Precision measurement of the atomic mass of /sup 6/Li using a Penning ion trap mass spectrometer

We have used a cryogenic (4 K) Penning ion trap mass spectrometer to measure the mass ratios of /sup 6/Li/sup +///sup 12/C/sup 2+/, /sup 6/Li/sup +//D/sub 3//sup +/, and D/sub 2//sup +//He/sup +/. We developed techniques to create ions outside of the cryogenic trap environment and to transport them into the trap where a small number (1-10) were confined. The ions' frequencies of oscillation were measured using a high-Q tuned circuit to detect image currents induced in the trap electrodes. The measurements involving /sup 6/Li/sup +/ result in a value for the atomic mass of /sup 6/Li of 6.015 122 795(16) u, with a fractional uncertainty of /spl plusmn/2.7/spl times/10/sup -9/ representing a factor of 30 improvement over the published, tabulated value. A measurement of the D/sub 2//sup +//He/sup +/ mass ratio has an uncertainty of /spl plusmn/1.1/spl times/10/sup -9/ and is within 0.6/spl times/10/sup -9/ of the tabulated value, thus demonstrating that our techniques are reliable.