A scintillator, based on the direct effect of a radiation upon a dissolved activator, has been suggested. Concentrated /2–2.5 mol/1/ solutions of Tb3+ in D2O and H2O, and aqueous solutions of HCl, HNO3, and HClO4 have been found to possess a high light output of scintillations affected by -particles of actionoids. The scintillation efficiency of terbium solution in D2O is higher than that of some well-known organic scintillators. The terbium scintillator is quenched feebly by actinoid salts. Besides, it is of low sensitivity for the - and -radiation. The scintillations in terbium solutions represent groups of separate single-electron pulses with an exponentially decreasing frequency of their occurrence within groups.