In Situ 14C on Surfaces at Secular Equilibrium

After 4 to 5 half-lives, an exposed, non-eroding surface reaches secular equilibrium between cosmogenic production and decay of the radionuclide. Knowing the decay constant and measuring the secular equilibrium concentration of the cosmogenic radionuclide yields the local production rate. All well-preserved surfaces exposed longer than ~25 kyr have reached equilibrium between 14C production and decay, and are suitable for direct calibration of the in-situ 14C production rate. A widely distributed network of 14C calibration sites can be used to define altitude and latitude scaling factors (averaged over the past ~25 kyr) and can also be used to quantify the production rates of other nuclides, once production-rate ratios have been measured.