Radioactivity: Expect the unexpected - Steve Weatherall

放射性元素:超乎你的想像 - Steve Weatherall

931,107 views

2012-12-10 ・ TED-Ed


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Radioactivity: Expect the unexpected - Steve Weatherall

放射性元素:超乎你的想像 - Steve Weatherall

931,107 views ・ 2012-12-10

TED-Ed


請雙擊下方英文字幕播放視頻。

00:00
Transcriber: Andrea McDonough Reviewer: Bedirhan Cinar
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譯者: Hao-Wei Chang 審譯者: Jephian Lin
00:13
It is only in the last 100 or so years that human kind has understood
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直到大約近一百多年,
00:18
that the nucleus of the chemical elements is not always fixed.
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人類才明白化學元素的 原子核並非永恆不變。
00:22
It can change spontaneously from one element to another.
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它可以自發性地 從一種元素轉變成另一種元素。
00:26
The name for this process is radioactivity.
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這就叫做放射性。
00:29
You probably already know something about the nucleus:
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你可能已經認識原子核:
00:33
it's much tinier than the atom,
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它比原子還要小的許多,
00:35
it's made of particles called protons and neutrons,
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且由一些被稱為質子和中子的粒子組成,
00:38
there are electrons orbiting around it.
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同時有電子圍繞運行。
00:41
And though the atoms can share or swap electrons when they bond together,
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當原子們形成鍵結時 共享或交換電子,
00:45
the nuclei themselves never change.
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但原子核本身並無改變。
00:47
Right?
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對嗎?
00:48
Well, no.
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嗯,不對。
00:50
Certain nuclei are not stable in that way.
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有些原子核並不穩定。
00:52
This means they may change suddenly,
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這表示它們會突然
00:55
spontaneously.
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且自發性地改變。
00:57
The radioactive nucleus flings out a small particle
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具放射性的原子核會射出粒子
01:00
and transforms into another element, just like that.
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並轉化成另一種元素。就是這樣!
01:03
For example,
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舉例而言:
01:04
the carbon nucleus can eject a fast-moving electron
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碳原子核可以在激發出高速電子之後
01:07
and turn into a nitrogen nucleus.
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轉變成氮原子核。
01:09
There are two different particles that can be emitted from radioactive nuclei,
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有兩種粒子可以被放射性原子核所射出。
01:13
but never together.
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但同個原子核不能同時射出兩種粒子。
01:14
The very fast electron is known as a beta particle.
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高速電子被稱為貝塔粒子。
01:18
If you know a little bit about electrons, you may be thinking,
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如果你對電子有一點點認識, 你可能會疑惑:
01:21
"What was the electron doing in the nucleus in the first place?"
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「為什麼原子核裡會有電子呢?」
01:25
The answer is there is a neutron in nucleus
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答案是因為原子核裡的
01:27
spontaneously changed into a proton,
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中子自發性的轉變為質子,
01:30
which stayed behind,
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並保留在原子核中,
01:31
and the electron flew out as a beta particle.
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而電子就被射出成為貝塔粒子。
01:35
This is not what chemistry has taught us to expect.
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這和我們化學課教的並不相同。
01:37
The nucleus is supposed to be stable.
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原子核應該很穩定才對。
01:40
Neutrons don't change into protons.
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中子應該不會變成質子。
01:42
Except, sometimes they do!
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但有時就是發生了!
01:44
The other particle it emits spontaneously
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另外一種會被自發性地
01:46
from an unstable nucleus is alpha.
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從不穩定的原子核中射出的阿爾法粒子。
01:49
An alpha particle is 8,000 times more massive than beta,
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阿爾法粒子的質量是貝塔粒子的8000倍,
01:53
and it's a bit slower.
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而且它的速度也較慢。
01:54
Alpha is made from two protons and two neutrons.
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阿爾法粒子由兩個質子和兩個中子組成。
01:58
If we trap all those alpha particles together,
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如果我們蒐集到很多的阿爾法粒子,
02:00
we get helium gas.
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我們就得到了氦氣。
02:02
Alpha is a helium nucleus.
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阿爾法粒子就是氦氣的原子核。
02:05
Like the beta particle, you would not have expected
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就像是貝塔粒子一般,你也不會預期
02:08
a heavier nucleus to throw out helium.
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一個較重的原子核會丟出氦原子核。
02:11
But again, it happens,
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但這仍然發生了!
02:13
and the nucleus becomes a new element.
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而這原子核也從而變成另一種元素。
02:16
So, is radioactivity useful or just dangerous?
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那麼,放射性元素到底是有用還是有害呢?
02:20
Wherever you are sitting,
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在你現在坐著的地方
02:21
it is quite likely that there is a device nearby
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就可能有一種裝置包含
02:24
which contains a source of alpha particles:
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可以釋放出阿爾法粒子的元素:
02:27
a smoke detector.
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煙霧偵測器。
02:28
The source is radioactive Americium.
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它含有放射性的鋂。
02:31
You are totally safe from these alpha particles,
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但是阿爾法粒子對你完全無害,
02:33
which cannot travel more than a few centimeters in air.
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它無法在空氣中前進超過數公分。
02:36
Beta particles penetrate much farther
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貝塔粒子相較於阿爾法粒子
02:38
through materials than alpha can.
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有更好的穿透力。
02:41
Radioactive atoms are used in medicine as traces,
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放射性元素可以當作醫用追蹤劑,
02:44
to show where chemicals travel in the patient.
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以顯示特定物質在人體內的移動。
02:46
Beta particles are emitted and have enough energy
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被射出的貝塔粒子具有足夠的能量
02:49
to emerge from the body and be detected.
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可以穿透身體而被偵測到。
02:51
There is a third type of nuclear radiation:
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還有第三種放射形式:
02:54
gamma, which is not a particle at all.
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伽馬,但它不是一種粒子。
02:56
It is an electromagnetic wave,
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它是一種電磁波,
02:58
like microwaves, or light,
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就像是微波或光一樣,
03:01
but it is actually 1,000 times more energentic than visible light.
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但是它比可見光的能量高出一千倍。
03:05
Gamma rays may pass right through your body.
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伽馬射線可以穿透人體。
03:08
Gamma is used to zap the bacteria in fruit to increase its shelf life,
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伽馬射線可以用在水果消毒,以延長保存時間。
03:12
or in radiotherapy to kill cancer cells.
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或是用在放射線治療上殺死癌細胞。
03:15
Radioactive substances get hot,
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放射性元素會放熱,
03:17
and this heat can be used to generate power.
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而這種熱能可以轉換成其他能量。
03:20
This heat has been brought to you since space probes,
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這種熱能被應用在太空探測器上,
03:22
and, in the past, in pacemakers for hearts.
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過去也能用在心臟起搏器中。
03:26
The more abruptly nuclear radiation is slowed down,
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如果放射出的波或粒子 被停下來的速度越快,
03:29
the more damage it does to the atoms it hits.
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對阻擋原子造成的損傷也越大。
03:32
This is called ionization.
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這就是離子化。
03:34
Alpha causes the most ionization as it crashes into other atoms
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阿爾法粒子撞擊其他原子 所造成的離子化程度最大,
03:39
and gamma the least.
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而伽馬射線最小。
03:41
In humans, the most serious effect of radiation
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放射線對人體最嚴重影響是
03:44
is the damage that it can cause to our DNA.
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造成 DNA 損害。
03:47
Although alpha cannot penetrate your skin,
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雖然阿爾法粒子並不足以穿透皮膚,
03:50
if you inhale or injest a radioactive nucleus,
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如果你吸入或吃入放射性元素,
03:52
the health consequences can be severe.
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對健康會有嚴重影響。
03:55
Radioactivity is both useful and deadly,
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放射性元素既有用且致命,
03:59
but it is all around us as a background to the natural world.
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但是它會一直存在我們四周。
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