Lifetimes of the 12+[631]→52+[622] E2 transitions in some actinide nuclei

Lifetimes of the E2 transitions from the 1/2 + [631] state to the 52+[622] state have been measured in several actinide nuclei using pulsed beam and delayed coincidence techniques. The 1/2 + [631] level was excited in U239 and Pu243 by the (d, t) reaction and in Pu241 by the (d, t) reaction, and the subsequent γ-ray decay to the 52+[622] level was observed between beam pulses. The corresponding E2 transitions were observed in Cm243 and Cm245 from the radioactive decay of Bk243 and Bk245, respectively, and the lifetimes were determined from electron-photon delayed coincidence experiments. The half-lives from these measurements are: U239 (0.78±0.04 μs); Pu241 (0.88±0.05 μs); Pu243 (0.33±0.03 μs); Cm243 (1.08±0.03 μs); and Cm245 (0.29±0.02 μs). Comparisons are made between the experimental transition probabilities and theoretical estimates. The differences between the transition rates in these nuclei are understood when pairing interactions are taken into account. NUCLEAR REACTIONS U238(d, pγ), Ed=12 MeV; Pu242(d, pγ) and Pu242(d, tγ), Ed=16 MeV; measured t12 of 133.7-, 161.4-, and 384.0-keV levels in U239, Pu241, and Pu243, respectively. Deduced B(E2) values. Enriched targets. RADIOACTIVITY Bk243 [from Am241(α, 2n)] and Bk245 [from Am243(α, 2n)]; measured Eγ, Ece, t12 of 87.4-keV level in Cm243 by K x-ray-ce delayed coin; measured t12 of 355.7-keV level in Cm245 by γ-ce delayed coin. Deduced B(E2) values. Mass-separated sources.