Single-particle structure and nucleon-nucleon correlations are a few topics of the R3B (Reactions with Relativistic Radioactive Beams) research program to be carried out at FAIR. CALIFA (CALorimeter for In-Flight detection of gamma rays and high-energy charged pArticles) is one of the detector systems of R3B. Components of the CALIFA Barrel are currently being assembled and tested. At the Bronowice Cyclotron Center in Krakow, a beam of 200-MeV protons was used to induce quasi-free (p, 2p) reactions on various targets such as 12C, 16O, 112Sn, 124Sn, and 208Pb. Light charged fragments and gamma rays were detected with several CALIFA Barrel detector modules consisting of CsI(Tl) crystals. Preliminary results from reactions on the 112Sn and 124Sn targets will be presented, with emphasis on the differences in reaction cross sections to the ground and excited states of the residual isotopes.