Evaluation of Positron Implantation Profiles in Various Materials for ²²Na Source

Abstract

Positron implantation profiles in various materials for22 Na isotope source are discussed. The spatial distribution of positrons in materials with densities from 1 to 21 g/cm 3 are simulated using GEANT4 code. The results indicate that depth distributions of thermalized positrons in any homogeneous medium can be described by the sum of two exponential functions. Contribution of the short-range exponent is about 11% in the materials. The both absorption coefficients can be well represented as a function of material density and atomic number. Proposed empirical model agrees well with available experimental data.

Review of Positron Lifetime Studies of Lattice Defects Formed during Tensile Deformation in a Hydrogen Environment

“…The maximum implantation depth of these positrons is estimated to be 100-200 μm in iron, steels, and nickel alloys. 26) The experimental positron lifetime spectrum, T(t) of samples containing open-volume defects includes the lifetime components of the bulk, lattice defects, and positron source. In positron lifetime spectrum analysis, the experimental positron lifetime spectrum is reconstructed as a sum of exponentially decaying components (Eq.…”

On the Reconstruction of the Mean Positron Lifetime Obtained from the Sequential Chemical Etching Procedure

“…(6) is placed in the denominator in Eq. (8). This significantly affects the accuracy of the average value of the actual mean positron lifetime.…”

“…Thus in Eqs. (8) and (9), we should use: w = 4µ/ 1 + e −1 ∆z = 2.924µ∆z, when ∆z < d in the experiment and w = 2µ/ 1 + e −1 ∆z = 1.462µ∆z, when ∆z > d.…”

“…Other authors suggest using different functions to describe the implantation profile, but they require more parameters than one, as in Eq. (10) [8,9]. However, at this stage, the Monte Carlo simulations can be used instead of experimental methods to determine them.…”

On the Characterization of Small-Scale Samples Using Radioisotope Positron Sources

“…So, the main energy losses interactions of positrons with matter are inelastic collisions, where secondary particles are ejected such as electrons or gamma and ions are formed. Similarly, to [5] we chose our default physics list to be electromagnetic PENELOPE (PENetration and Energy LOss of Positrons and Electrons) model. For purposes of source decay behavior, we implemented radioactive decay physics list.…”