The slowing down times of positrons emitted from selected β+ isotopes into metals
Abstract We report the GEANT4 Monte Carlo simulations and the approximated calculations of the slowing down time (SDT) for positrons emitted from three β+ isotopes, i.e., 22Na, 68Ge/68Ga and 48V. The first two isotopes are commonly used in the positron annihilation spectroscopy. The results revealed that the SDT exhibits the nonsymmetrical distribution and its average value depends on the end point energy of the isotope, the density and atomic number of the implanted material. For metals the average SDT varies from 0.4 ps to a few ps. We argue that this can affect the analysis of the measured positron lifetime and should be considered in theoretical calculations. The SDT in selected gases w…
The Computer Code for Calculations of the Positron Distribution in a Layered Stack Systems
In this paper we present experimental and theoretical studies of the implantation pro le of positrons emitted fromNa radionuclide into layered sample. The measured pro le for the nonsymmetrical, around the positron emitter, stack of aluminium and silver foils was measured using the depth scanning of implantation pro le technique. For the description of the obtained results two theoretical approaches were applied. The rst one was the Monte Carlo simulation using the GEANT4 tool kit. The generated pro le does not reproduce accurately the experimental pro le. We proposed the multiple scattering model based on the fact that a positron due to backscattering can travel as an energetic particle se…
The “accumulation effect” of positrons in the stack of foils, detected by measurements of the positron implantation profile
The profiles of positrons implanted from the radioactive source 22Na into a stack of foils and plates are the subject of our experimental and theoretical studies. The measurements were performed using the depth scanning of positron implantation profile method, and the theoretical calculations using the phenomenological multi-scattering model (MSM). Several stacks consisting of silver, gold and aluminum foils, and titanium and germanium plates were investigated. We notice that the MSM describes well the experimental profiles; however when the stack consisting of silver and gold foils, the backscattering and linear absorption coefficients differ significantly from those reported in the litera…
The multi-scattering model for calculations of positron spatial distribution in the multilayer stacks, useful for conventional positron measurements
The spatial distribution of positrons emitted from radioactive isotopes into stacks or layered samples is a subject of the presented report. It was found that Monte Carlo (MC) simulations using GEANT4 code are not able to describe correctly the experimental data of the positron fractions in stacks. The mathematical model was proposed for calculations of the implantation profile or positron fractions in separated layers or foils being components of a stack. The model takes into account only two processes, i.e., the positron absorption and backscattering at interfaces. The mathematical formulas were applied in the computer program called LYS-1 (layers profile analysis). The theoretical predic…