Combined Th/U/Pu Date of Supernova Explosion
Rapid neutron capture in the supernova at the birth of the solar system made U-238 (half-life = 4468 million yr) and Pu-244 (half-life = 81 million yr) which decayed away 55 times faster. Neither can be made by particle irradiation in the solar nebula. Kuroda and Myers combined Th,U,Pu age dating to show that a supernova made our actinide elements about 5 billion years ago [See Fig. 1, p. 173 of Radiochimica Acta 64 (1994) 167-174].