Deciphering the local Interstellar spectra of secondary nuclei with GALPROP/HelMod framework and a hint for primary lithium in cosmic rays

TL;DR

This study derives local interstellar spectra of secondary cosmic ray nuclei using advanced models and experimental data, revealing a potential primary lithium component and providing a comprehensive framework for understanding cosmic ray propagation.

Contribution

It introduces a combined GALPROP/HelMod framework with an iterative maximum-likelihood method to accurately derive LIS of secondary nuclei across a wide energy range.

Findings

LIS of secondary nuclei match measurements from Voyager 1, HEAO-3, ACE/CRIS, PAMELA, AMS-02.

Evidence suggests a flatter high-energy lithium spectrum indicating a possible primary lithium component.

Propagation parameters are consistent with previous results for various cosmic ray species.

Abstract

Local interstellar spectra (LIS) of secondary cosmic ray (CR) nuclei, lithium, beryllium, boron, and partially secondary nitrogen, are derived in the rigidity range from 10 MV to ~200 TV using the most recent experimental results combined with the state-of-the-art models for CR propagation in the Galaxy and in the heliosphere. The lithium spectrum appears somewhat flatter at high energies compared to other secondary species that may imply a primary lithium component. Two propagation packages, GALPROP and HelMod, are combined to provide a single framework that is run to reproduce direct measurements of CR species at different modulation levels, and at both polarities of the solar magnetic field. An iterative maximum-likelihood method is developed that uses GALPROP-predicted LIS as input to HelMod, which provides the modulated spectra for specific time periods of the selected experiments for the model-data comparison. The proposed LIS accommodate the low-energy interstellar spectra measured by Voyager 1, HEAO-3, and ACE/CRIS as well as the high-energy observations by PAMELA, AMS-02, and earlier experiments that are made deep in the heliosphere. The interstellar and heliospheric propagation parameters derived in this study are consistent with our earlier results for propagation of CR protons, helium, carbon, oxygen, antiprotons, and electrons.