Half-life, uses and safety · 半衰期、用途与安全
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| half-life/hɑːf laɪf/ | 半衰期 | bàn shuāi qī |
| isotope/ˈaɪsətəʊp/ | 同位素 | tóng wèi sù |
| mutations/mjuːˈteɪʃnz/ | 突变 | tū biàn |
| dose/dəʊs/ | 剂量 | jì liàng |
| shielding/ˈʃiːldɪŋ/ | 屏蔽 | píng bì |
Counting down
- We cannot say when one nucleus will decay — but a large sample is very predictable.
- That predictability is measured by the half-life 半衰期.
- It lets us date ancient bones, run smoke alarms, and treat cancer.
倒计时
- 我们不能说一个原子核何时会衰变——但一个大样本是非常可预测的。
- 那个可预测性由半衰期(half-life)测量。
- 它让我们给古老的骨头测年、运行烟雾报警器,并治疗癌症。
Half-life
- The half-life is the time for half the unstable nuclei in a sample to decay.
- After each half-life, the count rate (and the number of unstable nuclei) falls to half.
半衰期
- 半衰期是一个样本中一半不稳定原子核衰变的时间。
- 每个半衰期之后,计数率(和不稳定原子核的数量)下降到一半。
Half-life — watch the nuclei decay · 半衰期——观察原子核衰变
Each nucleus has a fixed chance of decaying, at random. Move time forward: about half the remaining nuclei decay every half-life — so the count halves, then halves again. · 每个原子核有一个固定的随机衰变机会。把时间向前移动:每个半衰期约一半剩余的原子核衰变——所以计数减半,然后再减半。
The half-life of a radioactive isotope is the time taken for: · 一个放射性同位素的半衰期是以下所花的时间:
Each half-life, half of the remaining unstable nuclei decay, so the count rate halves. · 每个半衰期,一半剩余的不稳定原子核衰变,所以计数率减半。
Using half-life
- After $n$ half-lives, the count rate has halved $n$ times.
- Example: a source of $800$ counts/min with a half-life of $3$ hours → after $6$ hours (two half-lives): $800 \to 400 \to 200$ counts/min.
- You can read a half-life off a graph: the time for the count rate to fall from any value to half of it.
使用半衰期
- $n$ 个半衰期之后,计数率减半了 $n$ 次。
- 例子:一个 $800$ 计数/分钟、半衰期 $3$ 小时的源 → $6$ 小时(两个半衰期)之后:$800 \to 400 \to 200$ 计数/分钟。
- 你能从一张图上读出一个半衰期:计数率从任何值下降到它的一半的时间。
A source reads $800$ counts/min and has a half-life of $3$ hours. What is the count rate after $6$ hours, in counts/min? · 一个源读 $800$ 计数/分钟,半衰期为 $3$ 小时。$6$ 小时后的计数率是多少,以计数/分钟计?
6 hours is two half-lives: $800 \to 400 \to 200$ counts/min. · 6 小时是两个半衰期:$800 \to 400 \to 200$ 计数/分钟。
What fraction of the unstable nuclei remain after 3 half-lives? (Give a decimal.) · 3 个半衰期后还剩多少分数的不稳定原子核?(给一个小数。)
Each half-life halves the number: $\left(\tfrac{1}{2}\right)^3 = \tfrac{1}{8} = 0.125$. · 每个半衰期使数量减半:$\left(\tfrac{1}{2}\right)^3 = \tfrac{1}{8} = 0.125$。
Uses of radioactivity
- The choice of isotope 同位素 depends on its radiation type and half-life:
- Smoke alarms — an alpha source (easily blocked, so safe; long half-life lasts for years).
- Sterilising equipment and food — penetrating gamma kills bacteria through sealed packaging.
- Thickness gauges for paper or metal — a beta source (the amount passing through changes with thickness).
- Finding and treating cancer — gamma rays can pass into (or out of) the body.
Radioactive decay and half-life
放射性的用途
- 同位素的选择取决于它的辐射类型和半衰期:
- 烟雾报警器——一个 α 源(容易被挡住,所以安全;长半衰期持续数年)。
- 给设备和食物消毒——穿透的 γ 穿过密封包装杀死细菌。
- 纸或金属的厚度计——一个 β 源(穿过的量随厚度变化)。
- 发现和治疗癌症——γ 射线能进入(或离开)身体。
放射性衰变与半衰期
Match each radioactive source to its use. · 把每个放射性源与它的用途配对。
Alpha (easily blocked) suits smoke alarms; beta passes through thin sheets for thickness gauges; penetrating gamma sterilises sealed items. · α(容易被挡住)适合烟雾报警器;β 穿过薄片用于厚度计;穿透的 γ 给密封的物品消毒。
Why is an alpha source used in a smoke alarm? · 为什么在一个烟雾报警器中使用一个 α 源?
Alpha is stopped by a little air or the alarm casing (safe), and a long half-life means it works for years. · α 被一点空气或报警器外壳挡住(安全),而一个长半衰期意味着它工作数年。
Safety
- Ionising radiation harms living cells — it can cause cell death, mutations 突变 and cancer.
- Keep the dose 剂量 low by: less time near the source, more distance from it, and shielding 屏蔽 (such as lead).
- Handle sources with tongs, point them away from people, and store them in a lead-lined box.
安全
- 电离辐射伤害活细胞——它能造成细胞死亡、突变和癌症。
- 通过以下保持剂量低:更少时间靠近源、更多距离远离它,以及屏蔽(如铅)。
- 用钳子处理源,把它们指向远离人,并把它们存放在一个铅衬的盒子里。
Select all · 所有 the ways to reduce the radiation dose you receive. · 选择所有减少你接收的辐射剂量的方式。
Less time, more distance and shielding all cut the dose. Handling a source with bare hands does the opposite — always use tongs. · 更少的时间、更多的距离和屏蔽都削减剂量。用裸手处理一个源则相反——总是用钳子。
You've got it
- half-life = time for half the nuclei (or the count rate) to halve
- after $n$ half-lives the count rate has halved $n$ times
- uses: α smoke alarms · β thickness gauges · γ sterilising and cancer treatment
- safety: cut the dose with less time, more distance, and shielding
你掌握了
- 半衰期 = 一半原子核(或计数率)减半的时间
- $n$ 个半衰期之后计数率减半了 $n$ 次
- 用途:α 烟雾报警器 · β 厚度计 · γ 消毒和癌症治疗
- 安全:用更少时间、更多距离和屏蔽削减剂量