The measurements of the hyperfine structure of free, naturally occurring, alkali atoms are reviewed. The experimental methods are discussed, as are the relationships between hyperfine structure data and other atomic constants.

Experimental determinations of the hyperfine structure in the alkali atoms

The development of on-line mass separators, which provide long chains of isotopes extending far off stability, immediately raised the question of how to gain access to the basic nuclear ground-state properties of these exotic nuclei—their spins, moments, radii, and masses. In general, the amount of radioactive material produced at these facilities is too small to form beams or targets for any kind of scattering or nuclear-reaction experiment. On the other hand, the traditional spectroscopic methods, namely, atomic, nuclear, and mass spectroscopy, have turned out to be very suitable for this application since they are easily adapted to the special on-line conditions.

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Nuclear Radii and Moments of Unstable Isotopes

Nuclear spin and magnetic moment of 11Li

The ground-state hyperfine constant $A$ and the nuclear-to-electronic $g$-factor ratio $\frac{{g}_{I}}{{g}_{J}}$ of $^{25}\mathrm{Mg}^{+}$ have been measured by a laser optical-pumping double-resonance technique. The ions were stored in a Penning trap at a magnetic field of about 1 T. The results are $A=\ensuremath{-}596.254 376(54)$ MHz and $\frac{{g}_{I}}{{g}_{J}}=9.299 484(75)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$. The magnetic field at the ions was stabilized by servoing it to an ($\ensuremath{\Delta}{m}_{I}=0$, $\ensuremath{\Delta}{m}_{J}=\ifmmode\pm\else\textpm\fi{}1$) electronic Zeeman transition. Other hyperfine ($\ensuremath{\Delta}{m}_{I}=\ifmmode\pm\else\textpm\fi{}1$, $\ensuremath{\Delta}{m}_{J}=0$) transitions were detected while the field was thus stabilized. The derivative of the $({m}_{I},{m}_{J})=(\frac{\ensuremath{-}3}{2}, \frac{1}{2}) \mathrm{to} (\frac{\ensuremath{-}1}{2}, \frac{1}{2})$ transition frequency with respect to magnetic field ${B}_{0}$ goes to zero at ${B}_{0}\ensuremath{\simeq}1.24$ T. The corresponding resonance was observed at this field with linewidths as small as 0.012 Hz ($Q=2.4\ifmmode\times\else\texttimes\fi{}{10}^{10}$) by implementing the Ramsey interference method with two coherent rf pulses separated in time by up to 41.4 s.

Precision measurement of the ground-state hyperfine constant ofMg+25

This study is concerned with the measurement and interpretation of magnetic hyperfine anomalies in electronic and muonic atoms ie effects of the distribution of nuclear magnetization on the magnetic dipole hyperfine interaction After a summary of the relevant theory and a review of experimental techniques, hyperfine anomaly results are discussed in terms of various nuclear models The use of the anomaly for yielding information about the origin of magnetic hyperfine interactions is outlined Experimental and theoretical hyperfine anomalies are tabulated

Magnetic hyperfine anomalies

Using the atomic beam magnetic resonance method and using the technique of separated oscillatory fields in combination with the triple resonance method the ratiosgI/gJ of the stable alkali isotopes Li, Na and K in the2S1/2-ground state have been measured at magnetic fields of about 3 kOe. Frequency shifts analogous to the Bloch-Siegert-shift, expected from theory, were observed and eliminated by extrapolation to vanishing rf-field strength. The results, uncorrected for atomic diamagnetism, are:6Li:gI/gJ=−0.22356978(10)·10−37Li:gI/gJ=−0.59042719(10)·10−323Na:gI/gJ=−0.40184406(40)·10−339K:gI/gJ=−0.07088613 (6)·10−341K:gI/gJ=−0.03890837 (4)·10−3 Furthermore, the hyperfine structure splitting constants in the2S1/2-ground states have been determined. Using the most precise absolutegJ-values available so far one can calculate absolute values for the uncorrectedgI- factors. The results are:Δν/MHz −gI·1036Li: 228.2052590(30) 0.4476540 (3)7Li: 803.5040866(10) 1.1822130 (6)23Na: 1771.6261288(10) 0.8046108 (8)39K: 461.7197202(14) 0.14193489(12)41K: 254.0138720(20) 0.07790600 (8) By comparing the absolutegI- factors with measurements received by the NMR-method, the chemical shifts of the NMR-frequencies caused by the hydrate surrounding of the alkali ions in the NMR-probe are determined.

Precision measurements of the nuclear magnetic dipole moments of6Li,7Li,23Na,39K and41K

Using the atomic beam magnetic resonance method the Zeeman interactions of12C in the3P1 and3P2 states at magnetic fields of about 3.4 kOe have been measured. The measured quantities aregJ(3P1)−gJ(3P2)=15.4(1.0)·10−6gJ(3P2)=1.5010616 (50), from which the following value for gJ(3P1) can be calculated:gJ(3P1)=1.5010770 (50). The experimental results are in moderate agreement with theoretical calculations.

A. Beckmann

Papers

Precision measurements of the nuclear magnetic dipole moments of6Li,7Li,23Na,39K and41K

Measurements of theg J -factors of12C in the3 P 1 and3 P 2 states