Implantation profile and linear absorption coefficients for positrons injected in solids from radioactive sources 22Na and 68Ge\68Ga

We present measurements of the penetration depths of positrons from Na-22 and Ge-68\Ga-68 sources into thick targets. These measurements were made using a new apparatus with an HpGe detector. These new measurements allow one to determine the mass absorption coefficients for dozens of materials. As expected their values were Z-dependent. Additionally for Z > 32 some oscillatory dependence was observed. Using these measurements we propose an improvement to the well known results of Gleasen et al. [G.I. Gleason, I.D. Taylor, D.L. Tabern, Nucleonics 8 (1951) 12] for the formula giving the value of the mass absorption coefficient. We carried out Monte Carlo simulations for the implantation profile, which indicated that only in some intermediate region does one expect the standard exponential behavior. In the near and far regions the simulations indicate behavior different from the intermediate region. Based on the experimental studies and the Monte Carlo simulations a new formula for the implantation profile is proposed. (c) 2006 Elsevier B.V. All rights reserved.