S. Hansen et al., A MOBILE POSITRON-LIFETIME SPECTROMETER FOR FIELD APPLICATIONS BASED ON BETA(-GAMMA COINCIDENCE()), Applied physics A: Materials science & processing, 65(1), 1997, pp. 47-52
A mobile positron-lifetime spectrometer based on a beta(+)-gamma coinc
idence measurement, which has been applied to in-situ examinations of
microstructural evolution processes during the fatigue of copper singl
e crystals, is described. Since no sandwich-type geometry is required,
it is applicable to all specimen geometries commonly used in material
s testing and to the non-destructive testing of engineering parts in s
ervice. As a radioactive source Se-72 generates the positron emitting
As-72, which provides two positron spectra with maximum energies of 2.
5 MeV and 3.3 MeV and a prompt gamma quantum of 835 keV. The positrons
emitted in the direction towards the specimen pass through a fast pla
stic scintillator and produce a scintillation signal, thereby losing a
bout 150 keV of their energy. This signal serves as a start signal for
the positron-lifetime measurement and is measured in coincidence with
the subsequent 511 keV annihilation quantum. After passage through th
e plastic scintillator the remaining positron energy is still high eno
ugh to penetrate deep into the material and to allow for real bull; ex
aminations. The prompt gamma quantum may serve as an on-line control o
f the stability of the electronic system which will be useful under no
n-constant service conditions in a proposed field application.