  The Jagiellonian Positron Emission Tomograph (J-PET) is the first PET device
built from plastic scintillators. It is a multi-purpose detector designed for
medical imaging and for studies of properties of positronium atoms in porous
matter and in living organisms. In this article we report on the commissioning
of the J-PET detector in view of studies of positronium decays. We present
results of analysis of the positron lifetime measured in the porous polymer.
The obtained results prove that J-PET is capable of performing simultaneous
imaging of the density distribution of annihilation points as well as positron
annihilation lifetime spectroscopy.
