Damage rate and recovery measurements on zirconium after electron irradiation at low temperatures

Abstract

Resistivity change as a function of electron irradiation near 8 °K and of annealing after irradiation has been measured on zirconium. Damage rates were measured as a function of incident electron energy from 0.70 to 1.9 MeV. A value of 24 eV for the displacement threshold energy was determined by extrapolation of the damage rate curve to zero damage production. A fit between the theoretical and experimental values of displacement cross section was achieved with an effective threshold energy of 28 eV, yielding 35 × 10⁻⁴ Ω-cm/fractional concentration for the Frenkel resistivity. The damage-rate curve indicates no tailing due to subthreshold displacements. Recovery in Zr is analogous to that of fcc and bcc elements studied, but with six substages in Stage I. Substage If (analogous to I _e in other materials) was analyzed by using the serpentine plot, which gives an indication of long-range migration of an interstitial between 120 and 150 °K, with an activation energy of 0.26 eV (second order kinetics is assumed). Stage III is in the temperature range 250 to 310 °K. The activation energy of Stage III was analyzed by use of the Meechan-Brinkman and second-order methods; this results in an average energy of 0.57 eV. The order of reaction kinetics was found to be a function of recovery.