Objective To investigate the characteristics of repair of DNA double strand breaks (DSB) induced by high-LET α-particle irradiation and their relationship with chromatin structure in the G0 lymphocytes of human peripheral blood,in order to provide the experimental basis for the judgement and dose evaluation of internal α-particle radiation.Methods Peripheral whole blood were collected from four healthy adults and lymphocytes were separated.A monocellular layer of human lymphocytes attached in Mylar film were irradiated with 0 and 0.5 Gy of α-particles and the lymphocytes suspensions were irradiated with 0 and 0.5 Gy of γ-rays.The formations of γH2AX foci as a surrogate marker of DSB and Rad51 foci as a marker of homologous recombination (HR) repair and their spatial localization in chromatin structure were measured by immunofluorescence staining technique at 10 min-48 h post-irradiation.Results Linear-γH2AX foci tracks were observe at 10 min-2 h post-irradiation in lymphocytes exposed to α-particle irradiation(t =11.12,14.40,16.56,P ＜ 0.05),and almost completely disppeared at 6 h postirradiation.The frequencies of γH2AX foci peaked at 30 min after α-particle irradiation (t =51.72,P ＜0.05) and then decreased rapidly during 6 h post-irradiation (t =29.83,P ＜ 0.05).The average number of foci remained only about 16％ at 24-48 h post-irradiation.Moreover,27％ of γH2AX foci located at DAPI-bright heterochromatin region at 10 min after α-particle radiation,suggesting that the efficacy of DSB repair may be decreased.In contrast,at 10 min-48 h after γ-ray irradiation,no linear γH2AX foci track was observed and the γH2AX foci diffused randomly in nucleus and predominantly located in DAPI-weak euchromatin region.The numbers of formative and residual γH2AX foci after γ-ray irradiation were significantly less than those after α-particle radiation.During 30 min-2 h after α-particle and γ-ray irradiation,the frequencies of Rad51 foci slightly but not significantly increased in comparison with background level,and the frequencies of co-localization of Rad51 foci and γH2AX foci were only 3％-8％.Conclusions The formation of linear γH2AX foci tracks induced by high-LET α-particle irradiation in Go human lymphocyte could be used as biological indicator to estimate whether a person has been exposed to internal α-particle radiation.Prolonged persistence of residual γH2AX foci may be applicable for biological dosimetry.