Irradiations of diamonds 'with layers' in nuclear reactor IPR-R1

The experimental results on the effects of diamonds irradiation with neutrons and other radiations, are presented. These results pointed out the consequent changing effects on the original colours and also on the determination of the regional characteristic impurities, pointed as the responsible for the changes in the corresponding coloration centers. Diamond samples containing a green, brown or yellow tiny film, and also colorless ones, were studied. Their typical occurrence is in some sedimentary deposits of the most important producing areas in the State of Minas Gerais. The samples were submitted to irradiations in the rotative rack of the nuclear reactor IPR-R1 TRIGA Mark I (100 kW), with a thermal neutron flux of 6,6 x 1011 n.cm-2.s-1. The results, obtained by the conventional neutron activation analysis methods associated with k0 technique, are represented by typical traces of the detected impurities. The two main hypotheses formulated for the origin of the layers, are: in situ irradiation from radioactive materials existing in the neighborhoods, or the presence of certain 'chromoforous' elements located in the outer layer of the crystals, inducing the coloration. The obtained data analysis showed an association among the two factors, depending on the beds' location with the direct presence of characteristic radioactive minerals, in this case: monazite and zircon, present in the vicinities of some investigated deposits. (author)