$\alpha$-decay chain of the short-lived isotope ${}^{220}\mathbf{Pa}$ established using a digital pulse processing technique

The decay properties of the short-lived isotope ${}^{220}\mathrm{Pa}$ were re-investigated via the reaction ${}^{40}\mathrm{Ar}+{}^{187}\mathrm{Re}$ at the gas-filled recoil separator Spectrometer for Heavy Atoms and Nuclear Structure. The digital pulse processing technique was applied to resolve the evaporation residues–$\alpha$ ($\mathrm{ER}-\alpha$) pileup signals in the decay of ${}^{220}\mathrm{Pa}$. The $\alpha$-decay chain of ${}^{220}\mathrm{Pa}$ leading to the well-known ${}^{216}\mathrm{Ac}$ isotope was established for the first time. The $\alpha$ energy and half-life were measured to be $E_{\alpha }=9.520\left(16\right)\mathrm{MeV}$ and $T_{1/2}=0.90\left(13\right)\mu \mathrm{s}$, respectively. The spin parity of the ground state of ${}^{220}\mathrm{Pa}$ was assigned to be $1^{-}$, based on the reduced $\alpha$-decay width.

Figure 1

Correlations between the $\alpha$-particle energies of parent and daughter nuclei. The time window is set as 10 $\mu \mathrm{s}$ for ER $\to {\alpha }_1$, the first generation decay, and 15 ms for ${\alpha }_1\to {\alpha }_2$, the second generation decay.

Figure 2

The decay spectra of ${}^{216}\mathrm{Ac}$ and ${}^{220}\mathrm{Pa}$ measured in the present work.

Figure 3

An example of pileup trace where ${}^{220}\mathrm{Pa}$ was registered.

Figure 4

The reduced $\alpha$-decay widths for the g.s. to g.s. decay of neutron-deficient $N=129$ isotones. The new data (solid symbol) of ${}^{220}\mathrm{Pa}$ is compared with those extracted from Faestermann's experimental results (triangle) [1] and the RIKEN results (circle) [2].