Photoelectic Driven Decomposition of Uracil via Hard X-Ray Irradiation

Radiation damage into biological samples creates substantial challenges across a wide range of fields, from biochemistry to materials science. This comprehensive study investigates the effects of x-ray irradiation on uracil, the only nucleobase exclusive to Ribonucleic acid (RNA), to understand how doping with 10% (by mass) of specific powdered elements impacts the sustained radiation damage. The experiments were conducted at the Brockhouse Undulator Beamline of the Canadian Light Source synchrotron. Virgin and doped uracil samples were irradiated with hard x-rays, above their respective absorption edges, and studied with x-ray diffraction to compare their decomposition behaviors. The Uracil reflections on the x-ray diffraction plots showed signs of radiation damage, increasing d-spacing and decreasing intensities, after extended irradiation. The decomposition yield was plotted against irradiation time and fit with a modified Avrami equation. This regression analysis revealed the linear nature of the radiation damage, with the decomposition yield of the doped samples growing faster compared to virgin uracil. This accelerated damage is attributed primarily to the photoelectric effect in the powdered dopants, where the absorption of x-ray photons above the electron binding energy leads to the emission of electrons and characteristic x-rays which bombard the uracil crystal structure and enhance the radiation damage. These findings offer insights into the effect elemental doping has on the stability of biological samples when exposed to hard x-rays as a method initiate and accelerate radiation damage.