091 泡利不相容原理
Pauli Exclusion Principle
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泡利不相容原理
Pauli Exclusion Principle and Nuclear Stability
泡利不相容原理與核穩定性
Atomic nuclei consist of protons and neutrons, which attract each other through the nuclear force, while protons repel each other via the electromagnetic force due to their positive charge. These two forces compete, leading to various stability of nuclei. There are only certain combinations of neutrons and protons, which forms stable nuclei. Neutrons stabilize the nucleus, because they attract each other and protons , which helps offset the electrical repulsion between protons. As a result, as the number of protons increases, an increasing ratio of neutrons to protons is needed to form a stable nucleus. If there are too many (neutrons also obey the Pauli exclusion principle) or too few neutrons for a given number of protons, the resulting nucleus is not stable and it undergoes radioactive decay. Unstable isotopes decay through various radioactive decay pathways, most commonly alpha decay, beta decay, or electron capture. Many other rare types of decay, such as spontaneous fission or neutron emission are known.
原子核由質子和中子組成，它們通過核力互相吸引，而質子由于帶正電荷而通過電磁力互相排斥。這兩種力互相競争，導緻原子核具有不同的穩定性。隻有中子和質子的某些組合才能形成穩定的原子核。中子能穩定原子核，因為它們互相吸引并吸引質子，這有助于抵消質子之間電的斥力。是以，随着質子數量的增加，中子與質子的比例就需要增加，才能形成穩定的原子核。對于給定數量的質子，如果有太多的中子（中子也遵循泡利不相容原理）或太少的中子，産生的原子核是不穩定的，并經曆放射性衰變。不穩定同位素通過各種放射性衰變途徑衰變，最常見的是α衰變、β衰變或電子俘獲。許多其他稀有類型的衰變，如自發裂變或中子發射，已為人所知。
The Pauli exclusion principle also influences the critical energy of fissile and fissionable nuclei. For example, actinides with odd neutron number are usually fissile (fissionable with slow neutrons) while actinides with even neutron number are usually not fissile (but are fissionable with fast neutrons). Heavy nuclei with an even number of protons and an even number of neutrons are (due to Pauli exclusion principle) very stable thanks to the occurrence of ‘paired spin’. On the other hand, nuclei with an odd number of protons and neutrons are mostly unstable.
泡利不相容原理也影響易裂變和可裂變核的臨界能量。例如，具有奇數中子數的锕系元素通常是易裂變的（對慢中子可裂變），而具有偶數中子數的锕系元素通常是不可裂變的（但對快中子可裂變）。由于“配對自旋”的出現，具有偶數個質子和偶數個中子的重原子核（由于泡利不相容原理）非常穩定。另一方面，質子和中子數量為奇數的原子核大多是不穩定的。
童年的泡利
（待續）