The characterization of dislocation loops in neutron irradiated zirconium

Dislocation loops formed in zirconium after neutron irradiation and subsequent annealing between 450° and 500°C are not pure edge loops. A general method for analysing such loops by transmission electron microscopy is discussed briefly and a technique for determining the loop plane normal to within ± 5° is described. The Burgers vectors of the loops in annealed irradiated zirconium are found to be of the type a/3 ⟨11 2 0⟩ while the loop plane normal is tilted by up to 35° towards the adjacent {20 2 1} pole. Two thirds of the loops present after annealing at 490°C are vacancy loops, while the remainder are interstitial. Zirconium irradiated at 300°C and not annealed also shows only loops with a/3 ⟨11 2 0⟩ Burgers vectors. The significance of these results in interpreting previously reported irradiation growth data is briefly discussed.