1993 ATOMIC MASS TABLES AND BEYOND

In the new tables, the masses of fundamental nuclides such as H, D, He -4, N-14, O-16 and even Ne-20 and Ar-40 could be given with a precisio n of a few parts in 10(10), due to Penning trap cyclotron frequency me asurements. The masses of stable Si atoms, of possible importance for the definition of the kg, the only base unit not yet defined in terms of natural constants, are given with 80 ppb (200 eV) accuracy. A repea ted Penning trap result for Si-28 with a 100 ppb precision confirms th e mass table result. Precision reaction and binding energies had now t o be given in terms of the 1990 representation of the eV which is 8.1 ppm larger than the preceding (1972) one. Penning trap technology has also been applied on even short-lived (few s) unstable nuclides, with a precision of about 10 keV. Time of flight measurements on very unsta ble nuclides gave their masses with about 100 keV accuracy. Similar or better accuracy applied to many masses derived from newly measured re action energies. Information is given on the way in which the mass val ues in the table have been derived from many thousands of experimental determinations of masses and nuclear reaction and decay energies.