Positron annihilation in carbon nanotube powders

Positron lifetime spectra have been measured in two kinds of carbon nanotube powders as a function of temperature range between 32 and 296 K. It has been found that all spectra are essentially temperature-independent in the above temperature range. The results of analysis show that there are three components in the powders of carbon nanotube with an average diameter of 30 nm, and four components in the powders of carbon nanotube with typical diameters of around 15 nm. The average values of lifetime components obtained at various temperatures are about 220, 390 ps, and 2.0 ns for the former, and about 140, 300, 650 ps and 6.4 ns for the latter.