Measurements of the positron annihilation coincidence count rate at the peak of the angular correlation curve (CCR) were performed as a function of temperature between 550 and 1350K. The α → β and β → γ phase transformations were reflected by discontinuities of the CCR. The low temperature slope of the curve, the change at the α → β transition at 941K and the initial slope in the β phase could be very well described by linear thermal expansion. The jump of the CCR at 1048K was predominantly due to the vacancy trapping effect. Applying the trapping model to the data, a lower limit of about 1eV was obtained for the monovacancy formation energy.

Investigation of Vacancy Formation and Phase Transformations in Uranium by Positron Annihilation. H.Matter, J.Winter, W.Triftshäuser: Journal of Nuclear Materials, 1980, 88[2-3], 273-8