Obtaining a History of the Flux of Cosmic Rays using In Situ Cosmogenic $^{14}$C Trapped in Polar Ice

TL;DR

This paper proposes using in situ cosmogenic $^{14}$C trapped in polar ice to reconstruct historical cosmic ray flux, offering a new method that bypasses uncertainties of other isotopic proxies.

Contribution

It introduces a novel approach to measure cosmic ray history through in situ $^{14}$C in ice, reducing transport and cycle-related uncertainties.

Findings

$^{14}$C in ice is dominated by in situ cosmogenic production.

Method can detect cosmic-ray flux variations over time.

Sensitivity estimates show potential for reconstructing cosmic ray history.

Abstract

Carbon-14 ($^{14}$C) is produced in the atmosphere when neutrons from cosmic-ray air showers are captured by $^{14}$N nuclei. Atmospheric $^{14}$C becomes trapped in air bubbles in polar ice as compacted snow (firn) transforms into ice. $^{14}$C is also produced in situ in ice grains by penetrating cosmic-ray neutrons and muons. Recent ice core measurements indicate that in the $^{14}$CO phase, the $^{14}$C is dominated by the in situ cosmogenic component at most ice coring sites. Thus, it should be possible to use ice-bound $^{14}$CO to reconstruct the historical flux of cosmic rays at Earth, without the transport and deposition uncertainties associated with $^{10}$Be or the carbon cycle uncertainties affecting atmospheric $^{14}$CO$_2$. The measurements will be sensitive to the cosmic-ray flux above the energy range most affected by solar modulation. We present estimates of the expected sensitivity of $^{14}$CO in ice cores to the historical flux of Galactic cosmic rays, based on recent studies of $^{14}$CO in polar ice.