Measurements of the positron annihilation coincidence count rate at the peak of the angular correlation curve (CCR) in uranium were performed as a function of temperature between 550 and 1350 K. The α → β and β → γ phase transformations are reflected by discontinuities of the CCR. The low temperature slope of the curve, the change at the α → β transition at 941 K, and the initial slope in the β phase can be very well described by linear thermal expansion. The jump of the CCR at 1048 K is predominantly due to the vacancy trapping effect. Applying the trapping model to the data in the 7 phase, a lower limit of about 1 eV has been obtained for the monovacancy formation energy EF 1v. This result leaves only a very small value for the vacancy migration energy EM 1v. © 1980.    «

Measurements of the positron annihilation coincidence count rate at the peak of the angular correlation curve (CCR) in uranium were performed as a function of temperature between 550 and 1350 K. The α → β and β → γ phase transformations are reflected by discontinuities of the CCR. The low temperature slope of the curve, the change at the α → β transition at 941 K, and the initial slope in the β phase can be very well described by linear thermal expansion. The jump of the CCR at 1048 K is predomi...    »