Radioactivity: Expect the unexpected - Steve Weatherall

Transcriber: Andrea McDonough Reviewer: Bedirhan Cinar

翻译人员: Yin Zhu 校对人员: Jenny Yang

It is only in the last 100 or so years that human kind has understood

近一百年来，人们渐渐明白

that the nucleus of the chemical elements is not always fixed.

化学元素的原子核并不总是稳定的。

It can change spontaneously from one element to another.

它可以瞬间变成另一个化学元素。

The name for this process is radioactivity.

这种演变的过程叫放射。

You probably already know something about the nucleus:

你可能对原子核已经有一定了解：

it's much tinier than the atom,

比如它比原子小，

it's made of particles called protons and neutrons,

再比如原子核是由质子和中子构成的，

there are electrons orbiting around it.

原子核周围还有电子围绕。

And though the atoms can share or swap electrons when they bond together,

虽然原子结合时，他们可以共享或交换电子，

the nuclei themselves never change.

但原子核保持不变。

Right?

对吗？

Well, no.

不对。

Certain nuclei are not stable in that way.

某些原子核并不稳定。

This means they may change suddenly,

这意味着，他们可能

spontaneously.

瞬间改变。

The radioactive nucleus flings out a small particle

有放射性的原子核会甩出小物质

and transforms into another element, just like that.

并同时变成另外一个化学元素。

For example,

比如，

the carbon nucleus can eject a fast-moving electron

碳元素的原子核可以甩出一个高速移动的电子，

and turn into a nitrogen nucleus.

并变成氮元素的原子核。

There are two different particles that can be emitted from radioactive nuclei,

有放射性的原子核可以甩出两种物质，

but never together.

但不能同时甩出这两种物质。

The very fast electron is known as a beta particle.

移动速度快的电子叫β粒子.

If you know a little bit about electrons, you may be thinking,

如果你对电子有了解，有可能会想，

"What was the electron doing in the nucleus in the first place?"

“为什么原子核里会有电子?”

The answer is there is a neutron in nucleus

答案是因为核中的中子，

spontaneously changed into a proton,

自发瞬间变成质子，

which stayed behind,

质子留在原子核内，

and the electron flew out as a beta particle.

但一个电子以贝塔粒子形式弹射出来。

This is not what chemistry has taught us to expect.

这不是传统化学所教的。

The nucleus is supposed to be stable.

原子核应该是稳定的。

Neutrons don't change into protons.

中子不会自发变成质子。

Except, sometimes they do!

但是，有时候他们却会！

The other particle it emits spontaneously

另一个从不稳定的原子核自发射出的粒子

from an unstable nucleus is alpha.

叫阿尔法粒子。

An alpha particle is 8,000 times more massive than beta,

阿尔法粒子是贝塔粒子质量的8，000倍，

and it's a bit slower.

而速度要慢些。

Alpha is made from two protons and two neutrons.

阿尔法粒子是由两个质子和两个中子构成的。

If we trap all those alpha particles together,

如果我们把弹射出的阿尔法粒子搜集起来，

we get helium gas.

我们将获得氦气。

Alpha is a helium nucleus.

阿尔法粒子是氦气的原子核。

Like the beta particle, you would not have expected

很难想象原子核会弹射出贝塔粒子，

a heavier nucleus to throw out helium.

更不要说重很多的氦气了。

But again, it happens,

但事实再一次超出我们想象，

and the nucleus becomes a new element.

弹射出的原子核变成一个新的元素。

So, is radioactivity useful or just dangerous?

那放射是有益还是有危害呢?

Wherever you are sitting,

其实无论你坐在哪里，

it is quite likely that there is a device nearby

周围很有可能有一件

which contains a source of alpha particles:

有阿尔法粒子的电器:

a smoke detector.

比如烟雾探测器。

The source is radioactive Americium.

里面就有带放射性的銤元素。

You are totally safe from these alpha particles,

这些阿尔法粒子对你完全无害，

which cannot travel more than a few centimeters in air.

因为它们只能在空气中传播几厘米。

Beta particles penetrate much farther

较阿尔法粒子而言，贝塔粒子穿透力

through materials than alpha can.

强很多。

Radioactive atoms are used in medicine as traces,

放射性元素在医学上被用做示踪剂，

to show where chemicals travel in the patient.

来显示药物到达了人体的哪个部位。

Beta particles are emitted and have enough energy

被释放的贝塔粒子有足够的能量

to emerge from the body and be detected.

穿透人体并被测量到。

There is a third type of nuclear radiation:

除了阿尔法和贝塔粒子外，还有第三种辐射：

gamma, which is not a particle at all.

伽马其实不是粒子。

It is an electromagnetic wave,

它是一种电磁波，

like microwaves, or light,

像微波或是光,

but it is actually 1,000 times more energentic than visible light.

但它是可见光能量的1，000倍。

Gamma rays may pass right through your body.

伽马射线可以轻松穿透你的身体。

Gamma is used to zap the bacteria in fruit to increase its shelf life,

伽马射线被用于农副产品的消毒，从而增加保质期，

or in radiotherapy to kill cancer cells.

或被用于放射疗法来杀死癌细胞。

Radioactive substances get hot,

放射性元素会发热，

and this heat can be used to generate power.

而热能可以用于发电。

This heat has been brought to you since space probes,

这种热能被用在空间探测仪上，

and, in the past, in pacemakers for hearts.

而过去被用在心率起搏器上。

The more abruptly nuclear radiation is slowed down,

核辐射减速越快，

the more damage it does to the atoms it hits.

对被击中的原子伤害就越大。

This is called ionization.

这被称之为电离。

Alpha causes the most ionization as it crashes into other atoms

阿尔法粒子撞击其他原子时造成的电离最大，

and gamma the least.

而伽马造成的电离最小。

In humans, the most serious effect of radiation

对人类而言，发射对人体最大的危害

is the damage that it can cause to our DNA.

在于其对DNA的伤害。

Although alpha cannot penetrate your skin,

尽管阿尔法粒子不能穿透皮肤，

if you inhale or injest a radioactive nucleus,

如果你误吸食了放射性原子核，

the health consequences can be severe.

对健康影响会严重。

Radioactivity is both useful and deadly,

发射既有用又有危险，

but it is all around us as a background to the natural world.

但它就在我们身边，像自然世界的背景一样。