For instance, the mass of a neutral helium atom is 4.002603 unified atomic mass units.

一个稳定的氦原子核的质量是4。002603u。

Molality refers to moles per unit mass and molarity refers to moles per unit volume.

摩尔浓度是指每单位质量的摩尔数， 摩尔浓度是指每单位体积的摩尔数。

Per unit mass natural latex rubber can store more energy than nearly any other elastic material, 7,000 joules per kilogram.

每单位质量的天然乳胶橡胶可以储存比几乎任何其他弹性材料更多的能量，每公斤可储存 7,000 焦耳。

That means that the nucleus of a helium atom has 0.030377 unified atomic mass units less mass than its component parts.

这意味着氦原子核的质量比其组成部分少 0.030377 个统一原子质量单位。

So the products of this reaction always have less total mass – as measured in unified atomic mass units – than the parent nucleus has.

因此，该反应的产物总质量（以统一原子质量单位衡量）总是小于母核。

But two neutrons and two protons – the component parts of a helium atom – taken together have a mass of 4.032980 unified atomic mass units.

但是两个中子和两个质子——氦原子的组成部分——加在一起的质量为 4.032980 个统一原子质量单位。

To quantify the mass of a nucleus, we use the unified atomic mass unit, written just as a small u, with a single neutral carbon-12 atom equaling exactly twelve unified atomic mass units.

为了量化原子核的质量，我们使用统一的原子质量单位，写成小写的 u，其中一个中性碳 12 原子恰好等于十二个统一的原子质量单位。