decays after the nucleosynthesis, is called a "secondary isotope". In interest of brevity, the next stage, an intricate photo-disintegration rearrangement, and the nuclear quasiequilibrium that it achieves, are referred to as silicon burning. The silicon burning in the star progresses through a temporal sequence of such nuclear quasiequilibria in which the abundance of Si slowly declines and that of Ni slowly increases. This amounts to a nuclear abundance change 2 Si ≫ Ni, which may be thought of as silicon burning into nickel (“burning” in the nuclear sense). The entire silicon-burning sequence lasts about one day in the core of a contracting massive star and stops after Ni has become the dominant abundance. The final explosive burning caused when the supernova shock passes through the silicon-burning shell lasts only seconds, but its roughly 50% increase in the temperature causes furious nuclear burning, which becomes the major contributor to nucleosynthesis in the mass range 28–60 . After the final Ni stage, the star can no longer release energy via nuclear fusion, because a nucleus with 56 nucleons has the lowest mass per nucleon of all the elements in the sequence. The next step up in the alpha-particle chain would be Zn. However Zn has slightly more mass per nucleon than Ni, and thus would require a thermodynamic energy loss rather than a gain as happened in all prior stages of nuclear burning. Ni (which has 28 protons) has a half-life of 6.02 days and decays via β decay to Co (27 protons), which in turn has a half-life of 77.3 days as it decays to Fe (26 protons). However, only minutes are available for the Ni to decay within the core of a massive star. This establishes Ni as the most abundant of the radioactive nuclei created in this way. Its radioactivity energizes the late supernova light curve and creates the pathbreaking opportunity for gamma-ray-line astronomy. See SN 1987A light curve for the aftermath of that opportunity. Clayton and Meyer have recently generalized this process still further by what they have named the secondary supernova machine, attributing the increasing radioactivity that energizes late supernova displays to the storage of increasing Coulomb energy within the quasiequilibrium nuclei called out above as the quasiequilibria shift from primarily Si to primarily Ni. The visible displays are powered by the decay of that excess Coulomb energy. During this phase of the core contraction, the potential