<Tr> <Td> Si </Td> <Td> 7001279769265324600 ♠ 27.976 926 532 46 (194) </Td> <Td> 92.2297 (7)% </Td> <Td> 92.21--92.25% </Td> </Tr> <Tr> <Td> Si </Td> <Td> 7001289764947000000 ♠ 28.976 494 700 (22) </Td> <Td> 4.6832 (5)% </Td> <Td> 4.67--4.69% </Td> </Tr> <Tr> <Td> Si </Td> <Td> 7001299737701710000 ♠ 29.973 770 171 (32) </Td> <Td> 3.0872 (5)% </Td> <Td> 3.08--3.10% </Td> </Tr> <P> The calculation is exemplified for silicon, whose relative atomic mass is especially important in metrology . Silicon exists in nature as a mixture of three isotopes: Si, Si and Si . The atomic masses of these nuclides are known to a precision of one part in 14 billion for Si and about one part in one billion for the others . However, the range of natural abundance for the isotopes is such that the standard abundance can only be given to about ± 0.001% (see table). </P>

Scientist who accurately measured the relative mass of an atom