Spectroscopic Measurement of the Nuclear Spin and Magnetic Moment of ^39Ar†

The nuclear spin and magnetic moment of argon 39 have been determined by high-resolution optical spectroscopy, using a pressure-swept Fabry–Perot interferometer, photoelectric detection, and digital data processing. The ³⁹Ar was produced through the ${}^{39}\mathrm{K}{\left(n,\mathcal{p}\right)}^{39}\text{Ar}$ reaction by pile neutron irradiation of KF. The spectrum of ³⁹Ar was excited in a miniature hollow cathode cooled by liquid nitrogen. Helium was used as a carrier gas. By application of the intensity rules, the nuclear spin was determined to be $\frac{7}{2}$, in agreement with the shell model. Anomalous spin values which were measured from some lines were shown to be caused by self-absorption from excited states. Using the A value of −23.76 ± 0.04 mK (1 mK = 10⁻³ cm⁻¹) measured for the 1s₂ level and the previous result for ³⁷Ar the nuclear magnetic moment has been determined to be −1.3 ± 0.3 nuclear magnetons. The measured B value for the 1s₂ level is B = +2.80 ± 0.02 mK. Several level structures and isotope shifts are reported.