A physicsweb.org article1 states that an international team working at the ISOLTRAP mass spectrometer at CERN has determined the masses of two isotopes of argon (32Ar and 33Ar) with the highest precision ever. This is important if you want “to place constraints on aspects of the weak interaction that are not included in the Standard Model”.
Abstract:1 masses of the short-lived radionuclides 32Ar (T1/2=98 ms) and 33Ar (T1/2=173 ms) have been determined with the Penning trap mass spectrometer ISOLTRAP. Relative uncertainties of 6.0×10-8 (δm=1.8 keV) and 1.4×10-8 (δm=0.44 keV), 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 32Ar will allow for a better constraint on scalar contributions to the weak interaction. New mass values have also been measured for 44Ar and 45Ar, and a 20σ deviation for 44Ar from the literature value was found and interpreted.
WebElements December 9th, 2009