The Distribution of Slowing-Down Times of Positrons Emitted from 22Na and 68Ge\68Ga Isotopes into Metals
The results of the Monte Carlo simulation, using GEANT4 codes, of the slowing-down time prior to the thermalization in metals for positrons emitted from the 22Na and 68Ge\68Ga sources are presented. Due to the energy spectrum and probabilistic processes accompanying positrons traversing a medium the slowing-down time exhibits a distribution which has a long tail. Nevertheless, the average value of the time is ranged from 0.4 ps to 8 ps depending on the density of the medium as it is for the 22Na positrons. For positrons emitted from the 68Ga nucleus the average value of the slowing-down time increases and it is ranged from 1 ps to 20 ps.
J. Dryzek and P. Horodek, "The Distribution of Slowing-Down Times of Positrons Emitted from 22Na and 68Ge\68Ga Isotopes into Metals", Materials Science Forum, Vol. 666, pp. 10-14, 2011