Discovery of proton-rich radioactive isotopes in the Z = 57 and 72 regions produced by the projectile fragmentation of a 345-MeV/nucleon 208Pb beam

Proton-rich new isotopes in the regions of atomic numbers Z = 57 and 72 were produced through the projectile fragmentation of a 345-MeV/nucleon 208Pb79 + beam at the RI Beam Factory, RIKEN. In addition to ¹¹⁸\;\: 58Ce, ¹²⁰\;\: 59Pr, 152,153\! 72Hf, and ¹⁵⁴\;\: 73Ta, which are new isotopes reported in our previous letter, ¹¹³\;\: 56Ba, ¹¹⁷\;\: 58Ce, and ¹²²\;\: 60Nd were newly confirmed. These highly proton-rich radioactive isotopes (RIs) were separated and identified using BigRIPS, the large-acceptance two-stage separator in RIKEN. Cross sections of the neighboring proton-rich RIs were measured and compared with predicted values of the semi-empirical formulas: FRACS1.1 and EPAX3.1a reproduced them fairly well. The cross sections of proton-rich RIs around Z = 58 produced from the 208Pb beam were approximately three times those produced from a 238U beam.