Interactions of positronium with Co2+ in water: mechanisms and temperature effects

The interactions of positronium (Ps) with the paramagnetic Co2μ ion are investigated in water at various temperatures by both lifetime spectroscopy and the Doppler broadening of annihilation radiation line shape technique. They are shown to arise essentially from spin conversion reactions. However, the consistent fitting of the various data indicates the presence of an additional process, ascribed to Ps complex formation. The relative contribution of the latter increases importantly with temperature while the spin conversion is almost temperature independent. This peculiar behavior is tentatively explained on the basis of weak spin interactions. 32 references, 5 figures, 2 tables