<Tr> <Td> 238 92 U </Td> <Td> → </Td> <Td> 234 90 Th </Td> <Td> + </Td> <Td> 2He2 + </Td> <Td> </Td> </Tr> <P> On the other hand, carbon - 14 naturally decays by radioactive beta decay, whereby one neutron is transmuted into a proton with the emission of an electron and an anti-neutrino . Thus the atomic number increases by 1 (Z: 6 → 7) and the mass number remains the same (A = 14), while the number of neutrons decreases by 1 (N: 8 → 7). The resulting atom is nitrogen - 14, with seven protons and seven neutrons: </P> <Dl> <Dd> <Table> <Tr> <Td> 14 6C </Td> <Td> → </Td> <Td> 14 7N </Td> <Td> + </Td> <Td> e − </Td> <Td> + </Td> <Td> ν </Td> </Tr> </Table> </Dd> </Dl> <Dd> <Table> <Tr> <Td> 14 6C </Td> <Td> → </Td> <Td> 14 7N </Td> <Td> + </Td> <Td> e − </Td> <Td> + </Td> <Td> ν </Td> </Tr> </Table> </Dd>

A bromine atom that has a mass number of 78