The Mass-5 Roadblock质量-5路障
Protons can combine to form alpha particles in proton-proton fusion. This can be presumed to have created alpha particles in the early universe, but the existence of the present universe depends upon the fact that alpha particles didn't combine to make heavier elements, clumping all the matter into heavy nuclei. 质子可以在质子-质子融合过程中结合形成氦核。这可以被假设为在早期宇宙中形成了氦核，但当前宇宙的存在依赖于一个事实：即氦核没有进一步结合形成更重的元素，使所有物质都聚集在重核中。
The alpha particle is extraordinarily tightly bound, with a particle binding energy of 28.3 MeV. It could form a mass-5 nucleus by adding a neutron to form 5He or a proton to form 5Li, but neither of these nuclides is stable. If you use the Weizsaecker formula to estimate the binding energy α粒子具有极高的结合能，其结合能为28.3 MeV。它可以通过添加中子形成质量为5的氦核或添加质子形成质量为5的锂核，但这两种核都不稳定。如果使用魏茨泽克公式来估算结合能。
E_b(⁵He) = 20.3 MeV
E_b(5Li) = 18.2 MeV
Both of these binding energies is much less than the binding energy of the alpha particle. If you look at the energetics of adding a proton or a neutron to an alpha particle: 这两种结合能都远小于α粒子的结合能。如果你看一下将质子或中子加到α粒子上的能量变化：
So an alpha particle plus either a free neutron or proton would have higher stability (lower mass) than either of these mass-5 nuclides. This mass-5 roadblock is an important part of the history of the universe. If the combination of protons and neutrons had been allowed to continue with the formation of all the heavier elements, there would have been no star and galaxy formation and no universe as we know it. 因此，一个α粒子加上一个自由中子或质子，其稳定性（更低的质量）会比这些质量为5的核素更高。这个质量为5的障碍是宇宙历史中的一个重要部分。如果质子和中子的结合能够继续形成所有更重的元素，就不会有星系和银河系的形成，也就不会有我们所知的宇宙。
|
Index
索引 | |||||||
|
Go Back
返回 |