IB Physics: Nuclear Reaction Types and Energy Calculations | IB物理：核反应类型与能量计算

📚 IB Physics: Nuclear Reaction Types and Energy Calculations | IB物理：核反应类型与能量计算

Nuclear physics is one of the most frequently tested areas in IB Physics, particularly the concepts of mass-energy equivalence, binding energy, and the distinction between fusion and fission. This article provides a comprehensive revision guide to nuclear reaction types and the quantitative energy calculations required at both SL and HL level.

核物理是IB物理中最常考的内容之一，尤其是质能等价、结合能以及聚变与裂变的区别。本文为SL和HL阶段提供核反应类型与能量计算的系统性复习指南，帮助同学们在考试中从容应对相关题目。

1. Mass-Energy Equivalence | 质能等价性

Albert Einstein’s famous equation E = mc² establishes the equivalence between mass and energy. In nuclear reactions, even a tiny change in mass (the mass defect) corresponds to a huge release of energy, because the speed of light squared (c² = 9 × 10¹⁶ m²/s²) is an enormous conversion factor.

爱因斯坦著名的质能方程 E = mc² 确立了质量与能量之间的等价关系。在核反应中，微小的质量变化（质量亏损）对应着极其巨大的能量释放，因为光速的平方（c² = 9 × 10¹⁶ m²/s²）是一个极大的转换系数。

E = mc²

Here, E is the energy in joules (J), m is the mass in kilograms (kg), and c = 3.0 × 10⁸ m/s is the speed of light in vacuum. In nuclear physics, energy is often expressed in electronvolts (eV) or mega-electronvolts (MeV), with 1 eV = 1.60 × 10⁻¹⁹ J.

式中E为能量，单位焦耳（J）；m为质量，单位千克（kg）；c = 3.0 × 10⁸ m/s为真空中的光速。在核物理中，能量常以电子伏特（eV）或兆电子伏特（MeV）为单位，其中1 eV = 1.60 × 10⁻¹⁹ J。

2. Mass Defect and Binding Energy | 质量亏损与结合能

The mass defect Δm of a nucleus is the difference between the total mass of the individual nucleons (protons and neutrons) and the actual mass of the nucleus itself. This “missing” mass has been converted into binding energy, the energy that holds the nucleus together.

原子核的质量亏损Δm是指组成原子核的各个核子（质子和中子）的质量总和与原子核实际质量之间的差值。这部分”缺失”的质量已经转化为结合能，即维持原子核稳定的能量。

Δm = (Z × mₚ + (A − Z) × mₙ) − m_nucleus

For example, consider helium-4 (⁴He): two protons and two neutrons have a combined nuclear mass of approximately 4.032 u, while the ⁴He nucleus has a mass of approximately 4.0015 u. The mass defect is therefore about 0.0304 u. Using E = Δmc², this corresponds to a binding energy of roughly 28.3 MeV.

例如，氦-4（⁴He）中，2个质子和2个中子的核质量总和约为4.032 u，而⁴He原子核的质量约为4.0015 u，因此质量亏损约为0.0304 u。根据 E = Δmc²，对应的结合能约为28.3 MeV。

3. Binding Energy per Nucleon | 每核子结合能

Dividing the total binding energy of a nucleus by its mass number A gives the binding energy per nucleon. This quantity is a direct measure of nuclear stability: the higher the binding energy per nucleon, the more stable the nucleus. The famous binding

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