We evaluated soft-error tolerance by heavy-ion irradiation test on three-types of flip-flops (FFs) named the standard FF (STDFF), the dual feedback recovery FF (DFRFF), and the DFRFF with long delay (DFRFFLD) in 22 and 65 nm fully-depleted silicon on insulator (FD-SOI) technologies. The guard-gate (GG) structure in DFRFF mitigates soft errors. A single event transient (SET) pulse is removed by the C-element with the signal delayed by the GG structure. DFRFFLD increases the GG delay by adding two more inverters as delay elements. We investigated the effectiveness of the GG structure in 22 and 65 nm. In 22 nm, Kr (40.3 MeV-cm2/mg) and Xe (67.2 MeV-cm2/mg) irradiation tests revealed that DFRFFLD has sufficient soft-error tolerance in outer space. In 65 nm, the relationship between GG delay and CS reveals the GG delay time which no error was observed under Kr irradiation.