 The second-lightest such nucleus, palladium-110 (46 protons, 64 neutrons, neutron–proton ratio of 1.391), is much heavier.Thanks to the neutron excess, the resulting nuclei were expected to be heavier and closer to the sought-after island of stability.Of the aimed for 117 protons, calcium has 20, and thus they needed to use berkelium, which has 97 protons in its nucleus.