Radiação: sua utilidade e perigo

(1º parágrafo do artigo) O interesse pelo conhecimento da constituição da matéria data da época dos gregos. Anaxágoras, Leucippo e Demócrito postularam que a matéria é constituída de aglomeração de partículas, que foram chamadas de átomos, para indicar a sua suposta indivisibilidade. Através dos séculos que seguiram, vários filósofos especularam sobre a estrutura da matéria. No começo do século XIX, as pesquisas sobre os pesos e os volumes de substâncias em reação química, realizadas por John Dalton e seus contemporâneos, conduziram estes ao enunciado, em base experimental, da teoria atômica da matéria.

Radiação: sua utilidade e perigo

(1º parágrafo do artigo) O interesse pelo conhecimento da constituição da matéria data da época dos gregos. Anaxágoras, Leucippo e Demócrito postularam que a matéria é constituída de aglomeração de partículas, que foram chamadas de átomos, para indicar a sua suposta indivisibilidade. Através dos séculos que seguiram, vários filósofos especularam sobre a estrutura da matéria. No começo do século XIX, as pesquisas sobre os pesos e os volumes de substâncias em reação química, realizadas por John Dalton e seus contemporâneos, conduziram estes ao enunciado, em base experimental, da teoria atômica da matéria.

Dating archaeological pottery through optically stimulated thermoluminescence (OSL) and electron paramagnetic resonance (ESR)

São descritas as propriedades de luminescência térmica ou óticamente estimulada em cristais iónicos, particularmente nos grãos de quartzo, visando suas aplicações na datação de vasos cerâmicos, terras queimadas, telhas e tijolos antigos. Essa luminescência é induzida pelas radiações provenientes de radioatividade natural do subsolo, onde as cerâmicas arqueológicas são coletadasWe describe here the chracterictics of th thermic or optically stimulated luminescence in ionic crystals,specially in quartz grains, aiming its use in the dating of ancient ceramic vases, burned soil, roof tiles and bricks. This luminescence is induced by radiations of the natural radioativity of the subsoil, where the ancient materials were deposite

Dating volcanic ash and pumice stones from volcano El Misti, Peru, by thermoluminescence

El Misti is one of active volcanos in Peru, and known because it is located close to an important city of Arequipa, at about 17 km. There has been in the past several eruptions and the volcano is covered with lava, ash, etc. from such eruptions. The edifice is composed of a stratotocone called Misti 1, two stratocones designated Misti 2 and Misti 3 and a summit cone Misti 4. In this work samples from Misti 3 have been collected for TL dating. In the past charcol has been used for radiocarbon measurements and found age varying from 25000 to 35000 years. The TL dating produces ages between 28700 and 32300 years

Study of Optical Absorption property of the composite Polypropylene/Yellow beryl submitted to several doses of gamma-radiation.

Yellow Beryl was obtained from Teófilolo Othoni, state of Minas Gerais, and added into a\ud matrix of Polipropileno (PP) made by Braskem. Here we have investigated the property of\ud optical absorption (OA) of this composite submitted to various doses of gamma-radiation. We\ud have almost no works on this type of composite (polymers/beryl) so far. The property of OA\ud of the composite has been measured in the NIR (Near Infrared) range before and after\ud irradiation. Have been used five different doses of gamma-radiation (1, 3, 5, 7 and 10 kGy)\ud and different rates of fraction of beryl (1%, 10%, 30%, 50%) with purpose to detect any\ud possible change on its spectra.CNPqCAPESFAPES

Thermoluminescence and defect centers in synthetic diopside

MgCaSi2O6 polycrystal was synthesized by the devitrification method. The dosimetric characteristics by TL of this prepared polycrystal was investigated. This material exhibits TL peaks at 115, 160, 210, 260 and 280 °C. The dosimetric peak occurs at 260 °C with a well defined glow curve structure. This peak shows a linear dose response. Electron paramagnetic resonance (EPR) studies have been carried out to identify the defect centers responsible for the TL peaks. Two defect centers in the region of g = 2.0 are found. One of the centers (center I) with a g factor equal to 2.0085 is identified as O− -ion and relates with the observed high temperature 250 and 300 °C TL peaks. Additional defect centers with g = 2.0012 (center II) and 1.982 (center III) are due to F+- centers (electron trapped at an oxygen vacancy). Center II and III correlate with the TL peaks at 160 °C and 106 °C, respectively.Campus Arequip