Search for direct two-proton radioactivity from Ti isotopes at the proton drip line

The neutron-deficient isotopes 39Ti and 40Ti have been produced as fragments of 58Ni projectiles at 65 MeV per nucleon. Decay by β-delayed charged-particle emission has been observed for both of them with half-lives of 26−7+8 ms for 39Ti and 56−12+18 ms for 40Ti. No evidence for direct two-proton emission from 39Ti was obtained. The conditions that would make such a new radioactive mode possible are discussed.