Abstract
The coincidence Doppler broadening (CDB) and positron annihilation lifetime (PAL) techniques were applied to study low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), and antioxidant containing polypropylene (PPA). It was demonstrated that the Doppler-broadened lines for LDPE and PPA could be decomposed into two components a narrow component due to positronium (Ps) annihilation and another broader one due to free positron annihilation. The determined Ps-component in the Doppler-broadened line was used to calculate the Ps-corrected CDB ratios for HDPE and PP to LDPE. Different ways to compare CDB ratios in polymers were discussed. During a long-term (∼500 h) positron-irradiation experiment at a low temperature (50 K), a significant enhancement of the carbonyl group concentration in PP was found by means of CDB technique, while the enhancement in HDPE was very slight.
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