Synthesis and decay properties of isotopes of element 110: ${}^{273}\mathrm{Ds}$ and ${}^{275}\mathrm{Ds}$

The ${}^{232}\mathrm{Th}$(${}^{48}\mathrm{Ca},5n$)${}^{275}\mathrm{Ds}$ and ${}^{238}\mathrm{U}$(${}^{40}\mathrm{Ar},5n$)${}^{273}\mathrm{Ds}$ reactions have been studied at the gas-filled separator DGFRS-2 at the Superheavy Element Factory at Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research. For the first time, a new isotope ${}^{275}\mathrm{Ds}$ with a half-life of $0.{43}_{-0.12}^{+0.29}$ ms and α-particle energy of $11.20\pm 0.02$ MeV was synthesized in the ${}^{48}\mathrm{Ca}$-induced reaction with the actinide nucleus and identified by measuring correlated α decays ending in known nuclei. The decay properties of nuclei originating from ${}^{273}\mathrm{Ds}$ and ${}^{275}\mathrm{Ds}$ are compared with theoretical calculations and decay schemes are proposed. The cross sections of the ${}^{232}\mathrm{Th}$(${}^{48}\mathrm{Ca},5n$)${}^{275}\mathrm{Ds}$ reaction of $0.{11}_{-0.09}^{+0.46}$ and $0.{34}_{-0.16}^{+0.59}$ pb were measured at excitation energies of the ${}^{280}\mathrm{Ds}$ compound nucleus $E^{*}=51$ and 56 MeV, respectively. The cross section of the $5n$-evaporation channel of the ${}^{238}\mathrm{U}+{}^{40}\mathrm{Ar}$ reaction at $E^{*}=49$ MeV of $0.{18}_{-0.12}^{+0.44}$ pb turned out to be comparable to that for ${}^{275}\mathrm{Ds}$ at close excitation energy.

Figure 1

Decay chains originating from ${}^{275}\mathrm{Ds}$ observed in the ${}^{232}\mathrm{Th}+{}^{48}\mathrm{Ca}$ reaction at the projectile energies $E1$ = 250.6 MeV and $E$2 = 257.0 MeV. The rows on the right side show evaporation residue (ER, blank square) energies and vertical and horizontal positions on the detector (in mm). The left rows provide the α particle [in yellow (light gray)] and SF [in green (dark gray)] energies and time intervals between the events. The energies of the summed signals are given in parentheses. The events marked with a shadow were registered during the beam-off periods (see Refs. [1, 2, 6, 7, 8, 9] for details). The α-particle energy errors are shown by smaller italic numbers. The probabilities of random origin of two events $P_{\mathrm{ran}}$ are shown; these particles escaped the focal detector, leaving low energy in it, but did not enter the side detector.

Figure 2

A proposed experimental and calculated decay scheme for ${}^{275}\mathrm{Ds}$ based on present and previously published data [10]. Alpha or γ transitions to approximate one-quasiparticle states and SF decays are shown by red (solid), blue (dashed), and green (dotted) lines, respectively. Alpha-decay energies ($Q_{\alpha }$) and half-lives are provided for states decaying by α decay ($T_{\alpha }$) or spontaneous fission ($T_{\mathrm{SF}}$). Hindrance factors $\mathit{HF}$ = $T$ $\begin{array}{c}\exp \\ 1/2\end{array}$ / $T$ $\begin{array}{c}\mathrm{calc}\\ 1/2\end{array}$ were derived from experimental and calculated half-lives according to Refs. [16, 17, 20, 21, 22] (see text). Population probabilities $P$ of energy levels for ${}^{271}\mathrm{Hs}$ are based on experimental data [10] and this paper.

Figure 3

The same as in Fig. 1, but for ${}^{273}\mathrm{Ds}$ observed in the ${}^{238}\mathrm{U}+{}^{40}\mathrm{Ar}$ reaction at the projectile energy of 212.2 MeV. The time interval for an α particle with $E_{\alpha }=8.397$ MeV following a “missing α” was measured from a preceding α decay with $E_{\alpha }=11.017$ MeV and is shown in italic.

Figure 4

Alpha-particle energy spectra for ${}^{273}\mathrm{Ds}$ and ${}^{269}\mathrm{Hs}$ observed in Refs. [10, 26, 27] and in this paper (only $E_{\alpha }=11.017$ MeV for ${}^{273}\mathrm{Ds}$ is given). The events observed for ${}^{269}\mathrm{Hs}$ after α decay of ${}^{273}\mathrm{Ds}$ in Refs. [26, 27] as well as a summary of known data are shown by full (blue) and open histograms, respectively.

Figure 5

The one-quasiparticle states and decay patterns for nuclei in the α-decay chain starting from ${}^{273}\mathrm{Ds}$.

Figure 6

Cross sections for the $3n$- to $5n$-evaporation channels for the ${}^{232}\mathrm{Th}+{}^{48}\mathrm{Ca}$ (closed symbols, Ref. [1] and this paper) and ${}^{238}\mathrm{U}+{}^{40}\mathrm{Ar}$ (open symbols, this paper) reactions. Vertical error bars correspond to total uncertainties. The symbols with arrows show the upper cross-section limits. The dashed lines through the data are drawn to guide the eye. The Bass barriers [36] are shown by open arrows for comparison.

Figure 7

Partial half-lives $T_{\alpha }$ vs neutron number for the isotopes of Ds. The results from the cold-fusion and ${}^{48}\mathrm{Ca}$-induced reactions are shown by black circles and blue squares, respectively; the results for ${}^{276}\mathrm{Ds}$ [1] and ${}^{275}\mathrm{Ds}$ from this paper are shown by red diamonds. The results of calculations [42] are shown by open circles connected by lines.