Precision X-ray wavelength measurements in helium-like argon recoil ions

Abstract

The authors report precise wavelength measurements of the 1s2 1S0-1s2p3P1,2,1P1 transitions in Ar16+ produced by collisions of 5.9 MeV amu-1 U66+ ions with an argon gas target. By use of this 'recoil source', the precision is not limited by Doppler shifts while the influence of spectator electrons is minimised by observation of their relative importance as a function of gas pressure. The accuracy obtained is at the 12 p.p.m. level dominated by the X-ray calibration standard. The measurement is thus sensitive to quantum-electrodynamic (QED) and electron correlation effects.