正电子在高能电子辐照聚乙烯和聚丙烯中的湮没特性

Positron annihilation characteristics in high energy electron-irradiated polyethylene and polypropylene

用正电子湮没寿命谱和多普勒展宽方法研究高能电子(12MeV)辐照聚丙烯和聚乙烯的不同特性,发现在160kGy剂量内,正电子在聚丙烯内的短寿命成分随着电子辐照剂量的增大而变长,中间成分的强度则减弱,但当剂量为320kGy时,各湮没寿命与没有辐照的样品类似。而长寿命成分的强度不随剂量增加而变化。在电子辐照的聚乙烯薄膜中,当剂量为80kGy时,正电子中间寿命强度Ⅰ_2增加,长寿命成分的强度Ⅰ_3则有所减少。之后,随着电子辐照剂量的增加,则不再变化。正电子湮没γ射线多普勒展宽S参数随电子辐照聚乙烯的剂量变化与Ⅰ_3相同。正电子湮没特性的差别表明高能电子辐照这两种聚合物所引起结构上的变化是不同的,并为其宏观特性(如力学性质变化)的改变提供了微观依据。

Positron annihilation lifetime spectra and Doppler broadening are used to investigate high energy(12MeV) electron-irradiated polyethylene and polypropylene. With increase of the electron dose less than 160kGy the short lifetime component of positrons for PP becomes longer while the intensity of the medium lifetime component decreases. When the irradiation dose reaches 320 kGy the lifetime components in the irradiated-PP are similar to those in virgin samples. However, the intensity of the longest lifetime component is nearly unchanged with increase of the irradiation dose. In the irradiated-PE both intensity of the longer lifetime component and shape parameter of Doppler broadening decrease quite a bit at the beginning but remain constant after 80 kGy electron irradiation. The mechanisms of different effects of high energy electron irradiation on the two polymers are discussed.