In-flight fast-timing measurements in ${}^{152}\mathrm{Sm}$

We report on the first application of in-flight fast-timing measurements, a method developed in order to directly measure lifetimes in the picosecond to nanosecond range. As a proof of principle of the method, lifetimes of the states belonging to the ground-state band in ${}^{152}\mathrm{Sm}$ are measured up to the 8${}_1^{+}$ state. An excellent agreement with recommended values is found. A slightly improved determination of the spectroscopic quadrupole moment of the 4${}_1^{+}$ state is also reported. In-flight fast-timing measurements open interesting opportunities for future studies of collective properties in radioactive nuclei.

Figure 1

(a) Schematic view of the detection system at the target position (see text for details). (b) Identification plot of nuclei transmitted to the vamos focal plane. (c) and (d) Doppler-corrected $\gamma$ spectrum and $\gamma \gamma$ matrix for ${}^{152}\mathrm{Sm}$ measured in coincidence with ${}^{136}\mathrm{Xe}$ selected in vamos.

Figure 2

Decay patterns associated with the $4_1^{+}\to 2_1^{+}\to 0_1^{+}$ coincidence in ${}^{152}\mathrm{Sm}$ measured in flight and in coincidence with (a) ${}^{136}\mathrm{Xe}$ and (b) ${}^{152}\mathrm{Sm}$ selected in vamos. Raw data are shown as a set of open symbols. Filled symbols display the data corrected for geometrical detection efficiency variation. Curves are the result of least-square adjustments. The deduced half lives and reduced ${\chi }^2$, ${\chi }^2/ndf$, are reported.

Figure 3

(a) $\gamma \gamma$ matrix measured for a ${}^{60}\mathrm{Co}$ source located at the target position. (b) Doppler-corrected $\gamma \gamma$ matrix measured via Coulomb excitation of ${}^{172}\mathrm{Yb}$. (c)–(f) time distributions associated with $\gamma \gamma$ coincidences in ${}^{172}\mathrm{Yb}$ with $E2=537$ keV and, respectively, $E1=182$, 280, 372, and 458 keV. (g) Prompt position as a function of $\gamma$-ray energy determined from ${}^{60}\mathrm{Co}$ and ${}^{172}\mathrm{Yb}$ data. Error bars are smaller than the symbol for most of the points. The curve displays the result of least-square adjustment.

Figure 4

(a) Centroid of time distributions associated with $\gamma \gamma$ coincidences measured in ${}^{152}\mathrm{Sm}$ with $E2=484$ keV corresponding to the ${10}_1^{+}\to 8_1^{+}$ transition. The curve shows the prompt position. (b) Half lives of intermediate states in $\gamma \gamma$ coincidences measured in ${}^{152}\mathrm{Sm}$ (see Fig. 1). For clarity, the points at 244 keV and 340 keV are shifted from each others in the energy scale.