核素质子数与质量数在数值上相等（核言碎语181）

134 原子质量数与原子质量（同位素质量）

Atomic Mass Number and Atomic Mass (Isotopic Mass)

（https://www.nuclear-power.com/）

原子质量数与原子质量（同位素质量）

The size and mass of atoms are so small that standard measuring units, while possible, are often inconvenient. Units of measure have been defined for mass and energy on the atomic scale to make measurements more convenient to express. The unit of measure for mass is the atomic mass unit (amu). One atomic mass unit is equal to 1.66 x 10-24 grams.

原子的大小和质量是如此之小，以致于标准的测量单位虽然可能，但常常是不方便的。原子尺度上的质量和能量的度量单位已经确定使得测量更方便地表达。质量的度量单位是原子质量单位（amu）。一个原子质量单位等于1.66x10^-24克。

Besides the standard kilogram, it is a second mass standard. It is the carbon-12 atom, which, by international agreement, has been assigned a mass of 12 atomic mass units (u). The relation between the two units is

除了标准千克，还有第二个质量标准。它是碳-12原子，根据国际协议，其质量是12个原子质量单位（u）。这两个单位的关系是

One atomic mass unit is equal:

1u = 1.66 x 10-24 grams.

一个原子质量单位等于:

1u = 1.66 x 10^-24克。

One unified atomic mass unit is approximately the mass of one nucleon (either a single proton or neutron) and is numerically equivalent to 1 g/mol.

一个统一的原子质量单位大约是一个核子（单个质子或中子）的质量，在数值上相当于1g /mol。

For 12C, the atomic mass is exactly 12u since the atomic mass unit is defined from it. The isotopic mass usually differs for other isotopes and is usually within 0.1 u of the mass number. For example, 63Cu (29 protons and 34 neutrons) has a mass number of 63, and an isotopic mass in its nuclear ground state is 62.91367 u.

对于12C，原子质量正好是12u，因为原子质量的单位是由其定义的。同位素质量通常与其他同位素不同，相差通常在0.1 u以内。例如，63Cu（29个质子和34个中子）的质量数为63，其核基态的同位素质量为62.91367 u。

There are two reasons for the difference between mass number and isotopic mass, known as the mass defect:

质量数与同位素质量的差异有两个原因，称为质量亏损:

1. The neutron is slightly heavier than the proton, increasing the mass of nuclei with more neutrons than protons relative to the atomic mass unit scale based on 12C with equal numbers of protons and neutrons.

1.中子比质子略重，相对于质子和中子数量相等的12C原子质量单位，中子比质子多的原子核的质量增加。

2. The nuclear binding energy varies between nuclei, and a nucleus with greater binding energy has lower total energy and a lower mass according to Einstein’s mass-energy equivalence relation E = mc2. For 63Cu, the atomic mass is less than 63, so this must be the dominant factor.

2.原子核之间的结合能是不同的，根据爱因斯坦的质能等价关系E = mc^2，结合能越大的原子核总能量越低，质量越小。对于63Cu，原子质量小于63，所以这一定是主导因素。

（待续）