LIFETIME OF 26S AND A LIMIT FOR ITS 2p DECAY ENERGY
The unknown isotope 26 S , expected to decay by two-proton (2p) emission, was studied theoretically and searched experimentally. The structure of this nucleus was examined within the relativistic mean field (RMF) approach. A method for taking into account the many-body structure in the three-body decay calculations was developed. The results of the RMF calculations were used as an input for the three-cluster decay model optimized for the study of a possible 2p decay branch of this nucleus. The experimental search for 26 S was performed by fragmentation of a 50.3 A MeV 32 S beam. No events of a particle-stable 26 S or 25 P (a presumably proton-unstable subsystem of 26 S ) were observed. Based on the obtained production systematics, an upper half-life limit of T1/2<79 ns was established from the time-of-flight through the fragment separator. Together with the theoretical lifetime estimates for two-proton decay, this gives a decay energy limit of Q2p>640 keV for 26 S . Analogous limits for 25 P are found as T1/2 < 38 ns and Qp>110 keV . In the case that the one-proton emission is the main branch of the 26 S decay, a limit Q2p>230 keV would follow for this nucleus. According to these limits, it is likely that 26 S resides in the picosecond lifetime range.