Detailed $\alpha$-decay study of ${}^{180}\mathrm{Tl}$

A detailed $\alpha$-decay spectroscopy study of ${}^{180}\mathrm{Tl}$ has been performed at ISOLDE (CERN). $Z$-selective ionization by the Resonance Ionization Laser Ion Source (RILIS) coupled to mass separation provided a high-purity beam of ${}^{180}\mathrm{Tl}$. Fine-structure $\alpha$ decays to excited levels in the daughter ${}^{176}\mathrm{Au}$ were identified and an $\alpha$-decay scheme of ${}^{180}\mathrm{Tl}$ was constructed based on an analysis of $\alpha -\gamma$ and $\alpha -\gamma -\gamma$ coincidences. Multipolarities of several $\gamma$-ray transitions deexciting levels in ${}^{176}\mathrm{Au}$ were determined. Based on the analysis of reduced $\alpha$-decay widths, it was found that all $\alpha$ decays are hindered, which signifies a change of configuration between the parent and all daughter states.

Figure 1

(a) All $\alpha$ decays registered in both silicon detectors at the implantation position. The strongest $\alpha$ decay of the low-spin state in ${}^{176}\mathrm{Au}$ at 6287(7) keV, marked with a plus sign, is taken from [17]. (b) $\alpha -\gamma$ coincidences for $\gamma$-ray energies in the range of 380–760 keV. (c) $\alpha -\gamma$ coincidences for $\gamma$-ray energies of 0–380 keV. For better presentation in (c), a smaller size of points was used and their density was decreased ($5\times$). Dotted blue diagonal lines enclose $\alpha -\gamma$ groups yielding the same total $Q_{\alpha ,\mathrm{tot}}=6702\left(7\right)$ keV as the 6553-keV $\alpha$ decay; see the main text. The dotted lines mark the region of $Q_{\alpha ,\mathrm{tot}}\pm 40$ keV. In (b) and (c), the labeled $\gamma$-ray transitions originate after $\alpha$ decays of ${}^{180}\mathrm{Tl}$ if not specified otherwise. The $\alpha -\gamma$ coincidences from ${}^{180}\mathrm{Hg}$ and ${}^{176}\mathrm{Au}$ (except for the 475-keV transition) were assigned based on published data [17, 18]. The transition marked with an asterisk is unassigned.

Figure 2

$\gamma$ rays in coincidence with $\alpha$ decays along the line of $Q_{\alpha ,\mathrm{tot}}$ of the 6553-keV $\alpha$ decay $\pm 40$ keV (a projection to $\gamma$-ray axis from the area between diagonal lines in Fig. 1). For better presentation, a different scale (1:500) is used for counts above energy of 380 keV. Tentative transitions have labels in italics, while background $\gamma$-ray peaks are marked by a plus sign.

Figure 3

Proposed $\alpha$-decay scheme of ${}^{180}\mathrm{Tl}$. Tentative levels and transitions are denoted by dashed lines. Transitions with energies in brackets were not observed, but they were placed into decay scheme based on indirect evidence; see text for details. Labels $M1/E2$ denote the possibility of $M1, E2$, or mixed multipolarity. The configuration of the ground state in ${}^{180}\mathrm{Tl}$ is taken from [21]. The tentative configuration of the daughter state in ${}^{176}\mathrm{Au}$ is taken from [22] and is discussed in Sec. 4.

Figure 4

$\gamma$ rays in coincidence with the 6354- or 6348-keV $\alpha$ transitions. The $\alpha$-particle energy range used for gating was 6310–6530 keV.

Figure 5

$\gamma$ rays in coincidence with: (a) the 6245-keV $\alpha$-decay transition, (b) the 6245-keV $\alpha$ and 210-keV $\gamma$ decay and (c) the 6245-keV $\alpha$ and 205-keV $\gamma$ decay. The energy range used as the $\alpha$ gate was 6220–6320 keV.

Figure 6

$\gamma$ rays in coincidence with (a) the 6199-keV or 6192-keV $\alpha$-decay transition, (b) the 6199-keV $\alpha$ and 210-keV $\gamma$ decay, and (c) the 6192-keV $\alpha$ and 205-keV $\gamma$ decay. The energy range used as the $\alpha$ gate was 6150–6210 keV.

Figure 7

$\gamma$ rays in coincidence with $\alpha$ decays in the region of 5944–6035 keV. The inset shows an expanded part of the spectrum for the energy region of 300–650 keV. The transition marked with the plus sign originates from the $\alpha$ decay of ${}^{176}\mathrm{Au}$; transitions marked by asterisks are unassigned. Remaining $\gamma$-ray peaks are assigned as coincident to 5977- or 5995-keV $\alpha$ decays of ${}^{180}\mathrm{Tl}$. The label in italics denotes tentative assignment.

Figure 8

$\gamma$ rays in coincidence with $\alpha$ decays in the region of 5830–5910 keV. The inset shows an expanded part of the spectrum for the energy region of 320–740 keV. Transitions marked by asterisks are unassigned. The 264-keV $\gamma$ rays marked by the plus sign originate from the $\alpha$ decay of ${}^{180}\mathrm{Hg}$. The remaining $\gamma$ ray peaks are assigned as coincident with 5873- or 5887-keV $\alpha$ decays of ${}^{180}\mathrm{Tl}$. The labels in italics denote tentative assignments.