How can nuclear energy be used in medicine

Nuclear medicine uses radiation to provide information about the functioning of a person's specific organs, or to treat disease. ... In some cases radiation can be used to treat diseased organs, or tumours. Five Nobel Laureates have been closely involved with the use of radioactive tracers in medicine.

Acids dissociate in water to release a proton. The proton then combines with water to form a  hydronium ion.  

HCl, hydrochloric acid dissociates in water to release proton H⁺ and chloride ion Cl⁻

HCl → H⁺ + Cl⁻

H⁺ + H₂O → H₃O⁺