Low Temperature Dependence of Positron Annihilation in Quenched Aluminum

Abstract

Doppler-broadened lineshapes of positron annihilation radiation in an aluminum single crystal after quenching have been measured as a function of temperature between 4.2 and 200 K. The peak parameter for positron annihilation in the trapped state at vacancies showed no significant temperature dependence below 80 K, while above 100 K, it showed an almost linear temperature dependence with a temperature coefficient about twice that found for positron annihilation in the free state. A low concentration of vacancies yielded a remarkable increase in the peak parameter as the temperature decreased below 80 K. The results showed a strong temperature dependence of the trapping rate of positrons at vacancies in the low temperature range.