📚 Combined 216: Nuclear Radiation and Radioactive Decay | 综合216：核辐射与放射性衰变
In Edexcel A-Level Physics, nuclear radiation and radioactive decay bring together atomic structure, conservation laws and exponential mathematics. The 'Combined 216' revision set covers the key equations, definitions and graph skills that examiners test regularly, especially in Topic 11 Nuclear Radiation.
在 Edexcel A-Level 物理中，核辐射与放射性衰变把原子结构、守恒定律和指数数学结合在一起。"综合216"复习套题涵盖考试中经常出现的关键方程、定义和图像技能，尤其是第11单元核辐射部分。
This article expands that revision set into a complete study guide: nuclear notation, isotopes, the three types of radiation, decay equations, background radiation, the inverse square law, the decay constant, half-life, log graphs, applications and the exam errors that cost marks.
本文把该复习套题扩展为完整学习指南：核素符号、同位素、三种辐射、衰变方程、本底辐射、平方反比定律、衰变常数、半衰期、对数图像、实际应用，以及最容易丢分的常见错误。
1. Atomic Nucleus and Notation | 原子核与符号
The nucleus is described by the proton number Z and the nucleon number A. A nuclide is written as ᴬZX, where X is the chemical symbol, Z is the number of protons and A is the total number of protons plus neutrons.
原子核由质子数 Z 和核子数 A 描述。核素写作 ᴬZX，其中 X 是化学符号，Z 是质子数，A 是质子与中子的总数。
umber of electrons equals Z, but nuclear reactions focus only on the nucleus, so electron counts do not appear in decay equations.
例如 ¹⁴₆C 有 6 个质子和 14 − 6 = 8 个中子。在中性原子中电子数等于 Z，但核反应只关注原子核，因此电子数不会出现在衰变方程中。
Nuclear notation is essential for balancing equations. Always write the mass number above and the atomic number below the left side of the symbol, and keep these numbers consistent in every reaction.
核素符号对于配平方程至关重要。始终把质量数写在符号左上角、原子序数写在左下角，并在每个反应中保持这些数字守恒。
Three quantities follow directly from Z and A:
由 Z 和 A 可以直接得到三个量：
- Protons = Z 质子数 = Z
- Neutrons = A − Z 中子数 = A − Z
- Nucleons = A 核子数 = A
A useful check: the neutron number can never be negative, and for stable light nuclei the neutron number is roughly equal to the proton number, while heavy stable nuclei need more neutrons than protons to stay bound together.
一个实用检查：中子数不可能为负；稳定的轻核中中子数与质子数大致相等，而稳定的重核需要中子多于质子才能束缚在一起。
Remember also that the proton number defines the element. Change Z and you have changed the element; change only the number of neutrons and you have made an isotope of the same element.
还要记住：质子数决定元素种类。改变 Z 就改变了元素；只改变中子数，得到的是同一元素的同位素。
2. Isotopes and Nuclides | 同位素与核素
Isotopes are atoms of the same element with the same Z but different A. They have identical chemical properties because electron configuration depends on Z, but their nuclear stability can be very different.
同位素是同一元素、质子数 Z 相同而核子数 A 不同的原子。由于电子排布取决于 Z，它们化学性质相同，但核稳定性可能差别很大。
The term nuclide refers to any specific nucleus defined by both Z and A, so isotopes are simply different nuclides of the same element. Carbon gives the classic example: ¹²₆C and ¹³₆C are stable, while ¹⁴₆C is radioactive with a half-life of about 5730 years.
"核素"指由 Z 和 A 共同确定的某种原子核，因此同位素就是同一元素的不同核素。碳是经典例子：¹²₆C 和 ¹³₆C
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