Octupole deformation in226Th

Abstract

Sources of ${}^{230}\mathrm{U}$ were prepared using the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of ${}^{230}\mathrm{Pa}$ produced in the reaction ${}^{232}\mathrm{Th}$ $(p,3n)$ with 34-MeV protons. These sources were used to determine the half-life of the ${1}^{\ensuremath{-}}$ state at 230.4 keV in ${}^{226}\mathrm{Th}$ using the Doppler shift method following \ensuremath{\alpha} decay of ${}^{230}\mathrm{U}$. An average value of the half-life of 3.5\ifmmode\pm\else\textpm\fi{}1.2 ps was observed. The half-life of the 226.4-keV ${4}^{+}$ state in ${}^{226}\mathrm{Th}$ was also measured to be 145\ifmmode\pm\else\textpm\fi{}20 ps. The absolute transition probabilities in Weisskopf units of the 230- and 158-keV transitions depopulating the ${1}^{\ensuremath{-}}$ state were determined as (2.50\ifmmode\pm\else\textpm\fi{}0.86)$\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ and (4.54\ifmmode\pm\else\textpm\fi{}1.55)$\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, respectively. These experimental values are compared with experimental values of ${}^{223}\mathrm{Ra}$ and theoretical calculations. Finally, experimental values of the intrinsic dipole moment ${D}_{0}$ and the ratio of the intrinsic dipole moment to the intrinsic quadrupole moment ${D}_{0}{/Q}_{0}$ were determined as 0.27\ifmmode\pm\else\textpm\fi{}0.05 $e$ fm and (3.5\ifmmode\pm\else\textpm\fi{}1.0)$\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{fm}}^{\ensuremath{-}1}$ respectively, and compared with various theories and experiments.