  Plastic scintillation detectors for Time-of-Flight (TOF) measurements are
almost essential for event-by-event identification of relativistic rare
isotopes. In this work, a pair of plastic scintillation detectors of 50
$\times$ 50 $\times$ 3$^{t}$ mm$^3$ and 80 $\times$ 100 $\times$ 3$^{t}$ mm$^3$
have been set up at the external target facility (ETF), Institute of Modern
Physics. Their time, energy and position responses are measured with $^{18}$O
primary beam at 400 MeV/nucleon. After the off-line walk-effect and position
corrections, the time resolution of the two detectors are determined to be 27
ps ($\sigma$) and 36 ps ($\sigma$), respectively. Both detectors have nearly
the same energy resolution of 3$\%$ ($\sigma$) and position resolution of 2 mm
($\sigma$). The detectors have been used successfully in nuclear reaction cross
section measurements, and will be be employed for upgrading RIBLL2 beam line at
IMP as well as for the high energy branch at HIAF.
