Positron-annihilation studies of voids in neutron-irradiated aluminum single crystals

We have measured the angular correlation of positron-annihilation radiation from single crystals of aluminum in which voids had been induced by neutron irradiation. The angular-correlation curve is narrower than that for aluminum containing vacancies. The data fit well a curve computed on the assumption that the positrons are annihilated at the void surfaces. After the sample was heated to 325°C the angular-correlation curve became identical to that of normal Al.