ISSN:
1432-0630
Keywords:
PACS: 78.70.Bj; 36.10.Dr; 61.41.+e
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Abstract. We have determined the positron mobility (μ+) in polyethylene samples (67.2% crystalline, glass transition temperature T g=151 K) in the 64–400 K temperature range by Doppler shift measurements. A method based on the simultaneous observation of two γ lines from 133Ba and 137Cs radioactive sources together with the positron annihilation γ line, was employed to measure the Doppler shift of the 511 keV γ line as a function of the electric field applied to the samples. With this method we were able to measure at the same time the drift velocity of positrons and the S parameter. This parameter is very important in the interpretation of the mobility trend in samples where the positron states change with temperature. The positron mobility was corrected for positronium formation. μ+ at 64 K is 31.7±0.8 cm2 V-1 s-1 then decreases up to 123 K, increases at 148 K and decreases again up to 170 K (μ+=26.9±0.8 cm2 V-1 s-1). This sharp change in mobility is centred around the glass transition temperature of our samples. Then the mobility remains almost constant up to 230 K. From 250 K to 377 K, μ+ increases and reaches the value of 38.4±1.0 cm2V-1s-1. The corrected experimental data were well fitted by a simple model taking into account scattering and a thermally activated process (hopping mechanism).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01538768
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