Posit Ron I Rr a Diati on Effe Cts on Positr on Ium Form Ati on in Poly Ca Rbon Ate S Duri Ng a Positr on -a Nnihila Ti on Ex Peri

The positronirrad iation e ̃ect on polycarb onate during a positronannihi lati on lif etime spectroscopy exp eriment w as investigated using di ̃erent intensities of 22 N a p ositron sources and Û -irradiated samples . T he decrease in I 3 was larger for a larger intensity of positron sources. In the case of a w eak source ( ¤ 140 kBq), I 3 did not change w ith the elapsed time for nonirradia ted samples. H owever, for 1 M Gy irradiated samples, I 3 measured w ith the weak source increased w ith the elapsed time. T his can b e attributed to a decrease in the radicals induced in the irradiated samples by Û -irradiati on. In order to explai n the change in I 3 measured at ro om and liqui d-ni trogen temp eratures, several e ̃ects, such as radicals, crosslinki ng, structure change, and charging, need to be considered. A lso, it is di £cult to explain the change in I 3 using only one of these e ̃ects.