[en] In an experiment performed at the NSCL/MSU A1900 separator the decay of ⁴⁵Fe was investigated in detail. Two-proton radioactivity channel was clearly identified and for the first time the correlations between two protons emitted from the nuclear ground state were determined. The comparison with a theoretical model indicates the genuine three-body character of this decay and sheds light on the shell structure of this exotic nucleus. The β decay channels of ⁴⁵Fe, followed by one-, two-, and three-proton emission, were also identified. The β3p decay channel was observed for the first time. The half-life of ⁴⁵Fe was found to be 2.6±0.2 ms and the 2p decay branching ratio is 70±4%. In the experiment a new type of gaseous detector has been applied in which a technique of digital imaging was used to record tracks of charged particles

[en] Recently the observation of a new type of spontaneous radioactive decay has been claimed in which two protons are simultaneously ejected by an atomic nucleus from the ground state1,2,3. Experimental data obtained for the extremely neutron-deficient nuclei 45Fe and 54Zn, were interpreted as the first evidence of such a decay mode which has been sought since 1960.4 However, the technique applied in those studies allowed only measurements of the decay time and the total energy released. Particles emitted in the decay were not identified and the conclusions had to be supported by theoretical arguments. Here we show for the first time, directly and unambiguously, that 45Fe indeed disintegrates by two-proton decay. Furthermore, we demonstrate that the decay branch of this isotope leads to various particle emission channels including two-proton and three-proton emission. To achieve this result we have developed a new type of detector V the Optical Time Projection Chamber (OTPC) in which digital photography is applied to nuclear physics for the first time. The detector records images of tracks from charged particles, allowing for their unambiguous identification and the reconstruction of decay events in three dimensions. This new and simple technique provides a powerful method to identify exotic decay channels involving emission of charged particles. It is expected that further studies with the OTPC device will yield important information on nuclei located at and beyond the proton drip-line, thus providing new material for testing and improving models of very unstable atomic nuclei