<Tr> <Th> </Th> <Td> trace </Td> <Td> 12.32 y </Td> <Td> β </Td> <Td> He </Td> </Tr> <Tr> <Th> Standard atomic weight (A) </Th> <Td> <Ul> <Li> (7000100784000000000 ♠ 1.007 84, 7000100811000000000 ♠ 1.008 11) </Li> <Li> Conventional: 1.008 </Li> </Ul> </Td> </Tr> <Ul> <Li> (7000100784000000000 ♠ 1.007 84, 7000100811000000000 ♠ 1.008 11) </Li> <Li> Conventional: 1.008 </Li> </Ul> <Li> (7000100784000000000 ♠ 1.007 84, 7000100811000000000 ♠ 1.008 11) </Li>

Each atom contains 1 proton and 2 neutrons