Lifetimes of the12+[631]→52+[622]E2transitions in some actinide nuclei

Abstract

Lifetimes of the $E2$ transitions from the \textonehalf{} + [631] state to the $\frac{5}{2}+[622]$ state have been measured in several actinide nuclei using pulsed beam and delayed coincidence techniques. The \textonehalf{} + [631] level was excited in $^{239}\mathrm{U}$ and $^{243}\mathrm{Pu}$ by the ($d, t$) reaction and in $^{241}\mathrm{Pu}$ by the ($d, t$) reaction, and the subsequent $\ensuremath{\gamma}$-ray decay to the $\frac{5}{2}+[622]$ level was observed between beam pulses. The corresponding $E2$ transitions were observed in $^{243}\mathrm{Cm}$ and $^{245}\mathrm{Cm}$ from the radioactive decay of $^{243}\mathrm{Bk}$ and $^{245}\mathrm{Bk}$, respectively, and the lifetimes were determined from electron-photon delayed coincidence experiments. The half-lives from these measurements are: $^{239}\mathrm{U}$ (0.78\ifmmode\pm\else\textpm\fi{}0.04 \ensuremath{\mu}s); $^{241}\mathrm{Pu}$ (0.88\ifmmode\pm\else\textpm\fi{}0.05 \ensuremath{\mu}s); $^{243}\mathrm{Pu}$ (0.33\ifmmode\pm\else\textpm\fi{}0.03 \ensuremath{\mu}s); $^{243}\mathrm{Cm}$ (1.08\ifmmode\pm\else\textpm\fi{}0.03 \ensuremath{\mu}s); and $^{245}\mathrm{Cm}$ (0.29\ifmmode\pm\else\textpm\fi{}0.02 \ensuremath{\mu}s). 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 $^{238}\mathrm{U}(d, p\ensuremath{\gamma})$, ${E}_{d}=12$ MeV; $^{242}\mathrm{Pu}(d, p\ensuremath{\gamma})$ and $^{242}\mathrm{Pu}(d, t\ensuremath{\gamma})$, ${E}_{d}=16$ MeV; measured ${t}_{\frac{1}{2}}$ of 133.7-, 161.4-, and 384.0-keV levels in $^{239}\mathrm{U}$, $^{241}\mathrm{Pu}$, and $^{243}\mathrm{Pu}$, respectively. Deduced $B(E2)$ values. Enriched targets.RADIOACTIVITY $^{243}\mathrm{Bk}$ [from $^{241}\mathrm{Am}(\ensuremath{\alpha}, 2n)$] and $^{245}\mathrm{Bk}$ [from $^{243}\mathrm{Am}(\ensuremath{\alpha}, 2n)$]; measured ${E}_{\ensuremath{\gamma}}$, ${E}_{\mathrm{ce}}$, ${t}_{\frac{1}{2}}$ of 87.4-keV level in $^{243}\mathrm{Cm}$ by $K$ x-ray-ce delayed coin; measured ${t}_{\frac{1}{2}}$ of 355.7-keV level in $^{245}\mathrm{Cm}$ by $\ensuremath{\gamma}$-ce delayed coin. Deduced $B(E2)$ values. Mass-separated sources.