
Chinese: 
E=mc^2
你常常聽到它
但它是什麼意思
愛因斯坦在它的狹義相對論中提出了質能守恆
而且它們可以在彼此間轉換
他描述了相對論的數學性，說明一個粒子的能量等於
它的質量乘上光速的平方
質能守恆對於核物理的研究相當重要
原子核的研究
這是一個物理的分支用以介紹四大基本作用力的其中兩個
一個是能讓元素在一瞬間轉換成另一種元素
另一種可以讓我們利用每個原子裡面強大的能量
另一種可以讓我們利用每個原子裡面強大的能量
(主題樂)
在我們進入核物理的奇妙世界前

English: 
E=mc^2
You hear it all the time.
But what does it mean?
During his study of special relativity, Albert
Einstein found that mass and energy are equivalent,
and that they can be converted back and forth
between one another.
He described that relationship mathematically,
saying that the energy of a particle is equal
to its mass, times the speed of light squared.
This mass-energy equivalence is critical to
the study of nuclear physics – the study
of the atomic nucleus.
This is a branch of physics that introduces
you to two of the four fundamental forces.
One in which an element can turn into an entirely
different element, in just an instant.
And one that has allowed us to unleash the
incredible energy that’s contained inside
every atom.
[Theme Music]
Before we can dive into the wonders of nuclear
physics, we need to recall a little bit about

English: 
the thing that makes it all tick: the nucleus!
The nucleus of any atom consists of protons
and neutrons.
The proton is positively charged, while the
neutron is electrically neutral, and both
particles have nearly the same mass.
With the exception of hydrogen, which only
has a single proton in its nucleus, every
element has both protons and neutrons.
Because of this, we’ll often refer the two
particles collectively as nucleons.
We can describe how many protons and neutrons
are in an atom’s nucleus using its atomic
and mass numbers.
An atomic number is how many protons are in
a nucleus, which also determines what element
the atom consists of.
The mass number, meanwhile, is how many protons
and neutrons combined make up a nucleus.
So if there are 6 protons and 6 neutrons in
a nucleus, then its atomic number would be
6, making it a carbon nucleus, and the mass
number would be 6+6, or 12!
And if there were 6 protons and 8 neutrons,
then it would still be a carbon nucleus, but
with a mass number of 14.
Let’s put these carbon nuclei in nuclear
notation to better show the differences between them.

Chinese: 
我們需要回頭看一下造就這些的源頭：原子核
任意原子核都由質子與中子組成
質子帶正電，而中子不帶電
而且兩種粒子的質量幾乎相同
唯一一個例外是氫原子，它只有一個質子
其它的都有質子與中子
因此，我們常常將兩種粒子的集合體當作原子核
我們可以藉由原子序與質量數描述一個原子裡有多少質子或中子
我們可以藉由原子序與質量數描述一個原子裡有多少質子或中子
原子序是原子核的質子數它也可以用來判斷這是什麼原子
原子序是原子核的質子數它也可以用來判斷這是什麼原子
質量數是指總共有多少質子與中子組成這個核
所以如果有一個核有6個質子6個中子，那它的原子序就是6
造出了一個碳原子，而它的質量數就是12
再者，如果有6個質子8個中子，那它還是碳原子
但是質量數會是14
我們把這些碳原子放入核子符號中以便於看出它們的差異

English: 
First, we start with the chemical symbol for
the nucleus, which is determined by its atomic number.
Then on the bottom left of the chemical symbol,
we write the atomic number, which will be
the same for both Carbon nuclei, 6.
Finally, we write the mass number on the top
left, to signify how many protons and neutrons
there are in the nucleus.
So for our carbon atom with six neutrons,
we’d take the Carbon chemical symbol, a
capital C, and write the atomic number, 6,
in the bottom left and the mass number, 12,
in the top left.
For the atom with two extra neutrons, the
upper left mass number becomes 14.
Any two nuclei that have the same atomic number
but different mass numbers are known as isotopes,
with most elements having one isotope that
is more common than the others.
For instance, 99% of the carbon on Earth is
Carbon-12, carbon with a mass number of 12.
Only a tiny fraction of all carbon on earth
is Carbon-14, since carbon is most stable
when the number of protons equals the number
of neutrons.
It’s important to know the masses of different
nuclei, since nuclear interactions are all
about mass-energy conversion.
To quantify the mass of a nucleus, we use
the unified atomic mass unit, written just

Chinese: 
首先我們從核的化學符號開始，這取決於它的原子序
然後在化學符號的左下角寫上原子序 ：
兩個都是碳的原子核，6
最後我們在左上角寫上這個原子中總共有多少質子與中子
最後我們在左上角寫上這個原子中總共有多少質子與中子
所以對於我們的碳原子而言有6個中子，我們寫上碳的化學符號
一個字母C，然後在左下寫上原子序6，在左上寫上質量數12
一個字母C，然後在左下寫上原子序6，在左上寫上質量數12
至於多了兩個中子的原子，上方的質量數則會變成14
任意兩個原子如果有相同的原子序，質量數卻不同的，兩者稱為同位素
大部分的原子都有同位素
例如：地球上99%的碳是碳-12
只有一小部分是碳-14
意思就是碳在質子數等於中子數時最穩定
了解不同原子的質量很重要，
因為核子的相互作用跟質能轉變有關
為了量化原子的質量，我們使用統一的單位原子質量，寫作"u"

Chinese: 
一個穩定的碳-12原子的質量會等於12個單位原子質量
這表示一個單位原子質量會等於1.6605*10^-27公斤
好的，現在我們有一個描述元素與它們的同位素的符號
我們可以說能量與它的原子核還有它們的鍵結有關
你必須知道的第一件事是：原子的總質量一定會比
原子核裡的質子中子的質量核少
例如：一個穩定的氦原子核的質量是4.002603u
但是兩個質子與兩個中子(氦原子的原子核組成)的質量是4.032980u
但是兩個質子與兩個中子(氦原子的原子核組成)的質量是4.032980u
意思是氦原子有0.30377u少於核的部位
意思是氦原子有0.30377u少於核的部位
為什麼？
由於那些不同的質量會等於一些能量，
特別是原子核的束縛能

English: 
as a small u, with a single neutral carbon-12
atom equaling exactly twelve unified atomic mass units.
This means that one unified atomic mass unit
is equal to 1.6605 times 10^-27 kilograms.
Okay, now that we have a notation for describing
elements and their isotopes, we can talk about
the energy associated with a nucleus and its
bonds.
The first thing you should know is that the
total mass of a stable nucleus is always less
than the total mass of the individual protons
and neutrons put together.
For instance, the mass of a neutral helium
atom is 4.002603 unified atomic mass units.
But two neutrons and two protons – the component
parts of a helium atom – taken together
have a mass of 4.032980 unified atomic mass
units.
That means that the nucleus of a helium atom
has 0.030377 unified atomic mass units less
mass than its component parts.
How can that be?
Well, that difference in mass is equal to
an amount of energy, specifically the total
binding energy of the nucleus.

English: 
That binding energy is how much energy you
would have to add to the helium atom in order
to break it apart its nucleus.
The amount of energy required to break up
a nucleus into its component particles gets
larger as the atomic number increases, with
iron having one of the highest binding energies
per nucleon.
But while the total binding energy still increases
for nuclei larger than iron, the binding energy
per nucleon, in fact, decreases.
This means that very large nuclei are not
held together as strongly as small nuclei.
And since binding energy accounts for the
missing mass, you can calculate it using – you
guessed it! – e equals m c squared.
Now, you might be wondering how a nucleus
is held together in the first place.
You’ve got neutral neutrons that have no
problem getting close to one another, but
what about all the positive protons? Shouldn’t
the repulsive electric force keep them apart?
Well, one of the four fundamental forces of
physics is the strong nuclear force, an attractive
force that acts between protons and neutrons
in a nucleus.
This strong force is substantial enough to
overcome the repulsive force between protons,

Chinese: 
那個束縛能就是你需要加進氦原子中才能分開它的原子核
那個束縛能就是你需要加進氦原子中才能分開它的原子核
為了分開原子所需的那些能量會隨著原子序增加
原子核的束縛能會在鐵元素達到最大
原子核的束縛能會在鐵元素達到最大
但是原子序比鐵大的原子核的束縛能不會增加
反而會減少
意思是較大的原子較小的原子不容易維持在一起
而因為束縛能來四消失的質量
所以我們可以使用，你猜到了！E=mc^2
現在，你可能想知道原子核剛開始是如何形成的
不帶電的中子要聚集在一起沒有太大問題
但是那些帶正電的質子呢?
不是有個靜電力會將它們排斥開嗎?
有一個物理上的基本作用力叫做強力
是一種發生於核中的質子與中子的吸引力
強力足夠強大去克服質子間的排斥力

Chinese: 
但它只會發生在非常短的距離內，而靜電力的作用距離比這在長一點
因為強力只會在極短的距離下作用
原子序高的大原子就需要有更多的中子
去克服核中的電磁力並穩定原子核
在高原子序的原子中，那些額外的中子必須要比原子序多30個
你可以在這張圖表上看到穩定原子中的質子數與中子數的關係
你可以在這張圖表上看到穩定原子中的質子數與中子數的關係
而當原子核"不"穩定時，它會衰變成一個更穩定的子核
這些不穩定核的衰變會伴隨著高能粒子的釋放，稱為放射性
這些不穩定核的衰變會伴隨著高能粒子的釋放，稱為放射性
亨利‧貝克勒受先發現了自然放射性
他觀察到一塊含有鈾的礦物會影響一個被紙包住的照相版
即使紙擋掉了可見光，由鈾發出的輻射線還是穿透了紙
並且在盤子上留下痕跡
之後的科學家就研究了不同種的衰變及它們的產物
並依據穿透力區分成三類

English: 
but it only acts over very small distances,
while the electric force acts over longer distances.
Since the strong force only works across such
tiny distances, larger atoms with high atomic
numbers actually require additional neutrons
to overcome the electromagnetic force and
maintain stability within the nuclei.
Those extra neutrons are necessary for atoms
with atomic numbers higher than thirty or
so, as you can see in this chart relating
the number of neutrons to the number of protons
in a stable atom.
And when a nucleus is UNstable, it can break
down into a more stable state.
This decay of unstable nuclei, accompanied
by emission of energetic particles, is known
as radioactivity.
Natural radioactivity was first discovered
by Henri Becquerel, who observed how a chunk
of mineral that contained uranium affected
a photographic plate that was covered up by paper.
Even though the paper was blocking out visible
light, the radiation from the uranium penetrated
the paper and left its mark on the plate.
Later scientists studied such decays and categorized
the emitted rays or particles into three different
groups, based on their penetrating power.

English: 
First, there’s alpha decay, which is released
when an unstable nucleus loses two protons
and two neutrons, becoming a different element
in the process.
In alpha decay, there’s a parent nucleus
– which is the original, unstable nucleus
– and it decays into a daughter nucleus
and an alpha particle, which is actually just
the nucleus of a Helium atom.
This decay occurs because the parent nucleus
is too large, and the strong force is no longer
sufficient to hold all the nucleons together.
For example, if the parent nucleus is radium,
it would decay into radon and emit a single
alpha particle.
The process of the nucleus changing from one
element to another is known as transmutation.
Note that the atomic number of radon is just
two units less than that of radium, and the
mass number is four less than radium’s.
In alpha decays, the sum of the atomic and
mass numbers are always equal on either side
of the equation.
But even though those numbers of nucleons
add up, remember: Mass and energy are equivalent.
So the products of this reaction always have
less total mass – as measured in unified
atomic mass units – than the parent nucleus
has.

Chinese: 
第一種是alpha衰變，它會從不穩定的母核中釋放出兩個質子和兩個中子
並形成一個不同的元素
在alpha衰變中，原本有一個不穩定的母核，
然後它會衰變成一個子核與alpha粒子
alpha粒子其實就是氦原子核
這種衰變是因為母核太大了，強力沒辦法再維持整個核而發生
這種衰變是因為母核太大了，強力沒辦法再維持整個核而發生
例如：
假設母核是鐳，它會衰變成氡和一個alpha粒子
例如：
假設母核是鐳，它會衰變成氡和一個alpha粒子
原子核由一個核衰變成另一個的過程稱為核嬗變
注意到氡的原子序比鐳少了2個
而質量數比鐳少了4個
在alpha衰變中，方程式兩邊的原子序與質量數的總和一定會相等
在alpha衰變中，方程式兩邊的原子序與質量數的總和一定會相等
但即便核中的數字被加總了，還是要記得：質能守恆
所以反應的產物總質量(測量得的原子基本質量)
一定會比反應物的質量少

English: 
The rest of mass turned into kinetic energy,
and the kinetic energy released in nuclear
reactions is what’s used to generate nuclear
power!
But alpha particles have the least penetrating
power of the three groups – they’re barely
able to pass through a piece of paper.
The second type of decay that can occur is
beta decay, when an unstable nucleus emits
a beta particle, which is just an electron.
You’ll see that whenever an electron is
produced, so is a neutrino.
A neutrino is a particle with a very small
mass that is electrically neutral.
Its existence is inferred from the conservation
of energy.
For example, when a nucleus at rest decays
into two fragments, it should give each fragment
the same amount of momentum.
If the nucleus decayed into the daughter nucleus
and an electron, the electron would always
have the same momentum, and the same energy.
But electrons from beta decay have been found
to have energies that vary greatly.
This suggests that a third particle must be
carrying away the rest of energy.
And experiments have confirmed that these
tiny, neutral neutrinos are responsible for
that missing energy.
Now, a unique part of beta decay is that no
nucleons are emitted during the decay process.

Chinese: 
失去的質量會轉變為動能，而這些反應產生的動能會被用作核電
失去的質量會轉變為動能，而這些反應產生的動能會被用作核電
但是alpha粒子的穿透力是最弱的
它連一張紙也很難穿過
第二種可能發生的衰變是beta衰變
而不穩定的核會發射出beta粒子，也就是電子
你會看到每當電子產生時，都會附帶微中子
微中子是質量非常小的電中性基本粒子
推斷它的存在是為了能量守恆
例如：
當一個核衰變成兩個部分時
每個部分都會帶有相同的動量
如果母核衰變成子核及電子
每個電子需要帶有一樣的動量與能量
但是從beta衰變來的電子被發現到它們帶有的能量差異很大
這意味著還有第三個粒子攜帶著剩下的能量
實驗確認了這些微小、中性電的微中子確實負責了這些失去的能量
實驗確認了這些微小、中性電的微中子確實負責了這些失去的能量
現在，一個beta衰變的特別部分是當衰變產生時沒有一個核子

Chinese: 
取而帶之的，一個中子轉變成了質子
再來為了平衡電量的改變，中子又釋放了一個電子
即使這些電子來自核衰變
它們還是與在標準軌域上運行的電子為同種粒子
當中子轉變為質子，核就會從一種元素變為另一種
又是一個核嬗變的例子
而beta衰變是因為另一種基本作用力：弱力
當強力在核子中作用時，弱力會改變夸克
一種組成質子中子的基本粒子
藉由改變一種夸克成另一種
弱力做到了將中子變成質子
至於穿透力，beta粒子居中，可以被幾毫米的鋁板擋住
至於穿透力，beta粒子居中，可以被幾毫米的鋁板擋住
第三種是gamma衰變，藉由釋放gamma射線，讓核的能量下降
第三種是gamma衰變，藉由釋放gamma射線，讓核的能量下降
這個衰變當一個核處在一個高能的狀態下發生
核子會從一個高能的粒子衰變為一個能量較低的粒子
核子會從一個高能的粒子衰變為一個能量較低的粒子

English: 
Instead, one of the neutrons changes into
a proton.
And to compensate for the change in charge,
the neutron emits an electron.
And although these electrons come from nuclear
decay, they’re the same kind of electrons
that orbit a standard nucleus.
Once the neutron changes into a proton, the
nucleus changes from one element to another,
again an instance of transmutation.
And beta decay is caused by the fourth fundamental
force, the weak force.
While the strong force acts on nucleons, the
weak force alters quarks, the fundamental
particles that make up both protons and neutrons.
By converting quarks of one type into another,
the weak force causes the neutron to turn
into a proton.
As for their penetrating power, beta particles
are typically stopped by a few millimeters
of aluminum.
The third kind of decay is gamma decay, which
is what results when a nucleus emits high-powered
photons, in what are known as gamma rays.
This kind of decay usually occurs when a nucleus
is in an excited state, which can happen because
the nucleus is decaying from a larger form,
or because it collided with a high-energy
particle, among other reasons.

Chinese: 
重點是：如果原子想從高能轉變為低能
它可以藉由釋放質子達成
不像前面兩種，gamma衰變不是一種核嬗變
反而，從高能粒子衰變成低能粒子與gamma射線
gamma射線是穿透力最強的，需要一層很厚的鉛板才能阻擋
gamma射線是穿透力最強的，需要一層很厚的鉛板才能阻擋
其實如果有時間的話還有許多東西可以討論
半衰期、放射碳定年法、核能的基礎......等等
但是E=mc^2，現在至少你知道它是什麼意思
還有小小的原子如何釋放出巨大的能量
10分鐘怎麼夠呢?
今天我們學到了核物理的基礎，包含原子序、質量數、
還有如何使用它們的符號
我們同時也討論了束縛能與質能守恆
還有強力、弱力
最後，我們認識了三種主要的放射性衰變：alpha、beta、gamma衰變
(訂閱)

English: 
But the point is, when a nucleus is excited,
it wants to transition to a lower-energy state,
which it can do by releasing a photon.
Unlike alpha and beta decay, no transmutation
occurs in gamma decay.
Instead, the excited nucleus just decays into
a ground state nucleus and a gamma ray.
Gamma rays have the highest penetrating power,
requiring large amount of concrete or lead
to stop their propagation.
And there’s so much more we could talk about
if we had the time! Half-lives, radiocarbon
dating, the basics of nuclear power, just
to name a few.
But, e=mc squared – now at least you know
what it means, and how such tiny objects as
atoms can release such enormous power.
That’s worth 10 minutes of your time, right?
Today we learned the very basics of nuclear
physics, including atomic number, mass number,
and how to use them in nuclear notation.
We also discussing binding energy and mass-energy
equivalence, as well as the strong and weak
nuclear forces.
Finally, we discussed the three major types
of radioactive decay: alpha, beta, and gamma.
Crash Course Physics is produced in association
with PBS Digital Studios.

Chinese: 
(訂閱)
(訂閱)
(訂閱)
(訂閱)

English: 
You can head over to their channel to check
out a playlist of the latest amazing shows like:
Gross Science, Coma Niddy, and Blank on Blank.
This episode of Crash Course was filmed in
the Doctor Cheryl C. Kinney Crash Course Studio
with the help of these amazing people and
our equally amazing graphics team, is Thought Cafe.
