The most neutron-rich doubly-magic nucleus

Nickel-78, has had its lifetime measured. In a classical chart of the standard nuclides, only 10 nuclei have both their neutron and proton shells filled. Of those, ⁷⁸ Ni and ⁴⁸ Ni are the most exotic, the least stable, and the most difficult to observe. Scientists at the National Superconducting Cyclotron Laboratory at Michigan State University have now culled 11 specimens of ⁷⁸ Ni from the debris of trillions of medium-energy nuclear collisions. From those events they deduced a lifetime of 110 milliseconds—some 2–4 times shorter than previous theoretical estimates. Lifetimes were also determined for the neighboring isotopes of ⁷⁷ Ni, ⁷⁶ Ni, and ⁷⁵ Ni. The new result has implications for the astrophysical rapid neutron-capture process, known as the r-process, whereby elements heavier than iron are produced. (For more on the r-process, see the article in October 2004, page 47 ) Indeed, the shorter-than-expected lifetime of ⁷⁸ Ni means that the rapid nucleosynthesis is further accelerated. (P. T. Hosmer et al., Phys. Rev. Lett. 94, 112501, 2005 http://dx.doi.org/10.1103/PhysRevLett.94.112501 .)