Lifetime measurements of first excited states inC16,18

Physical Review C2008Vol. 78(1)

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Abstract

The electric quadrupole transition from the first ${2}^{+}$ state to the ground ${0}^{+}$ state in $^{18}\mathrm{C}$ was studied through a lifetime measurement by an upgraded recoil shadow method applied to inelastically scattered radioactive $^{18}\mathrm{C}$ nuclei. The measured mean lifetime is $18.9\ifmmode\pm\else\textpm\fi{}0.9(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}4.4(\mathrm{syst})$ ps, corresponding to a $B$($E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{\mathrm{g}.\mathrm{s}.}^{+}$) value of $4.3\ifmmode\pm\else\textpm\fi{}0.2\ifmmode\pm\else\textpm\fi{}1.0 {e}^{2}$ fm${}^{4}$, or about 1.5 Weisskopf units. The mean lifetime of the first ${2}^{+}$ state in $^{16}\mathrm{C}$ was remeasured to be $18.3\ifmmode\pm\else\textpm\fi{}1.4\ifmmode\pm\else\textpm\fi{}4.8$ ps, about four times shorter than the value reported previously. The discrepancy between the two results was explained by incorporating the \ensuremath{\gamma}-ray angular distribution measured in this work into the previous measurement. These transition strengths are hindered compared to the empirical transition strengths, indicating that the anomalous hindrance observed in $^{16}\mathrm{C}$ persists in $^{18}\mathrm{C}$.

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Abstract

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