The energy spectrum of ultraheavy nuclei above 10$^{20}$ eV

TL;DR

This paper models the energy spectrum of ultraheavy cosmic ray nuclei above 10^20 eV, predicting a staircase profile due to progressive injection failure of lighter nuclei, culminating in a spectrum dominated by nuclei heavier than Copper at the highest energies.

Contribution

It introduces a model for the energy spectrum of ultraheavy nuclei above 10^20 eV, incorporating a filter effect that causes a stepwise suppression of lighter nuclei.

Findings

Spectrum maintains a 2.67 index up to 2.4×10^21 eV.

Injection of nuclei fails progressively from protons to heavier elements.

At 7.5×10^20 eV, only nuclei heavier than Copper are present.

Abstract

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$^2$.