ON THE PHASE TRANSITION IN TIN OBSERVED BY POSITRON LIFETIME MEASUREMENTS.

For the first time the phase transition from beta - to alpha -tin was detected by measuring positron lifetimes. The transition was manifested at 230 K by an increase of the mean lifetime from 200 to about 280 ps. It was even possible to observe the state of the transition as a function of time. The temperature of the phase transition found corresponds very well to the temperature of the maximal growth rate of the alpha -phase published in the literature. The influence of other effects on the phase transition will also be discussed.