0 the mass of a specific isotope of a particular chemical element, usually expressed in atomic mass units -- 原子質量（某化學元素同位素的質量，通常以原子質量單位的形式表達）
Heavy hydrogen could be separated from the ordinary hydrogen isotopes of atomic mass 1 at a cost of about £25,000 a ton.
O, where the 16, 17 and 18 refer to the atomic mass.
This means low atomic mass elements are favoured.
One unified atomic mass unit is approximately the mass of one a single proton or neutron.
It is numerically equal to the relative atomic mass (or atomic weight) in grams.
It serves to define the atomic mass unit and is, by definition, equal to 1 u.
As of 2003, at least 33 radioisotopes have also been synthesized, ranging in atomic mass from 60 to 92.
For example, a sample of chlorine contains 75.8% chlorine-35 and 24.2% chlorine-37, giving an average atomic mass of 35.5 atomic mass units.
