In 1977 at Rice University Clayton had been named Co-Investigator for the NASA-approved proposal for the OSSE spectrometer on Compton, and in 1982 he summarized physical expectations for several gamma-ray-line emitting young nuclei. Key to the intense supernova radioactivity had been Clayton's 1967 discovery that rapid-silicon-burning was dominated by abundances of radioactive alpha-particle nuclei (those having equal numbers of protons and neutronsPrinciples of Stellar Evolution and Nucleosynthesis, Chap. 7 (1968)). Clayton has quipped that SN explosions are "the largest nuclear accidents of all time". Supernova 1987A ejected 20,000 times the mass of the earthDonald D. Clayton, Handbook of Isotopes in the Cosmos, p. 256 (iUniverse, New York, 2009) as pure radioactive 56Ni nuclei! Abundant iron of our world was demonstrated to be a daughter of radioactive nickel, the most important of the radioactive nuclei. Modern studies of supernovae are dominated by their intensely radioactive natures. Spacetime data for cosmology relies on 56Ni radioactivity providing the energy for the optical brightness of supernovae of Type Ia, which are the "standard candles" of cosmology but whose diagnostic 847keV and 1238keV gamma rays were first detected only in 2014, fully 47 years after Clayton's prediction of their emission by supernovae. Clayton's work earned for him NASA's 1992 Exceptional Scientific Achievement Award and in the same year the NASA Public Service Group Achievement Award for the OSSE Spectrometer on the Compton Gamma Ray Observatory. Both the OSSE instrument and the Comptel instrument confirmed predictions."The 57Co Abundance in Supernova 1987A", Astrophys. J. (Lett.), 399, L141-L144 (1992) Clayton had previously attempted to establish gamma-ray-line astronomy from r process radioactive nuclei; but r-process nuclei are much less abundant in supernovae than are the nuclei fused during silicon-burning. So it was the latter that became the demonstrated source of radioactive nuclei. Chapters 8, 11, 17 and 18 in Catch a Falling Star, whose title Clayton has said he chose as an allusion to the gravitational core collapse that triggers these supernovae.
