Jaschek and Malaroda1 identified lines of gold and uranium in the peculiar A star 73 Draconis. According to Van den Heuvel's concept2, the peculiar A-type stars were secondaries in binary systems in which the primaries exploded as supernovae. The surface material in 73 Dra may thus be regarded as having been transferred from a massive primary in which it had been subjected to rapid neutron capture. All the elements up to fermium might have been produced in the r process, but they would have decayed rapidly, and after about 104 yr only the three most long-lived heavy elements would have survived: Pu, U, and Th. Now provided a sufficiently high neutron flux was available in the primary during the r process, all the heavy elements with Z ≤ 100 might have been produced in comparable amounts. With the very short lifetimes of the transplutonium elements, this leads to a temporary accumulation of Pu in the time interval between 103 and 108 yr after the nucleosynthesis in the r process had occurred. Even if U and Pu are produced in comparable amounts, the abundance of plutonium exceeds the uranium abundance during the first 105 yr after synthesis by about one order of magnitude, and after 107 yr the U/Pu ratio is approximately 8/3 (provided all nuclides with mass numbers from 233 up to 253 were produced initially in equal numbers, which seems to be a reasonable assumption). This is because plutonium has three relatively long-lived isotopes (with half-lives of 2.4 × 104 yr, 3.8 × 105 yr, and 7.6 × 107 yr).
Jaschek, M., and Malaroda, S., Nature, 225, 246 (1970).
Van den Heuvel, E. P. J., Bull. Astron. Inst. Netherlands, 19, 11 (1967).
Kuba, J., et al., Koinzidenz-Tabellen der Atom-Spektroskopie (Tschech. Akad. Wiss., Prague, 1964).
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KUCHOWICZ, B. Search for Plutonium Lines in 73 Dra and Other Ap Stars. Nature 227, 156 (1970). https://doi.org/10.1038/227156a0
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