《高级英语下翻译英汉对照》由会员分享，可在线阅读，更多相关《高级英语下翻译英汉对照（10页珍藏版）》请在金锄头文库上搜索。
1、13Radioactivity 放射性Radioactivity放射性Atomic nuclei consist of combinations of protons, or positively-charged particles, and neutrons, or uncharged particles. 原子核是由质子与中子相结合而构成;质子也叫带正电荷的粒子，中子也叫不带电荷的粒子。The number of protons and neutrons in each element can vary, but only certain combinations are stable.
2、每一种元素中质子和中子的数目可能有所不同，而只有一些元素的组合比较稳定。For example, calcium-48, having 20 protons and 28 neutrons, is a stable isotope of calcium. 例如钙-48含有 20 个质子和28 个中子，是钙的稳定同位素。But if there is an excess or deficiency of neutrons in any combination, the isotope will be unstable. 可是在任何一种组合中，如果中子数目不足或者过剩，同位素就不稳定。A nucl
3、eus is more likely to be unstable if it is aheavy one that is, if it containsa large number of protons and neutrons. 如果原子核是重核，也就是说原子核如含有大量质子和中子，就可能更加趋于不稳定。Unstable nuclei attempt to achieve stability by emitting some form of radiation, until they transform themselves into stable isotopes.不稳定的原子核总是要通
4、过放射出某种放射线的方式达到稳定，也就是说直到原子本身衰变为稳定的同位素才能稳定。There are radioactive isotopes of every element, either those existing in nature or else those activated artificially by bombardment of stable nuclei with nuclear particles such as protons, alpha-particles or neutrons. 每种元素都有放射性同位素。有的放射性同位素是自然界中存在的，有的利用诸如质子、
5、粒子或中子一类的核子，对稳定的原子核进行轰击而用人工方法制造的。However, a particle will not be absorbed by the target nucleus unless its velocity correspondswith one of the energy levels of the nucleus. 然而，除非粒子的速度与原子核的一个能级相适应， 否则粒子就不可能为靶子核所吸收。Heavy nuclei, having more energy levels than light nuclei, are more likely to effect cap
6、ture of a particle a fact which helps to explain the importance of uranium, thorium and other very heavy atoms in nuclear research.重核比轻核具有更多的能级，因而可更有效地俘获粒子。这一事实有助于阐明铀、钍和其他重原子在核研究中的重要性。Since the neutron is uncharged, it is not affected by the charged electrons and protons of the target atom, and is t
7、herefore more likely to be captured than any other particle, provided that it is in resonance with an energy level of the nucleus. 由于中子不带电荷，所以不受带电粒子和靶原子的质子的影响。而且，如果中子同核的能级协调一致，就会更易于被其他任何粒子俘获。In the event of neutron capture, the mass number of the nucleus will be raised, and it will thus become unsta
8、ble and radioactive. 一旦俘获了中子，原子核的质量数便会增加，因而也就会变得不稳定并且具有放射性。As radiation continues, the level of radioactivity falls exponentially, and the time 随着放射线的不断放出，放射性的能级呈指数式衰减，原子数衰减到原子原始数值的一taken for it to reach half its original value is known as the half-life of the isotope, which may vary from a fraction
9、 of a second to millions of years. 半时所经历的时间称为同位素的半衰期。半衰期从零点几秒到几百万年各有不同。Isotopes with long half-lives have many uses in medicine and industry, but they must be handled and disposed of with great care, in case they cause radiation damage.半衰期长的同位素在医学和工业方面有许多用途，但必须极其慎重而严格地控制和处理，以免招致辐射的伤害。Neutron bombard
10、ment of the very heavy uranium atoms may have a quite different result. 用中子对非常重的铀原子进行轰击，可能会产生全然不同的结果。It may cause the nucleus of the fissile U-235 atom to split into two parts. 轰击可以使可裂变的铀-235原子核裂成两部分。This nuclear fission releases large quantities of energy which finally takes the form of the great e
11、nergy, and at the same time other neutrons are ejected from the nucleus. 这种核裂变能释放出大量最终以热能形式出现的能量。与此同时，从核子里还放出另外一些中子。The fission fragments are highly radioactive, and will contaminate the fissile uranium if they are not removed periodically. 分裂的裂片有着很强的放射性，而且如不定期清除，就会污染裂变的铀。A number of these fission p
12、roducts, such as Caesium-137, are very useful as irradiation sources, and it is now possible to separate out the desired isotope from the spent fuel.有一些裂变产物，例如铯-137,就是一种很有用的辐射源；目前已经能够从废弃的燃料中分离出我们所期望的同位素。14Chain Reaction 连锁反应Chain Reaction连锁反应When fission occurs, an average of 2-5 neutrons are emitte
13、d from the nucleus. 核发生裂变时，原子核平均会放射出2 至 5个中子。If the fission process can be so arranged thatone of these liberated neutrons is captured by another U-235 nucleus to produce another fission, then the reaction will become self-sustaining.倘若所设计的裂变过程能使得所放出的一个中子被铀-235的另一个核子所俘获并进而产生另一裂变，那么随后反应就会自动持续进行。When
14、emitted neutrons travel at a high velocity, and it is known that such fast neutrons have little chance of being captured by the fissile uranium. 中子被放射出时以高速运动。正如所知，这种高速运动的中子几乎不可能被可裂变铀俘获。However, if slowed down to thermal speeds, their probability of capture is greatly increased. 然而，如能使中子减速到热运动速度，热中子被
15、俘获的可能性就会大大增加。In the normal thermal reactor, the uranium is 在普通的热核反应堆中，铀被围在大量的减surrounded by a large mass of moderating material. 速材料当中。The liberated neutrons collide repeatedly with the light atoms of the moderator in such a way thatthey lose much of their energy and eventually become thermalized. 释
16、放出的中子与缓和剂的轻原子反复不断相互碰撞。碰撞的结果，中子便会失掉大量能量，于是最终会变成热速化中子。The moderator may be either a liquid such as heavy water, or a solid such as graphite. 缓和剂可以是液体，如重水， 也可以是固体，如石墨。Both these substances are of low atomic weight and have low neutron absorption cross-sections. 这两种物质的原子量都低，而且中子吸收截面也低。With the graphite moderator, the uranium which is generally in the form of rods is inserted into channels cut out of the graphite. 在使用石墨缓和剂的情况下，铀通常以铀棒形式插进石墨切槽内。These channels are so arranged as to form a lattice
