Chris Nelson

Idaho State University/Idaho Accelerator Center

A new method for obtaining positron lifetimes based on a Lagrangian approach is presented. Mono and divacancy lifetimes are calculated and shown to be within 20% of experimental values for crystalline silicon. Currently physicists at the IAC are preparing an experiment to measure changes in positron annihilation parameters in crystalline silicon due to laser induced shock waves. Using the imported code MIKA, we calculate the rate of change of positron lifetimes in crystalline silicon as a function of lattice parameter as calculated by the Lagrangian method above, and the monovacancy lifetimes are seen to be more sensitive to lattice changes than bulk positron lifetimes. A one dimensional model has been developed as a precursor to a 3-d model for delocalized positrons. Effects of lattice contraction on positron lifetimes with respect to annihilation of core and valence states will be discussed.