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We studied the DNA fragmentation induced in human fibroblasts by iron-ion beams of two different energies: 115 MeV/nucleon and 414 MeV/nucleon. Experimental data were obtained in the fragment size range 1-5700 kbp; Monte Carlo simulations were performed with the PARTRAC code; data analysis was also performed through the Generalized Broken Stick (GBS) model. The comparison between experimental and simulated data for the number of fragments produced in two different size ranges, 1-23 kbp and 23-5700 kbp, gives a satisfactory agreement for both radiation qualities. The Monte Carlo simulations also allow the counting of fragments outside the experimental range: The number of fragments smaller than 1 kbp is large for both beams, although with a strong difference between the two cases. As a consequence, we can compute different RBEs depending on the size range considered for the fragment counting. The PARTRAC evaluation takes into account fragments of all sizes, while the evaluation from the experimental data considers only the fragments in the range of 1-5700 kbp. When the PARTRAC evaluation is restricted to this range, the agreement between experimental and computed RBE values is again good. When fragments smaller than 1 kbp are also considered, the RBE increases considerably, since gamma rays produce a small number of such fragments. The analysis performed with the GBS model proved to be quite sensitive to showing, with a phenomenological single parameter, variations in double-strand break (DSB) correlation.

DNA fragmentation was studied in the fragment size range 0.023-5.7 Mbp after irradiation of human fibroblasts with iron-ion beams of four different energies, i.e., 200 MeV/nucleon, 500 MeV/nucleon, 1 GeV/nucleon and 5 GeV/nucleon, with gamma rays used as the reference radiation. The double-strand break (DSB) yield (and thus the RBE for DNA DSB induction) of the four iron-ion beams, which have LETs ranging from 135 to 442 keV/mum, does not vary greatly as a function of LET. As a consequence, the variation of the cross section for DSB induction mainly reflects the variation in LET. However, when the fragmentation spectra were analyzed with a simple theoretical tool that we recently introduced, the results showed that spatially correlated DSBs, which are absent after gamma irradiation, increased markedly with LET for the iron-ion beams. This occurred because iron ions produce DNA fragments smaller than 0.75 Mbp with a higher probability than gamma rays (a probability that increases with LET). These sizes include those expected from fragmentation of the chromatin loops with Mbp dimensions. This result does not exclude a correlation at distances smaller than the lower size analyzed here, i.e. 23 kbp. Moreover, the DSB correlation is dependent on dose, decreasing when dose increases; this can be explained with the argument that at increasing dose there is an increasing fraction of fragments produced by DSBs caused by separate, uncorrelated tracks.

This paper reports on DNA DSB induction in human fibroblasts by iron ions of different energies, namely 5, 1 GeV/u, 414 and 115 MeV/u, in absence or presence of different shields (PMMA, Al and Pb). Measure of DNA DSB was performed by calibrated Pulsed Field Gel Electrophoresis using the fragment counting method. The RBE–LET relationships for unshielded and shielded beams were obtained both in terms of dose average LET and of track average LET. Weak dependence on these parameters was observed for DSB induction. The shielding efficiency, evaluated by the ratio between the cross sections for unshielded and shielded beams, depends not only on the shield type and thickness, but also on the beam energy. Protection is only observed at high iron ions energy, especially at 5 GeV/u, where PMMA shield gives higher protection compared to Al or Pb shields of the same thickness expressed in g/cm2.

Experimental data on DNA double strand break (DSB) induction in human fibroblasts (AG1522), following irradiation with several radiation qualities, namely gamma rays, 0.84 MeV protons, 58.9 MeV u(-1) carbon ions, iron ions of 115 MeV u(-1), 414 MeV u(-1), 1 GeV u(-1), and 5 GeV u(-1), are presented. DSB yields were measured by calibrated Pulsed Field Gel Electrophoresis in the DNA fragment size range 0.023-5.7 Mbp. The DSB yields show little LET dependence, in spite of the large variation of the latter among the beams, and are slightly higher than that obtained using gamma rays. The highest yield was found for the 5 GeV u(-1) iron beam, that gave a value 30% higher than the 1 GeV u(-1) iron beam. A phenomenological method is used to parametrise deviation from randomness in fragment size spectra.

12th International Congress of Radiation Research

Protons and high energy heavy ions (HZE particles ) are the components of space radiation of major concern. Their biological consequences are expected to be related to DNA lesions. Since DNA double strand breaks (DSB) and other lesions produced by these charged particles occurs in a correlated manner along the particle track, the current working hypothesis is that spatial correlation of damage, that depends on the particle type and energy, affects its reparability. Several characteristic distances for damage correlation can be considered, related to various levels of chromatin organization. We have investigated, in AG1522 human fibroblasts, the DNA fragmentation patterns in the size range 23 kbp - 5.7 Mbp, characteristic of the loop structure of chromosomes, using calibrated Pulsed Field Gel electrophoresis (PFGE). We have compared various beams i.e., low -energy protons of 0.88 MeV (representative of stopping protons at the Bragg peak) and Fe ions of 1050 and 414 MeV/u, using g-rays as reference. Irradiations with protons were performed at the Laboratori Naz ionali di Legnaro (Padova, Italy), those with 1050 MeV/u Fe ions at the Brookhaven National Laboratory (USA) and those with 414 MeV/u Fe ions at the National Institute for Radiological Sciences (Chiba, Japan). DSB yields were evaluated from the number of DNA fragments induced in the size range studied, at doses between 40 and 200 Gy. The results until now obtained show the general trend of a linear, or almost linear, increase of DSB with the dose. 1050 MeV/u Fe ions are the most effective particles in terms of both unit dose and unit fluence. The frequency distributions of fragments induced by the charged particles are shifted towards smaller sizes with respect to that induced by comparable doses of g-rays. These distributions also suggest that at doses of the order of 100 Gy most of the fragments induced by protons have size > 23 kbp, while for Fe ions it is expected a significant amount of fragments smaller than that size, not revealed by the mentioned PFGE analysis. This is in agreement with recent experimental measurements of DNA fragments induced by 1050 MeV/u Fe ions in the size range 2 - 23 kbp. The occurrence of such small fragments (and even smaller) further increases the effectiveness for DSB induction of HZE particles compared to protons., 34th COSPAR Scientific Assembly

The 2nd International Workshop on Space Radiation Research

Revisão de literatura sobre conceitos de bibliotecas no suporte para a educação a distância. Apresenta conceitos referentes a bibliotecas digitais, eletrônicas e virtuais. Tece considerações sobre o trabalho virtual nas bibliotecas. Literature review about some library concepts to support distance education. Presents some concepts about digital, electronic and virtual libraries. Also considerated the virtual work at the libraries.

Dissertação (Mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Neste texto apresentamos os resultados sobre a busca de novas metodologias para auxiliar na alfabetização infantil. A proposta respaldada-se em uma fundamentação científica tendo como base dois aspectos fundamentais: o pedagógico e as novas tecnologias. O modelo deverá ser inovador e que represente efetivamente um avanço, contribuindo para a solução de um dos problemas mais sérios do ensino no Brasil: o elevado índice de repetência e de evasão registrado nas séries iniciais de ensino. A nossa proposta está baseada na metodologia de alfabetização desenvolvida pelos professores do GEEMPA (Grupo de Estudos sobre Educação, Metodologia de Pesquisa e Ação), sob coordenação de Esther P. Grossi. Esta metodologia foi inspirada no Método Silábico de alfabetização desenvolvido por Emília Ferreiro. Os resultados obtidos pelo GEEMPA em Porto Alegre e a credibilidade internacional das criadoras desta metodologia garantem o respaldo pedagógico necessário. Para a implementação da proposta utilizaremos técnicas de Realidade Virtual para a construção de um ambiente suficientemente capaz de envolver o aluno, povoado por agentes que comandarão o processo, conduzindo o aluno para o mundo das letras de forma agradável e praticamente imperceptível.

A research program in space radiobiology has been recently funded by the Italian Space Agency (ASI) and is under way in collaboration with NASA and NIRS. The program is focused on the effect of the shielding on the biological effects of heavy ions. In the past year, we have performed two experiments with high-energy iron ions accelerated at the HIMAC accelerator. Chromosomal aberrations, delayed reproductive death, and DNA double-strand breaks have been measured in human cells exposed to the direct 56Fe beam (200 MeV/n or 500 MeV/n) or after shielding with PMMA (lucite) or aluminum. Preliminary results demonstrate that shielding of heavy ions enhances the biological effectiveness of the primary beam.

Our experiments aim to determine genetic effects of heavy ions with or without shielding. Preliminary results about chromosomal aberrations in human peripheral blood lymphocytes induced by 56Fe ions accelerated at HIMAC are presented here.

There is a strong need for radiobiological experiments on carbon ions, to better determine the biological effectiveness as a function of radiation quality and to optimise the clinical use. The goal of this experiment is to measure biological effects of accelerated carbon ions in different cell lines with different radiosensitivity to photon radiation. Results will be used to determine the RBE of carbon ions for radiosensitive and radioresistant cells.