Figure 1

(a) A part of the correlated ${\alpha }_1$-energy spectrum for the reaction ${}^{56}\mathrm{Fe}$(259 MeV) $+{}^{141}\mathrm{Pr}\to {}^{194}\mathrm{At}{}^{*}$ registered in the PSSD within 1500 ms after the recoil implantation. The positions of the known $\alpha$-decay lines from ${}^{193,195}\mathrm{At}$ are marked by arrows. $\alpha$-decay energies are given in keV. (b) The $E_{\alpha 1}\text{−}{E}_{\gamma }$ spectrum for ${\alpha }_1$ events from (a) in coincidence with $\gamma$ rays within the TAC time interval $0<\Delta T({\alpha }_1\text{−}\gamma )⩽5$ μs. Some $\gamma$-ray groups are indicated with their energies in keV. (c) The two-dimensional $E_{\alpha 1}\text{−}{E}_{\alpha 2}$ plot for $\Delta T(\mathrm{recoil}\text{−}{\alpha }_1)⩽1500$ ms and $\Delta T({\alpha }_1\text{−}{\alpha }_2)⩽15$ s. Rectangles “A” and “B” denote the regions of correlations of ${}^{194}\mathrm{At}$ with the “main”; 6456-keV $\alpha$ decay of ${}^{188}\mathrm{Bi}{}^{m1}$ and with the main 6431-keV $\alpha$ decay of ${}^{188}\mathrm{Bi}{}^{m2}$, respectively. (d) The ${\alpha }_1$-energy spectrum for the region “A” of (c). (e) The ${\alpha }_1$-energy spectrum for the region “B” of (c).Reuse & Permissions

Figure 2

(a) Expanded $E_{\alpha 1}\text{−}{E}_{\gamma }$ spectrum from the recoil-[${\alpha }_1\text{−}\gamma$] analysis from Fig. 1b with a condition $\Delta T({\alpha }_1\text{−}\gamma )⩽5\hspace{0.5em}\mu$s. $\gamma$-ray groups are indicated with their energies in keV. The decay events of ${}^{193,195}\mathrm{At}$ are marked by the ovals. For the regions denoted by the rectangles the time distributions $\Delta T({\alpha }_1\text{−}\gamma$) are shown in Fig. 4. (b) Projection on the $E_{\gamma }$ axis of the events from panel (a).Reuse & Permissions

Figure 3

Time difference $\Delta T(\mathrm{recoil}\text{−}[{\alpha }_1\text{−}{\alpha }_2$]) for events from the regions “1A” and “1B” of Fig. 1c with the condition of $E_{\alpha 2}⩾7050$ keV. The ${\alpha }_2$(6431 keV)-γ(294 keV) coincident events have been used to produce the decay curve for ${}^{194}\mathrm{At}{}^{m2}$; see text for details. The data and the exponential fits are shown by the symbols and solid lines, respectively.Reuse & Permissions

Figure 4

The time difference $\Delta T(\alpha \text{−}\gamma$) between the coincident $\alpha$ and $\gamma$ decays from recoil-[${\alpha }_1\text{−}\gamma$] analysis (see text for details). (a) $\alpha$(6431 keV)-γ(294 keV) decay of ${}^{190}\mathrm{Bi}{}^{m2}$. The definitions of the “prompt” and “delayed” time windows are shown (see text for details); (b) 76-keV $E1$ decay in ${}^{190}\mathrm{Bi}$, an exponential fit is shown by the solid line. (c) $K_{\beta }$ Bi x rays; (d) 46.5-keV $M1$ decay in ${}^{190}\mathrm{Bi}$; (e) 40.3-keV decay in ${}^{190}\mathrm{Bi}$.Reuse & Permissions

Figure 5

Recoil-${\alpha }_1\text{−}{\alpha }_2$ and recoil-[${\alpha }_1\text{−}\gamma ]\text{−}{\alpha }_2$ analysis for ${}^{194}\mathrm{At}{}^{m2}$ (left column) and ${}^{194}\mathrm{At}{}^{m1}$ (right column). [(a) and (g)] ${\alpha }_1$ spectra from recoil-${\alpha }_1\text{−}{\alpha }_2$ analysis [the copies of Figs. 1e and (d), respectively]. [(b) and (h)] 2D ${\alpha }_1\text{−}\gamma$ spectra within the prompt coincidence time $\Delta T({\alpha }_1\text{−}\gamma )\hspace{0.5em}⩽1450$ ns. For the regions denoted by rectangles the projections on the $E_{\alpha 1}$ axis are shown in the following panels. [(c) and (i)] Projections on the $E_{\alpha 1}$ axis of events in prompt coincidence with the 76-keV $\gamma$ rays. [(d) and (j)] Projections on the $E_{\alpha 1}$ axis of events in prompt coincidence with the 46.5- and 40.3-keV $\gamma$ rays, respectively. Panels (e)/(f) and (k)/(l) show the delayed spectra for ${}^{194}\mathrm{At}{}^{m1,m2}$ within the time interval of 1450 $\mathrm{ns}⩽\Delta T({\alpha }_1\text{−}\gamma )⩽5000$ ns. See the main text for details.Reuse & Permissions

Figure 6

(a) Projection on the $E_{\gamma }$ axis of all prompt coincident events from Fig. 5b. (b) The same for events from Fig. 5h. Some $\gamma$-ray groups are indicated with their energies in keV.Reuse & Permissions

Figure 7

Decay schemes of the ${}^{194}\mathrm{At}{}^{m1,m2}$ isomers deduced in our work. Shown are isomer assignments, $\alpha$-decay energies $E_{\alpha }$, relative intensities $I_{\alpha }$, reduced $\alpha$ widths ${\delta }_{\alpha }^2$, and hindrance factors ${\mathrm{HF}}_{\alpha }$, energies and multipolarities of coincident $\gamma$ rays (if known). The $\gamma$-ray energy uncertainty is 0.5 keV. The reduced $\alpha$-decay widths were calculated with the Rasmussen prescription [30] by assuming $\Delta L=0$ decays. The ${\mathrm{HF}}_{\alpha }$ values were calculated relative to the strongest $\alpha$ decay within each isomer, for which ${\mathrm{HF}}_{\alpha }=1$ was assumed. The panels to the extreme left and right show simplified level sequences and unhindered $\Delta L=0\hspace{0.5em}\hspace{0.5em}\alpha$ decays of the neighboring odd-$A$ isotopes ${}^{193,195}\mathrm{At}$ to the states in the respective daughter nuclides ${}^{189,191}\mathrm{Bi}$, modified from Refs. [21, 22]. Simplified decay schemes of ${}^{190}\mathrm{Bi}{}^{m1,m2}$ are taken from Refs. [8, 10]. All spin and parity assignments shown in the figure are tentative and are based on systematics and $\alpha$-decay and in-beam studies.Reuse & Permissions