Variations in Radiocarbon Production in the Earth's Atmosphere

Abstract

We have investigated solar phenomena associated with unusual changes in the production rates of 14 C in the atmosphere. 14 C is produced in interactions of cosmic ray neutrons with nitrogen in the atmosphere. Intensity of the neutrons varies globally and fluctuates with time as a result of interactions of galactic cosmic rays which generate neutrons with plasma and magnetic fields of the solar wind. We estimate the total mean production rate of 14 C for solar cycle 20, specifically 1965 to 1975, to be 2.25 ± 0.1 nuclei-cm −2 sec −1 from galactic cosmic rays alone, with negligible integrated contribution from solar particle events. Annual averages of R z , the Zurich sunspot number, and the production rate of 14 C, n( 14 C), were related by n( 14 C) = 2.60–5.53 × 10 –3 R z ± 3 percent. The contribution of solar flare particles and the zero sunspot limit are discussed with relation to major fluctuations that appear in the radiocarbon versus dendrochronology over short (∼100 years) integration times.