The Ionization Potential of DNA and Liquid Water

There are multiple applications in medical physics and space radiation health, such as hadron therapy for cancer treatment ofthe irradiation of biological systems by energetic ion beams. Therefore, for a better control and understanding of the effects of radiation damage in living tissues, it is necessary to advance an accurate description of the energy loss from the ion beam to the target. In the present work PPA of the dielectric formalism has been used to calculate the probability for an energetic proton to produce electronic excitations in DNA as well as the average energy of the target electronic excitations as a function of the projectile energy. Our results show that the protons with energy between 0.05 MeV to 2.5 MeV are very efficient in producing secondary electrons in DNA, which are able to produce strand breaks and could be very effective for the biological damage of malignant cells. The ionization potential (the so-called I-value) is the most important material quantity in the calculation of the electronic stopping power of energetic ions (>1 MeV u−1) through Bethe’s formula and represents its main source of uncertainty at high energies, I DNA found to be ≅ 80.01 eV and I H2O ≅78.17eV. Our present results are compared with previous work and show good agreement.