Fission fragment damage in zircon

Abstract

X-ray diffraction, electron microscope and optical studies have been : ade on zircons damaged by fission fragments derived from the action of neutrons on uranium impurities in the zircon lattice. A dosage of about 10¹⁴ fission events · cm⁻³ was required to produce diffuse x-ray scattering, observable by conventional photographic methods, and a dosage of about 10¹⁶ fission events · cm⁻³ appears to be required to render a zircon amorphous. An optical absorption band, generated apparently by γ-rays, was observed near 270 nm in undoped zircon. The valence state of the uranium impurities was unchanged by irradiation with 10¹⁴ fission events · cm⁻³, 2 × 10¹⁸ nvt of fast neutrons, or ∼10¹⁰ R of γ-rays. A fission event in zircon was deduced to produce ∼10⁴ times more displacement damage than an α-recoil atom. Individual fission tracks were observed directly by electron microscopy after dosage of 10¹⁰-10¹³ fission events - cm⁻³, the tracks being similar in appearance to those found by other workers in other materials. With increasing dosage, fission fragment uradiation appears to produce a progressive disordering of the lattice, as was previously deduced for the case of α-recoil irradiation, rather than the formation of new crystallographic phases.