The new method described in this article allows the detection of low concentrations of radical species created in water for high linear energy transfer (LET) pulse radiolysis. The time-resolved chemiluminescence was used in a pulse radiolysis experiment at the Grand Accelerateur d'Ions Lourds (Caen, France) with an Ar-40(18+) ion beam for the determination of radical yields. In water, for an LET of 280 eV/nm, the yield of OH is 2.2 x 10(-8) mol/J. A minimum value of the e(aq)(-) and HO2/O-2(-) yields is obtained. These experimental G values are compared to those obtained for the same LET. They are in good agreement with the values in the literature. The sensitivity of the time-resolved chemiluminescence method allows the measurement of concentrations of radicals species as low as 2 x 10(-7) M.