Positron Annihilation with Cancer Cells

摘要

Positron annihilation spectroscopy (PAS) is a known technique in the community of solid-state physicists and material scientists for the determination of vacancies and defects at a sensitivity on the order of ppm. The basic principle of this novel application is that the positron (the anti-electron) is found to preferentially localize in defect sites where a low electron density exists and the measured annihilation rate of the positron with electrons in defects is lower than those in occupied sites. Recently, PAS has been successfully developed to be a useful tool in the detection of free volumes and voids in polymeric materials at a size on the order of 0.1 to 2 nm and of nm to μm. The sensitivity and selectivity of detecting those nanometer defects in complicated polymeric systems is magnified by the fact that the Positronium (Ps, a bound atom consisting of a positron and an electron) is preferentially localized in free volumes and voids. The measured Ps annihilation lifetime and its probability provide information about free-volume size, distribution and fraction, respectively.