Radiation from Radioactive Substances | 放射性物质发出的辐射

📚 Radiation from Radioactive Substances | 放射性物质发出的辐射

Radioactivity is the spontaneous and random emission of radiation from unstable atomic nuclei. The three main types of radiation emitted by radioactive substances are alpha (α), beta (β) and gamma (γ). They differ in charge, mass, ionising power and penetrating ability, which are central ideas in the CIE A Level Physics syllabus. Understanding how to compare these radiations and how to use decay equations, activity and half-life is essential for exam success.

放射性是不稳定原子核自发且随机地发出辐射的过程。放射性物质发出的三种主要辐射是 α、β 和 γ。它们在电荷、质量、电离能力和贯穿本领上各不相同，这是 CIE A Level 物理课程的核心内容。理解如何比较这些辐射，以及如何运用衰变方程、活度和半衰期，对考试成功至关重要。

1. The Nature of Radioactive Radiation | 放射性辐射的本质

An unstable nucleus has excess energy or an imbalance of neutrons and protons. It decays to a more stable configuration by emitting radiation. The emission is spontaneous because it is not caused by temperature, pressure or chemical reactions; it is random because we cannot predict which nucleus will decay next, only the probability of decay per unit time.

不稳定原子核具有过剩能量或中子-质子比例失衡。它通过发出辐射衰变到更稳定的结构。这种发射是自发的，因为它不受温度、压强或化学反应影响；它也是随机的，因为我们无法预测哪一个核接下来会衰变，只能给出单位时间内衰变的概率。

2. Alpha Particles | α 粒子

An alpha particle is a helium nucleus, written as ⁴₂He or α. It consists of two protons and two neutrons, so it carries a charge of +2e and has a mass of about 4 u. Alpha particles are emitted at speeds of about 0.05c to 0.1c. Because their charge is large and their speed is relatively low, they interact strongly with atoms and remove many electrons per unit length, giving them the highest ionising power of the three radiations.

α 粒子是氦原子核，写作 ⁴₂He 或 α。它由两个质子和两个中子组成，因此带 +2e 的电荷，质量约为 4 u。α 粒子的发射速度约为 0.05c 到 0.1c。由于电荷大且速度相对较低，它们与原子作用强烈，单位长度内能电离很多电子，因此电离能力在三种辐射中最强。

Alpha particles have a very short range and are stopped by a sheet of paper or a few centimetres of air. Despite their high ionising power, they are not very penetrating because they lose energy rapidly in a small distance.

α 粒子的射程很短，一张纸或几厘米空气就能将其阻挡。尽管电离能力强，但它们的贯穿本领不强，因为它们在很短的距离内就迅速损失能量。

3. Beta Particles | β 粒子

Beta-minus (β⁻) radiation is the emission of fast electrons, ⁰₋₁e, from the nucleus when a neutron changes into a proton. Beta-plus (β⁺) radiation is the emission of positrons, ⁰₊₁e. A beta particle has a charge of ±e and a very small mass, about 1/2000 u. It can travel at speeds up to about 0.99c.

β⁻ 辐射是原子核内中子转变为质子时发射快电子 ⁰₋₁e。β⁺ 辐射发射正电子 ⁰₊₁e。β 粒子带 ±e 的电荷，质量很小，约为 1/2000 u。它的速度可高达约 0.99c。

Beta particles have a continuous energy spectrum because a neutrino or anti-neutrino is emitted at the same time and shares the energy. Their ionising power is weaker than that of alpha particles, but they can penetrate a few millimetres of aluminium and travel further in air.

β 粒子具有连续能量

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