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

A three-detector BaF2 positron-lifetime spectrometer is described. The spec trometer is suited for investigations of the neutron-irradiated reactor pre ssure vessel steels with a high content of Co-60. Both timing and energy in formation about annihilation gamma-rays is used for selection of coincidenc e 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 Na-22 posit ron source are simultaneously achieved. Test measurements performed have sh own that in this mode the Co-60 prompt-peak contribution in the positron-li fetime spectrum is suppressed to be below 1% when Co-60 activity of a pair of specimens studied does not exceed the level of 4 MBq. (C) 2000 Elsevier Science B.V. All rights reserved.