New Decay Modes

In an experimental tour de force, live digital photography of di-proton emission from the ground state of the extremely neutron-deficient nucleus 45Fe has been achieved, demonstrating this exotic decay mode unambiguously and clarifying its nature. Near the doubly magic neutron-deficient nucleus 100Sn, where protons and neutrons occupy the same shell model orbits, the fastest known alpha decay was discovered. Together with the discovery of the gamma ray depopulating the first excited state of 101Sn, these measurements are the first steps to determine the shell structure of extremely neutron-deficient heavy nuclei in a region that also represents the possible endpoint of the astrophysical rapid proton capture process powering X-ray bursts. In connection with Penning Trap precision mass measurements of neutron-deficient unstable nuclei in the critical mass 64–72 region, this has led to an impressive reduction in the nuclear physics uncertainty in advanced X-ray burst models which now include all relevant nuclear reactions.

new decay
Credit: Miernik et al., Phys. Rev. Lett. 99, 192501 (2007)

The figure shows a digital photograph of the two-proton decay of 45Fe taken at the NSCL. A 45Fe nucleus, with the very short half-life of 5 ms, entered the picture from the bottom, was stopped, and then decayed by emission of two protons.