Conformational properties of DNA after exposure to gamma rays and neutrons.

DNA aqueous solutions were irradiated with 0-40 Gy of 60Co gamma rays and 0-1.5 Gy of (Pu-Be) neutrons. Thermal transition spectrophotometry (TTS) was used to trace the changes in the DNA conformation at the above doses. Previous results using the perturbed angular correlation (PAC) method were used to complement to the current analysis. The TTS and PAC methods are two different approaches to the study of the effects of radiation on DNA. Both showed that neutrons are more effective than gamma rays in inducing DNA damage. The TTS method showed that neutrons are 11 +/- 5 times more efficient than gamma rays, while the PAC method had shown this value to be 34 +/- 4. From the current study we deduced that the radiation damage to DNA is not a spontaneous effect but rather is an ensemble of damaging events that occur asynchronously. Any single method selected for the study of such damages can concentrate on only a part of the damage, leading to over- or underestimation of the relative effectiveness of the neutrons.