A large area plastic scintillator counter is described which is used for identifying the mass of light charged particles (p, d, t) of 20–100 MeV with a β-range-energy method, and for measuring their energies as well as that of neutrons of about the same energy by means of the time-of-flight method with a time resolution of 380 ps. The counter is used in an experiment concerning the stopped negative pion absorption in light nuclei. It could be used, however, in other experiments where the identification and the energy measurement of p, d, t, and n in the aforesaid energy range are required.
