Determination of DNA single-strand breaks by low-energy heavy ion and analysis of dose-effect curves

Calf thymus DNA was exposed to low-energy heavy ions (N⁺) and⁶⁰Co-γ-rays, and the dose-effect on DNA single-strand breaks (SSB) has been investigated. The results indicate that the dose-effect curve by N⁺ irradiation is different from that of conventional ionizing radiation. While the curve from γ-irradiation follows exponential type, the effect curve produced by N⁺ ion is of “saddle type”. The yield of DNASSB per dose unit per DNA unit remained at a certain level under different doses of γ-rays. In contrast, the DNASSB at low dosage region of N⁺ showed an obvious peak before it decreased rapidly to a lower level.