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The scheme of excited states in $^{66}$Ni populated in $\beta^-$ decay of $^{66}$Co. The spin assignments and the energies of the unobserved states are taken from Ref. \cite{Darcey1971,Broda2012,Leoni2017}. The $\beta$-feeding of the states should be treated as upper limits and the log(\textit{ft}) values as lower limits due to the pandemonium effect.

(Color online) Time behavior of the 471 keV transition as a function of time after PP (red circles) with the fitted function (black straight line) and the background area of the 471 keV transition (blue squares) with the fitted function (blue dash-dotted line). Insert: posterior probability density function of $^{66}$Fe half-life. The 16, 50 and 84 percentiles are indicated with vertical, dotted lines.

(Color online) T-plots of the selected states in the $A=66$ chain.

(Color online) Single-$\gamma$ spectrum collected in the \textit{laser-on} mode (black) and the \textit{laser-off} mode (red/medium grey, upscaled 5 times for better visual comparison), and $\beta$-$\gamma$ coincidence spectrum collected in the \textit{laser-on} mode (blue/light grey) from 0 to 1500 keV (top panel) and 1500 keV to 3500 keV (bottom panel) with the mass separator set to $A=66$. Peaks attributed to the decay of $^{66}$Mn and daughter activities are marked.

The scheme of excited states in $^{66}$Fe populated in $\beta^-$ decay of $^{66}$Mn. $Q_{\beta^-}$ and $S_n$ values are taken from Ref. \cite{Wang2017}. The $\beta$-feeding of the states should be treated as upper limits and the log(\textit{ft}) values as lower limits due to the pandemonium effect. Half-life and $P_n$ are determined in the analysis. Spin assignments were made based on the experimental data and the Monte Carlo Shell Model calculations, see text for details. The level at 1413.9 keV is shifted 40 keV upwards on the scheme for better visual representation.

Time behavior of the 176 keV $\gamma$-ray transition as a function of time after the 806 keV $\gamma$-ray transition. Insert: posterior probability density function of the half-life of the first isomeric state in $^{66}$Co ($T_{1/2} = 823^{+22}_{-21}$~ns). The 16, 50 and 84 percentiles are indicated with vertical, dotted lines.

(Color online) The fit results of the $\gamma$-decay curves to the number of $\beta$ particles registered in time (red circles). The $\beta$-decay curve (Eq. \ref{eq:gsfassumptionsnew}) is plotted as a black straight line. The contribution of the $^{66}$Mn, $^{66}$Fe and $^{66}$Co decays is represented by the red straight line (Eq. \ref{eq:gsfbatemanfe}), green dashed line (Eq. \ref{eq:gsfbatemanco}) and blue dash-dotted line (Eq. \ref{eq:gsfbatemanni}), respectively. The purple dotted line represents a constant from Eq. \ref{eq:gsfassumptionsnew}. Insert: posterior probability density functions of the direct feeding to the ground state of (from left) $^{66}$Fe, $^{66}$Co and $^{66}$Ni, and the probability of $\beta$-delayed-neutron emission. The 16, 50 and 84 percentiles are indicated with vertical, dotted lines.

(Color online) Single-$\gamma$ spectrum collected in the \textit{laser-on} mode (black) and the \textit{laser-off} mode (red/medium grey, upscaled 5 times for better visual comparison), and $\beta$-$\gamma$ coincidence spectrum collected in the \textit{laser-on} mode (blue/light grey) from 0 to 1500 keV (top panel) and 1500 keV to 3500 keV (bottom panel) with the mass separator set to $A=66$. Peaks attributed to the decay of $^{66}$Mn and daughter activities are marked.

(Color online) Time behavior of the 574 keV transition as a function of time after PP (red circles) with the fitted function (black straight line) and the background area of the 574 keV transition (blue squares) with the fitted function (blue dash-dotted line). Insert: posterior probability density function of $^{66}$Mn half-life. The 16, 50 and 84 percentiles are indicated with vertical, dotted lines.

A portion of the $\gamma$-delayed-$\gamma$ coincidence spectrum gated on the 176 keV transition (coincidence time window $-2.5$ to $-0.2$ $\mu$s). The coincide transitions are labeled with the energy in keV.

(Color online) The $\beta$-gated-$\gamma$ counts in the 511 keV transition peak area as a function of time after PP (red circles) with the fitted function (Eq. \ref{eq:model511}, black straight line) and te $\beta$-gated-$\gamma$ counts in the background area (blue squares) with the fitted function (Eq. \ref{eq:comptonbackground}, blue dash-dotted line). The contributions of the decay of $^{66}$Fe ($N_{Fe}$), $^{66}$Mn decay high-energy $\gamma$-rays ($N_{Mn}$), the environmental background ($N_{off}$) and other sources ($N_{o}$) are represented by the red straight line, the green dashed line, the cyan dash-dotted line and the purple dotted line, respectively. Insert: posterior probability density function of the 511 keV transition intensity. The 16, 50 and 84 percentiles are indicated with vertical, dotted lines.

(Color online) The comparison of the observed states in $^{66}$Co, log(\textit{ft}) values and relative branching ratios from selected levels with the MCSM calculations. The states up to 1.2 MeV are presented. The theoretical intensities are calculated by taking experimental energies and B(M1) and B(E2) values from MCSM. Dashed lines represent transitions which were not observed experimentally. The spherical states are drawn in red, oblate in green, prolate in blue and the negative-parity states in brown. The calculated $4^+_1$ state is shifted $-10$~keV and the $6^+_1$ state is shifted $-20$~keV for better visual representation.

The comparison of the observed states in $^{66}$Fe, log(\textit{ft}) values and relative branching ratios from selected levels with the MCSM calculations. The states up to 3.1 MeV are presented. The theoretical intensities are calculated by taking experimental energies and B(M1) and B(E2) values from MCSM. Dashed lines represent transitions which were not observed experimentally. Experimental levels at 1407 and 1414 keV are shifted for the better visual representation. The calculated $4^-_2$ level is shifted $-20$~keV.

(Color online) The comparison of the states in $^{66}$Ni observed in the $\beta^-$ decay of $^{66}$Co (straight lines) and other experiments (dashed lines) \cite{Darcey1971,Broda2012,Leoni2017}, and the log(\textit{ft}) values with the MCSM calculations. The states up to 4 MeV are presented. The experimental $3^+_1$ level is shifted $-20$~keV and the theoretical $6^-_1$ level is shifted $20$~keV. The spherical states are drawn in red, oblate in green, prolate in blue and negative-parity states in brown.

The scheme of excited states in $^{66}$Co populated in $\beta^-$ decay of $^{66}$Fe. The $\beta$-feeding of the states should be treated as upper limits and the log(\textit{ft}) values as lower limits due to the pandemonium effect. The $Q_{\beta^-}$ value is taken from Ref. \cite{Wang2017} and the limit for the half-life of the second isomeric state from Ref. \cite{Grzywacz1998}. The half-life of the parent nucleus and the first excited state at 176 keV come from our analysis. The spin and parity assignments are made based on the experimental results and the Monte Carlo Shell Model calculations, see text for details. When indicated with an asterisk (*), the log(\textit{ft}) value was calculated assuming second-forbidden unique transition.

(Color online) Counts in the peak area of the 176 keV $\gamma$-ray transition as a function of time after the $\beta$ particle (red circles) with the fitted function (black straight line) and counts in the background area (blue squares) with the fitted function (blue dash-dotted line). Insert: a portion of the $\beta$-delayed-$\gamma$ spectrum (coincidence time 0.5 to 10 $\mu$s) in the 176 keV $\gamma$-ray transition region with marked peak area (dark shade) and background areas (light shades). See text for details.

A portion of the $\gamma$-$\gamma$ coincidence spectrum gated on the 511 keV transition. Transitions at 371 and 471 keV are assigned to the decay of $^{66}$Fe. There are also visible transitions assigned to the decay of $^{66}$Mn: escape peaks (ep) of the high energy $\gamma$-ray transition and their coincidences (the transition at 574 keV).

Time behavior of the 364 keV $\gamma$-ray transition as a function of time after the $\beta$ signal with the fitted function. Insert: posterior probability density function of the half-life of the second isomeric state in $^{65}$Fe ($T_{1/2} = 409^{+29}_{-27}$~ns). The 16, 50 and 84 percentiles are indicated with vertical, dotted lines.

A $\gamma$-$\gamma$ coincidence spectrum gated on the 574 keV transition. The most intense coincidences are labeled with the energy given in keV.

A portion of the $\gamma$-$\gamma$ coincidence spectrum gated on the 471 keV transition. Beyond 600~keV no peaks were observed.

The excited states in $^{65}$Fe populated in $\beta^-$-delayed-neutron decay of $^{66}$Mn. Dotted lines represent transitions reported in Ref. \cite{Olaizola2013}, not observed in our analysis, and their energies are the differences between levels energies. Intensities are normalized to 100 units of the 364 keV transition. Spin assignments and half-lifes of the states in $^{65}$Fe, except the half-life of 398 keV level, are taken from Ref. \cite{Olaizola2013}.

A portion of the $\gamma$-$\gamma$ coincidence spectrum gated on the 1425 keV transition. The coincide transitions are labeled with the energy in keV.

A portion of the $\gamma$-delayed-$\gamma$ spectrum with background subtraction gated on the 364 keV transition (coincidence window: $-5$ to $-0.5$ $\mu$s). A peak at 163 keV is visible.