First determination of ground state electromagnetic moments of ${}^{53}\mathrm{Fe}$

The hyperfine coupling constants of neutron deficient ${}^{53}\mathrm{Fe}$ were deduced from the atomic hyperfine spectrum of the $3d^{6}4s^2{}^5{D}_4\leftrightarrow 3d^{6}4s4p{}^5{F}_5$ transition, measured using the bunched-beam collinear laser spectroscopy technique. The low-energy ${}^{53}\mathrm{Fe}$ beam was produced by projectile-fragmentation reactions followed by gas stopping, and used for the first time for laser spectroscopy. Ground state magnetic-dipole and electric-quadrupole moments were determined as $\mu =-0.65\left(1\right){\mu }_N$ and $Q=+35\left(15\right)e^2{\mathrm{fm}}^2$, respectively. The multiconfiguration Dirac-Fock method was used to calculate the electric field gradient to deduce $Q$ from the quadrupole hyperfine coupling constant, since the quadrupole coupling constant has not been determined for any Fe isotopes. Both experimental values agree well with nuclear shell model calculations using the GXPF1A effective interaction performed in a full $fp$ shell model space, which support the soft nature of the ${}^{56}\mathrm{Ni}$ nucleus.

Figure 1

The BECOLA facility. ${\mathrm{Fe}}^{+}$ ions are sent to the RFQ cooler/buncher from either the PIG ion source or the online beam. Following the cooler/buncher, the ion beam is overlapped with the laser light, and sent through a charge-exchange cell (CEC) containing sodium vapor. The laser-resonant fluorescence from the neutral atoms is collected using an elliptical mirror and detected by a photomultiplier tube (PMT). The static potential applied to the RFQ cooler/buncher and the scanning potential applied to the CEC were recorded with high precision using two digital voltmeters (DVMs).

Figure 2

${}^{53}\mathrm{Fe}$ time spectrum as a function of time relative to trigger signals for the release of the ion bunches. This spectrum includes total photon counts over $\sim 12$ h data accumulation time. The time spectrum was measured with a PMT at the photon detection system and includes both resonant photons and non-resonant photons following the charge-exchange process.

Figure 3

Simulated population distribution after charge-exchange (CE) of 29.85 keV ${\mathrm{Fe}}^{+}$-ion beam with a sodium vapor. The horizontal axis shows electronic levels of the Fe atom. Blue squares are the initial distribution right after the CE reactions, red circles are the distribution at the photon detection system 40 cm away from the CEC, and the dashed line is the entry energy of the electron from sodium.

Figure 4

The fluorescence spectrum of ${}^{56}\mathrm{Fe}$. The number of detected photons is plotted as a function of the relative laser frequency from an arbitrary value of 805 678.7330 GHz. The solid line is the best fit to the data using an asymmetric Voigt profile. The underlying plot shows the deviation from the fit line divided by the error of the data point.

Figure 5

The hyperfine spectrum of ${}^{53}\mathrm{Fe}$. The number of detected photons is plotted as a function of the relative laser frequency from an arbitrary value of 805 678.7330 GHz. The solid line is the best fit to the data using an asymmetric Voigt profile. The underlying plot shows the deviation from the fit line divided by the error of the data point.