Extending Precision Atomic Mass Measurement to Higher Mass

Precise atomic masses of the alkalis and certain other metals are important for photon-recoil ($h/m)$ determinations of the fine structure constant, while a series of precisely measured atomic masses up to high mass-number would provide convenient references for mass spectrometers used in nuclear physics. Using single ions in a Penning trap, with image charge detection and a phase-coherent technique for measuring the cyclotron frequency, we have measured the atomic masses of various heavy stable atoms, including $^{84,86}$Kr, $^{129,132,136}$Xe, with fractional precision of $\sim $0.1ppb; work on potassium and other alkalis is in progress. The measurements involve comparisons of multi-charged ions with singly-charged ions at similar $m/q$. Systematic errors originating from this difference in charge and other problems relating to high mass will be discussed.