A time resolution of plastic scintillation detector and its application to positron annihilation spectroscopy

We have measured the effect of the sizes and kinds of scintillators on the time resolution of the fast coincidence system. Two pairs BaF₂ scintillation detectors with different sizes and one pair plastic scintillation detector was used in the measurement. After calibrating the TAC (time to amplitude converter), it was obtained that the time resolution of plastic scintillation system was better than others as ~300 ps when measured with ⁶⁰Co for a ²²Na energy window. In addition to that, we recognized that the resolution was dependent of the length of the delay line in the CFD (constant fraction discriminator) panel, neglecting the size of scintillators. We prepared three kinds of Polyaniline and used the fast coincidence system for positron annihilation spectroscopy to measure the positron lifetime. That is, the positron lifetime in solid state Polyaniline was measured as a function of three distinctive conductivities. We obtained the result that the lifetime of the positron decreases with increasing Polyaniline conductivity