Absolute nuclear radii of Ir isotopes determined by EUV spectroscopy of highly charged ions *

High-statistics, precision EUV spectroscopy was implemented in measuring the nuclear radii difference between Os and Ir for determination of the absolute nuclear radius of Ir.  The EBIT facility at NIST produced highly charged ions at a beam energy of about 18 keV.  Flat-field grazing incidence spectrometer with a CCD pixel resolution of about 0.1 eV was used to record the Na-like 3s_1/2–3p_1/2 D1 line and the Mg-like and 3s­­^{2 1}S₀–3s3p-¹P₁ line of both elements. The energy shifts of the elements’ transitions were measured over several days by cycling the injection of Os, Ir, and Ne into the EBIT. The measured shifts are directly related to the mean square radii through the nuclear Seltzer moment. Calculations were performed by GRASP2K and RMBPT packages.