Specifically the mass of the nucleus, exactly 15.99 atomic mass units, is lower than the mass of its individual nucleons put together, in this case 16.13 amu's.

具体来说，原子核的质量恰好是 15. 99 个原子质量单位，低于其单个核子的质量总和， 在本例中为 16. 13 amu。