Solid phase transition of overpressurised helium bubbles seen from positron annihilation studies

Positron lifetime and Doppler broadening measurements on highly overpressur ised (P similar to 10P(eq)) helium bubbles in Al indicated abnormal variati ons at low temperatures, which is being assigned to the transformation of d ense helium bubbles into the solid phase, as expected from the Simon-Glatze l equation. The bubble pressure calculated using separate models for the fl uid and solid phases shows consistency with the helium freezing characteris tics. The solid phase transition is further confirmed by verifying an expon ential variation of the ultrasonic velocity with the solid bubble pressure. (C) 2001 Elsevier Science B.V. All rights reserved.