物理专业英语翻译

第一章

Our material world(物质世界) is composed of many substances distinguished(区别) by their chemical, mechanical, and electrical properties(特性). They are found in nature in various physical states(物理状态)---the familiar solid, liquid, and gas, along with(连同) the ionic "plasma "(等离子体) However, the apparent diversity(多样性) of kinds and forms of material is reduced by the knowledge that there are only a little over 100 distinct chemical elements(元素) and that the chemical and physical features of substances depend merely on the strength of force bonds(结合) between atoms. 我们的物质世界(物质世界)是由许多物质(以区别区别被其化工、机械、、电气性能(特性)。他们是在大自然中找到的材料在不同的物理状态(物理状态)——而且熟悉的固体、液体和气体,随着(连同)离子“等离子体”(等离子体)然而,明显的多样性(多样性)各类形式的资料将减少知识只有一个小超过100种特定的化学元素(元素),化学和物理特征的物质的力量仅仅看力债券(结合)之间的原子。

In turn(依次), the distinctions between the elements of nature arise from(起于) the number and arrangement of basic particles(基本粒子)—electrons(电子), protons(质子), and neutrons(中子). At both the atomic and nuclear levels, the structure of elements is determined by internal forces and energy(内力和内能).

1.1 FORCES AND ENERGY（力和能量）反过来(依次),区别自然元素(源自起于)电话号码和安排基本粒子)-electrons基本粒子(电子),质子((质子),和中子(中子)。在两个原子与核水平,结构是由元素的内力和能量(内力和内能)。11力量和能量(力和能量

*If the specific heat of iron is 0.45J/g·o C, how much energy is required to bring 0.5kg of iron from 0 o C to 100 o C? 如果的比热铁变形、0.45J / g·需要多少能量将铁0.5kg从0(oC)到100(oC)吗?

*State the concept of temperature. What's the difference between the Celsius scale and Kelvin scale? 国家温度的概念。有何区别式温标摄氏度的规模和吗?

*Give some examples of SI units?

1.6 SUMMARY（概要）

*Associated with each basic type of force is an energy, which may be transformed to another form for practical use.The addition of thermal energy to a substance causes an increase in temperature, the measure of particle motion.Electromagnetic radiation arising from electrical devices, atoms or nuclei may be considered as composed of waves or of photons.Matter can be converted into energy and vice versa （反之亦然）; according to Einstein's formula E = mc2.The energy of nuclear fission is millions of times as large as that from chemical reactions.Energy is fundamental to all of man's endeavors and indeed to his survival.

举些例子SI单位简介(概要? 1.6)与相关各基本类型的力量是一种力量,它可以被转化为实际使用另一种形式的热能。增加对某种物质的温度升高引起了一场的方法、质点运动。电磁辐射引起原子或核设备、电子可以被看作是由波或是的光子。物质可以转化为能量,反之亦然(反之亦然);根据爱因斯坦的公式 E = mc2。这些能量的核子分裂在内也远在数百万倍大能量从化学反应。我们的基本人的努力,也正是为了他的性命

第二章 原子与原子核

2.1 ATOMIC THEORY （原子理论）

A complete understanding of the microscopic structure of matter (物质微观结构 ) and the exact nature of the forces acting (作用力的准确性质) is yet to (有待于) be realized. However, excellent models have been developed to predict behavior to an adequate degree of accuracy for most practical purposes. These models are descriptive (描述的) or mathematical often based on analogy (类推) with large-scale process, on experimental data (实验数据), or on advanced theory.

1. 对物质的微观结构和作用力的准确性质的完全认识仍有待于实现。然而，为了实际的用途，能足够精确地预

知物质在微观世界行为的模型已经被研究出来。这些模型是描述性的或数学的，基于对大尺度过程的类推、实验数据或先进的理论。

The most elementary concept (元素概念) is that matter is composed of individual particles (单个粒子) – atoms – that retain their identity (同一性, 特性) as elements in ordinary physical and chemical interactions. Thus a collection of helium atoms (氦原子) that forms a gas has a total weight that is the sum of the weights of the individual atoms. Also, when two elements combine (结合) to form a compound (化合物) (e.g., if carbon atoms (碳原子) combine with oxygen atoms (氧原子) to form carbon monoxide molecules (一氧化碳分子)), the total weight of the new substance is the sum of the origin elements.

2. 公认的物质的概念是：物质是由单个粒子——原子组成，在普通的化学和物理反应中原子保持了元素的特性。因此，因此一团由氦原子组成的气体的重量就是其中每一个原子重量的总和。同样，当两种元素结合成化合物时（例如：碳原子与氧原子结合成一氧化碳分子。），新物质的总重量是原先的元素的质量之和。 There are more than l00 known elements. Each is given an atomic number (原子序数) in the periodic table of the elements (元素周期表)– examples are hydrogen (H) l, helium (He) 2, oxygen (O) 8, and uranium (U) 92. The symbol Z is given to the atomic number, which is also the number of electrons in the atom and determines its chemical properties (性质). The atomic weight (原子质量) M is the weight in grams of a definite (明确的) number of atoms, 6.02 ? 1023 , which is A vogadro’s number (阿佛伽德罗常数), N a .

3. 有超过100种的已知元素。每种元素在元素周期表中都有一个给定的原子序数。例如氢（H ）1，氦（He ）2，

氧（O ）8以及铀（U ）92。符号Z 表示原子序数，这也正是决定着原子化学性质的原子中电子的数目。 原子量M （单位：克）是6.02 ? 1023个原子的质量之和。6.02 ? 1023就是阿佛伽德罗常数，用N a 来表示。 We can easily find the number of atoms per cubic centimeter (每立方厘米) in a substance if its density ρ in grams per cubic centimeter is known. This procedure (程序, 手续) can be expressed as a convenient (便利的) formula for finding N , the number per cubic centimeter for any material

如果每立方厘米内的物质密度ρ已知，我们就可以很容易地求出每立方厘米中原子的个数。任何物质中每立方厘米的原子数都法可以方便的用这个公式算出。

2.2 GASES (气体) Substances in the gaseous state (气态) are described approximately by the perfect gas law 理想气体规律(方程), relating pressure, volume, and absolute temperature (绝对温度), pV=nkT.

An increase in the temperature of the gas due to heating causes greater molecular motion, which results in an increase of particle bombardment (n 炮击；轰击) of a container wall and thus of pressure on the wall.

The particles of gas, each of mass m , have a variety of(多种的) speeds v in accord with 与……一致Ma xwell’s gas theory (麦克斯韦气体理论) as shown in Fig. 2.1.

4. 气态的物质可以用与压力、体积和绝对温度有关的理想气体规律方程pV=nkT 来近似地描述。温度上升将引

起分子运动的加剧——从而引起粒子对容器内壁的碰撞的增加而导致其压力的增大。每种质量（m ）的气体粒子具有的不同速度与图2.1所示的麦克斯韦理论一致。

a

N N M ρ=a

N N M ρ=

The most probable speed(最概然速率), at the peak of Maxwellian distribution (麦克斯韦分布) , is dependent on temperature according to the relation (关系式)……. The kinetic theory of gas ( 气体动力学) provides a basis for calculating properties such as the specific heat (比热). Using the fact from Chapter l that the average energy of gas molecules is proportional (成比例的) to the temperature, , we can deduce (推想), that the specific heat of a gas consisting only of atoms is , where m is the mass of one atom. 5. 从麦克斯韦分布图上可以看到，在其峰值处出现的气体粒子的最概然速率，按照这个关系式……，是与温度

紧密相关的。气体动力学为计算诸如比热之类的一些性质提供了基础。用第一章中气体分子的平均能量正比于温度的事实， ，我们可以推断出单元子气体的比热 ，在公式中m 是一个原子的质量。 2.3 THE ATOM AND LIGHT(原子与光) Until the 20th century the internal structure of atoms was unknown, but it was believed that electric charge (电荷) and mass were uniform (统一的). Rutherfor performed (执行) some crucial (至关紧要的) experiments in which gold atoms were bombarded by charged particles. He deduced (推断)in 1911 that most of the mass and positive charge （正电荷） of an atom were concentrated (集中的) in a nucleus of radius only about l0-5 times that of the atom, and thus occupying a volume of about 10 - l5 times that of the atom. The new view of atoms paved the way for (为…铺平道路) Bohr to find an explanation for the production of light.

6. 直到20世纪，原子的内部结构仍然是未知的，但是人们确信核电荷数与原子质量是相同的。卢瑟福进行了

一些重要的实验，包括用带电粒子轰击金原子。他在1911年推断出：原子的质量和正电荷都集中在半径为l05

分之一的原子核，占原子体积的10 l5分之一。关于原子的新观点为波尔解释光的产生铺平了道路。

The measured (有规则的) distribution of light among the different wavelengths (波长) at a certain temperature can be explained by the assumption (假设) that light is in the form of photons. These are absorbed and emitted with definite (一定的) amounts of energy E that are proportional to the frequency ν, according to E = hv , where h is Planck’s constant , 6.63×l0-34 J-sec. For examp1e, the energy corresponding to(相当于) a frequency of 5.l ×l014 is (6.63×l0-34) (5.l ×1014) = 3.4×l0-19 J, which is seen to be a very minute (微小的) amount of energy.

7.

在一定温度不同波长光的有规则分布可以用光是光子形式存在的假设来解释。这要吸收或者放出一定数量的能量E ，根据公式 E = hv （这里的h 表示普朗克常量6.63×l0-34 J-sec ），能量与频率成正比。例如：频率为5.l ×l014的光的能量相当于(6.63×l0-34) ×(5.l ×1014) = 3.4×l0-19 J ，这通常被看做是非常微小的能量。

He(Bohr) assumed that the atom consists of a single electron moving at constant speed in a circular orbit about a nucleus --the proton--as sketched in Fig. 2.2. Each particle has an electric charge of l.6×l0-l9 coulombs, but the proton has a mass that is 1836 times that of the electron. (Figure 2.2 )

8. 波尔假设（氢）原子由一个单独的电子绕着一个核子——质子，以圆形轨道作恒定速度的移动——见图2.2，

每个粒子有l.6×l0-l9库伦的电量，质子的质量是电子质量的1836倍。

The energy of the photon hv is equal to the difference between energies in the two orbits. The smallest orbit has a radius R 1 = 0.53 ×l0-l0 m, while the others have radii increasing as the square (平方) of integers (called quantum numbers (量子数)). Thus if n is l, 2, 3, . . . , the radius of the n th orbit is R n = n 2R l .

9. 光子的能量 hv 等于两个轨道能量之差。最小轨道半径为R 1 = 0.53 ×l0-l0 m ，其它轨道半径随着整数的平

方（量子数）增长。因此，如果n 是1、2、3……，那么第n 层轨道半径应为R n = n 2R l 。

The energy of the atom system when the electron is in the first orbit is E 1 = -l3.5 eV, where the negative sign (负号) means that energy must be supplied to remove the electron to a great distance and leave the hydrogen as a positive ion (阳离子). The energy when the electron is in the n th orbit is E n = E 1/n 2

. The various discrete (不连续的) levels are sketched (绘图) in Fig. 2.4.

10. 当电子在第一个轨道时，原子系统的能量为E 1 = -l3.5 eV ，负号表示把电子移到一个较远的距离只剩下阳

离子时外界必须提供的能量。电子处于n 轨道时，能量为E n = E 1/n 2，各种不连续的等级见图2.4 。

The electronic structure of the other elements is described by the shell model (壳模型), in which a limited number of electrons can occupy a given orbit or shell. The atomic number Z is unique (独特的) for each chemical 32E kT

=32c k m

=32

c k m

=3

2E kT =

element, and represents (描绘) both the number of positive charges on the central massive (结实的) nucleus of the atom and the number of electrons in orbits around the nucleus.

The chemical behavior of elements is determined by the number of electrons in the outermost (最外面的) or valence (原子价) shell.

11.其它元素的电子模型是用壳模型来描述的，一定限制数量的电子能够占据一个给定的轨道或壳层。对每一个

化学元素，原子序数Z是唯一的，它代表了原子中央结实核子的正电荷数以及围绕核子的轨道的电子数。最外层的电子数或化合价层，决定了元素的化学性质。

2.4 LASER BEAMS(激光束)

Ordinary light as in the visible range (可见区) is a mixture of many frequencies, directions, and phases(状态). In contrast, light from a laser(“Light Amplification by Stimulated Emission of Radiation”) consists of a direct beam of one color and with the waves in step (相干).

Lasers can be constructed from several materials. The original one (1960) was the crystalline gem ruby (水晶红宝石). Others use gases such as a helium-neon(氦-氖) mixture, or liquids with dye in them, or semiconductors(半导体 ).

Lasers are widely used where an intense (强烈的) well-directed beam is required, as in metal cutting and welding, eye surgery (眼部外科手术) and other medical applications, and accurate surveying and range finding(精确的测量和测距). Newer applications are noise-free phonographs (无噪声留声机, 电唱机), holograms (全息摄影) ( 3D images), and communication between airplane and submarine (潜水艇).

12.普通光，例如可见光区，是由许多频率、方向和状态不同的光混合而成的。相对的是，激光是由同一方向的

单一颜色的光束组成，而且是相干波。激光的产生可以来源于多种材料。最早的一种是1960年使用的水晶红宝石。其它的还可以用气体（如氦-氖混合气体），或者染料液体，以及半导体来做激光发生器。激光可以被广泛地应用于需要良好方向性光/热束的地方，例如金属的切割与焊接，眼部外科手术及它医疗应用还有精确的测量和测距上。新出现的应用还包括无噪声留声机、全息摄影以及飞机和潜艇的通讯。

Most elements are composed of particles of different weight, called isotopes (同位素). For instance, hydrogen has three isotopes of weights in proportion l, 2, and 3 -ordinary hydrogen, heavy hydrogen (deuterium氘), and tritium(氚).

The nucleus of ordinary hydrogen is the positively charged proton(带正电的质子); the deuteron(氘核)consists of a proton plus a neutron, a neutral particle(中性粒子) of weight very close to that of the proton; the triton(氚核) contains a proton plus two neutrons.

13.大多数元素是由重量不同的粒子构成，我们称之为“同位素”。例如：氢元素有三种同位素，原子量比为1：

2：3——普通氢（氕）、重氢（氘）以及超重氢(氚)。普通氢的原子核是一个带正电的质子；氘核由一个质子加一个重量十分接近质子的中性粒子（中子）组成；氚核则是由一个质子加两个中子组成。

2.6 SIZES AND MASSES OF NUCLEI (核的大小和质量)

The dimensions (尺寸) of nuclei (nucleus的复数) are found to be very much smaller than those of atoms.

Since the proton weight is much larger than the electron weight, the nucleus is extremely dense. The nuclei of other isotopes may be viewed as closely packed particles of matter-neutrons and protons-forming a sphere whose volume, 4/3πR3, depends on A, the number of nucleons. A useful rule of thumb (凭经验的方法) to calculate radii of nuclei is R(cm) = l.4 x 10- l3A l/3.

The masses of atoms, labeled M, are compared on a scale in which an isotope of carbon 12C has a mass of exactly 12. For 11H, the atomic mass is M = 1.007825, for 21H, M = 2.0l4102, and so on. The atomic mass of the proton is 1.007277, of the neutron l.008665, the difference being only about 0.1%. The mass of the electron on this scale is 0.000549.

14.原子核的尺寸相较原子来说非常小。由于质子的重量远大于电子，所以，原子核的密度非常大。

其它同位素的原子核可以被看做是由紧紧压在一起的粒子（中子和质子）构成的一个体积（4/3πR3）由核子数A决定的球体。根据经验可以算出原子核的半径为R(cm) = l.4 x 10- l3A l/3 。原子的质量（记为M）是一个与有着精确质量数12的同位素12C的质量的比值。例如11H原子的质量M = 1.007825，21H原子的质量M = 2.0l4102 ……质子的原子

量为1.007277，中子的为l.008665，两者相差只有大约0.1%。在这种比例下电子的质量为0.000549。

The atomic mass unit (amu) (原子质量单位), as 1/12 the mass of 12C, corresponds to (相应于) an actual mass of l.66 ? l0-24 g. To verify (校验) this, merely divide l g by Avogadro’s number 6.02 ? l023. It is easy to show that 1 amu is also equivalent to 931 MeV. We calculate the actual masses of atoms and nuclei by multiplying (乘) the mass in atomic mass units by the mass of 1 amu.

15.原子质量单位amu表示一个12C原子质量的1/12，相应于实际的质量是l.66 ?l0-24克。要校验这个值，只

需用1克除以阿伏伽德罗常数6.02 ? l023 。很明显：1 amu也相当于931兆电子伏(E = mc2 )。我们可以用原子质量乘以每一原子质量单位的质量来计算原子和核子的确切质量。

2.7 BINDING ENERGY(结合能)

The force of electrostatic repulsion (静电排斥) between like charges (同种电荷), which varies inversely (相反地) as the square of their separation, would be expected to be so large nuclei could not be formed. The fact that they do exist is evidence (证明) there is an even larger force of attraction. The nuclear force (核力) is of very short range, as we can deduce from(从…推论出) the above rule of thumb. The nuclear force acts only when the nucleons are very close to each other, and binds them into a compact structure (紧凑结构). Associated with the net force is a potential energy of binding(结合势能).

16.同种电荷之间的静电斥力随着它们距离的平方成反比变化，可以想见其会大到核子无法形成的地步。我们可

以凭经验推断出——核力的作用范围一定非常短的。只有当核子之间靠得很近时，核力才起作用将它们紧密地结合在一起。与这种合力相关的是结合势能。

To disrupt (使分裂) a nucleus and separate it into its component (组成的) nucleons, energy must be supplied from the outside. Recalling Einstein's relation between mass and energy, this is the same as saying that a given nucleus is lighter than the sum of its separate nucleons, the difference being the binding mass-energy. Let the mass of an atom including nucleus and external electrons be M and let m n and m H be the masses of the neutron and the proton plus matching electron (匹配电子). Then the binding energy is

B = total mass of separate particles - mass of the atom

or B = Nm n + Z m H - M.

17.要想把一个原子核分裂成组成它的核子，必须从外部给它一定的能量。回想爱因斯坦质能方程，也可以换个

说法：一个的原子核要比组成它的所有核子的质量之和要轻，而这个差值就是其结合能。

CHAPTER 3 Radioactivity（放射性）

Many naturally occurring and man-made isotopes have the property of radioactivity(放射性), which

is the spontaneous(自发的) disintegration (decay) (衰变) of the nucleus with the emission of a particle.

The process takes place in minerals (矿物质) of the ground, in fibers (纤维) of plants, in tissues (组织) of animals, and in the air and water, all of which contain traces (痕迹,微量) of radioactive elements.

1、许多天然和人造同位素都具有放射性，这是核子发射出粒子的自发衰变。这个过程发生在地表的矿物中、植物的纤维中、动物的组织中、空气和水中，所有的一切都存在着放射性元素的痕迹（放射性元素无处不在）。

3.1 RADIOACTIVE DECAY（放射性衰变）

Many elements that are found in nature or man-made are radioactive(放射性的), emitting alpha

partic1es(α), beta particles (β) (including electron or negatron and positron), neutrinos(中微子) , and gamma rays(γ). Some examples are as following:

2、许多天然和人造的元素都具有放射性，能发射阿尔法(α)粒子、贝塔(β)粒子（包括电子或者负电子和正电子）、中微子和伽马(γ)射线。举例如下：……

3.2 THE DECAY LAW(衰变规律)

The rate at which a radioactive substance disintegrates (and thus the rate of release of particles)

depends on the isotopic species(种类，核素), but there is a definite (一定的) “decay law” that governs(管理,支配) the process. In a given time period, say one second, each nucleus of a given isotopic species has the same chance of decay. If we were able to watch one nucleus, it might decay in the next instant (立即的), or a few days later, or even hundreds of years later.

3、放射性物质的衰变率（粒子释放率）决定于同位素的种类，但是也确定存在着“衰变规律”支配着这个过程。在一个给定的时间段，譬如一秒，给定同位素的每个核子都具有相同的衰变几率。如果我们能对某个核子进行观察的话，它可能

在下一个瞬间发生衰变，也有可能在几天甚至几百年以后才发生衰变。

Such statistical(统计学的) behavior is described by a constant property of the atom called

half-life (半衰期). This time interval(间隔), symbolized by t H is the time required for half of the nuclei to decay, leaving half of them intact(完整无缺的). We should like to know how many nuclei of a radioactive species remain at any time. If we start at time zero with N 0 nuclei, after a length of time t H there will be N 0/2; by the time 2t H has elapsed (流逝), there will be N 0/4; etc. A graph of the number of nuclei as a function of time is shown in Fig. 3.l.

4、这种统计学上的表现可以用原子的一个恒定属性——半衰期来表示。这个用t H 表示的时间间隔指的是一半的核子发生衰变所需要的时间。我们想知道在任意时间放射性核素的剩余量。如果在一开始有N 0 个核子，那么经过了t H 的时间以后，核子还剩下N 0/2 个；经过2t H 时，核子还剩下N 0/4个……核子数与时间的函数关系可以用图3.l

来表示。

For any time t on the curve (曲线图), the ratio of the number of nuclei present to the initial (

初始的

) number is given by

Half-lives range from very small fractions (小部分, 片断) of a second to billions of (数十亿) years, with each radioactive isotope (放射性同位素) having a definite half-life.

5、曲线上任一时刻t ，当前的核子数与初始的核子数的比率如下式表示：

半衰期从零点几秒到数十亿年不等，每种放射性同位素都有一个确定的半衰期。 The formula for N/N 0 is not very convenient for calculations except when t is some integer multiple

of t H . Defining the decay constant λ (lambda), as the chance of decay of a given nucleus each second, an equivalent

(同意义的) exponential (指数的) formula for decay is We find that λ = 0.693/t H

6、N/N0这个公式并十分便于计算，除非t 是t H 的整数倍。衰变常数λ的定义是：一个原子核在单位时间内发生衰变的几率，可以得到一个意义相同的指数方程：

我们可以得出 λ = 0.693/t H 。

The number of disintegrations per second (dis/sec) of a radioisotope is called the activity, A.

Since the decay constant λ is the chance of decay each second of one nucleus, for N nuclei the activity is the product (乘积)A = λ N.The unit dis/sec is called the becquerel (Bq), honoring the scientist who discovered radioactivity (放射性活度). Another older and commonly used unit of activity is the curie (Ci) named after the French scientists Pierre and Marie Curie who studied radium (镭). The curie is 3.7 ?1010

dis/sec, which is an early measured value of the activity per gram of radium.

7、放射性同位素每秒衰变的原子数称为活度（记作A ）。既然衰变常数λ是核子每秒衰变的几率，N 个核子的活度是乘积A=λN 。单位dis/sec 称为“贝克勒尔”（Bq ），用来纪念这位发现放射性活度的科学家。另一个更早的曾被普遍使用的放射性活度的单位是“居里”（Ci ），这是以研究镭的法国科学家皮埃尔和玛丽·居里的名字命名的。1居里等于3.7 ?1010 贝克。

3.3 MEASUREMENT OF HALF-LIFE(半衰期的测量)

Finding the half-life of an isotope provides part of its identification (鉴定), needed for

beneficial use or for protection against radiation hazard. Let us look at a method for measuring the half-life of a radioactive substance. As in Fig. 3.2, a detector 探测器 (that counts the number of particles striking it ) is placed near the source of radiation (放射源).

8、为了有益的应用或者是为防止辐射危害而需鉴定放射性核素，而找出它的半衰期，则可为鉴定同位素提供线索。让我们来看看一种检测放射性物质半衰期的方法。如图3.2所示，一个探测器（统计击打到它上的粒子数）放置在放射源的附近。

From the number of counts observed in a known short time interval, the counting rate (计数率)is H t t N N ??

? ??=210t e N N λ-=0H t t N N ??? ??=210t e N N λ-=0

computed. It is proportional to the rates of emission of particles or rays from the sample and thus to the activity A of the source. The process is repeated after an elapsed time for decay. The resulting values of activity are plotted on semi-log graph paper (半对数坐标纸) as in Fig. 3.3, and a straight line drawn through the observed points. From any pairs of points on the line λ and t H= 0.693/λ can be calculated (see Exercise 3-8).

9、计数率可以通过一段时间间隔内的计数计算出来。计数率与样本发射粒子或射线的速率成正比，也就是说与活度A 成正比。在衰变发生的一段时间内重复这个过程：把活度的结果标记在如图3.3那样的半对数坐标纸上，然后画一条直线穿过这些观察点。从直线上任意两个点可以计算出λ，这样，半衰期 t H = 0.693/λ就求出来了。

The measurement of the activity of a radioactive substance is complicated by the presence (存

在) of background radiation (本底辐射), which is due to cosmic rays (宇宙射线) from outside the earth or from the decay of minerals in materials of construction (建筑物) or in the earth. It is always necessary to measure the background counts (本底计数) and subtract (减去) them from those observed in the experiment.

10、放射性物质活度的测量因“本底辐射”的存在而变得复杂，这源于地球之外的宇宙射线或来自建材抑或土壤中的矿石的衰变。我们经常需要测量本底计数并把它们从实验观测计数中减去。

CHAPTER 4 Nuclear Processes （核过程）

Nuclear reactions (核反应)---those in which atomic nuclei participate (参与) ---may take place

spontaneously (自然地), as in radioactivity, or may be induced (感应, 诱发 ) by bombardment (轰击, 撞击 ) with a particle or ray. Nuclear reactions are much more energetic(精力充沛的, 高能的) than chemical reactions, but they obey the same physical laws---conservation(守恒) of momentum(动量), energy, number of particles, and charge.

1、核反应（有原子核参与）可能会自然发生，如放射性，或可能被粒子或射线轰击诱发。核反应比化学反应剧烈的多，但它们遵守同样的物理定律-----动量、能量、粒子数、电荷守恒。

The number of possible nuclear reactions is extremely large because there are about 2000 known

isotopes and many particles that can either be projectiles (发射体, 入射粒子) or products (产物)---photons, electrons, protons, neutrons, alpha particles, deuteron (氘核), and heavy charged particles(重带电粒子).

In this chapter we emphasize (强调, 着重 ) induced reactions, especially those involving neutrons.

2、可能发生核反应的数量是非常大的，因为有大概2000种已知的同位素以及许多粒子，他们既可是发射体又可能是产物-------光子、电子、质子、中子，α粒子，氘核，重带电粒子。在这一章中我们强调辐射引发的反应，尤其是包含中子的反应。

4.1 TRANSMUTATION OF ELEMENTS（元素的嬗变）

The conversion of one element into another, a process called transmutation (变形, 嬗变), was first

achieved in 19l9 by Rutherford in England. He bombarded nitrogen (氮) atoms with alpha particles from a radioactive source to produce an oxygen isotope and a proton. (Fig.4.1)

It is difficult for the positively charged(带正电子的) alpha particle to enter the nitrogen nucleus

because of the electrical forces (静电斥力) between nuclei. The alpha particle thus must have several MeV energy.

3、一种元素转变成另一种的过程称为嬗变，1919在英格兰被卢瑟福实现。他用放射源发出的α粒子轰击氮核产生了一种氧的同位素和一个质子。

由于核子间的静电斥力，带正电的α粒子要进入氮核是困难的。除非α粒子具有几兆电子伏的能量。

Nuclear transmutations can also be achieved by charged particles that are electrically accelerated

to high speeds.

4、在电场中加速到高速的带电粒子也可以实现核嬗变。

Since the neutron is a neutral (中性的) particle it does not experience electrostatic repulsion

(静电排斥) and can readily penetrate (穿透) a target nucleus (靶核). Neutrons are thus especially useful as projectiles to induce reactions. Several examples ： The conversion of mercury (汞) into gold, the alchemist (炼金术士)'s dream, is described by

5、因为中子是中性的粒子，它不受静电排斥所以能够轻易穿透靶核。中子作为入射粒子诱发的反应时非常有用的。这里有几个例子：炼金术士的梦想，把汞变成黄金，如下列化学式所示：

A shorthand (简化) notation (符号) is used to represent (描绘) nuclear reactions. Let an incoming

particle (入射粒子) a strike a target nucleus X to produce a residual nucleus (余核) Y and an outgoing particle (出射粒子) b, with equation a + X = Y+ b. The reaction may be abbreviated (缩写) X(a, b)Y.

6、我们可以用简化了的符号来描绘核反应。让一个入射粒子轰击靶核X产生一个余核和一个出射粒子b，满足方程a+X=Y+b。这个反应可缩写为X(a,b)Y。

The interpretation (解释) of nuclear reactions often involves the concept of compound nucleus

(复合核). This intermediate (中间的,中级的) stage is formed by the combination of a projectile and target nucleus. It has extra energy of excitation and breaks up into the outgoing particle or ray and the residual nucleus.

7、核反应的解释通常牵涉到复合核的概念。这个中间阶段是由一个入射粒子和靶核组合而成。它有更多的激发能把复合核分解为出射粒子或射线和剩余核。

—————————————————————————————————————————————

4.2 ENERGY AND MOMENTUM CONSERVATION（能量与动量守恒）

The conservation of mass-energy is a firm (坚定的, 严格的) requirement for any nuclear reaction.

Recall from Chapter l that the total mass is the sum of the rest mass m0 and the kinetic energy E k (in mass units).

8、质能守恒是任何核反应必定遵守的规律。回顾第一章，我们知道：总质量是静止质量m和动量E k的总和。

The calculations just completed tell us the total kinetic energy of the product particles but do

not reveal (显示) how much each has, or what the speeds are. To find this information we must apply the principle of conservation of momentum (动量守恒法则). Recall that the linear momentum (线动量) p of a material particle of mass m and speed v is p= mv. This relation is correct in both the classical (经典的) and relativistic (相对论的) senses. The total momentum of the interacting particles before and after the collision is the same.

9、刚才的计算结果求出了产出粒子的总动量但并没有算出其中每一个粒子的动量，或是速度。我们须用动量守恒法则来算出这些数据。一个质量为m速度为v的物质粒子的线动量p=mv。这个关系在经典力学的和相对论的领域都是适用的。在碰撞前后，这些相互作用的粒子的总动量总是守恒的。

4.3 REACTION RATES（反应率）

We can perform a set of imaginary experiments that will clarify (阐明) the idea of cross section

(截面). Picture, as in Fig. 4.2(a) a tube of end area (截面积) 1 cm2 containing only one target particle.

A single projectile is injected (注入) parallel to (平行于) the tube axis, but its exact location is not

specified. It is clear that the chance of collision, labeled σ (sigma) and called the microscopic cross section (微观截面), is the ratio of the target area to the area of the tube, which is 1.

10、我们可以进行一套假想的实验来阐明截面的概念。如图4.2（a）一个截面积为1 cm2的试管仅含有一个靶粒子。从平行于试管的X轴注入一个入射粒子，但它的准确位置是不确定的。很明显，一个入射粒子碰撞的几率，即微观截面（记为σ），等于靶面积与试管的截面积的比值。

In a time of one second, the number of them (projectiles) that pass through the target volume is

nv, and since the chance of collision (碰撞) of each with one target atom is σ, the number of collisions is nvNσ. We can thus define the reaction rate (反应率) per unit volume, R = nvNσ

11、一秒钟的时间内，通过给靶区的入射粒子数是nv，一个靶原子的碰撞几率是σ，碰撞数是nvNσ。我们可以定义每单位体积内的反应率为R = nvNσ

When a particle such as a neutron collides with a target nucleus, there is a certain

chance of each of several reactions. The simplest is elastic scattering (弹性散射), in which the neutron is visualized (想象, 形象化) as bouncing (弹跳) off the nucleus and moving in a new direction with a change in energy. Such a collision, governed by classical physics (经典物理), is predominant (主要的,突出的) in

light elements.

12、当一个粒子如中子与靶核相撞，有一定的几率发生几种反应中的一种。最简单的是弹性散射，在反应中，可以想像中子从核子中弹开并以某种的能量向新的方向飞去了。这种遵循经典物理学的碰撞，在轻元素中尤为突出。

In the inelastic scattering (非弹性散射) collision, an important process for fast neutrons in

heavy elements, the neutron becomes a part of the nucleus.

The cross section σs is the chance of a collision that results in neutron scattering. The neutron may instead be absorbed by the nucleus, with cross section σa . Since σa and σs are chances of reaction, their sum is the chance for collision or total cross section σ = σa + σs .

13、在非弹性散射碰撞中，重元素中的快中子的一个重要过程，是中子变成核子的一部分。

微观截面σs 是导致中子散射的几率。中子可能反被核子吸收，微观截面为σa 。因为σa 和σs 是反应的机会，它们的和是碰撞的几率或总微观截面σ = σa + σs

4.4 PARTICLE ATTENUATION (粒子衰减

)

Visualize an experiment in which a stream of particles of common speed and direction is allowed

to strike the plane surface of a substance as in Fig.4.4.

14、想象一个实验中一束粒子如图4.4

那样以同样的速度和方向撞击物质的水平表面。

Collisions with the target atoms in the material will continually remove projectiles from the stream, which will thus diminish (使……减少) in strength with distance, a process we label attenuation (衰减).

15、与材料中靶原子的碰撞会不断地把入射粒子从粒子束弹出，这将使得其可穿透的深度大大降低，这个过程我们称之衰减。

4.5 NEUTRON CROSS SECTIONS (中子截面

)

The cross section for neutron absorption in materials depends greatly on the isotope bombarded

and on the neutron energy. For consistent (一致的) comparison and use, the cross section is often cited (引

用) at 0.0253 eV, corresponding to neutron speed 2200m/sec.

The dependence of absorption cross section on energy is of two types, one called l/v , in which

σa varies inversely (相反地) with neutron speed, the other called resonance (共振), where there is a very strong absorption at certain neutron energies.

16、中子在物质中的吸收截面极大依赖于被轰击的同位素和中子能量。为了比较和使用上的一致，通常引用0.0253eV 的截面，相对应的中子速度为2200m/sec 。

吸收截面对于能量的依赖有两种类型，一个称1/v ， σa 与中子速度成反比，另一个叫共振，对一定能量的中子吸收非常强。

4.6 NEUTRON SLOWING AND DIFFUSION

（中子慢化与扩散）

When fast neutrons, those of energy of the order of 2 MeV, are introduced into a medium, a sequence

(序列) of collisions with nuclei takes place. The neutrons are deflected (偏离) in direction on each collision, they lose energy, and they tend to migrate (移动) away from their origin.

17、当能量为2MeV 的快中子被引入媒介，中子会与原子核发生一系列的碰撞。每次碰撞后中子都将偏离原来的方向，

损失能量，而且它们趋向从原来的位置移走。

The process of diffusion (扩散) of gas molecules is familiar to us. If a bottle of perfume (香

水) is opened, the scent (香味) is quickly observed, as the molecules of the substance migrate away from the source. Since neutrons in large numbers behave as a gas, the descriptions of gas diffusion may be applied.

18、我们熟悉气体分子的扩散过程。当打开一瓶香水时，因为物质分子的散出，我们很快闻到香味。大量中子的行为和

气体一样，用于描述气体扩散的方法也可以用于描述中子扩散。

We can guess that the larger the neutron speed v and the larger the transport mean free path (平

均自由程)λt , the more neutron flow will take place. Theory and measurement show that if n varies in the

z -direction, the net flow of neutrons across a unit area each second, the net current density, is 19、我们可以猜到中子的速度v 越大平均自由程λt 越远，而且将会产生更多的中子流。理论和测量显示：如果n 在z

轴方向发生改变，每秒穿过单位面积的净中子流（净流密度）是 3t v dn j dz λ-=3t

v dn j dz

λ-=

4.7 SUMMARY(总结)

Chemical and nuclear equations have similarities (相似性) in the form of equations and in the

requirements on conservation (守恒) of particles and charge.

The bombardment (轰击) of nuclei by charged particles or neutrons produces new nuclei and particles.

Final energies are found from mass differences and final speeds from conservation of momentum (动量守恒).

20、化学和核子方程在方程的组成和粒子电量守恒是相似的。

带电的粒子或中子轰击原子核产生新的原子核和粒子。最终的能量来自质量差异以及速度来自动量守恒。

The cross section for interaction of neutrons with nuclei is a measure of the chance of collision.

Reaction rates depend mutually (相互地) on neutron flows and macroscopic cross section (微观截面). A stream of uncollided (未经碰撞的) particles is reduced exponentially (指数的; logarithmic 对数的) as it passes through a medium (媒介).

21、中子和原子核的反应的截面积是碰撞几率的量度。反应率在中子流和微观截面上相互依赖。一股未经碰撞的粒子当它穿过媒介时是呈指数减少的。

Neutron absorption cross sections (吸收截面) vary (改变) greatly with target isotope and with

neutron energy, while scattering cross sections (散射截面) are relatively constant. Neutrons are slowed readily by collisions with light nuclei and migrate (移动) from their point of origin. On reaching thermal energy they continue to disperse (散开), with the net flow dependent on the spatial variation of flux.

22、中子吸收截面因靶同位素和中子能量改变很大，然而散射截面相对来说是一定的。中子通过与轻原子核碰撞轻易减速并从它们的原先位置移开。达到一定热能时继续散开，净流依赖空间连续的改变。

CHAPTER 5 Radiation and Materials (辐射与物质)

The word “radiation” will be taken to embrace (包含) all particles, whether they are of material

or electromagnetic origin. We include those produced by both atomic and nuclear processes and those resulting from electrical acceleration, noting that there is no essential (本质的) difference between X-rays from atomic collisions and gamma rays from nuclear decay; protons can come from a particle accelerator, from cosmic rays (宇宙射线) , or from a nuclear reaction in a reactor (反应堆). The word “materials” wil1 refer to (涉及) bulk (大多数) matter, whether of mineral or biological origin, as well as to the particles of which the matter is composed, including molecules, atoms, electrons, and nuclei.

1.“辐射”这个词涵盖了所有的粒子，不论他们来自某种物质还是电磁场。我们如果将那些由原子和核过程产生的以及那些来自电子加速的粒子加以比较的话，可以发现由原子碰撞产生的X射线和核子衰变产生的γ射线并没有本质上的区别；质子可以由粒子加速产生，也可以来源于宇宙射线或反应堆中的核反应。“物质”这个词涉及大多数物体，无论是矿物质还是生物组织，也包括组成物质的粒子：分子、原子、电子和核子。

When we put radiation and materials together, a great variety of possible situations must be considered.

Bombarding particles may have low or high energy, they may be charged, uncharged, or photons; they may be heavy or light in the scale of masses. The targets may be similarly (同样地) distinguished, but they may also exhibit (展示) degrees o f binding that range from none (“free” particles), to weak (atoms in molecules and electrons in atoms), to strong (nucleons in nuclei).

2.当我们把放射物和物质放在一起，很多种可能的情况必须要考虑。轰击粒子的能量或高或低，可能带电、不带电或是光子；它们的质量可能或重或轻。靶物质可能有同样的区别，但它们可能也显示结合的程度，从没有（“自由”粒子），到弱（分子中的原子以及原子中的电子），再到强（原子核中的核子）。

5.1 EXCITATION AND IONIZATION BY ELECTRONS (电子所致激发与电离)

These processes occur in the familiar fluorescent light-bulb (日光灯), in an X-ray machine (X光机),

or in matter exposed to beta particles. If an electron that enters a material has a very low energy, it will merely migrate (移动) without affecting the molecules significantly (值得注意的). If its energy is larger, it may impart (给予) energy to atomic electrons as described by the Bohr theory (波尔理论) (Chapter 2), causing excitation of electrons to higher energy states (能态) or producing ionization, with subsequent (并发的) emission of light.

3.这些过程发生在熟悉的日光灯中，X光机中，或暴露在贝塔粒子下的物质中。如果一个进入物质的电子能量很低，则电子仅仅在物质中发生移动而不会显著地影响其分子。如果它的能量稍大，它可能如波尔理论描述的那样给予原子中的电子以能量，导致电子激发到高能态或产生电离并发出光。

P49 第二段

Beta particles as electrons from nuclear reactions have energies in the range 0.0l-l MeV, and thus

are capable of (能够) producing large amounts of ionization as they penetrate (穿透) a substance. As a rough rule of thumb (经验方法 ), about 32 eV of energy is required to produce one ion pair (离子对). The beta particles lose energy with each event, and eventually are stopped. For electrons of l MeV energy, the range (射程), as the typical distance of penetration, is no more than a few millimeters (毫米) in liquids and solids or a few meters in air.

4.如同来自核反应中的电子，贝塔粒子的能量范围是0.0l-l MeV，并且当它们穿透物质时能够产生大量的电离作用。粗略地估计，产生一个离子对大概需要32 eV的能量。贝塔粒子在每次碰撞中都会损失能量，直到最终停下。对l MeV能量的电子，其射程，即穿透距离，在液体和固体不超过几毫米，在气体中也不过几米远而已。

5.2HEAVY CHARGED PARTICLE SLOWING BY ATOMS (原子对重带电粒子的慢化)

Charged particles such as protons, alpha particles, or ions such as the fragments of fission (裂变

碎片) are classed as (分类为) heavy particles, being much more massive (厚重的) than the electron. For the same particle energy they have far less speed than an electron, but they are less readily deflected (偏转) in their motion than electrons because of their inertia (惯性) . The mechanism (机制) by which heavy ions slow down in matter is primarily electrostatic interaction (静电相互作用) with atomic electrons.

5.带电的粒子如质子、阿尔法粒子、离子（例如裂变碎片），由于它们比电子重得多，可以归类为重粒子。同样粒子能量下它们的速度远小于电子，因为惯性它们比电子不易发生偏转。重离子在物质中慢化的原因主要是由于其与原子中电子的静电相互作用。

(P49倒数12行)It is found that (业已发现) the kinetic energy lost in one collision is proportional

to (正比于) the square of Z, the number of external electrons in the target atom, and inversely proportional to (反比于) the kinetic energy of the projectile.

6.业已发现在一次碰撞中损失的动能正比于靶原子内部电子数Z的平方，靶原子中的外层的电子数量，反比于入射粒子的动能。

5.3 HEAVY CHARGED PARTICLE SCATTERING BY NUCLEI (核对重带电粒子的散射)

When a high-speed charged ion such as an alpha particle encounters (遇到) a very heavy charged nucleus,

the mutual (相互的) repulsion (排斥) of the two particles causes the projectile to move on a hyperbolic (双曲线的 ) path, as in Fig. 5.2. Such a collision can take place in a gas or in a solid if the incoming particle passes close to the nucleus.

7.当一个像阿尔法粒子的高速带电离子遇到一个非常重的带电核，两个粒子的相互排斥导致入射粒子以双曲线的轨迹移动，如图5.2。在气体或固体中当入射粒子从靠近核子的地方通过时，这样的碰撞就可能发生。

The projectile is scattered (散射)through an angle (角) that depends on the detailed nature of the

collision, i.e., the initial (初始的) energy and direction of motion of the incoming ion relative to (相对于) the target nucleus, and the magnitude (数量) of electric charge (电荷) of the interacting particles (相互作用粒子). Unless the energy of the bombarding particle is very high and it comes within the short range of the nuclear force, there is a small chance that it can enter the nucleus and cause a nuclear reaction.

8.入射粒子以某一个角度散射，这角度取决于碰撞的具体性质，比如，入射离子的初始能量、相对靶核的运动方向以及相互作用粒子的电荷数。除非碰撞粒子的能量非常高并且它在短程核力范围内，否则它很难有机会进入核子并引发核反应。

5.4 GAMMA RAY INTERACTIONS WITH MATTER ( 射线与物质的相互作用

We now turn to a group of three related processes involving (使…陷于) gamma ray photons produced by

nuclear reactions. These have energies as high as a few MeV. The interactions include simple scattering of the photon, ionization by it, and a special nuclear reaction known as pair production.

(a) Photon-Electron Scattering (光电散射)

(b) Photoelectric Effect (光电效应)

(c) Electron-Positron Pair Production(电子对产生效应)

9.现在我们转向于与核反应产生的γ射线光子有关的三个过程，这些光子的能量可达几兆电子伏。反应包括简单的光子散射、电离，以及众所周知的一个特殊核反应——电子对效应。

(a) Photon-Electron Scattering（光电散射）

One of the easiest processes to visualize (设想, 显现) is the interaction of a photon of energy E=hv

and an electron of rest mass m0. Although the electrons in a target atom can be regarded as moving and bound to their nucleus, the energies involved are very small (eV) in comparison with those of typical gamma rays (keV or MeV). Thus the electrons may be viewed as (被视为) free stationary (固定的) particles. The collision may be treated by the physical principles of energy and momentum conservation.

10.设想中最简单的核反应的过程之一是能量为hv的光子与静止质量为m0的电子的反应。尽管靶原子中的电子可看做是被他们的核子所束缚着绕核运动，其间的能量（eV）与那些典型的γ射线（KeV 或Mev）相比非常小。因此，这种电子可被视为自由的温定粒子。碰撞过程遵守能量和动量守恒定律。

(P51倒数11行)(Fig. 5.3) the photon is deflected in its direction and loses energy, becoming a photon

of new energy E’= hv’.The electron gains energy and moves away (离开) with high speed v and total mass-energy mc2, leaving the atom ionized. In this Compton effect (康普顿效应), named after its discoverer, one finds that the greatest photon energy loss occurs when it is scattered backward (l80o) from the original direction.

11.光子偏离原来的方向并损失一定的能量，变成能量为E’= hv’的光子。电子获得能量以很高的速度v离开原子，其总质能为mc2，而原子则变成了离子。在以其发现者命名的康普顿效应中，人们发现当光子发生l80o散射时其能量损失最大。

(P53)The probability of Compton scattering (康普顿散射) is expressed by a cross section (截面), which

is smaller for larger gamma energies as shown in Fig. 5.4 for the element lead (铅plumbum), a common material for shielding against X-rays or gamma rays. We can deduce (推论) that the chance of collision increases with each successive (逐次的, 相继的) loss of energy by the photon, and eventually the photon disappears.

12.康普顿散射发生的概率可用截面表示，如图Fig. 5.4，对一种常用于防护X射线或γ射线的铅来说，伽马能量越大反应截面越小。我们可以推断，碰撞几率随着光子能量的持续丧失而上升，最终光子消失。

(b) Photoelectric Effect （光电效应）

This process is in competition with (与…竞争) scattering. An incident photon of high enough energy

dislodges (驱逐) an electron from the atom, leaving a positively charged ion. In so doing, the photon is absorbed and thus lost (see Fig. 5.5). The cross section for the photoelectric effect decreases (减少) with increasing (增加) photon energy, as sketched in Fig.5.4 for the element lead (铅).

13．这个过程可与散射相媲美。能量足够高的光子导致原子中的电子被驱逐出来，留下一个带正电的离子，而这个光子最终会被吸收而消失。如Fig.5.4中描绘的铅元素的吸收截面那样，光电效应的截面随光子能量的增加而减少。

The above two processes are usually treated separately even though both result in ionization. In the

Compton effect, a photon of lower energy survives (生还), but in the photoelectric effect, the photon is eliminated (消除). In each case, the electron released may have enough energy to excite or ionize other atoms by the mechanism (机制) described earlier. Also, the ejection (排出物) of the electron is followed by light emission or X-ray production, depending on whether an outer shell or inner shell is involve

14.以上两个过程虽然都导致电离，但它们通常被区别对待。在康普顿效应中，能量较低的光子仍然存在，但在光电效应中，光子消失。在两种情况下，被释放的电子有足够的能量通过前面描述的机制去激发或使其他原子电离。同样，伴随着被打出的电子，放出光还是X射线，取决于它处于外壳层还是内壳层。

The third process to be considered is one in which the photon is converted into matter. This is entirely

in accord with Einstein’s theory of the equivalence of mass and energy (质能关系式). In the presence of a nucleus, as sketched in Fig. 5.6, a gamma ray photon disappears and two particles appear---an electron and a positron.

15.第三个过程被认为是光子转变成物质的过程。完全符合爱因斯坦的质能关系式的理论。如Fig. 5.6所示，一个伽马射线光子撞击一个核子，光子消失以后产生了两个新的粒子——一个负电子和一个正电子。

(P53倒数第1行)Since these are of equal charge but of opposite sign, there is no net charge after the

reaction, just as before, the gamma ray having zero charge. The law of conservation of charge is thus met. The total new mass produced is twice the mass-energy of the electron, 2(0.5l) = l.02 MeV, which means that the reaction can occur (发生) only if the gamma ray has at least this amount of energy. The cross section for the process of pair production rises from zero as shown in Fig. 5.4 for lead.

16.因为电量相同而电性相反，所以在反应后没有净电荷。如反应前一样，伽马射线的电荷为零，符合电荷守恒定律。新产物的总质能是电子的两倍，2(0.5l) = l.02 MeV,这意味着只有伽马射线的能量至少有这么多时这个反应才有可能发生。铅产生电子对效应的截面从零开始上升，如图Fig. 5.4所示。

(P54倒数第2行) The reverse process (逆过程) also takes place (Fig. 5.7). when an electron and a positron

combine, they are annihilated ( 湮没) as material particles, and two gamma rays of energy totaling at least l.02 MeV are released. That there must be two photons is a consequence of the principle of momentum conservation.

17.当正负电子结合时，逆过程也会发生(如图5.7)，作为物质粒子它们发生湮没，同时发射出的两束总能量至少有l.02 MeV的伽马射线。根据动量守恒定律的推断，必然有两个（方向相反、能量相等的）光子产生。

Figure 5.4 shows that the total gamma ray cross section curve (曲线) for lead (Pb), as the sum of the

components for Compton effect, photoelectric effect, and pair production, exhibits a minimum around 3 MeV energy. This implies that gamma rays in this vicinity (附近) are more penetrating (有穿透力的) than those of higher or lower energy. In contrast with (与…对比) the case of beta particles and alpha particles, which have a definite range (确定的射程), a certain fraction of incident gamma rays can pass through any thickness of material.

18.如图5.4所示铅的伽马射线反应总截面曲线（总截面是康普顿效应，光电效应截面以及电子对效应截面之和）显示最小截面出现在3 MeV能量处。这就表明当伽马射线的能量在3MeV左右时，其穿透力最强。与有确定的射程的阿尔法粒子和贝塔粒子相比，某些伽马射线的能够穿透任何厚度的物质。

5.5 NEUTRON REACTIONS （中子反应）

For completeness, we mention the interaction of neutrons with matter. Neutrons may be scattered by

nuclei elastically or inelastically, may be captured (俘获) with resulting gamma ray emission, or may cause fission (裂变). If their energy is high enough, neutrons may induce (引起, 诱发) (n, p) and (n, α) reactions as well.

19.出于完整性的考虑，我们介绍一下中子和物质的反应。中子可能与核发生弹性散射和非弹性散射，也可能会被俘获而放出伽马射线，甚至可能导致裂变。如果它们的能量足够高，中子也会引发(n, p)和(n, α)反应。

We are now in a position to understand the connection between neutron reactions and atomic processes.

When a high-speed neutron strikes the hydrogen atom in a water molecule, a proton is ejected (逐出), resulting in chemical dissociation (离解, 分裂) of the H2O. A similar effect takes place in molecules of cells in any biological tissue (生物组织). Now, the proton as a heavy charged particle passes through matter, slowing and creating ionization along its path. Thus two types of radiation damage (辐射危害) take place---primary and secondary (初级与次级).

20.我们现在能够理解中子反应和原子反应之间的联系。当一个高速的中子撞击水分子中的氢原子，一个质子会被逐出，导致H2O的化学分解。类似的过程发生在任何生物组织的细胞中。质子作为重带电粒子穿过物质，在慢化过程中产生电离。因而产生两种辐射危害——初级电离与次级电离。

After many collisions, the neutron arrives at a low enough energy that it can be readily absorbed.

If it is captured by the proton in a molecule of water or some other hydrocarbon (碳氢化合物), a gamma ray is released, as discussed in Chapter 4. The resulting deuteron recoils (氘核反冲) with energy that is much smaller than that of the gamma ray, but still is far greater than the energy of binding (结合能) of atoms in the water molecule. Again dissociation (分裂) of the compound (混合物) takes place, which can be regarded as a form of radiation damage.

21.在许多次碰撞后中子达到了一个低得可以被容易地吸收的能量。如第四章讨论的那样，如果中子被水分子中的质子或一些其他碳氢化合物吸收，则会释放出伽马射线。氘核反冲的能量比伽马射线反冲的能量小的多，但仍比水分子中原子的结合能大得多。化合物再次发生分裂，这被看做是辐射损伤的形式之一。

总结

Radiation of especial interest includes electrons, heavy charged particles, photons, and neutrons

特别重要的辐射包括电子，重带电粒子，光子和中子。

Each of the particles tends to lose energy by interaction with the electrons and nuclei of matter,

and each creates ionization in different degrees.

每个粒子在与物质的电子和核子的反应过程中会丧失能量，每次在不同程度上产生离子。

The ranges of beta particles and alpha particles are short, but gamma rays penetrate (穿透) in accord

with an exponential law (指数规律). Gamma rays can also produce electron-positron pairs. Neutrons of both high and low energy can create radiation damage in molecular materials.

贝塔粒子和阿尔法粒子的射程很短，但伽马射线穿透符合指数规律。伽马射线也可以产生正负电子对。能量高和低的中子都可以在物质分子中产生辐射损伤。

CHAPTER 6 Fission (裂变)

Out of many nuclear reactions known, that resulting in fission has at present (目前) the greatest

practical significance (意义). In this chapter we shall describe the mechanism (机制) of the process, identify (识别, 鉴别) the byproducts (副产品), introduce the concept (概念) of the chain reaction (链式反应), and look at the energy yield (出产) from the consumption (消费) of nuclear fuels (核燃料).

1. 目前，在许多已知的核反应中，导致裂变的反应最有实用意义。在这一章中我们将描述这一过程的机制，认识其副产物，介绍链式反应的概念，搞清楚从核燃料的消耗中产出的能量。

6.1 THE FISSION PROCESS(裂变过程)

The absorption (吸收) of a neutron by most isotopes involves radiative capture (辐射俘获), with the

excitation energy (激发能) appearing as a gamma ray. In certain heavy elements, notably (特别地,尤其) uranium (铀) and plutonium (钚), an alternate (交替的) consequence is observed---the splitting (分裂) of the nucleus into two massive fragments (重碎片), a process called fission. Figure 6. 1 shows the sequence (序列) of events, using the reaction with U-235 to illustrate (举例).

2. 大多数核素吸收中子的过程都涉及辐射俘获，同时激发能以伽马射线的形式出现。在某些重元素中，特别是铀和钚，可以观察到一个交替的结果---核子分裂成两个重碎片，这个过程称为裂变。图 6. l以铀-235的反应为例显示了这一过程。

In Stage A, the neutron approaches (接近) the U-235 nucleus. In Stage B, the U-236 nucleus has been

formed, in an excited state (激发态). The excess (过度的, 额外的) energy in some cases may be released as a gamma ray, but more frequently (常常, 频繁地), the energy causes distortions (变形) of the nucleus into a dumbbell shape (哑铃形状), as in Stage C. The parts of the nucleus oscillate (振荡) in a manner analogous to (类似于) the motion of a drop of liquid. Because of the dominance (优势) of electrostatic repulsion over nuclear attraction, the two parts can separate, as in Stage D. They are then called fission fragments (裂变碎片), bearing (具有) most of the energy released.

3. 在A阶段，中子接近U-235核。在B阶段，U-236核形成并处于激发态。C阶段：在一些情况下过多的能量以伽马射线的形式释放出来，但更有可能的是，能量导致核子变形成哑铃状。，D阶段：核子的各部分的振荡在一定程度上类似于一滴液体的运动。因为静电斥力大于核引力，这两个部分可能分离。它们被称作裂变碎片，具有大部分的释放能。

They fly apart at high speeds, carrying some 166MeV of kinetic energy out of the total of around 200MeV

released in the whole process. As the fragments (碎片) separate, they lose atomic electrons, and the resulting high-speed ions lose energy by interaction with the atoms and molecules of the surrounding medium. The resultant thermal energy is recoverable (可重获的) if the fission takes place (发生) in a nuclear reactor. Also shown in the diagram are the prompt (瞬发)gamma rays and fast neutrons that are released at the time of splitting.

4. 它们带着166MeV的动能以高速飞离，而整个过程中释放的总能量大概是200MeV。当碎片分开，它们的原子失去电子，高速运动的离子与周围介质中的原子和分子反应损失能量。如果裂变发生在核反应堆中，发出的热能可持续获得。图表中也显示了分裂时放出的伽马射线和快中子。

6.2 ENERGY CONSIDERATIONS (裂变能量)

The absorption of a neutron by a nucleus such as U-235 gives rise to (引起) extra internal energy (内

能) of the product, because the sum of masses of the two interacting particles is greater than that of a normal U-236 nucleus. 235U + n → (236U)*,

where the asterisk ([`?st?risk]星号) signifies (表示) the excited state (激发态). The mass in atomic mass units of (U-236)* is the sum 235.043925 + 1.008665 = 236.052590. However, U-236 in its ground state (基态) has a mass of only 236.045563, lower by 0.007027amu or 6.5MeV. This amount of excess energy (过剩能量) is sufficient (充分的) to cause fission.

5. 一个核子（比如U-235）吸收一个中子后引起产物的内能过多，因为两个参加反应的粒子的总质量比普通的U-236核子大。 235U + n → (236U)*,

这里的星号表示激发态。(U-236)*的重量用原子质量单位表示的总数是235.043925 + 1.008665 = 236.052590.然而，U-236的基态的质量仅为236.045563，比前者低了0.007027amu或6.5MeV。过剩能量足够导致裂变的发生。

The above calculation did not include any kinetic energy brought to the reaction by the neutron, on

the grounds that (由于，因为) fission can be induced by absorption in U-235 of very slow neutrons. Only one natural isotope (天然同位素), 235U, undergoes (经历) fission in this way, while 239Pu and 233U are the main artificial isotopes (人工同位素) that do so. Most other heavy isotopes require significantly larger excitation energy to bring the compound nucleus (复合核) to the required energy level for fission to occur, and the extra energy must be provided by the motion of the incoming neutron.

6. 因为铀235吸收慢中子可以诱发裂变反应，以上的计算没有包括中子带到反应中的任何动能。只有一种天然同位素铀235以及人工同位素中的钚239和铀233U以这种方式发生裂变。绝大多数其他重同位素需要极大的激发能来使复合核达到发生裂变所需的能量，额外的能量必须由入射中子的运动提供。

The precise terminology (术语学) is as follows: fissile (裂变的) materials are those giving rise to

fission with slow neutrons; many isotopes are fissionable (可裂变的), if enough energy is supplied. It is advantageous to use fast neutrons--of the order of 1MeV energy--to cause fission. As will be discussed in Chapter l3, the fast reactor (快堆) permits the “breeding ”(增殖) of nuclear fuel. In a few elements such as californium (锎Cf), spontaneous fission (自发裂变) takes place. The isotope 252Cf, produced artificially by a sequence (一连串的) of neutron absorption, has a half-life of 2.646 yr, decaying by alpha emission (97%) and spontaneous fission (3%).

7. 准确的术语如下：由慢中子可以引起的裂变物质称为易裂变物质；如果提供足够的能量，许多同位素是可裂变的。使用能量为1MeV以上的快中子产生裂变是有利的。在13章我们将讨论快堆使核燃料增值。一些元素（例如锎）能自发地发生裂变。同位素锎252是经过一系列中子吸收而人工制造的，半衰期为2.646年，发生α衰变占97%，自发裂变占3%。

It may be surprising that the introduction of only 6.5MeV of excitation energy can produce a reaction

yielding (出产) as much as 200MeV. The explanation (解释) is that the excitation triggers (引起) the separation of the two fragments (碎片) and the powerful electrostatic force (静电力) provides them a large amount of kinetic energy. By conservation of mass-energy (质能转换), the mass of the nuclear products is smaller than the mass of the compound nucleus (复合核) from which they emerge (形成).

8. 这可能会很令人惊讶，仅仅引入6.5MeV的激发能就可以导致产生多达200MeV能量的反应。对此的解释是激发能引起两个碎片的分离，同时，强大的静电力给它们提供巨大的动能。通过质能转换，核反应产物的质量比由它们形成的复合核的质量小。

6.3 BYPRODUCTS OF FISSION (裂变产物)

Accompanying (伴随) the fission process is the release of several neutrons, which are all-important

for the practical application to a self-sustaining (自行持续) chain reaction. The numbers that appear ν (nu) range from l to 7, with an average in the range 2 to 3 depending on the isotope and the bombarding neutron energy. For example, in U-235 with slow neutrons the average number ν is 2.42. Most of these are released instantly, the so-called prompt neutrons (瞬发中子), while a small percentage, 0.65% for U-235, appear later as the result of radioactive decay of certain fission fragments. These delayed neutrons (缓发中子) provide considerable inherent (固有的) safety and controllability (可控性) in the operation of nuclear reactors.

9. 裂变过程同时伴随着少量中子的释放，这对自行持续链式反应是极其重要的。中子数目ν的范围从1到7不等，平均是2到3个，这取决于同位素和轰击中子的能量。例如，慢中子轰击U-235平均产生的中子数ν为2.42。大部分中子都是瞬间释放出来的，即所谓的瞬发中子，对U-235，某一个裂变碎片发生放射性衰变而放出的中子到后来才出现。这种中子只占0.65%这样很小的比例。这些缓发中子为核反应堆在运行过程中的固有安全性和可控性提供了有力的保障。

The nuclear reaction equation (核反应方程式) for fission resulting from neutron absorption in U-235

may be written in general form (通式), letting the chemical symbols for the two fragments be labeled F1 and F2 to indicate many possible ways of splitting. Thus

235U + n → A1Fl + A2F2 + νn + energy.

The appropriate (适当的) mass numbers and atomic numbers are attached. One example, in which the fission fragments are isotopes of krypton (氪) and barium (钡), is

235U + n → 90Kr + 144Ba + 2n + E.

Mass numbers ranging from 75 to l60 are observed, with the most probable at around 92 and l44 as sketched in Fig.6.3.

10. U-235吸收中子产生的裂变的核反应方程式可以用一个通式表示。两个碎片的化学元素用F1和F2表示，这个通式可以用来表示许多可能的分裂方式。如下

235U + n → A1Fl + A2F2 + νn +能量

适当的质量数和原子序数可以被附上（代入）。举个例子，反应中裂变碎片是氪和钡的同位素

235U + n → 90Kr + 144Ba + 2n + E.

质量数范围为75到160不等，最有可能是92到144这个范围。如图6.3所示。

The total energy from fission, after all of the particles from decay have been released, is about 200MeV.

This is distributed among the various processes as shown in Table 6.1. The prompt gamma rays (瞬发γ) are emitted as a part of fission; the rest are fission product (裂变产物) decay gammas. Neutrinos (中微子) accompany the beta particle emission, but since they are such highly penetrating (穿透性) particles their energy cannot be counted as part of the useful thermal energy yield of the fission process. Thus only about l90MeV of the fission energy is effectively available.

11.在衰变过程中所有粒子被释放出来之后，裂变放出的总能量大约为200 MeV。这些能量分配给如表格6.1所示的各种过程。瞬发γ作为裂变的一部分被放出；其它是伽马衰变的裂变产物。中微子连同贝塔粒子一起发射出来，但由于它是如此高穿透性粒子，它的能量不能计为裂变过程产生的有用的热能。因此仅仅只有l90MeV的裂变能是可以有效利用的。

Although fission is the dominant (占优势的) process, a certain fraction of the absorptions of neutrons

in uranium merely result in radiative capture (辐射俘获), according to

235U + n → 236U + γ

The U-236 is relatively stable (稳定的), having a half life of 2.34×l07 yr. About 14% of the absorptions are of this type, with fission occurring in the remaining 86%. This means that η(eta), the number of neutrons produced per absorption in U-235 is lower than ν, the number per fission. Thus using ν = 2.42, η is (0.86) (2.42)=2.07. The effectiveness (效力) of any nuclear fuel (核燃料) is sensitively dependent on the value of η.

12. 尽管裂变是主要过程，但是铀中一小部分吸收中子仅仅导致辐射俘获，根据

235U + n → 236U + γ

U-236是相对稳定的，半衰期2.34×l07年。大概14%的中子吸收是这种形式，剩余的86%发生裂变。这就意味着在每次U-235吸收中产生的中子数η(eta)低于每次裂变释放出的中子数量ν。因此当ν = 2.42,则η为 (0.86) (2.42)=2.07。任何核燃料的效力都与η的值紧密相关。The possibility of a chain reaction was recognized as soon as it was known that neutrons were released in the fission process. If a neutron is absorbed by the nucleus of one atom of uranium and one neutron is produced, the latter can be absorbed in a second uranium atom, and so on. In order to sustain (维持) a chain reaction as in a nuclear reactor or in a nuclear weapon, the value of η must be somewhat (稍微) above l because of processes that complete with absorption in uranium, such as capture in other materials and escape from the system.

一旦知道裂变反应中放出的中子链式反应的可能性就可被发现。如果一个铀原子吸收一个中子并产生一个中子，

后者可被下一个铀原子吸收，如此下去。为了在核反应堆或核武器维持链式反应，η的值必须稍微高于1因为过程中包括铀

中的吸收，比如在其他物质中俘获以及逃离这个系统。

The size of η has two important consequences. First, there is a possibility of a growth of neutron population with time. After all extraneous (外来的) absorption and losses have been accounted for (考虑), if one absorption in uranium ultimately (最后) gives rise to say 1.1 neutrons, these can be absorbed to give (l.l)(l.l) = l.2l, which produce 1.33l, etc. The number available increases rapidly with time. Second, there is a possibility of using the extra neutron, over and above (除…之外) the one required to maintain (维持) the chain reaction, to produce new fissile materials (裂变材料). "Conversion" involves the production of some new nuclear fuel to

replace that used up, while "breeding" is achieved if more fuel is produced than is used.

η的大小有两个重要的影响。首先，随时间中子数增殖是可能的。在考虑了所有的外来吸收和损耗，如果铀中的一次吸收最后产生1.1个中子，这些可被吸收产生(l.l)(l.l) = l.2l,产生1.33l,等等。数量虽时间迅速增加。其次，使用额外的中子是可能的，除一个用来维持链式反应之外，来产生裂变材料。“转化”包括产生的一些新的能量来替代用完的，然而“增殖”发生在当产生的多于消耗的时候。

Out of the hundreds of isotopes found in nature, only one is fissile, 235U. Unfortunately, it is the less abundant (丰富的) of the isotopes of uranium, with weight percentage in natural uranium of only 0.7ll, in comparison, with 99.3 % of the heavier isotope 238U. The two other most important fissile materials, plutonium-239 and uranium-233, are “artificial” in the sense that they are man -made by use of neutron irradiation (照射) of two fertile (富饶的) materials, respectively (

分别地), uranium-238 and thorium-232.

在自然界发现的成百上千的同位素中，只有一种是可裂变的，235U.遗憾的是，铀的同位素是不丰富的，自然界的铀235的重量比例仅为0.711，与此对照，铀238占99.3 %。其他两个最重要的可裂变的材料，环239和铀233，它们是人造的，是用中子照射两中富饶的材料，分别是铀238

和杜232.

The reactions by which 239Pu is produced are

238U + n → 239U 239U → 239Np + e- 239Np → 239Pu + e-

while the yielding 233U are

232Th + n → 233Th 233Th → 233Pa + e- 233Pa → 233U + e-

6.4 ENERGY FROM NUCLEAR FUELS(核燃料产生的能量)

The practical significance (实际意义) of the fission process is revealed (显示) by calculation of the amount of uranium that is consumed (消耗) to obtain a given amount of energy. Each fission yields l90MeV of useful energy, which is also (l90MeV)(l.60×l0-13 J/MeV)=3.04×l0-11J. Thus the number of fissions required to obtain l W-sec of energy is 1/(3.04×l0-11) = 3.3×1010. The number of U-235 atoms consumed in a thermal reactor (热

堆) is larger by the factor 1/0.86 = 1.l6 because of the formation of U-236 in part of the reactions.

裂变的实际意义显示在通过计算消耗的铀产生的能量。每次裂变产生l90MeV 有用能量，也即(l90MeV)(l.60×l0-13 J/MeV)=3.04×l0-11J.这样获得l W-sec 能量所需的裂变数是1/(3.04×l0-11) = 3.3×1010.热堆消耗掉的U-235原子数因因子1/0.86 = 1.l6

存在而更大，因为反应的一部分要形成铀236.

In one day's operation of a reactor per megawatt of thermal power, the number of U-235 nuclei burned

is

在核反应堆一天的运行中每兆瓦热能，燃烧的铀235是

Then since 235 g corresponds to Avogadro's number of atoms 6.02×1023, the U-235 weight consumed at l MW power is

In other words, 1.3 g of fuel is used per megawatt(兆瓦)-day of useful thermal energy released. In

61021(l0W)( 3.310fissions/W-sec)(86,400 sec/day)(0.86 fissions/absorptions)= 3.3210absorptions/day ??21-123(3.3210day )(235g) 1.3g/day.(6.0210)??

a typical reactor, which produces 3000 MW of thermal power, the U-235 fuel consumption (消耗量) is about 4 kg/day. To produce the same energy by the use of fossil fuels (矿物燃料) such as coal (煤), oil, or gas, millions of times (

数百万倍) as much weight would be required.

换言之，1.3克燃料用于每兆瓦天的热能释放。在一个典型的核反应堆，产生3000 MW 热能，铀235消耗量为大概4千克每天。用矿物燃料比如煤，石油或天然气产生相同的能量，需要数百万倍的重量。

6.5 SUMMARY (总结

)

Neutron absorption by the nuclei of heavy elements gives rise to fission, in which heavy fragments, fast neutrons, and other radiations are released. Fissile materials are natural U-235 and the man-made isotopes Pu-239 and U-233. Many different radioactive isotopes are released in the fission process, and more neutrons are produced than are used, which makes possible a chain reaction and under certain conditions “conversion (转化)” and “breeding (增殖)" of new fuels. Useful energy amounts to l90MeV per fission, requiring only l.3 g

of U-235 to be consumed to obtain l MW-day of energy.

重元素吸收中子发生裂变，重裂片，快中子和射线被释放。易裂变材料是铀235和人造的同位素Pu-239和U-233.在裂变过程中许多不同的放射性同位素放射出，产生的中子多于使用的，使链式反应和特定条件下新燃料的“转化”和“增殖”成为可能。每次裂变的有用能量达l90MeV ，

CHAPTER 7 Fusion (聚变

)

When two light nuclear particles combine or “fuse ”(熔合) together, energy is released because the product nuclei have less mass than the original particles. Such fusion reactions can be caused by bombarding targets with charged particles, using an accelerator, or by raising the temperature of a gas to a high enough level for nuclear reactions to take place. In this chapter we shall describe the interactions in the microscopic sense and discuss the phenomena (现象) that affect our ability to achieve a practical large-scale source of energy from fusion.

1. 当两个轻核粒子结合或“熔合”在一起，因为产生的新的核子的质量比原粒子轻，因此会放出能量。这样的聚变反应发生于带电粒子轰击靶核的过程中，可以使用一个加速器，或者通过把气体的温度提升到一个非常高的水平来使核反应发生。在这一章节我们将在微观状态下描述这些反应并且讨论这种影响我们从聚变中获取大量能源的现象。

7.1 Fusion reactions (

聚变反应)

The possibility of release of large amounts of nuclear energy can be seen by comparing the masses of nuclei of low atomic number. Suppose that one could combine two hydrogen nuclei and two neutrons to form the helium nucleus.

The mass-energy difference (using atom masses) is

2(1.007825)+2(1.008665)-4.002603=0.030377 amu Which corresponds to 28.3 MeV energy.

2.

通过比较较小原子数的核子的质量可以看出释放大量核能的可能性。假设由两个氢核和两个中子组成氦核的反应。质量差为：2(1.007825)+2(1.008665)-4.002603=0.030377 amu 相应的能量为28.3 MeV

。 A comparable (比得上的) amount of energy would be obtained by combining four hydrogen nuclei to form

helium plus two positrons. This reaction in effect (有效) takes place in the sun and in other stars through the so-called carbon cycle (碳循环), a complicated chain of events involving hydrogen and isotopes of the elements carbon, oxygen, and nitrogen.

3.

通过将四个氢核组合成氦加上两个正电子可以获得与上一个反应相当的能量。这个称为碳循环的反应有效地发生

在太阳和其他恒星中，这个反应与氢、碳，氧，氮的同位素有着一系列复杂的关联。 In the “hydrogen bomb (氢弹),” on the other hand, the high temperatures created by a fission reaction cause the fusion reaction to proceed in a rapid (迅速的) and uncontrolled (不可控的) manner. Between these extremes (极端的状况) is the possibility of achieving controlled fusion reaction that utilizes (利用) inexpensive and abundant fuels.

4. 在氢弹中，另一方面，裂变反应产生的高温导致聚变以迅速和不可控的方式进行。在这些极端的状况之间的是利

11410222H n He +→14012142H He e →+

用廉价且丰富的燃料实现聚变反应的可能。

As yet, a practical fusion device has not been developed, and considerable (相当可观的) research and development will be required to reach that goal. Let us now examine the nuclear reactions that might be employed (使用). There appears to be no mechanism by which four separate nuclei can be made to fuse directly, and thus combinations of two particles must be sought (seek 的过去分词).

5.

但是，一个实用的聚变装置还没有研制出来，仍需进行相当可观的研究和开发才能达到目标。现在让我们来研究

一下可能使用的核反应。似乎没有使四个独立的核子直接熔合的机制，同时还必须找到将两个粒子结合的方法。 The fusion of two deuterons--deuterium nuclei--in what is designated (指定, 称呼) the D-D reaction results in two processes of nearly equal likelihood (可能性). The other reactions yield more energy but involve the artificial isotopes tritium, abbreviated T, and helium-3. We note that the products of the first and second equations appear as reactants (反应物) in the third and fourth equations. This suggests that a composite (混合的) process might be feasible (可行的).

6. 两个氘核的聚合反应（称作D-D 反应）导致了可能性几乎相等的两个过程。另外一个反应产生更多的能量，但包括人造同位素氚（简写为T ）和氦3。我们注意到第一个和第二个方程的产物作为第三个和第四个方程的反应物。这就表明

混合过程是可行的。

Adding all the equations, we find that the net effect (净效应

) is to convert deuterium into helium according to The energy yield per atomic mass unit of deuterium fuel would thus be about 6 MeV, which is much more favorable (有利的) than the yield per atomic unit of U-235 burned, which is only 190/235=0.81 MeV.

7.

把所有的方程加起来，我们发现净效应是把氘转化成氦。 每原子质量单位的氘燃料产生的能量大约为6 MeV ，比每原子质量单位的U-235燃烧产生的要多，后者仅为190/235=0.81 MeV 。

7.2 ELECTROSTATIC AND NUCLEAR FORCES (

静电力和核力)

The reactions described above do not take place merely by mixing the ingredients (成分, 因素), because of the very strong force of electrostatic repulsion between the charged nuclei. Only by giving one or both of the particles a high speed can they be brought close enough to each other for the strong nuclear force to dominate (占优势, 支配) the electrical force. This behavior is in sharp contrast to the ease (安逸, 悠闲) with which neutrons interact with nuclei.

8.

仅仅把这些成分混合在一起，上述反应并不会发生，因为带电核子之间的静电斥力非常强。除非给其中的一个或所有的粒子一个很高的速度，它们才能靠的足够近，从而让强核力大于电荷力。这种行为同中子与核子轻松反应形成鲜明对比。

There are two consequences (推论, 结果) of the fact that the coulomb force (库仑力) between two charges of atomic numbers Z 1 and Z 2 varies with separation R according to Z 1Z 2/R 2. First, we see that fusion is unlikely in elements other than (除了) those low in the periodic table (元素周期表).

9. 关于两个原子序数为Z 1和Z 2的电荷之间的库仑力根据公式Z 1Z 2/R 2 随电荷间距离R 变化有两个推论。首先，我们

知道除了那些在元素周期表中靠前的元素外是不可能发生聚变的。 Second, the force and corresponding potential energy of repulsion is very large at the 10-15 m range of nuclear forces, and thus the chance of reaction is negligible (可以忽略的) unless particle energies are of the order of keV. Figure 7.1 shows the cross section for the D-D reaction. The strong dependence on energy is noted, with σDD rising by a factor of 1000 in the range 10-75 keV.

10. 其次，在10-15

米核力范围内，核力和对应的排斥势能都是非常大的，这样，除非粒子能量可达几keV ，反应的机会几乎可以忽略。图 7.1显示D-D 反应的吸收截面。注意到截面显著地依赖于能量，在10-75keV 范围内，截面σDD 上升了1000倍。

P67第二段

Energy in the kilo-electron-volt (KeV) and million-electron-volt (MeV) range can be achieved by a variety of charged particle accelerators. Bombardment of a solid or gaseous deuterium target by high-speed deuterons 24124247.7.

H He MeV →+

gives fusion reactions, but most of the particle energy goes into electrostatic interactions that merely heat up the bulk of (大多数) the target. The amount of energy required to operate the accelerator greatly exceeds the recoverable fusion energy, and thus some other technique is required.

11.能量在千电子伏到兆电子伏的粒子可以通过多种带电粒子加速器获得。用高速氘核轰击固态或气态氘靶可以引发聚变反应，但是大多数的粒子能量进入到仅仅使得大多数靶粒子被加热的静电相互作用中。由于运行加速器所需要的能量远远超过了获得的聚变能，因此还需要运用一些其它的技术。

7.3 THERMONUCLEAR REACTIONS IN A PLASMA (等离子体中的热核反应)

The most promising (有前途的) medium in which to obtain the high particle energies that are needed for

practical fusion is the plasma (['pl?zm?] 等离子体). It consists of a highly ionized gas (高度离子化的气体) as in an electrical discharge (放电) created by the acceleration of electrons. Equal numbers of electrons and deuterons are present, making the medium electrically neutral.

等离子体是最有望获得粒子聚变所需高粒子能的介质。等离子体，如通过电子加速而产生的放电，由高度离子化的

气体组成。由于有相同电量的电子和氘核存在，使得等离子体呈电中性。Through the injection (注射) of enough energy into the plasma its temperature can be increased, and the deuterons reach the speed for fusion to be favorable (有利的, 顺利的). The term (术语) thermonuclear (热核反应) is applied to reactions induced by high thermal energy, and the particles obey a speed distribution similar to (类似于) that of a gas, as described in Chapter 2.

通过向等离子体中注入足够能量，等离子体的温度会身高，并且氘核会达到适宜聚变的速度。术语——热核反应应

用于由高热能诱发的反应，粒子的速度遵循类似于第二章描述的气体的速度分布。Such a temperature (77,000,000K) greatly exceeds the temperature of the surface of the sun, and is far beyond any temperature at which ordinary materials melt (熔化) and vaporize (蒸发). The plasma must be created and heated to the necessary temperature under the constraint (约束) of electric and magnetic fields. Such forces on the plasma are required to assure (保证) that thermal energy is not prematurely (过早地) lost.

如此高的温度(77,000,000K)极大地超过了太阳表面的温度，也远远超过了任何通常物质熔化和蒸发的温度。等离

子体必须被产生并在电场和磁场的约束下加热到必要的温度。这种加于等离子体的作用力是保证热能不会过早地损失所必需的。Moreover, the plasma must remain intact (完整无缺的) long enough for many nuclear reactions to occur, which is difficult because of inherent (固有的, 内在的) instabilities (不稳定的) of such highly charged media. Recalling from Section 2.2 the relationship pV=nkT, we note that even though the temperature T is very high, the particle density n/V is low, allowing the pressure p to be manageable (易处理的).

此外，为了核反应能够发生，等离子体必须在足够长的时间内保持完整，而由于其固有不稳定性，这对于如此高的

带电介质来说是非常困难的。回想2.2节的关系式pV=nkT，我们注意到即使温度T很高，如果粒子密度n/V低的话，也会让压力p容易控制。The achievement of a practical energy source is further limited by the phenomenon of radiation losses (辐射损失), In Chapter 5 we discussed the bremsstrahlung radiation (轫致辐射) produced when electrons experience acceleration. Conditions are ideal for the generation (产生) of such electromagnetic radiation (电磁辐射) since the high-speed electrons in the plasma at elevated (提高的) temperature experience continuous accelerations and decelerations (减速) as they interact with (与…相合) other charges.

12.粒子能量源的获得进一步受限于辐射损失现象。在第五章，我们讨论了当电子经历了加速会产生轫致辐射。产生这种电磁辐射的条件是理想化的，由于高速电子在等离子体提高温度时不断被加速，当电子与其它电荷结合时则会减速。

The radiation can readily escape from the region, because the number of electrons and particles is very

small. In a typical plasma, the number density of electrons and deuterons is 1015, which corresponds to a rarefied (纯净的, 稀薄的) gas. The amount of radiation production (and loss) increases with temperature at a slower rate than does the energy released by fusion, as shown in Fig. 7.2.

13.因为电子和粒子的数目非常小，射线可以很容易地从该区域逃离。在一个典型的等离子体中，电子和氘核的密度数为1015，相当于稀薄气体。如图7.2所示，辐射产物的数量随温度的增长率比通过核聚变释放的能量随温度的增长率低。