[en] In order to clarify the characteristics of the intra-track reactions induced by irradiation with high LET radiation, a pulse radiolysis study using 6 MeV ¹H⁺ (8.5 eV/nm) and 24 MeV ⁴He²⁺ (35 eV/nm) beams has been carried out in the aqueous solutions of methyl viologen containing formate. The yields of the methyl viologen radical cation as a function of formate concentration in the radiolysis with electron, proton and helium ion beams were determined. The yields are strongly dependent on the LET value of radiation; the higher LET, the smaller radical yield. By the combination of the yields in the presence of tert-butanol, G-values of OH and e_aq^- + H have been evaluated separately as a function of OH scavenging capacity. It was revealed that a larger fraction of the intra-track reaction takes place in high LET radiolysis. In addition, an aqueous solution of 0.5 mM methyl viologen containing 10 mM formate is a promising and useful dosimeter in ion beam radiolysis for steady state and pulse irradiation. (author)