the effect of thermal oxidation on the structural integrity of HTGR candidate graphites are described, and some results are presented and discussed. This work includes the study of graphite properties which may play decisive roles in the graphites' resistance to oxidation and fracture: pore size distribution, specific surface area and impurity distribution. Studies of strength loss mechanisms in addition to normal oxidation are described. Emphasis is placed on investigations of the gas permeability of HTGR graphites and the surface burnoff phenomenon observed during recent density profile measurements. The recently completed studies of catalytic pitting and the effects of prestress and stress on reactivity and ultimate strength are also discussed

[en] It has been established that the treatment with Histamine (Hi) produces a significant growth inhibition of different cell lines derived from human neoplasia. In a model of Knockout mice completely depleted of endogenous Hi, it was observed a significant delay in bone marroe repopulation after whole body irradiation. These results are in agreement with the hypothesis that histamine has a role in the regulation of haematopoiesis as well as an inhibitory effect on apoptosis. The objective of this paper was to study the possible effect of Hi as protector of normal cells and radiosensitizer of malignant ones. To study the effect of Hi on small-intestine and bone marrow, thirty made mice were randomly separeted into two groups: Control irradiated (C), and irradiated receiving Histamine (HI-group). All animals received a single dose of 10 Gy on whole-body employing a ''137Cs source of 189 TB_q (Dose rate: 7.7 Gy/min) calibrated with TLD 700 dosimeter. Hi-group recieved a daily se injection (0.1 mg/kg) starting 20 hs before irradiation. Mice were sacrificed 5 days after irradiation. Histopathological analysis indicated that intestinal mucosae of C group showed important injury, whist mucosae of Hi-treated mice showed mild mucosal atrophy with conservation of villous projections and absence of vascular congestive changes. In order to investigate the effect of Hi on radiosensitivity of transformed cells, MDA-MB-231 (human breast carcinoma cells) were irradiated in vitro with doses ranging from 0 to 10 Gy. Results of radiobiological parameters indicate a significant increase on radiosensitivity of malignant cells. Employing specific fluorescent dyes and flow cytometric analysis we determined that the intracellular levels of hydrogen peroxide (H₂O₂) are significant increased by Hi 10 μM in control and also in irradiated MDA-MB-231 cells, while the levels of superoxide (SO₂) were not significantly modified by Hi-treatment. (Author) 9 refs

[en] Experiments carried out in the authors' laboratories have shown that the isoindole-4, 7-diones are potential radiosensitizers. The main problem with these quinones is their low stability in aqueous solutions. Therefore, the authors' most recent efforts have been directed to synthesize isoindole-4,7-diones substituted with polar groups on either the heterocyclic or the quinone ring to increase their water solubility. Cytotoxicity studies of these new analogues on chinese hamster ovary cells (CHO) have been carried out. The effects that different concentration of isoindole-4,7-diones have on cell growth as a function of time after treatment on both systems (oxic and hypoxic) have been determined. Most isoindole quinones tested show radiosensitization efficiency under hypoxic conditions. Glutathione depletion was also measured in both systems. These compounds deplete the concentration of glutathione in CHO cells. The radiation sensitization efficiency of new synthesized quinoxaline-1,4-dioxides has also been measured. Some of these new compounds also show promise as chemical sensitizer agents. The authors anticipate that new potential radiosensitizer agents will be developed as a result of these investigations

[en] Cutaneous melanoma is a skin cancer resulting from the malign transformation of skin-pigment cells, the melanocytes. The radiotherapy, alone or in combination with other treatment, is an important therapy for this disease. the objective of this paper was to determine in vitro the radiosensitivity of two human melanoma cell lines with different metastatic capability: WM35 and MI/15, and to study the effect of drugs on radiobiological parameters. The Survival Curves were adjusted to the mathematical Linear-quadratic model using GrapsPad Prism software. Cells were seeded in RPMI medium (3000-3500 cells/flask), in triplicate and irradiated 24 h later. The irradiation was performed using an IBL 437C H Type equipment (189 TBq, 7.7 Gy/min) calibrated with a TLD 700 dosimeter. The range of Doses covered from 0 to 10 Gy and the colonies formed were counted at day 7th post-irradiation. Results obtained were: for WM35, α=0.37±0.07 Gy''-1 and β=0.06±0.02 Gy''-2, for M1/15m α=0.47±0.03 Gy''-1 and β=0.06±0.01 Gy''-2. The α/β values WM35: α/β values WM35: α/β=6.07 Gy and M1/15: α/β₇.33 Gy were similar, independently of their metastatic capabillity and indicate that both lines exhibit high radioresistance. Microscopic observation of irradiated cells showed multinuclear cells with few morphologic changes non-compatible with apoptosis. By means of specific fluorescent dyes and flow cytometry analysis we determined the intracellular levels of the radicals superoxide and hydrogen peroxide and their modulation in response to ionizing radiation. The results showed a marked decreased in H₂O₂ intracellular levels with a simultaneous increase in superoxide that will be part of a mechanism responsible for induction of cell radioresistance. This response triggered by irradiated cells could not be abrogated by different treatments like histamine or the combination of oligo elements plus phospholipase. (Author) 19 refs