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

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.

Presented at the International Cosmic Ray Conference (ICRC2019) in Madison, WI, USA, July 2019. 8 pages, 2 figures