Half-Life and the Magic Number 693 | 半衰期与神奇数字693

📚 Half-Life and the Magic Number 693 | 半衰期与神奇数字693

Radioactive decay is a spontaneous process in which unstable nuclei lose energy by emitting radiation. The half-life is a fundamental concept that allows scientists to predict how quickly a radioactive substance decays. Interestingly, the number 693 – more precisely 0.693, or 693 × 10⁻³ – appears when we connect the half-life to the decay constant in mathematics.

放射性衰变是不稳定的原子核通过发射辐射而失去能量的自发过程。半衰期是一个基本概念，使科学家能够预测放射性物质衰变的速度。有趣的是，当我们用数学将半衰期与衰变常数联系起来时，数字693——更准确地说是0.693，即693 × 10⁻³——会出现。

1. What is Radioactive Decay? | 什么是放射性衰变？

Radioactivity is the emission of particles or electromagnetic waves from the nucleus of an unstable atom. There are three main types of radiation: alpha (α), beta (β) and gamma (γ). Each type has different penetrating power and ionising ability.

放射性是来自不稳定原子核的粒子或电磁波的发射。主要辐射类型有三种：阿尔法（α）、贝塔（β）和伽马（γ）。每种类型都有不同的穿透能力和电离能力。

During decay, a radioactive nucleus changes into a more stable one. The original nucleus is called the parent nucleus and the new one is called the daughter nucleus.

在衰变过程中，放射性原子核转变成更稳定的原子核。原来的原子核称为母核，新形成的称为子核。

• Alpha is a helium nucleus (2 protons, 2 neutrons).

  阿尔法是氦原子核（2个质子，2个中子）。

• Beta is a fast-moving electron.

  贝塔是快速运动的电子。

• Gamma is electromagnetic radiation.

  伽马是电磁辐射。

2. Defining Half-Life | 定义半衰期

The half-life of a radioactive isotope is the time taken for half the unstable nuclei to decay, or the time for the activity (the number of decays per second) to fall to half its original value.

放射性同位素的半衰期是指一半的不稳定原子核发生衰变所需的时间，或者是指活度（每秒衰变次数）降为初始值一半所需的时间。

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For example, if a sample has a half-life of 2 hours, then after 2 hours only half of the original radioactive nuclei remain. After 4 hours, only one quarter remains, and after

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