In-beam γ-ray and α-decay spectroscopy of ${}^{170}\mathrm{Ir}$

Excited states in the highly neutron deficient odd-odd nucleus ${}^{170}\mathrm{Ir}$ have been investigated. The experiment was performed using the ${}^{112}\mathrm{Sn}$(${}^{60}\mathrm{Ni}$, $\mathit{pn}$)${}^{170}\mathrm{Ir}$ reaction and employing the recoil-decay tagging technique. Gamma rays were detected using the JUROGAM γ-ray spectrometer and those belonging to ${}^{170}\mathrm{Ir}$ were selected based on recoil identification provided by the RITU gas-filled recoil separator and the GREAT spectrometer at the RITU focal plane. A partial level scheme of ${}^{170}\mathrm{Ir}$ is presented for the first time. New α-decay branches are assigned to ${}^{170}\mathrm{Ir}$ and a tentative level structure for ${}^{166}\mathrm{Re}$ is deduced from a study of the α-decay fine structure and the associated α-γ correlations.

Figure 1

Energy spectrum for α decays occurring after a recoil implantation in the same pixel of the DSSD with recoil-α correlation times up to 10 s. The ${}^{173}\mathrm{Pt}$ and ${}^{172}\mathrm{Pt}$ decay lines are present because of impurities in the target.

Figure 2

Prompt γ ray spectra from the decay of excited states in ${}^{170}\mathrm{Ir}$ correlated with the 6007-keV (top panel) and 6053-keV (bottom panel) α decay lines. Strong contaminant peaks from ${}^{174}\mathrm{Pt}$ and ${}^{169}\mathrm{Ir}$ are marked by filled circles and squares, respectively. The spectra are produced by using a search time limit of 2 s between a recoil implant and its subsequent α decay.

Figure 3

Partial level scheme of ${}^{170}\mathrm{Ir}$.

Figure 4

Spectra gated by the 267-keV (top) and 341-keV (bottom) γ-ray transitions (see the text for more details).

Figure 5

(a) Energy spectrum for α decays occurring after recoil implantation in the same pixel of the DSSD, with a recoil-α correlation time of up to 3 s (a). (b) The α-decay energy spectrum resulting from correlations between the prompt coincidence of pairs of γ rays identified as belonging to ${}^{170}\mathrm{Ir}$ and recoils is imposed (see the text for details).

Figure 6

Recoil α-gated prompt-γ-ray spectra for the new α lines associated with the decay of ${}^{170}\mathrm{Ir}$. The spectra were partially cleaned by subtracting a fraction of similarly produced spectra from α gates on peaks that partially overlap with the α decays of ${}^{170}\mathrm{Ir}$. The filled circles indicate contamination from ${}^{174}\mathrm{Pt}$ from overlapping α gates. The open circle indicates contamination from ${}^{166}\mathrm{Os}$, which has a ground-state α-decay energy within the range of this gate.

Figure 7

Gamma-ray spectra obtained from a germanium detector placed at the focal plane of RITU, gated on the α decay of ${}^{171}\mathrm{Ir}$ and on the α-decay branches of the high-spin isomeric state in ${}^{170}\mathrm{Ir}$ indicated in Figs. 5 and 6.

Figure 8

Tentative level structure of ${}^{166}\mathrm{Re}$ deduced from the α-decay study of ${}^{170}\mathrm{Ir}$.

Figure 9

Aligned angular momentum values for the $h_{11/2}$ band in ${}^{171}\mathrm{Ir}$ [25], and the observed rotational band in ${}^{170}\mathrm{Ir}$ obtained from the present work. The Harris parameters used are $J_0=10$ MeV${}^{-1}\hslash {}^2$ and $J_1=50$ MeV${}^{-3}\hslash {}^4$, which are taken from Ref. [25]. The signatures $-1/2$ and +1/2 in ${}^{171}\mathrm{Ir}$ are indicated by open and filled circles, respectively, and the filled and open squares represent the signatures 0 and 1 in ${}^{170}\mathrm{Ir}$. In both cases the K value is taken to be 5.5. For ${}^{170}\mathrm{Ir}$ the bandhead spin is taken as $I=9$.

Figure 10

Calculated total Routhian surfaces at zero rotational frequency for configuration $\pi :(-,-1/2),\nu :(+,+1/2)$. Minima are found at a weakly deformed triaxial shape with ${\beta }_2\approx 0.15$ and $\gamma \approx \pm {15}^{°}$. Similar minima are found in the calculation for the $\pi :(-,-1/2),\nu :(-,\pm 1/2)$ configurations.

Figure 11

Single-particle energy levels for protons (upper plot) and neutrons (lower plot) as a function of the triaxial deformation parameter γ for ${\beta }_2=0.15$ and $\hslash \omega =0.0$ MeV. The Fermi surface for protons at $\gamma =0^{°}$ lies between $-0.062$ and $-1.3126$ MeV and for neutrons between $-10.1383$ and $-10.9414$ MeV. The solid and dotted curves indicate ($\pi ,\alpha )=(+,\pm 1/2)$ and the dashed and dash-dotted curves ($\pi ,\alpha )=(-,\pm 1/2).$ (The solid and dotted lines overlap at $\hslash \omega =0.0$ MeV, as do the dashed and dash-dotted curves.) As can be seen, the level structure near the Fermi surface remains largely the same in the interval $-15⩽\gamma ⩽15$.

Figure 12

Energy staggering in the rotational bands of ${}^{171}\mathrm{Ir}$ and ${}^{170}\mathrm{Ir}$. The filled and open squares represent $\alpha =0$ and $\alpha =1,$ respectively, in ${}^{170}\mathrm{Ir}$; filled and open circles correspond to $\alpha =-$1/2 and $\alpha =+$1/2 for ${}^{171}\mathrm{Ir}$. For ${}^{170}\mathrm{Ir}$ the bandhead spin is taken as $I=9$.

Figure 13

Measured $B(M1)/B(E2)$ values in the observed rotational band plotted against the spin value relative to the bandhead spin. Calculations using the Dönau-Frauendorf semiclassical formula [30] are shown as lines. From our TRS calculations the value of the quadrupole moment used for the calculation is $Q_0=6.2e$ b and $\gamma =-{15}^{°}$.