People are exposed to low-level ionizing radiation from both natural sources and manmade sources throughout their lives. Because radiation can cause cancers and genetic defects, it is very important to know the mechanism involved in the radiation process. As the damage mainly occurs on the DNA, DNA base derivatives crystalline complexes, which are similar to the base pairs of the DNA double helix, are used in the study. Theoretical calculations are performed on the co-crystals 1-Methylthymine:9-Methyladenine and 1-Methyluracil:9-Ethyladenine and on the radicals observed in the experiment.The calculated aisotropic hyperfine constants and isotropic fermi contact couplings show good agreement with the experimental results.