Positron Irradiation Effects in HDPE during PAL Measurement at room temperature

J. Kansy1 and M. Ziąbka2  

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

Positrons emitted from 22Na induce irradiation damage in polymer - intensity of the longest-lived component I3 decreases gradually with the measurement time.

Small dose of irradiation deposing (~ 1kGy e+ and 102 Gy )– large effect on I3 = I3 (t) (t ~ 10 h)

3 not effected by positron source irradiation

Positron irradiation effect in polymers

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)

Positron irradiation effects in polymers of various crystallinity

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

Positron irradiation effect in non-polar and polar polymers

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

Positron irradiation effect in HDPE (0.960g/cm3) - present work

Time dependence of the o-Ps intensity I3 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

Model of spectrum J Kansy and T Suzuki, Radiation Physics and Chemistry 76 (2007) 759–765

Delayed Formation of Ps (DFP)

Analysis with „LT Polymers” software

Delayed Formation of Positronium – Results for HDPE

- correlation

- correlation in HDPE and LDPE at low temperatures (30 K)

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

- correlation in ethylene-methyl methacrylate copolymers (EMMA) at low temperature (30 K)

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

Modified DFP model

e+ trapping rate into free volume ()

e+ te+ ortho p

400 ps 956 ps 2.43 ns 0.511

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

Conclusions

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www.prac.us.edu.pl/~kansy

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