Some Remarks on the Discovery of ${}^{244}\mathrm{Md}$

In two recent papers by Pore et al. and Khuyagbaatar et al., discovery of the new isotope ${}^{244}\mathrm{Md}$ was reported. The decay data, however, are conflicting. While Pore et al. report two isomeric states decaying by $\alpha$ emission with $E_{\alpha }(1)=8.66(2)\mathrm{MeV}$, $T_{1/2}(1)={0.4}_{-0.1}^{+0.4}\mathrm{s}$ and $E_{\alpha }(2)=8.31(2)\mathrm{MeV}$, $T_{1/2}(2)\approx 6\mathrm{s}$, Khuyagbaatar et al. [Phys. Rev. Lett. 125, 142504 (2020).] report only a single transition with a broad energy distribution of $E_{\alpha }=(8.73–8.86)\mathrm{MeV}$ and $T_{1/2}={0.30}_{-0.09}^{+0.19}\mathrm{s}$. The data published in Pore et al. are very similar to those published for ${}^{245m}\mathrm{Md}$ [$E_{\alpha }=8.64(2)$, 8.68(2) MeV, $T_{1/2}={0.35}_{-0.16}^{+0.23}\mathrm{s}$ [V. Ninov, F. P. Heßberger, S. Hofmann, H. Folger, G. Münzenberg, P. Armbruster, A. V. Yeremin, A. G. Popeko, M. Leino, and S. Saro, Z. Phys. A 356, 11 (1996).] ]. Therefore, we compare the data presented for ${}^{244}\mathrm{Md}$ in Pore et al. with those reported for ${}^{245}\mathrm{Md}$ in Ninov et al. and also in Khuyagbaatar et al. We conclude that the data presented in Pore et al. shall be attributed to ${}^{245}\mathrm{Md}$ with small contributions (one event each) from ${}^{245}\mathrm{Fm}$ and probably ${}^{246}\mathrm{Md}$.

Figure 1

Summary of decays attributed to ${}^{245}\mathrm{Md}$ in Ref. [3] (squares) as well as in Ref. [2] (triangles) together with data reported by Pore et al. [1] [circles: events attributed to ${}^{245}\mathrm{Md}$ by the present authors, diamonds: events attributed to ${}^{245}\mathrm{Fm}$ or (tentatively) to ${}^{246}\mathrm{Md}$]. The dashed lines are to guide the eyes: the red lines represent the $\alpha$ energies given for ${}^{245}\mathrm{Md}$ (8640, 8680 keV) in Ref. [3] and the energy given for ${}^{244}\mathrm{Md}$ (8663 keV) in Ref. [1]; the blue lines represent the $\alpha$ energy for ${}^{241}\mathrm{Es}$ (8113 keV) given in Ref. [3] and the highest daughter energy (P5) in Ref. [1]; the purple line represents the literature value of the $\alpha$ energy of ${}^{241}\mathrm{Cf}$ (7335 keV) [6]. The orange hatched area marks the range of $\alpha$ energies where the events attributed to ${}^{244}\mathrm{Md}$ in Ref. [2] were observed.

Figure 2

Excitation function for ${}^{40}\mathrm{Ar}+{}^{209}\mathrm{Bi}$. The energies refer to production in the center of the target. The error bars for the energies refer to the energy loss of ${}^{40}\mathrm{Ar}$ ions in the bismuth targets [12]. Systematic errors in the accelerator energy are typically 0.2% for the UNILAC accelerator and are neglected. For the data of Pore et al. [1] an energy loss of $\approx 12.5\mathrm{MeV}$ in the titanium backing foil [12] is considered. No systematic error for the accelerator energy is given by Pore et al. Lines are the result of HIVAP [8] calculations; full lines represent $xn$ channels, dashed lines represent $pxn$ channels. Points are defined in the figure. The arrow marks the energy reported in Ref. [1] for the observation of ${}^{247}\mathrm{Md}$.