章节大纲

  • Cooling towers of a nuclear power plant emitting harmless water vapor steam.

    Steam rises from the cooling towers of this nuclear power plant. The steam is only harmless water vapor. Unlike a power plant that burns fossil fuel , a nuclear power plant doesn’t release pollution into the air. That’s because a nuclear power plant produces power by nuclear fission, a type of nuclear reaction.  
    ::蒸汽只是无害的水蒸气。 与燃烧化石燃料的发电厂不同,核电厂不会向空气释放污染。 这是因为核电厂通过核裂变(一种核反应)发电。

    What Is Nuclear Fission?
    ::什么是核裂变?

    Nuclear fission  is the splitting of the nucleus of a radioactive into two smaller nuclei. This type of reaction releases a great deal of from a very small amount of matter. Fission of a single fuel pellet that contains radioactive uranium-235, like the one pictured in the Figure , releases as much energy as burning 1,000 kilograms of coal!
    ::核裂变是将放射性核核分裂成两个较小的核核。 这种反应从非常小的物质中释放出大量物质。 一种含有放射性铀-235的燃料粒子的裂变,就像图中图象的一样,释放的能量相当于燃烧1 000公斤煤炭的能量!

    A hand holding a uranium-235 fuel pellet, illustrating its use in nuclear reactors.
    Fuel pellets containing uranium-235 used in a nuclear reactor.

    Q: What causes the nucleus of a uranium-235 atom to fission?
    ::问题:是什么原因导致铀-235原子核心裂变?

    A: A collides and is absorbed by the uranium-235 nucleus.
    ::A:碰撞,由铀-235核心吸收。

    How Nuclear Fission Occurs
    ::核纤维作用如何

    The Figure shows how nuclear fission of uranium-235 occurs. It begins when a uranium nucleus gains a neutron. This can happen naturally when a free neutron strikes it, or it can occur deliberately when a neutron is crashed into it in a nuclear power plant. In either case, the nucleus of uranium-235 becomes extremely unstable with the extra neutron. As a result, it splits into two smaller nuclei, krypton-92 and barium-141. The reaction also releases three neutrons and a great deal of energy. It can be represented by this nuclear equation:
    ::图中显示了铀-235的核裂变是如何发生的。当铀核核核获得中子时,它就开始了。当一个自由中子击中它时,这自然会发生,或者当一个中子坠入核电厂时,它会故意发生。无论哪种情况,铀-235的核心随着额外的中子而变得极不稳定。结果,它分裂成两个较小的核子,Krypton-92和-141。反应还释放了三个中子和大量能量。它可以用核方程式来表示:

    92 235 U + 1 neutron → 36 92 K r + 56 141 B a + 3 neutrons + energy

    Note that the subscripts of the symbols represent numbers of and the superscripts represent numbers of protons plus neutrons.  
    ::注意符号的下标代表质子和中子的编号,上标代表数字,上标代表质子和中子的编号。

    Nuclear fission of uranium-235, showing neutron absorption and resulting products.

    Nuclear Chain Reaction
    ::核电链反应

    The neutrons released when uranium-235 fissions may crash into other uranium nuclei and cause them to fission as well. This can start a nuclear chain reaction. You can see how this happens in the Figure . In a chain reaction, one fission reaction leads to others, which lead to others, and so on. A nuclear chain reaction is similar to a pile of wood burning. If you start one piece of wood burning, enough is produced by the burning wood to start the rest of the pile burning without any further help from you. 
    ::当铀-235裂变可能撞入其他铀核核并导致它们裂变时释放出的中子。这可以引发核链反应。你可以在图中看到这种情况是如何发生的。在连锁反应中,一个裂变反应导致其他反应,从而导致其他反应,等等。核链反应类似于一堆木柴燃烧。如果你开始燃烧一块木柴,那么燃烧的木柴就足以在没有你任何进一步帮助的情况下开始燃烧堆积的其余部分。

     

     

     

     

     

     

     

    A nuclear chain reaction process associated with nuclear fission.

    Using Energy from Nuclear Fission
    ::利用核裂变产生的能源

    If a nuclear chain reaction is uncontrolled, it produces a lot of energy all at once. This is what happens in an atomic bomb. However, if a nuclear chain reaction is controlled, it produces energy much more slowly. This is what occurs in a nuclear power plant. The reaction is controlled by inserting rods of neutron-absorbing material into the fissioning material to manage the chain reaction. You can see this in the Figure . The radiation from the controlled fission is used to heat water and turn it to steam. The steam is under pressure and causes a turbine to spin. The spinning turbine runs a , which produces electricity.
    ::如果核链反应不受控制,它会同时产生大量能量。这是原子弹中发生的情况。然而,如果核链反应受到控制,它会产生更慢的能量。这是核电厂中发生的情况。这种反应是通过在裂变材料中插入吸收中子材料的棒来控制的,以管理链反应。从图中可以看到这一点。受控裂变产生的辐射被用来加热水,将水变成蒸汽。蒸汽受到压力,导致涡轮机旋转。旋转涡轮机运行电源。

    Water heating and turbine setup in a nuclear power plant.

    Pros and Cons of Nuclear Energy
    ::核能的利弊

    In the U.S., the majority of electricity is produced by burning coal or other fossil fuels. This causes air pollution that harms the health of living things. The air pollution also causes rain and contributes to global warming. In addition, fossil fuels are nonrenewable resources , so if we keep using them, they will eventually run out. The main advantage of nuclear energy is that it doesn’t release air pollution or cause the other environmental problems associated with the burning of fossil fuels. On the other other hand, radioactive elements are nonrenewable like fossil fuels and could eventually be used up.
    ::在美国,大部分电力都是用燃煤或其他化石燃料发电的。这造成了空气污染,危害了生物的健康。空气污染也造成了降雨和全球变暖。 此外,化石燃料是不可再生的资源,因此如果我们继续使用,它们最终就会耗尽。 核能的主要好处是它不会释放空气污染,也不会引起与燃烧化石燃料有关的其他环境问题。 另一方面,放射性元素和化石燃料一样不可再生,最终也会被使用。

    The main concern over the use of nuclear energy is the risk of radiation. Accidents at nuclear power plants can release harmful radiation that endangers people and other living things. Even without accidents, the used fuel that is left after nuclear fission reactions is still radioactive and very dangerous. It takes thousands of years for it to decay until it no longer releases harmful radiation. Therefore, used fuel must be stored securely to protect people and other living things. 
    ::对核能使用的主要关切是辐射风险。核电厂的事故可以释放危害人类和其他生物的有害辐射。即使没有事故,核裂变反应后留下的废燃料仍然是放射性的,而且非常危险。它需要数千年才能腐烂,直到不再释放有害辐射。因此,废燃料必须安全地储存起来,以保护人类和其他生物。

     

    Summary
    ::摘要

    • Nuclear fission is the splitting of the nucleus of an atom into two smaller nuclei. This type of reaction releases a great deal of energy from a very small amount of matter. It begins when the nucleus of a radioactive atom gains a neutron.
      ::核裂变是将原子核心分割成两个较小的核核。 这种反应从非常小的物质中释放出大量的能量。 当放射性原子核心获得中子时,它就开始了。
    • In uncontrolled nuclear fission, one fission reaction starts a chain reaction, in which neutrons produced in one reaction cause other reactions, which cause more reactions, and so on.
      ::在不受控制的核裂变中,一种裂变反应引发连锁反应,一种反应产生的中子引起其他反应,引起更多的反应,等等。
    • Energy released by nuclear fission is used to produce electrical energy in nuclear power plants. Production of nuclear energy doesn’t produce air pollution but it poses the risk of accidents that release harmful radiation.
      ::核裂变释放的能源被用来在核电厂生产电力。 核能的生产不会产生空气污染,但会产生释放有害辐射的事故风险。

    Review
    ::回顾

    1. What is nuclear fission?
      ::什么是核裂变?
    2. Outline how nuclear fission occurs.
      ::概述核裂变是如何发生的。
    3. Describe a nuclear chain reaction.
      ::描述核链反应。
    4. How is nuclear fission controlled in a nuclear power plant?
      ::核电厂如何控制核裂变?
    5. Compare and contrast the use of fossil fuels and nuclear fission to produce energy.
      ::比较和比较利用化石燃料和核裂变生产能源的情况。

    Explore More
    ::探索更多

    Watch the video about nuclear fission and then answer the questions below. 
    ::观看关于核裂变的视频,然后回答下面的问题。

     

     

     

     

     

     

     

    1. How was nuclear fission discovered?
      ::核裂变是怎么发现的?
    2. Describe in detail what happens to a uranium-235 nucleus when it is struck by a neutron, and explain why the nucleus splits in two. Your answer should include the role of nuclear forces in the reaction.
      ::详细描述铀-235核被中子撞击时发生的情况,并解释核为何分裂为两个。 您的回答应该包括核力量在反应中的作用。