Krypton-67, a new atomic nucleus detected


When Krypton-67 disintegrates, two protons are emitted. This is a highly unusual form of radioactivity.

Two-proton radioactivity is an extremely rare phenomenon. To date, it has only been observed in three different atomic species. A fourth type of atomic nucleus, that of Krypton-67, has now been added to the list following an experiment carried out by CENBG11. Centre d’Etudes Nucléaires de Bordeaux Gradignan (CNRS/Université de Bordeaux), in collaboration with international teams physicists at the Rikagaku Kenkyusho Institute of Physical and Chemical Research (RIKEN) in Japan. Two-proton radioactivity was discovered in 2002, and only occurs in nuclei with a large excess of protons compared to the number of neutrons. This imbalance makes the nucleus highly unstable, causing it to split into two protons, a unique process in the subatomic world.

Researchers indirectly detected this emission in the Krypton-67 nuclei, resulting from the violent collision between heavy stable nuclei and a target. Yet in contrast to the three species described previously, the lifespan measured for this new nucleus differed from the theory. The unusual shape of the nucleus, or a more complex emission mechanism, could explain this discrepancy.

To address this question further, new experiments will attempt to locate the protons emitted directly. This should provide new insight into this specific type of radioactivity, as well as, on a wider scale, the interactions between the components of the atomic nucleus.

Physical Review Letters, 2016