Three-detector setup for positron-lifetime spectroscopy of solids containing 60Co radionuclide

A three-detector BaF2 positron-lifetime spectrometer is described. The spectrometer is suited for investigations of the neutron-irradiated reactor pressure vessel steels with a high content of 60Co. Both timing and energy information about annihilation γ-rays is used for selection of coincidence events. In the triple-coincidence mode, the time resolution of around 220 ps FWHM and the coincidence count rate of 15 s−1 for a 4 MBq 22Na positron source are simultaneously achieved. Test measurements performed have shown that in this mode the 60Co prompt-peak contribution in the positron-lifetime spectrum is suppressed to be below 1% when 60Co activity of a pair of specimens studied does not exceed the level of 4 MBq.