Original Paper

Physics and Chemistry of Minerals

, Volume 34, Issue 7, pp 437-444

Color centers in topaz: comparison between neutron and gamma irradiation

  • K. KrambrockAffiliated withDepartamento de Física, ICEx, Universidade Federal de Minas Gerais Email author 
  • , L. G. M. RibeiroAffiliated withDepartamento de Física, ICEx, Universidade Federal de Minas Gerais
  • , M. V. B. PinheiroAffiliated withDepartamento de Física, ICEx, Universidade Federal de Minas Gerais
  • , A. S. LealAffiliated withCentro de Desenvolvimento da Tecnologia Nuclear (CDTN), Comissão Nacional de Energia Nuclear (CNEN), Serviço de Reator e Irradiações - TR3
  • , M. Â. de B. C. MenezesAffiliated withCentro de Desenvolvimento da Tecnologia Nuclear (CDTN), Comissão Nacional de Energia Nuclear (CNEN), Serviço de Reator e Irradiações - TR3
  • , J. -M. SpaethAffiliated withUniversität Paderborn

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Abstract

Neutron- and gamma irradiation-induced paramagnetic centers in natural colorless topaz from four different Brazilian localities were studied by electron paramagnetic resonance (EPR) and optical absorption as a function of irradiation dose and thermal treatment. Gamma irradiation doses were applied up to 1,000 kGy with a dose rate of 15 kGy h−1. For the neutron irradiation experiments, a neutron flux of 4 × 1012 cm−2 s−1 was used with an integrated flux of up to 1 × 1018 cm−2. From the experiments, it is concluded that brownish colors are induced by gamma-rays and may be associated with a single broad isotropic EPR line with g = 2.015(2). Both the EPR line and the related optical absorption band at 460 nm (2.7 eV) are lost during thermal treatments between 150 and 200°C. Fast neutrons create the paramagnetic peroxyl radicals O2 and the paramagnetic O hole centers. The O centers have the same thermal stability as the optical absorption band at 620 nm (2.0 eV). It is confirmed that the absorption due to the O center is responsible for the blue color in topaz. Both color centers and their absorption bands are discussed in the context of O bound small polarons.

Keywords

Topaz Color Color enhancement Color centers EPR Irradiation Small polaron