The energy spectrum of ultraheavy nuclei above 10²⁰ eV

A major feature of the energy spectrum of the cosmic radiation above 10$^{19}$ eV is the increasing fraction of heavy nuclei with respect to light nuclei. This fact, along with other simple assumptions, is adopted to calculate the energy spectrum of the cosmic radiation up to 2.4$\times$10$^{21}$ eV. The predicted spectrum maintains the index of 2.67 observed at lower energies which is the basic, known, empirical well-assessed feature of the physical mechanism accelerating cosmic rays in the Galaxy. Indeed above 10$^{19}$ eV the injection of nuclei is inhibited by some filter and this inhibition causes a staircase profile of the energy spectrum. It is argued that particle injection failure versus energy commences with protons, followed by Helium and then by other heavier nuclei up to Uranium. Around 7.5$\times$10$^{20}$ the cosmic radiation consists solely of nuclei heavier than Copper and the estimated intensity is 1.8$\times$10$^{-30}$ particles/GeV s sr m$^2$.