The double-proton radioactivity. A new way of decay

For some proton-very-rich nuclei the emission of one proton is forbidden and the only way that complies with the energy conservation law is the emission of 2 protons simultaneously, which is called the double-proton decay. This way of decay was predicted from theoretical studies about the existence of nucleon pairing inside the nucleus. The production of new isotopes through the collisions of heavy ions has led to the experimental confirmation of first, the one-proton decay (in the eighties at Darmstadt through Lu151 → Yb150 + p) and then, the double-proton decay (in GANIL and in GSI, in 2002) through Fe45 → Cr43 + p + p. In the GANIL experiment the Fe45 nuclei were produced in the collisions of high energy Ni58 nuclei with a target of natural nickel (200 g/cm2). In some collisions (called fragmentation reactions) the target nuclei strip the nucleus incident of some nucleons producing a lighter nucleus, here Fe45. In order to produce one nucleus of Fe45, it has required in the GANIL conditions, the fragmentation of 1015 to 1016 incident nuclei of Ni58. In GSI similar results have been obtained with the double-proton decay of Zn54. (A.C.)