Contribuição ao estudo da influência de radiações ionizantes sobre a côr da Turmalina

Abstract

The author checked the effects concerning the colour changes of tourmalines caused by radiations with gamma rays and neutrons produced in the atomic pile (I.E .A . — RI), swimingpool type, of 5 Mw, belong ng to the “Instituto de Energia Atômica, University of São Paulo” His observations were made on pink, red, green, and blue tourmalines from different localities m the State of Minas Gerais, Brazil. The results of his observations are reported in 15 diagram - ms, corresponding to the absortion spectra, and in photographs, included in the present work, w here are shown the effects of bombardment and, at times, subsequent thermic treatment. Observations concerning the effects of heating of non-irradiated tourmalines are likewise listed in the present work but are only remarkable on the pink and red coloured tourmalines. Other observations were made on pink and light green zoned tourmalines showing zoning parallel to the basal pedion as well as in zoning parallel to the prism faces. The behaviour of cut stones related to ionizing radiations was also rem arkable. It was observed that the hue intensification was in direct correlation with the stone volume and time of exposition to the atomic pile. The author ascertained the despicable influence of gamma rays in changing colours in tourmalines, affecting only slightly the pink and red samples. The hue grows progressively to brown after an extensive exposition. The green and blue tourmalines keep their colours which are modified when irradiated for a relatively long time. They turn brown after the bombardment, although with a different hue, especially on the pink and red samples. It was verified, nevertheless, that in the very light green zones on the zoned samples used the exposition to neutrons results in a appreciable colour alteration that can vary from red to brown depending on the intensity of the original green colour Concerning the heating of non-irradiated tourmaline, the author has ascertained that only the pink and red samples are clearly affected and, depending on the temperature, they can become colourless. Inrelaton to the same procedure made with previously bombarded stones the same thing can be observed in samples which in the pre-irradiation stage were pink and red. The gleen and blue tourmalines which became brown coloured by energicionic irradiation, when heated, recover their original colours. The author concludes that the colours of the tourmalines studied in the present work may depend not only upon a cause acting separately but also it may depend upon chemical or physical phenomens or both; that the green and blue colours seem to depend only on isomorphism, but the pink and red colours seem to depend mainly on natural radioactivity and yet that it would be possible that the colour of tourmalines and other halochromatic minerals of different origins may depend upon different causes. The author believes that the colour of the pink and red tourmalines are linked to colour-centers and admits the possibility that Lithium takes part in its colour formation. The author also thinks that admiting the radioactive origin of these colours and measuring its relative intensities, it would be possible to make a estimate of the quantity of external radioactivity and perhaps of the period of its action