Secondary protons from ultra high energy cosmic ray nuclei: is the Greisen-Zatsepin-Kuzmin cutoff unavoidable?

We discuss the production of ultra high energy secondary protons by cosmic ray primary nuclei propagating in the intergalactic space through Cosmic Microwave Background (CMB) and Infrared (IR) radiations. Under the assumption that only primary nuclei with a fixed atomic mass number $A_0$ are accelerated, the spectrum of secondary protons is calculated. It is found that for all $A_0$ the diffuse flux of secondary protons starts to dominate over that of primary nuclei at energy $E\sim (1-2)\times {10}^{19}$ eV, and thus the standard Greisen-Zatsepin -Kuzmin (GZK) cutoff is produced.