Avaliação da atenuação da vegetação da Mata Atlantica a radiação gama natural emitida pela superficie

AUTOR(ES)
DATA DE PUBLICAÇÃO

1997

RESUMO

Several natural alpha, beta and gamma radionuclides are known. Most of them occur in rock-forming minerals Potassium, uranium and thorium are the main natural gamma radiation producers. This radiation can be measured in the laboratory, field or from aircrafts. In this case, besides atmospheric attenuation, vegetation can absorb substantial amounts of radiation emitted by soil, but can contribute with radiation from potassium contained in its structure. A forest is an anisotropic medium of emission and absortion, that acts like a shield to the gamma radiation emitted by the surface and also as source of gamma radiation due to potassium accumulated in the trunks and leaves. This means that there are some aspects associated to forests that change the gamma field. This work intends to evaluate, through aerial. terrestrial and laboratory gammaespectrometry, the effect of attenuation presented by vegetation to natural gamma radiation emitted from the surface. Laboratory data indicated attenuation of trunks and leaves, the Iater absorbing less gamma radiation than the first. Comparing terrestrial and airborne data from the Quadrilátero Ferrifero region, dose to the town of Santa Bárbara, it was verified that both groups of data have equivalent values in the levels of the elements Th, U and K. It was observed that the vegetation in some points presented attenuation in high percentages. Laboratory measurements, mass attenuation coefficients and field data, were applied to a mathematical model that simulate the situation of an airborne measurement, yielding a value for the attenuation of the vegetatian cover. LANDSA T - TM images were used to obtain biomass estimatives, and from these were elaborated correction models for the effects of the gamma radiation attenuation

ASSUNTO(S)

raios gama

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