1. J. Kansy 1 and M. Ziąbka 2 1 Institute of Material Science, Silesian University, Bankowa 12, 40- 008 Katowice, Poland 2 Faculty of Materials Science and Ceramic, University of Science and Technology, A. Mickiewicza 30, 30-059 Krakow, Poland

2.  Positron irradiation effect at room temperature  Conventional descriptions of polymer PALS spectrum and their drawbacks  Delayed Formation of Positronium – the DFP model of spectrum  Results of fitting DFP to a series of HDPE lifetime spectra  Modified DFP model  Conclusions

3.  Positrons emitted from 22 Na induce irradiation damage in polymer - intensity of the longest- lived component I 3 decreases gradually with the measurement time.  Small dose of irradiation deposing (~ 1kGy e+ and 10 2 Gy  )– large effect on I 3 = I 3 (t) (t ~ 10 h)   3 not effected by positron source irradiation M. Welander and F.H.J. Maurer. Matter. Sci. Forum. 105/110, 1811 (1992) T. Suzuki at al. Radiat. Phys. Chem. 45, 657 (1995) Z.L. Peng at al. phys.stat.sol. (a) 155, 299 (1996)

4. T. Suzuki at al. Radiat. Phys. Chem. 45, 657 (1995)

5. Z.L. Peng at al. phys.stat.sol. (a) 155, 299 (1996)

6. Time dependence of the o-Ps intensity I 3 in HDPE (crystallinity 57%). Data collected at 300 K. The measurement was discontinued (sample separated from positron source) at point a) for 10 days, at point b) – for 2 days, and at point c) – for 17 days – process partially recoverable

7. J Kansy and T Suzuki, Radiation Physics and Chemistry 76 (2007) 759–765 Delayed Formation of Ps (DFP)

11. J Kansy and T Suzuki, Radiation Physics and Chemistry 76 (2007) 759–765

12. J Kansy and T Suzuki, ACTA PHYSICA POLONICA A 110 (2006), 593

13. e + trapping rate into free volume (  )  e+  t e+  ortho p 400 ps956 ps2.43 ns0.511

14.  The DFP model well described the HDPE lifetime spectra collected at room temperature  The positronium formation seems to be connected with positron trapping in free volume at vicinity of a negative charge  The decrease in efficiency of Ps formation with the time of measurement (=time of sample irradiation) is due to scavenging of quasi-free electrons by free radicals induced by the source irradiation

15. Address of Website with programs LT9, LT10, LT Polymer and others: www.prac.us.edu.pl/~kansywww.prac.us