中子Neutron

质子之间存在静电排斥，中子不带电，却与质子一样受到强核力的吸引，从而把原子核结合在一起。轻核的中子数与质子数大致相等，重核需要更多中子才能稳定，如 ²⁰⁸Pb 有 82 个质子和 126 个中子。中子数过多或过少的原子核不稳定，会发生放射性衰变。

Protons repel one another electrostatically; neutrons carry no charge but feel the attractive strong nuclear force just as protons do, holding the nucleus together. Light nuclei have roughly equal numbers of neutrons and protons, while heavy nuclei need more neutrons to be stable: ²⁰⁸Pb has 82 protons and 126 neutrons. Nuclei with too many or too few neutrons are unstable and decay radioactively.

中子不带电，在电场和磁场中不偏转，能深入物质内部直至撞上原子核。原子核外的自由中子不稳定，平均寿命约 15 分钟，衰变为质子、电子和反中微子：n → p + e⁻ + ν̄。中子由夸克构成（一个上夸克和两个下夸克）。

Being uncharged, neutrons are not deflected by electric or magnetic fields and penetrate matter until they hit a nucleus. A free neutron outside a nucleus is unstable, with a mean lifetime of about 15 minutes, decaying into a proton, an electron and an antineutrino: n → p + e⁻ + ν̄. The neutron is made of quarks (one up and two down).

中子轰击 ²³⁵U 引起核裂变，并放出新的中子形成链式反应，这是核反应堆和原子弹的原理。中子衍射可以确定晶体中氢原子的位置，是 X 射线衍射的重要补充。中子活化分析用于测定样品中的微量元素。

Neutrons striking ²³⁵U cause nuclear fission, which releases more neutrons and sets up a chain reaction, the principle of nuclear reactors and atomic bombs. Neutron diffraction locates hydrogen atoms in crystals and complements X-ray diffraction. Neutron activation analysis measures trace elements in samples.