Methods of Data Reduction in Analyzing Positron Annihilation Lifetime Spectra

The methods of data reduction used in processing the positron annihilation lifetime spectra are thoroughly discussed. For curves which are believed to represent a multi-exponential scheme the methods of least squares is still found to be the most useful one. Its convergence properties, the confidence level of its result and the effect of instrument noise to the result are also discussed. The method of Fourier transforms can also provide reasonable answers, however, its precision is quite limited. For curves which do not appear as multi-exponentials the calculation of time dependent annihilation rate ¿(t) is one of the simplest methods. A direct calculation of energy dependent annihilation rate ¿(E), or cross section, in general, is not possible since diffusion approximation is not always applicable and our knowledge in the scattering process is quite limited. However, in inert gases, without strong annihilation, a fair estimate of ¿(E) may be obtained after certain approximations are made.