Reconstruction of past solar activity using radiocarbon

Galactic cosmic rays cause hadronic showers in the terrestrial atmosphere and produce various isotopes. The typical isotope is radiocarbon 14C. Because the intensity of galactic cosmic rays impinging to the earth depends on the interplanetary magnetic field, which is influenced by solar activity, the production rate of the radiocarbon also reflects the variation of solar activity. In this review, I describe the methods of reconstruction of past solar activity from measurements of radiocarbon and introduce some recent results of the reconstruction. (author)