Number 125 (Story #1), April 22, 1993 by Phillip F. Schewe and Ben Stein|
NEW MEASUREMENTS OF ATOMIC MASSES with 20 to 1000 times the precision of previous values have been made by an MIT team. Masses of hydrogen, deuterium, oxygen, neon, and argon have been measured at precision levels of around 100 parts per trillion. The researchers made their measurements using Penning trap, a device in which an isolated ion's cyclotron motion in a magnetic field is compared to that of a reference ion. The ratio of the cyclotron frequencies determines their relative masses. These are then converted to a scale based on the carbon-12 mass. David Pritchard (617-253-6812) of MIT announced his values for the atomic masses at the APS April meeting, where he also mentioned that he hoped to "weigh" the binding energies of chemical bonds; but this requires a tenfold improvement in precision. Pritchard believes an improvement of this magnitude entails the development of a technique in which the two ions occupy the Penning trap simultaneously. Robert Van Dyck (206-685-1097) of the University of Washington reported that Penning trap measurements of the mass difference between helium-3 and tritium gives a value of 18,590.1 eV with an uncertainty of 1.7 eV. This measurement provides a systematic check of tritium beta decay experiments investigating the possibility of a nonzero neutrino mass.