The Nuclear Atom
A-Level Physics Topic 11 19:00 English narration · English + 中文 subtitles burned in
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Over a hundred years ago, physicists fired tiny alpha particles at a sheet of gold foil, thinner than paper.
一百多年前，物理学家把微小的阿尔法粒子射向一张比纸还薄的金箔。
They expected the particles to sail straight through, like bullets through mist.
他们以为这些粒子会径直穿过去，就像子弹穿过薄雾。
And most did.
大多数确实如此。
But every so often, a particle bounced almost straight back.
但每隔一会儿，就有一个粒子几乎笔直地弹了回来。
Rutherford was stunned.
卢瑟福大为震惊。
He said it was as if you fired a shell at tissue paper, and it bounced back and hit you.
他说这就好像你朝一张薄纸射出一发炮弹，它却弹回来打中了你。
The only explanation: hidden inside each atom is a tiny, dense core — the nucleus.
唯一的解释是： 每个原子内部都藏着一个微小而致密的核心——原子核。
Here is the apparatus.
这就是实验装置。
An alpha source sits inside an evacuated chamber, so the particles are not stopped by air.
阿尔法源放在抽成真空的腔室里，这样粒子不会被空气挡住。
A thin gold foil stands in the beam.
一束金箔立在射线路径上。
A zinc sulfide screen on a movable microscope detects flashes where alpha particles hit.
装在可移动显微镜上的硫化锌屏，在阿尔法粒子打到的地方闪出光点。
By swinging the detector round to different angles, Geiger and Marsden counted how many particles went straight on, how many deflected a little, and how many scattered through large angles — even back the way they came.
盖革和马斯登把探测器转到不同角度，数出有多少粒子径直前进、有多少略微偏转、 又有多少大角度散射——甚至原路弹回。
About one in eight thousand bounced through more than ninety degrees.
大约八千分之一会偏转超过九十度。
That rare event changed the model of the atom forever.
那个罕见事件彻底改变了原子模型。
Three details of the apparatus are asked as often as the result.
关于装置的三个细节，考的次数和结果一样多。
The foil is thin so that each alpha particle meets at most one nucleus and is not absorbed.
金箔要薄，这样每个 α 粒子最多只遇到一个原子核，而且不会被吸收。
The chamber is a vacuum so the alpha particles are not stopped or scattered by air.
腔体要抽成真空，这样 α 粒子不会被空气阻挡或散射。
And gold is used because it can be beaten into a very thin sheet.
用金是因为它能被打成非常薄的一片。
Only a particle that approaches almost head-on is turned back: both are positive, so the electrostatic repulsion is enormous at small separation, and because the nucleus is far more massive it is the alpha particle that reverses.
只有几乎正对着原子核飞过去的粒子才会被弹回来： 两者都带正电，所以在很小的间距上静电斥力极大， 而由于原子核质量大得多，反向的是 α 粒子。
The paths tell the story.
轨迹本身就在讲故事。
Most alpha particles sail nearly straight through with very little deflection, so the atom is mostly empty space.
大多数阿尔法粒子几乎直线穿过、偏转很小，所以原子绝大部分是空的。
A few curve gently, deflected by the electric field of a concentrated positive charge.
少数轻轻弯折，被一处集中的正电荷的电场偏转。
A rare head-on approach is flung almost straight back.
极少数迎头撞上，几乎原路弹回。
Rutherford concluded: a tiny, dense, positively charged nucleus sits at the centre, and almost all of the atom's mass is packed there.
卢瑟福得出结论：中心有一个微小、致密、带正电的原子核，原子几乎全部质量都挤在那里。
Order of magnitude: the atom is about ten to the minus ten metres across; the nucleus is about ten to the minus fifteen metres — roughly a hundred thousand times smaller.
数量级上：原子直径大约是十的负十次方米；原子核大约是十的负十五次方米—— 比原子小大约十万倍。
The mark scheme pairs the three results with their conclusions exactly like this, so learn them as pairs.
评分标准把三个结果和它们的结论严格地这样配对，所以要成对地记。
The vast majority pass straight through with little or no deflection — so most of the atom is empty space.
绝大多数粒子直接穿过，几乎没有偏转——所以原子的大部分是空的。
A small number are deflected through small angles — so there is a concentrated positive charge that repels the positive alpha particles.
一小部分被偏转了小角度——所以存在一个集中的正电荷，排斥带正电的 α 粒子。
And a very small minority, about one in eight thousand, are deflected through more than ninety degrees, some straight back — so the nucleus is very small compared with the atom and contains almost all of its mass.
而极少数，大约八千分之一，偏转超过九十度，有些甚至被原路弹回—— 所以原子核相对原子非常小，而且几乎集中了原子的全部质量。
Inside every atom is a hidden world.
每个原子内部都是一个隐藏的世界。
Today: the nucleus and what it is made of, the radiation it gives off, and the fundamental particles that build everything.
今天：原子核以及它由什么构成、它放出的辐射， 以及构筑万物的基本粒子。
Let's begin.
让我们开始吧。
Here is the model.
这就是这个模型。
At the centre sits the nucleus, made of protons and neutrons, packed tightly together.
中心坐着原子核，由质子和中子紧紧地挤在一起构成。
Around it, far away, orbit the electrons.
在它周围、很远的地方，电子在绕行。
The nucleus is astonishingly small — if the atom were a stadium, the nucleus would be a marble at its centre.
原子核小得惊人——如果原子是一座体育场， 原子核就是场中央的一颗弹珠。
Two numbers describe it: the proton number, how many protons there are, and the nucleon number, the protons and neutrons together.
用两个数来描述它：质子数，也就是有多少个质子； 以及核子数，也就是质子和中子加在一起的总数。
Look at two simple models.
看两个简单模型。
Helium has two protons and two neutrons in the nucleus, and two electrons on one shell.
氦核里有两个质子和两个中子，壳层上有两个电子。
Lithium has three protons and four neutrons, with electrons on two shells — two inner, one outer.
锂有三个质子和四个中子，电子分布在两层壳上——内层两个，外层一个。
Protons carry charge plus e; neutrons carry zero; electrons carry minus e.
质子带正电荷，中子不带电，电子带负电荷。
The proton and neutron have almost the same mass — roughly one unified atomic mass unit each.
质子和中子质量几乎相同—— 大约各是一个统一原子质量单位。
The electron is far lighter: about one over one thousand eight hundred thirty-six of the proton's mass.
电子轻得多：大约只有质子质量的一千八百三十六分之一。
A neutral atom has the same number of electrons as protons.
中性原子的电子数与质子数相等。
We write a nucleus like this: the chemical symbol, with the nucleon number on top, and the proton number below.
我们这样书写一个原子核：化学符号，上方写核子数，下方写质子数。
The proton number fixes which element it is.
质子数决定它是哪种元素。
But the number of neutrons can vary — and those variations are called isotopes: same element, same protons, but different masses.
但中子的数目可以变化——这些变体就叫做同位素：同一种元素、相同的质子数，但质量不同。
Carbon-twelve and carbon-fourteen are both carbon, just with different numbers of neutrons.
碳十二和碳十四都是碳，只是中子数不同。
For any nuclide written A Z X, three linked numbers matter.
对写成核子数、质子数加符号的任何核素，有三个互相关联的数。
The proton number Z — also called the atomic number — counts the protons and fixes the element.
质子数也叫原子序数，数的是质子，并决定元素种类。
The nucleon number A — also the mass number — counts all nucleons: protons plus neutrons.
核子数也叫质量数，数的是全部核子：质子加中子。
The neutron number is then N equals A minus Z.
于是中子数等于核子数减去质子数。
Isotopes share the same Z but differ in A, so they differ in N.
同位素有相同的质子数但不同的核子数， 所以中子数也不同。
Chemically they behave alike; in the nucleus they do not.
化学性质相同；核里的行为却不同。
Nuclear masses need a handy unit.
核质量需要一个方便的单位。
The unified atomic mass unit, symbol u, is defined so that a carbon-twelve atom has mass exactly twelve u.
统一原子质量单位的符号是尤，定义为碳十二原子质量恰好等于十二个尤。
Numerically, one u equals one point six six one times ten to the minus twenty-seven kilograms.
数值上，一尤等于一点六六一乘以十的负二十七次方千克。
A proton has mass about one point zero zero seven u; a neutron about one point zero zero nine u; an electron about five point five times ten to the minus four u — almost negligible beside a nucleon.
质子质量大约一点零零七尤；中子大约一点零零九尤；电子大约五点五乘以十的负四次方尤—— 和核子比几乎可以忽略。
An unstable nucleus rearranges itself and throws out radiation — this is radioactive decay — and there are three kinds.
不稳定的原子核会重新排列并放出辐射——这就是放射性衰变——一共有三种。
Compare them on four things: charge, mass, ionising power and penetration.
要从四个方面比较它们：电荷、质量、电离能力和穿透能力。
Alpha is a helium nucleus — two protons and two neutrons, heavy and positive; it is stopped by paper.
阿尔法是一个氦核——两个质子和两个中子， 又重又带正电；一张纸就能挡住它。
Beta is a fast electron — light and negative; it is stopped by aluminium.
贝塔是一个高速电子——又轻又带负电；一层铝就能挡住它。
Gamma is a burst of pure energy — no mass, no charge; it takes thick lead to stop it.
伽马是一束纯能量——没有质量、没有电荷；要用厚厚的铅才能挡住它。
Heaviest to lightest: alpha, beta, gamma.
从最重到最轻：阿尔法、贝塔、伽马。
Compare penetrating power side by side.
并排比较贯穿本领。
Alpha is stopped by a sheet of paper — or a few centimetres of air.
阿尔法被一张纸挡住——或者几厘米的空气。
Beta travels about a metre in air and needs a few millimetres of aluminium.
贝塔在空气中大约能走一米，需要几毫米铝才能挡住。
Gamma goes much further; it is only strongly attenuated by several centimetres of lead or about a metre of concrete, and in free space it follows the inverse-square law.
伽马走得远得多；只有几厘米铅或大约一米混凝土才能强烈衰减它， 在自由空间里它服从平方反比定律。
Ionising power runs the other way: alpha is the strongest ioniser, beta weaker, gamma the weakest.
电离本领则相反：阿尔法最强，贝塔较弱，伽马最弱。
The particles that stop soonest dump their energy fastest.
最先停下来的粒子把能量泄得最快。
A cloud chamber makes alpha tracks visible.
云室能让阿尔法径迹可见。
Each alpha particle leaves a short, straight, thick trail of tiny droplets as it ionises the cold gas.
每个阿尔法粒子电离冷气体时，留下一条短而直、粗的微滴轨迹。
The trails fan out from a small source — here americium-two-forty-one.
轨迹从小源向外散开——这里是镅二百四十一。
Notice the short, nearly equal lengths: the alphas all carry about the same kinetic energy.
注意那些短而几乎等长的轨迹： 阿尔法粒子的动能几乎都相同。
That matches a discrete energy spectrum — one decay gives alphas at one or a few sharp energies.
这与分立能谱相符——一次衰变给出一个或少数几个尖锐能量。
Alpha mass is about four u; charge is plus two e.
阿尔法质量约四个尤；电荷为正二倍基本电荷。
There are two kinds of beta particle.
贝塔粒子有两种。
Beta-minus is a fast electron, given out when a neutron turns into a proton.
贝塔负是高速电子，在中子变成质子时放出。
Beta-plus is the positron — the electron's antiparticle — given out when a proton in a proton-rich nucleus turns into a neutron.
贝塔正是正电子——电子的反粒子——在富质子核里的一个质子变成中子时放出。
Both have mass about one over one thousand eight hundred thirty-six u, much less than alpha.
两者质量大约都是一千八百三十六分之一尤，远小于阿尔法。
Charge is minus e for beta-minus, plus e for beta-plus.
贝塔负电荷为负，贝塔正电荷为正。
Their energy spectrum is continuous, up to a maximum.
它们的能谱是连续的，一直到某个最大值。
Gamma radiation is a high-energy photon — part of the electromagnetic spectrum.
伽马辐射是高能光子——电磁波谱的一部分。
Rest mass zero, charge zero.
静质量为零，电荷为零。
A nucleus often emits a gamma ray as a tidy-up step after an alpha or beta decay leaves the daughter nucleus in an excited state.
原子核常在阿尔法或贝塔衰变之后放出伽马射线作为整理步骤， 因为子核被留在了激发态。
As the daughter drops between nuclear energy levels, it releases a gamma photon at a sharp energy.
子核在核能级之间下落时，放出能量尖锐的伽马光子。
So the gamma spectrum shows discrete energies, like alpha — not continuous like beta.
所以伽马能谱是分立的，像阿尔法——不像贝塔那样连续。
When a nucleus decays, it transforms — changing into a different nucleus, and firing out a particle.
当一个原子核衰变时，它会转变——变成另一种原子核，并射出一个粒子。
Watch an unstable nucleus break apart.
看一个不稳定的原子核裂开。
Two things are always conserved: the total nucleon number, and the total charge.
有两样东西永远守恒：总核子数和总电荷。
Whatever happens, the totals on both sides of the equation must match.
无论发生什么，方程两边的总和都必须相等。
Nothing is created or destroyed — the books always balance.
没有东西被创造或消灭——账目永远是平的。
Let's write it down.
我们把它写下来。
In alpha decay, a nucleus loses two protons and two neutrons.
在阿尔法衰变中，一个原子核失去两个质子和两个中子。
Uranium-two-thirty-eight becomes thorium-two-thirty-four, plus an alpha particle.
铀二三八变成钍二三四，加上一个阿尔法粒子。
Check the top numbers: two thirty-eight equals two thirty-four plus four.
核对上面的数：二三八等于二三四加四。
Check the bottom: ninety-two equals ninety plus two.
核对下面的数：九十二等于九十加二。
In beta-minus decay, a neutron turns into a proton, and out shoots an electron.
在贝塔负衰变中，一个中子变成一个质子， 并射出一个电子。
Every equation must balance, top and bottom.
每一个方程，上下都必须平衡。
A nucleus at rest recoils, and that is a momentum question in disguise.
静止的原子核会反冲，这其实是一道伪装过的动量题。
When a stationary nucleus emits an alpha particle, momentum is conserved, so the daughter nucleus and the alpha particle move off in opposite directions with momenta of equal magnitude.
静止的原子核放出 α 粒子时动量守恒， 所以子核和 α 粒子朝相反方向飞出，动量大小相等。
Since p equals m v, the lighter alpha particle moves much faster; and since kinetic energy is p squared over two m, it also carries away much the larger share of the energy.
因为 p 等于 m v，较轻的 α 粒子速度快得多； 又因为动能等于 p 平方除以二 m，它也带走了大得多的那份能量。
Here are the general patterns.
这是一般形式。
In alpha decay, nucleon number falls by four and proton number by two: A Z X goes to A-minus-four, Z-minus-two Y, plus the alpha.
阿尔法衰变中，核子数减四、质子数减二：母核变成核子数减四、质子数减二的子核， 加上阿尔法。
In beta-minus decay, A stays the same and Z rises by one: the nucleus emits an electron and an antineutrino.
贝塔负衰变中，核子数不变，质子数加一：核放出一个电子和一个反中微子。
Check every time: total A before equals total A after; total charge before equals total charge after.
每次都要核对：衰变前总核子数等于衰变后；衰变前总电荷等于衰变后。
Those two conservation rules are how you balance any nuclear equation.
这两条守恒律就是平衡任何核方程的方法。
Determine quantitatively the changes, which is the phrasing the question uses.
「定量确定这些变化」，题目就是这么问的。
Alpha emission: the nucleon number falls by four and the proton number by two.
α 衰变：核子数减少四，质子数减少二。
Beta-minus emission: the nucleon number is unchanged and the proton number rises by one.
β 负衰变：核子数不变，质子数增加一。
Beta-plus emission: the nucleon number is unchanged and the proton number falls by one.
β 正衰变：核子数不变，质子数减少一。
Gamma emission changes neither.
γ 衰变：两者都不变。
Worked example.
例题。
Uranium-two-thirty-eight decays by alpha emission: daughter thorium-two-thirty-four.
铀二三八发生阿尔法衰变：子核是钍二三四。
Carbon-fourteen decays by beta-minus emission: A stays fourteen, Z rises from six to seven — so the daughter is nitrogen-fourteen, plus an electron and an antineutrino.
碳十四发生贝塔负衰变： 核子数仍是十四，质子数从六升到七——所以子核是氮十四，加上电子和反中微子。
For beta-plus decay the pattern flips: A stays the same, Z falls by one, and a positron plus a neutrino come out.
贝塔正衰变的模式相反：核子数不变，质子数减一，放出正电子和中微子。
Same balancing rules, every time.
每次都用同一套平衡规则。
Here is a clue that revealed a hidden particle.
这里有一条线索，它揭示了一个隐藏的粒子。
Alpha particles always come out with the same, exact energy — a sharp spike.
阿尔法粒子总是带着相同、精确的能量射出—— 一道尖锐的峰。
But beta particles come out with a whole range of energies — a smooth spread.
但贝塔粒子却带着一整段范围的能量射出——一片平滑的分布。
Something was carrying off the missing energy.
有什么东西把缺失的能量带走了。
That something is the neutrino: a ghostly particle, almost impossible to detect, emitted alongside every beta decay.
那个东西就是中微子：一种幽灵般的粒子，几乎无法探测， 在每一次贝塔衰变中一同被放出。
Why the difference?
为什么会不同？
In alpha decay the energy released is shared between just two particles: the daughter nucleus and the alpha.
阿尔法衰变中，释放的能量只在两个粒子之间分配：子核和阿尔法。
Conservation of momentum and energy then fixes the alpha's kinetic energy to one value — discrete.
动量守恒和能量守恒于是把阿尔法的动能固定为一个值——分立。
In beta decay the energy is shared between three particles: the daughter, the beta, and the neutrino or antineutrino.
贝塔衰变中，能量在三个粒子之间分配：子核、贝塔，以及中微子或反中微子。
The beta can take any share from zero up to a maximum, so its spectrum is continuous.
贝塔可以从零一直分到最大值的任意份额，所以它的谱是连续的。
Every particle has an antiparticle with the same mass but opposite charge.
每个粒子都有一个反粒子，质量相同但电荷相反。
The positron is the antiparticle of the electron.
正电子是电子的反粒子。
In beta-minus decay an antineutrino is always emitted with the electron; in beta-plus decay a neutrino comes out with the positron.
贝塔负衰变中总是伴随电子放出一个反中微子；贝塔正衰变中则伴随正电子放出一个中微子。
Neutrinos and antineutrinos have zero charge, very small mass, and barely interact — they are very hard to detect — but they must be there to balance energy, momentum, and other conserved quantities.
中微子和反中微子电荷为零、质量极小、几乎不相互作用——极难探测—— 但它们必须存在，才能平衡能量、动量和其他守恒量。
Antimatter as the syllabus states it: every particle has an antiparticle of the same mass and opposite charge, so a positron and an electron are alike in mass and in the size of their charge, and differ only in its sign.
考纲对反物质的说法是： 每一种粒子都有一种质量相同、电荷相反的反粒子， 所以正电子和电子质量相同、电荷大小相同，只有符号不同。
An antihydrogen atom is the whole idea in one object — an antiproton with a positron in orbit around it, instead of a proton with an electron.
反氢原子把这个想法浓缩成一个物体—— 一个反质子，外面绕着一个正电子，而不是质子配电子。
But protons and neutrons are not the end of the story.
但质子和中子并不是故事的终点。
They are built from even smaller things, called quarks — truly fundamental, as far as we know.
它们是由更小的东西构成的，叫做夸克—— 据我们所知，它们是真正基本的。
There are six flavours: up, down, strange, charm, top, and bottom.
夸克有六种味：上、下、奇、粲、顶、底。
Each carries a fraction of the electron's charge.
每一种都带有电子电荷的一个分数。
The up quark has plus two-thirds; the down quark has minus one-third.
上夸克带正三分之二；下夸克带负三分之一。
And every quark has an antiquark, with the opposite charge.
而且每一个夸克都有一个反夸克，带相反的电荷。
Here are the six flavours by charge.
这是六种味按电荷排列。
Up, charm, and top each carry plus two-thirds e.
上、粲、顶各带正三分之二基本电荷。
Down, strange, and bottom each carry minus one-third e.
下、奇、底各带负三分之一。
Each antiquark flips the sign: anti-up is minus two-thirds, anti-down is plus one-third.
每个反夸克把符号反过来：反上是负三分之二，反下是正三分之一。
No other quark property is tested at this level — charge composition is the key exam skill.
本级别不考夸克的其他性质——电荷组成才是关键应试技能。
Add the fractions carefully when you build a proton or a neutron.
搭建质子或中子时，把分数仔细加起来。
Now build the particles.
现在来搭建粒子。
A proton is two up quarks and one down.
一个质子是两个上夸克加一个下夸克。
A neutron is one up and two down.
一个中子是一个上夸克加两个下夸克。
Check the charges — they add up perfectly.
核对一下电荷——它们加起来正好。
Particles made of quarks are called hadrons.
由夸克构成的粒子叫做强子。
Three quarks make a baryon, like the proton.
三个夸克组成一个重子， 比如质子。
A quark and an antiquark make a meson.
一个夸克加一个反夸克组成一个介子。
And electrons?
那电子呢？
They are not made of quarks at all — they are leptons, fundamental on their own.
它根本不是由夸克构成的—— 它是轻子，自身就是基本粒子。
Classify everything on one tree.
用一棵树给万物分类。
Particles split into fundamental ones and hadrons.
粒子分成基本粒子和强子。
Fundamental means quarks, and leptons such as the electron and the neutrino — point-like, with no smaller parts as far as we know.
基本的是夸克，以及电子、中微子这类轻子—— 据我们所知是点状的、没有更小的部件。
Hadrons are made of quarks: baryons like the proton and neutron from three quarks, and mesons from a quark plus an antiquark.
强子由夸克构成：重子如质子和中子由三个夸克组成， 介子由一个夸克加一个反夸克组成。
So protons and neutrons are not fundamental — they are baryons built from quarks.
所以质子和中子不是基本的——它们是由夸克搭建的重子。
That is the exam answer to "which are fundamental?"
这就是“哪些是基本粒子”的考试答案。
Beta decay is really a quark, changing flavour.
贝塔衰变其实是一个夸克在改变它的味。
In beta-minus decay, one down quark inside a neutron flips into an up quark — turning the neutron into a proton, and releasing an electron.
在贝塔负衰变中，中子里的一个下夸克翻转成一个上夸克—— 把中子变成质子，并放出一个电子。
In beta-plus decay, an up quark flips to a down — turning a proton into a neutron.
在贝塔正衰变中，一个上夸克翻转成一个下夸克—— 把质子变成中子。
Deep down, radioactivity is quarks, transforming.
归根到底，放射性就是夸克在转变。
Follow the diagram.
跟着图走。
A neutron is up-down-down.
中子是上下下。
One down quark turns into an up quark, so the trio becomes up-up-down — a proton.
一个下夸克变成上夸克，三人组就变成上上下——质子。
Out go a beta-minus particle and an electron antineutrino.
放出一个贝塔负粒子和一个电子反中微子。
In symbols: d goes to u, plus beta-minus, plus antineutrino.
符号上：下变成上，加上贝塔负，加上反中微子。
Charge check on the quarks: minus one-third becomes plus two-thirds, a jump of plus one, matching the emitted electron's charge of minus one on the other side of the ledger.
夸克电荷核对：负三分之一变成正三分之二，跳了正一，与另一边放出电子的负电荷相匹配。
A bubble chamber reveals the curved tracks of charged particles in a magnetic field.
气泡室能显示带电粒子在磁场中的弯曲径迹。
Only charged particles leave tracks; neutrinos slip through invisible.
只有带电粒子留下轨迹；中微子悄无无息地穿过。
Curvature tells you momentum and the sign of the charge.
曲率告诉你动量和电荷符号。
This is how particle physicists first mapped hadrons, leptons, and the products of decays — and why the classification tree is not just theory.
粒子物理学家正是靠这个首次描绘出强子、轻子和衰变产物—— 分类树并不只是理论。
Remember: leptons such as electrons and neutrinos are fundamental; hadrons are not.
记住：电子和中微子这类轻子是基本的；强子不是。
Three marks to secure.
三个要拿稳的分。
First, in every decay equation, nucleon number and charge must both balance.
第一，在每一个衰变方程中，核子数和电荷都必须平衡。
Second, alpha is a helium nucleus, beta is an electron, gamma is a photon.
第二，阿尔法是氦核，贝塔是电子，伽马是光子。
Third, a proton is up-up-down, a neutron is up-down-down.
第三，质子是上上下，中子是上下下。
Master these, and the nuclear atom is yours.
掌握这些，原子核就是你的了。
The fixed-wording definitions, one answer only.
固定措辞的定义，只给一个答案。
Proton number: the number of protons in a nucleus.
质子数：原子核中质子的数目。
Nucleon number: the total number of protons and neutrons.
核子数：质子和中子的总数。
Isotopes: nuclei of the same element — the same number of protons — with different numbers of neutrons; defining them by "different mass" alone does not score.
同位素：同一元素的原子核——质子数相同——但中子数不同； 只说「质量不同」不得分。
A nuclide: a nucleus with a particular number of protons and a particular number of neutrons.
核素：具有特定质子数和特定中子数的原子核。
The unified atomic mass unit: one twelfth of the mass of an atom of carbon-12.
统一原子质量单位：碳十二原子质量的十二分之一。
An antiparticle: the same mass as its particle, opposite charge.
反粒子：质量与对应粒子相同、电荷相反。
A fundamental particle: one that cannot be broken down further.
基本粒子：不能再被分解成更小粒子的粒子。
A hadron: a particle made of quarks — a baryon of three, or a meson of a quark AND AN ANTIQUARK.
强子：由夸克构成的粒子——三个夸克组成重子，一个夸克加一个反夸克组成介子。
A lepton: a fundamental particle not made of quarks.
轻子：不由夸克构成的基本粒子。
The traps.
陷阱。
The straight-through result shows empty space; it is the large-angle deflections that show the concentrated positive charge.
直接穿过的结果说明的是原子内部大部分是空的； 是大角度偏转才说明存在集中的正电荷。
A positron is written with plus one, and Z goes DOWN by one.
正电子写作上标零、下标正一，而且 Z 是减一。
Beta-minus goes with the antineutrino, beta-plus with the neutrino.
β 负衰变伴随反中微子，β 正衰变伴随中微子。
Protons and neutrons are not fundamental — only quarks and leptons are.
质子和中子不是基本粒子——只有夸克和轻子才是。
And an antiquark's charge has the opposite sign to its quark's.
另外反夸克的电荷与对应夸克符号相反。