Speaker
Description
Measurements of long-lived isotopes in meteoritic data indicate the flux of Galactic cosmic rays (GCRs) has been constant for several Myr, however these measurements may be uncertain by 30% or more, due to confounding factors such as solar and geomagnetic modulation of the GCR flux. $^{14}$C produced in situ by interactions between cosmic ray muons and $^{16}$O atoms in ice can serve as a new proxy for historical GCRs, where the energy requirement for underground muon propagation filters out contamination from low energy solar and geomagnetic variations in the cosmic ray spectrum. We present a model of the relationship between cosmic rays at the top of the atmosphere and radiocarbon monoxide ($^{14}$CO) formed in ice, using atmospheric and in-ice particle cascades. By examining the concentration of $^{14}$CO in shallow ice cores extracted from Dome C, Antarctica, we can reconstruct changes in the GCR flux over a ∼7 kyr timescale with higher precision than other methods. This approach requires accurate characterization of the muon flux in ice, muon interaction cross-sections, and ice accumulation history to track the formation and transport of $^{14}$CO. We show results from archival measurements at Taylor Glacier, Antarctica and discuss preliminary measurements at Dome C and expected constraints on the recent history of the GCR flux.
