Thermalization of Positrons in Argon

The slowing down times of positrons emitted from selected β+ isotopes into metals

“…The first one is commonly used in the positron lifetime spectroscopy, however the energy end-point of b + decay, i.e., about 545 keV, is low which gives the low implantation range and hence the expected low value of the SDT. The end-point energy of 48 V isotope is higher than 22 Na and it is equal to 695 keV. As it was shown in Ref.…”

“…In our simulation we assumed that positrons from 22 Na, 68 Ge/ 68 Ga and 48 V sources are emitted randomly from a point in solid angle with the energy distribution corresponding to energy in b + decay of the nucleus [7]. Each positron path was traced until it reached the energy low enough to annihilate at rest with en electron into two photons and then path history was printed in a report.…”

“…Certainly the initial positron energy E i varies from E f to E max , the end-point of the Fermi distribu- Table 1 The average SDT evaluated using CSDA calculations and GEANT4 simulations for positrons emitted from following emitters: 22 …”

“…Usually, the emission is tagged by the emission of gamma photon from excited state of daughter nucleus in the b + decay which is a positron source. For the isotope 22 Na it is the photon of 1.275 MeV which is emitted from the excited state of 22 Ne. The annihilation radiation of energy of 0.511 MeV tags the end of positron stay in a sample.…”

“…The continuous slowing down approximation (CSDA) with the formula for the positron stopping power for ionization and the braking radiation was the second one. Our studies were performed for three positron emitters 22 Na, 48 V and 68 Ge/ 68 Ga. The first one is commonly used in the positron lifetime spectroscopy, however the energy end-point of b + decay, i.e., about 545 keV, is low which gives the low implantation range and hence the expected low value of the SDT.…”