Light emission from polymers under positron and electron bombardment

Light emission from polymers (anthracene dissolved in polystryrene) under both low-energy positron and electron bombardment has been studied. Results show a clear difference between optical emissions induced by positrons and electrons. For positrons, a blue band and a weak sub-blue band are observed, while the blue band and a yellow band are induced by electrons. The light emissions in the blue band are due to production of electron-hole pairs for both electron and positron cases. The yellow band is interpreted as a secondary process, involving the excitation of metastable states generated by the electron beam. The sub-blue band, observed only under positron bombardment, is believed due to transitions to the electron vacancy generated by positron annihilation.