Confirmation of the new isotope ${}^{178}\mathrm{Pb}$

The extremely neutron-deficient isotope ${}^{178}\mathrm{Pb}$ has been produced. The GREAT spectrometer at the focal plane position of the gas-filled separator RITU was used to study the $\alpha$ decay of ${}^{178}\mathrm{Pb}$ and its $\alpha$-decay chain through $\alpha \text{−}\alpha$ correlations. The $\alpha$ decay was measured to have an energy and half-life of $E_{\alpha }$= 7610(30) keV and $t_{1/2}=0.{21}_{-0.08}^{+0.21}$ ms, respectively. The half-life is consistent with recent theoretical calculations using the Coulomb and proximity potential model. The $\alpha$-decay reduced width and hindrance factor for ${}^{178}\mathrm{Pb}$ were deduced and correspond to an unhindered $\mathrm{\Delta }l$ = 0 transition. In addition, the mass excess of ${}^{178}\mathrm{Pb}$ and the $\alpha$-decay $Q$ value were calculated from the experimental results and compared to theoretical values.

Figure 1

(a) A matrix of parent and child $\alpha$-particle energies. Maximum searching times of 5 and 50 ms were used for recoil-parent pairs and parent-child pairs, respectively. The letter $\omega$ represents an unidentified $\alpha$ particle with an energy and half-life of $E_{\alpha }=7700$ keV and $t_{1/2}\simeq 4$ ms; (b) overlay of the $\alpha$-decay spectra within a 5-ms correlation time, where the black line shows the real correlation and the shaded spectrum (blue color) represents the random correlations (see text for details).

Figure 2

$\alpha$-decay chains of ${}^{178}\mathrm{Pb}$. The word escape above the arrows corresponds to only part of the $\alpha$-particle energy being deposited in the DSSD, while $E_{\alpha }$ and $\mathrm{\Delta }t$ represent the $\alpha$-particle energy detected only in the DSSD and the time difference between each generation in the chains, respectively.

Figure 3

Time spectrum of the ${}^{178}\mathrm{Pb}$ $\alpha$ decay, which shows the logarithm of the time difference ln($dt$) between the implanted recoil and $\alpha$ decay of ${}^{178}\mathrm{Pb}$ within a 5 ms correlation-searching time. The red line is a plotted distribution described in Ref. [25] using decay constant value from the maximum-likelihood method.

Figure 4

(a) Logarithmic experimental spectroscopic-factor log ${}_{10}\left[S^{\exp }\right]$ for even-$A$ lead isotopes. The theoretical $\alpha$-decay half-life values were obtained from Refs. [8, 27] using the CCPM, the GLDM models, and Rasmussen method, respectively; (b) $\alpha$-decay reduced-width values as function of neutron number for even-$A$ lead, mercury, and platinum nuclei. The experimental values of the Pb isotopes in both panels (a) and (b) are obtained from Refs. [5, 28, 29, 30, 31, 32, 33, 34], while the experimental values used in Hg and Pt reduced-width calculation were obtained from ENSDF [35].

Figure 5

The $\alpha$-decay $Q$ values as a function of the neutron number for different lead isotopes. The filled triangles represent the experimental values including the ${}^{178}\mathrm{Pb}$ $Q$ value from this work. The filled squares and circles show the values obtained from Möller et al. [36] and Santhosh et al. [8], respectively.