Positron annihilation in irradiated and unirradiated polyethylenes

Abstract

SYNOPSISPositron lifetimes were measured for four kinds of polyethylene samples and were resolved into four components. The temperature dependence of the two longlived components was examined in detail. In agreement with other results, the longest lived component could be reasonably assigned to ortho-positronium located in amorphous regions. This component was shown to be sensitive to the defects in high-density polyethylene introduced in the course of its production. Both the intensity and the lifetime of the second longest lived component were structure insensitive, i.e., they did not change even on passing through the melting point. This component has been tentatively assigned to a positronium compound state. The effect of gamma-ray irradiation was also examined. Although the intensity (Z4) of the longest lived component was reduced by the irradiation, correlation between Z4 and the free radical concentration was poor, and the reduction in I4 caused by the irradiation is considered to be due to structure change and not to chemical reasons. Keywords: positron annihilation in polyethylene, before and after irradiation polyethylene, positron annihilation in, effect of radiation on 517

Ultrahigh molecular weight polyethylene free volume hole structure studied by positron annihilation lifetime technique

“…2. The obtained values of s i and I i are in good agreement with the values published in [16][17][18] but they are not in accordance with those published in. [10] The value of the longest lifetime, s 3 L 1.8 ns in, [10] is too short even if taking into account that the value of the longest-lived o-Ps component for the three-term analysis is somewhat smaller than for the four-term ones.…”

“…[14,17,18,27] The localization of the sites relevant to s 3 is still not clear. Dlubek et al [17,18] consider s 3 as due to o-Ps annihilation in the crystalline regions of PE, while Suzuki et al [16] claimed that it is impossible to connect s 3 in PE with crystalline regions themselves or with their interfaces as s 3 was also observed in the fully melted samples. For the samples studied here I 3 changes slightly, while I 4 decreases with X c .…”

“…[5,6] Polyethylene (PE) has often been an object of PAL technique studies. [7][8][9][10][11][12][13][14][15][16][17] In the recent paper of Dlubek et al [18] a critical analysis of the physical meaning of the lifetime components received by a three-and four-term decomposition of lifetime spectra in PE has been made. The conclusion is that the constrained four-component fit gives a consistent physical picture of positron annihilation in semicrystalline PE.…”

“…Of course, other views about lifetimes have also been published. [16] The aim of this study is to find out the differences in the free-volume hole structure of the studied samples considering the published results from positron annihilation in PE. The PAL technique was used.…”

Vacancy Spectroscopy Using Positronium

“…It will be worthwhile to add that similar decrease of I 3 takes place not only by the self-irradiation of e + . The decrease in I 3 is also a well-known phenomenon when the sample is pre-irradiated with external source of -rays or electrons, but the mechanism that leads to the observed I 3 decrease, whether it is due to radicals or structural changes, is not yet fully clarified 32) .…”