From measurements on the Pioneer 11 spacecraft, electrons and protons under Saturn's A-B-C rings were reported by Simpson et al. (1980) and Chenette et al. (1980) and identified as the secondary products of cosmic ray nucleons with energies >10 GeV interacting with ring matter. We have extended their analysis and have also found both secondary gamma ray fluxes with energies >15 MeV and fragmentation nuclei (H and heavier nuclei) with energies 25 MeV and protons >67 MeV). The surface density of the optically thick B ring is measured for the first time. Two analyses with separate data sets yield surface densities for the B ring of 90+70-46 and 62¿25 g/cm2. The latter value yields a B ring mass of 1.0 ¿ 0.4¿1022 g; we obtain a value for the A-B-C ring mass of 2.7+1.0-0.6¿10-8 Mg, where Mg (Saturn's mass)=5.7¿1029 g. Our surface density measurements are shown to be consistent with results derived from Voyager ring radio/optical opacity measurements and the observed damping of density waves in the ring.