A Compensated Penning Trap Mass Spectrometer and the3

The use of a compensated Penning trap to measure an ion's mass relative to some calibration ion is described along with the leading systematic effects which must be considered. In this respect, magnet stability should no longer be a major limitation. This particular spectrometer has recently been used to determine preliminary atomic masses of both 3H and 3He and can be combined to yield a preliminary endpoint energy for the tritium decay (relative to neutral ground states) of 18 588(10) eV.