New isotope ${}^{286}\mathrm{Mc}$ produced in the ${}^{243}\mathrm{Am}+{}^{48}\mathrm{Ca}$ reaction

In this paper, we present results of the second experiment on the synthesis of Mc isotopes in the ${}^{243}\mathrm{Am}+{}^{48}\mathrm{Ca}$ reaction performed at the gas-filled separator DGFRS-2 of the SHE Factory at JINR. The new isotope ${}^{286}\mathrm{Mc}$ was synthesized, and its half-life of $20\begin{array}{c}+98\\ -9\end{array}$ ms and α-particle energy of $10.71\pm 0.02$ MeV were determined. A ${}^{286}\mathrm{Mc} \alpha \text{−}\mathrm{decay}$ chain was recorded down to the spontaneous fission of ${}^{266}\mathrm{Db}$. The spontaneous fission of ${}^{279}\mathrm{Rg}$ was observed for the first time in one of four new decay chains of ${}^{287}\mathrm{Mc}$. The excitation function of the reaction was measured at three ${}^{48}\mathrm{Ca}$ energies of 242, 250, and 259 MeV; the latter resulted in the first observation of the $5n\text{−}\mathrm{evaporation}$ channel with a cross section of $0.5_{-0.4}^{+1.3}$ pb. The decay properties of 21 previously known $\mathrm{odd}\text{−}Z$ isotopes were improved. The potential for an electron-capture decay mode is discussed for ${}^{288}\mathrm{Mc}$ and ${}^{284}\mathrm{Nh}$ isotopes. The half-lives of spontaneously fissioning nuclei produced in the ${}^{48}\mathrm{Ca}\text{−}\mathrm{induced}$ reactions with actinide targets are compared with several theoretical predictions.

Figure 1

Alpha-particle energy spectra for ${}^{286-289}\mathrm{Mc}$ and descendant nuclei. The events observed in [3] and in this work as well as a summary of previously known and new data are shown by full (red) and open histograms, respectively. The $Y\text{−}\mathrm{axis}$ scale values begin at zero.

Figure 2

Cross sections for the $2n\text{−}, 3n\text{−}, 4n\text{−}$, and $5n\text{−}\mathrm{evaporation}$ channels for the ${}^{243}\mathrm{Am}+{}^{48}\mathrm{Ca}$ reaction. Vertical error bars correspond to total uncertainties. Symbols with arrows show upper cross-section limits. Data are shown by open (from Ref. [14]), half-closed (from Ref. [4]), and closed symbols (from Ref. [3] and this work). The cross sections of nuclei observed at BGS at $E^{*}=36$ MeV [13] and assigned by us to the $2n\text{−}$ and $3n\text{−}\mathrm{evaporation}$ channels, are specified arbitrarily (see the text). The dashed lines through the data are drawn to guide the eye.

Figure 3

Common logarithm of partial spontaneous fission half-life $\left[\mathrm{lo}{\mathrm{g}}_{10}\left(T_{\mathrm{SF}}\left[\mathrm{s}\right]\right)\right]$ vs neutron number for isotopes of elements with $Z=100-114$. The area of half-lives of even-even isotopes with $Z=104-110, N=160–164$ and $Z=110–114, N=164–177$ predicted in [43] is highlighted in gray. Partial half-lives of nuclei produced in the ${}^{48}\mathrm{Ca}\text{−}\mathrm{induced}$ reactions with actinide targets are shown by filled symbols.