We use this basic idea to identify point defects such as impurity atoms and lattice vacancies near probe atoms in metallic systems. PAC allows a direct measurement of these nuclear precessions in the time domain. Atomic fluorescence has its counterpart in transitions between nuclear levels. When transition energies are lower than about 30 keV, there is a significant probability that the transitions taking place will be recoilless . In that case, one can use a scanning spectroscopy to resolve the extremely small energy differences between magnetic quantum substates of the probe nucleus.
Positrons annihilate with electrons, their antiparticles.
In general, the lifetime of a positron varies inversely with the density of electrons at its location. Positrons tend to trap in open spaces in a crystal such as lattice vacancies, where the electron density is low, and therefore live longer. Fitted lifetimes are measures of the electron densities wherever the positrons annihilate. Back to our group's home page.