3. Measurement of two-photon gamma annihilation characteristics
Since positron annihilation with an electron is a statistical process, it is necessary to record the annihilation of at least 10 6 positrons to determine annihilation characteristics. In materials where only positron annihilation takes place, for example the annihilation of e + –e - quasi-free pairs, the annihilation characteristics commonly measured to study defects in solids are the positron lifetime distribution and the energy distribution of annihilation gamma photons in the two-gamma annihilation process. In insulating solids, where a fraction of positrons can form positronium (Ps) atoms, the pick-off process
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Measurement of two-photon gamma annihilation characteristics
Determining the free volume of defects in the core or surface of materials
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Installation costs
In terms of budget, the electronic part of the three classic techniques costs around e30,000 (in 2000) each. More sophisticated set-ups can obviously increase this price. To the price of the electronics and sources, we must of course add the cost of the cryogenic facilities and the mechanical parts of the apparatus (angular correlation). Finally, a complete bibliography can be found in the works cited in the references...
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