“…Cosmogenic radioactive and stable nuclides in chondrites have preserved important records of their exposure history during the last ten million years (e.g., Michel, 1999;Vogt et al, 1990;Caffee et al, 1988). For example, activity of typical neutron-capture product, 60 Co has been used as an indicator of their preatmospheric size (e.g., Eberhardt et al, 1963;Spergel et al, 1986), and those of spallation products, 22 Na, 54 Mn and 26 Al etc.…”