$\alpha$-decay properties of ${}^{220}\mathrm{Pa}$

The isotope ${}^{220}\mathrm{Pa}$ produced in the reaction ${}^{40}\mathrm{Ar}+{}^{187}\mathrm{Re}$ at a beam energy of 198.7 MeV was reinvestigated via the $\alpha$-spectroscopic method. A new $\alpha$-decaying state in ${}^{220}\mathrm{Pa}$ has been observed with an energy $E_{\alpha }=9664\left(40\right)\mathrm{keV}$ and with a half-life $T_{1/2}={233}_{-56}^{+108}\mathrm{ns}$. The spin parity of the state is tentatively suggested to be ($3^{-}$). The $\alpha$ energy and half-life of the ($1^{-}$) ground state are measured to be $E_{\alpha }=9548\left(30\right)\mathrm{keV}$ and $T_{1/2}=0.75\left(8\right)\mu \mathrm{s}$, respectively. The reduced $\alpha$ width, inferred from the present data, fits well into the systematics for $N=129$ isotones.

Figure 1

Energy spectra from the PSSDs. Panels (a) and (b) show the energies of the first ($\alpha 1$) and second ($\alpha 2$) decays when it is required that the decays occur following an implant in the same place (a vertical position window of $\pm 1.5\mathrm{mm}$) and that $\alpha 1$ occurs within $4.5\mu \mathrm{s}$ of ER, preceding the $\alpha 2$ lines with the energy range of 8940–9160 keV, and $\alpha 2$ occurs within 2 ms of $\alpha 1$, respectively. The values written vertically on the panels give the energies associated with the centroids. The newly observed events from ${}^{220}\mathrm{Pa}$ are labeled by the blue dotted ellipse.

Figure 2

$\alpha$-decay energies $Q_{\alpha }$ of g.s.-to-g.s. transitions for the neutron-deficient Pa isotopes. The black solid circles represent literature values taken from Ref. [12]. The red solid circle refers to the value of ${}^{220}\mathrm{Pa}$ measured in the present paper, compared to the values deduced from Faestermann et al. [1], Miyatake et al. [2], and Huang et al. [3]. The dashed line refers to the theoretical predictions taken from Bao et al. [8].

Figure 3

The distributions of time differences between successive events in the PSSDs. Panels (a) and (b) show the time differences between the implanted recoil (ER) and the first decay ($\alpha 1$). Panel (c) shows the time differences between the first decay ($\alpha 1$) and the second decay ($\alpha 2$). The dotted lines are fitted decay curves as defined in Ref. [9].

Figure 4

Systematics of the reduced $\alpha$ widths for the $N=129$. The black solid square refer to the ${\delta }^2$ values were deduced from Refs. [5, 12]. The red solid square refers to the value of ${}^{220}\mathrm{Pa}$ measured in the present paper, compared to the values deduced from Faestermann et al. [1], Miyatake et al. [2], and Huang et al. [3].

Figure 5

Scheme of the $\alpha$-decay chain from ${}^{220}\mathrm{Pa}$ to ${}^{212}\mathrm{Fr}$ resulting from the current paper $\alpha$-decay energies, and energies of excited levels are in keV.