nuclear energy.doc

OUR MATERIAL world is composed of many substances distinguished by their chemical, mechanical, and electrical properties. They are found in nature in various physical statesthe familiar solid, liquid, and gas, along with the ionic “plasma.”However, the apparent diversity of kinds and forms of material is reduced by the knowledge that there are only a little more than 100 distinct chemical elements and that the chemical and physical features of substances depend merely on the strength of force bonds between atoms.我们的物质世界由许多物质组成，这些物质由它们的化学性质、机械特性和电的性质区分开来。物质在自然界中以各种各样的状态被发现，有熟悉的固态，液态和气态，还有离子的等离子体态。然而，由于人们已认识到目前仅仅存在100多种不同的化学元素，并且物质的化学性质和物理性质仅仅是由原子间力键的强度所决定，因此物质种类和形式的表面上的多样性可以被归纳简化。We recall that radiant energy may be released by heating of solids, as in the wire of a light bulb; by electrical oscillations, as in radio or television transmitters; or by atomic interactions, as in the sun. The radiation can be viewed in either of two waysas a wave or asa particledepending on the process under study. In the wave view it is a combination of electric and magnetic vibrations moving through space. In the particle view it is a compact moving uncharged object, the photon, which is a bundle of pure energy, having mass only by virtue of its motion. 我们知道，加热的固体可以释放出辐射能，例如在灯泡里的灯丝上，又比如在无线电或电视发射机中的电振荡，或太阳内部的原子相互作用都可以释放这种能量。依据研究的方法，可以用两种方式来看待辐射，即一束波或者一个粒子。从波的角度，辐射可以看作通过空间传输的电磁振荡的混合。从粒子的角度，辐射可以看作一个紧凑的不带电的物体光子。因为光子只有运动才具有质量，所以光子是一束纯能量。A COMPLETE understanding of the microscopic structure of matter and the exact nature of the forces acting is yet to 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 or mathematical, often based on analogy with large-scale processes, on experimental data, or on advanced theory.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。An increase in the temperature of the gas as a result of heating causes greater molecular motion,which results in an increase of particle bombardment of a container wall and thusof pressure on the wall.加热使得气体温度上升，温度上升又引起分子运动的加剧导致粒子对容器内壁碰撞的增加，使得气体对器壁压力增大。The electronic structure of the other elements is described by the shell model,in which a limited number of electrons can occupy a given orbit or shell. Theatomic number Z is unique for each chemical element and represents both thenumber of positive charges on the central massive nucleus of the atom and thenumber of electrons in orbits around the nucleus.其他元素的电子结构用壳层模型来描述。在此模型中，占据给定能级或壳层的电子数目是有限的。对每一个化学元素，原子序数Z是唯一的。原子序数代表两个数目：一个是中心重的原子核上的正电荷数，另一个是核周围轨道上的电子数。The force of electrostatic repulsion between like charges, which varies inverselyas the square of their separation, would be expected to be so large that nucleicould not be formed. The fact that they do exist is evidence that there is an evenlarger force of attraction. 同种电荷之间的静电排斥力与他们距离的平方成反比，预期核内排斥力很大，以至于不能形成原子核。而原子核的确存在的事实，表明存在着一个甚至更大的吸引力。To disrupt a nucleus and separate it into its component nucleons, energy must be supplied from the outside. Recalling Einsteins 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. 要想分裂一个原子核，并将原子核分离成它的组成成分，就必须从外部供给能量。联系爱因斯坦的质能等价关系式，这也就是说，一个给定的原子核比其各个核子的总的质量要轻，它们之间质量只差，就是结合质能。MANY NATURALLY occurring and man-made isotopes have the property of radioactivity,which is the spontaneous disintegration (decay) of the nucleus with the emissionof a particle. The process takes place in minerals of the ground, in fibers ofplants, in tissues of animals, and in the air and water, all of which contain tracesof radioactive elements.许多天然和人造同位素都具有放射性的特性，即原子核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，所有的这些物质都存在着放射性元素的痕迹（放射性元素无处不在）。Whereas the electron (sometimes called negatron) is a normal part of any atom, the positron is not. It is an example of what is called an antiparticle, because its properties are opposite to those of the normal particle. Just as particles form matter, antiparticles form antimatter.然而，电子（有时称为阴电子）是任何原子一个正常的部分，正电子则不是。正电子是反粒子中的一个例子。反粒子的性质与正常的例子的性质相反，正如粒子形成物质，反粒子形成反物质。The measurement of the activity of a radioactive substance is complicated by the presence of background radiation, which is due to cosmic rays from outside the earth or from the decay of minerals in materials of construction or in the earth. It is always necessary to measure the background counts and subtract them from those observed in the experiment.放射性物质活度的测量因“本底辐射”的存在而变得复杂，本底辐射来自地球外的宇宙射线，建筑物材料中或地球中的矿物质的衰变。因此，总是必须测量本底计数，并从实验中所观察到的那些计数中扣除本底。 NUCLEAR REACTIONSthose in which atomic nuclei participatemay take placespontaneously, as in radioactivity or may be induced by bombardment with aparticle or ray. Nuclear reactions are much more energetic than chemical reactions,but they obey the same physical lawsconservation of momentum, energy,number of particles, and charge.核反应（有原子核参与）可能会自然发生，如放射性，或可能由粒子或射线轰击诱发。核反应比化学反应能量高得多，但它们都遵守相同的物理定律-动量、能量、粒子数、电荷守恒。The interpretation of nuclear reactions often involves the concept of compoundnucleus. This intermediate stage is formed by the combination of a projectileand target nucleus. It has extra energy of excitation and breaks up into theoutgoing particle or ray and the residual nucleus.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。In the case of reactions that produce a positron, however, either nuclear masses or atomic masses with the subtraction of the mass-energy required to create an electron-positron pair should be used, 0.0011 amu or 1.02 MeV.在产生正电子的反应中，进行计算时要么采用核的质量，要么采用减去了产生一对正负电子对（0.0011 amu 或1.02Mev）的原子的质量。When fast neutrons, those of energy of the order of 2 MeV, are introduced into amedium, they make inelastic or elastic collisions with nuclei. On each elastic collisionneutrons are deflected in direction, they lose energy, and they tend tomigrate away from their origin.We include those particles produced by both atomic and nuclear processes and those resulting from electrical acceleration, noting that there is no essential difference between X-rays from atomic collisions and gamma rays from nuclear decay; protons can come from a particle accelerator, from cosmic rays, or from a nuclear reaction in a reactor. The word “materials” will refer to bulk 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.我们包含了有原子和核两种过程产生的辐射，以及由电加速产生的辐射，注意到由原子碰撞产生的X射线和由核衰变产生的伽马射线没有根本的区别。质子可能来自粒子加速器，来自宇宙射线，或者来自反应堆中的核反应。“物质”这个词指的是大量的物质，无论其起源是矿物的或生物的，“物质”这个词还指组成物质的粒子，包括分子，原子，电子和原子核。In addition to the X-rays as a result of transitions in the electron orbits, a similar radiation called bremsstrahlung (German: braking radiation) is produced. It arises from the deflection and resulting acceleration of electrons as they encounter nuclei.除了电子轨道的跃迁会产生X射线外，一种被称为轫致辐射的辐射（德语：刹车辐射）可以产生类似的X射线。轫致辐射是当电子与核相遇的时候，由于电子方向的偏转产生的加速所产生的。Charged particles such as protons, alpha particles, and fission fragment ions are classified as heavy , being much more massive that the electron.带电粒子，例如质子，粒子，和裂变碎片离子，因为它们的质量比电子重得多，所以被归类为重离子。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.除非轰击粒子的能量是非常的高，并且能进入到核力的短的力程内，轰击粒子进入到原子核并引起核反应的几率非常小。In the presence of a nucleus, a gamma ray photon disappears and two particles appear-an electron and a positron. 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. 在原子核存在的情况下，一个伽马射线的光子消失了并产生了两个粒子电子和正电子。因为这两个粒子电荷数相等只是符号相反，所以反应后没有净电荷产生，就像反应前一样，伽马射线不带电。If neutron is captured by the proton in a molecule of water or some other hydrocarbon, a gamma ray is released. The resulting deuteron recoils with energy that is much smaller than that of the gamma raybut still is far greater than the energy of binding of atoms in the water molecule.Again dissociation of the compound takes place, which can be regarded as a form of radiation damage.如果中子被水或者其他碳水化合物的一个分子中的质子所俘获，会释放出伽马射线。产生的氘核的反冲能比伽马射线的能量小得多，但是仍然远大于水分子中原子的结合能量。化合物分子再一次的发生分解，这可以被看作一种形式的辐射损伤。The energy of slow neutron can be neglected in calculation of fission energy, on the grounds that fission can be induced by absorption in U-235 of very slow neutrons. Only one natural isotope, 235U, undergoes fission in this way, while 239Pu and 233U are the main artificial isotopes that do so. Most other heavy isotopes require significantly larger excitation energy to bring the compound nucleus to the required energy level for fission to occur, and the extra energy must be provided by the motion of the incoming neutron. 根据U-235核吸收非常慢的中子能诱发核裂变，所以在计算裂变能量的过程中慢中子的能量可以忽略。只有一种天然的同位素铀-235能吸收慢中子产生裂变，而Pu-239，U-233是用慢中子诱发裂变的重要的人工同位素。大部分其他的重同位素，要求明显更大的激发能才能达到发生裂变的能量水平。这些超出的能量必须由入射中子的运动来提供。It may be surprising that the introduction of only 6.5 MeV of excitation energy can produce a reaction yielding as much as 200 MeV. The explanation is that the excitation triggers the separation of the two fragments and the powerful electrostatic force provides them a large amount of kinetic energy. By conservation of mass-energy, the mass of the nuclear products is smaller than the mass of the compound nucleus from which they emerge.仅仅引入6.5兆电子伏特的激发能就能产生多大200兆电子伏特的能，这是令人惊讶的。对此的解释是：核的激发引起两个碎片分离，强大的静电力为两个碎片提供了巨大的动能。按照质-能守恒，核产物的质量小于核产物形成的复合核的质量。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 a chain reaction as in a nuclear reactor or in a nuclear weapon, the value of h must be somewhat above l because of processes that compete with absorption in uranium, such as capture in other materials and escape from the system.如果一个中子被一个铀原子的原子核吸收，并产生一个中子，后者又可以被一个铀原子吸收，又会产生一个中子，等等。因为一些反应过程会吸收中子与铀吸收中子发生竞争，例如，其他材料俘获中子，中子逃离出系统，在核武器或者核反应堆中为了维持链式反应，h的值必须稍微大于1。There is a possibility of using the extra neutron, over and above the one required to maintain the chain reaction, to produce new fissile materials. 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.除了一个中子要求维持链式反应外，用多余的中子来生产新的易裂变材料是可能的。核燃料“转化”包括用产生的某个新的核燃料代替用完的核燃料，而如果产生的核燃料比用掉的核燃料要多，核燃料的“增值”就实现了。When two light nuclear particles combine or “fuse” 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. 因为产物核的质量比原来的核粒子的质量要小，当两个轻的核粒子组合或融合在一起的时候，会释放出能量。这种聚变反应可以用加速器产生的带电粒子轰击靶物质产生，或者可以通过提升气体的温度达到足够高的水平，使得聚变反应发生。The fusion of two deuteronsdeuterium nucleiin what is designated the DD reaction results in two processes of nearly equal likelihood.两个氘核聚变会导致两个几乎相等可能性反应过程出现。氘核是同位素氘的核，两个氘核聚变的反应，称之为D-D反应。The fusion reactions do not take place merely by mixing the reactants, 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 the electrical force. 因为带电的原子核之间存在非常强的静电排斥力，所以仅仅通过混合反应物粒子，聚变反应是不会发生的。只有给其中的一个粒子或两个粒子一个高的速度，才能使得反应物粒子足够的互相靠近，达到强的核力大于电场力的时候，才能发生聚变反应。Energies in the kilo-electron-volt and million-electron-volt range can be achieved by a variety of charged particle accelerators. Bombardment of a solid or gaseous deuterium target by high-speed deuterons gives fusion reactions, but most of the particle energy goes into electrostatic interactions that merely heat up the bulk of the target. For a practical system, the recoverable fusion energy must significantly exceed the energy required to operate the accelerator. Special equipment and processes are required to achieve that objective.通过采用各种各样的带电粒子加速器，可以达到千电子伏特和百万电子伏特的能量。采用高速的氘核轰击固态和气态的氘靶来产生聚变反应，但是大部分的粒子能量都去进行静电相互作用，而静电相互作用只是加热了大部分的靶。对于一个实际的系统，聚变重新获得的能量必须明显超出运行加速器要求的能量。为实现这个目标，需要特殊的设备和方法。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.实际的聚变反应需要高的粒子能量。获得高粒子能量的最有希望的媒质就是等离子体。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. Moreover,the plasma must remain intact long enough for many nuclear reactions to occur, which is difficult because of inherent instabilities of such highly charged media.等离子体必须在电场和磁