Radiolysis of phenylalanine in solution with Bragg-Peak energy protons

Phenylalanine aqueous solutions were irradiated with Bragg-Peak energy protons (0.6-5.6 MeV). An innovative circulation setup has been developed for the irradiation of these solutions with low-energy protons. Every detectable radiolysis product has been identified and quantified after irradiation. While tyrosines are well-known products of phenylalanine radiolysis, 2,5-dihydroxyphenylalanine and dimers were detected in high quantities, for the first time. The track-yields (G'-values) of all products formed under proton irradiation were determined and compared to those obtained with gamma-rays, and 2,5-dopa and dimers production seems to be specific to accelerated ions. A bi-radical mechanism could explain their higher production with a higher density of energy deposition in the track structure.