Masses of the short-lived radionuclides ${}^{32}\mathrm{A}\mathrm{r}$ ($T_{1/2}=98\mathrm{m}\mathrm{s}$) and ${}^{33}\mathrm{A}\mathrm{r}$ ($T_{1/2}=173\mathrm{m}\mathrm{s}$) have been determined with the Penning trap mass spectrometer ISOLTRAP. Relative uncertainties of $6.0\times {10}^{-8}$ ($\delta m=1.8\mathrm{k}\mathrm{e}\mathrm{V}$) and $1.4\times {10}^{-8}$ ($\delta m=0.44\mathrm{k}\mathrm{e}\mathrm{V}$), respectively, have been achieved. At present, these new mass data serve as the most stringent test of the quadratic form of the isobaric-multiplet mass equation. Furthermore, the improved accuracy for the mass of ${}^{32}\mathrm{A}\mathrm{r}$ will allow for a better constraint on scalar contributions to the weak interaction. New mass values have also been measured for ${}^{44}\mathrm{A}\mathrm{r}$ and ${}^{45}\mathrm{A}\mathrm{r}$, and a $20\sigma$ deviation for ${}^{44}\mathrm{A}\mathrm{r}$ from the literature value was found and interpreted.

• Received 7 May 2003

DOI:https://doi.org/10.1103/PhysRevLett.91.260801