Nuclear Fusion

In physics and nuclear chemistry, nuclear fusion is the process by which multiple atomic particles join together to form a heavier nucleus. It is accompanied by the release or absorption of energy. Iron and nickel nuclei have the largest binding energies per nucleon of all nuclei and 1)________. The fusion of two nuclei lighter than iron or nickel generally releases energy while the fusion of nuclei heavier than iron or nickel absorbs energy; vice-versa for the reverse process, nuclear fission.

Nuclear fusion occurs naturally in stars. Artificial fusion in human enterprises has also been achieved, although not yet completely controlled. Building upon the nuclear transmutation experiments of Ernest Rutherford done a few years earlier, fusion of light nuclei (hydrogen isotopes) was first observed by Mark Oliphant in 1932, and the steps of the main cycle of nuclear fusion in stars were subsequently worked out by Hans Bethe throughout the remainder of that decade. 2)__________, as part of the Manhattan Project, but was not successful until 1952. Research into controlled fusion for civilian purposes began in the 1950s, and continues to this day.

Fusion reactions power the stars and produce all but the lightest elements in a process called nucleosynthesis. Whereas the fusion of light elements in the stars releases energy, 3)_________.

When the fusion reaction is a sustained uncontrolled chain, it can result in a thermonuclear explosion, such as that generated by a hydrogen bomb. Reactions which are not self-sustaining can still release considerable energy, as well as large numbers of neutrons.

Research into controlled fusion, with the aim of producing fusion power for the production of electricity, has been conducted for over 50 years. It has been accompanied by extreme scientific and technological difficulties, and as of yet has not been successful in producing workable designs. As of the present, the only self-sustaining fusion reactions produced by humans have been produced in hydrogen bombs, 4)_________. While some plans have been put forth to attempt to use the explosions of hydrogen bombs to generate electricity (e.g. PACER - programmed analysis and calculation of equipment reliability), none of these have ever moved far past the design stage.

It takes considerable energy to force nuclei to fuse, even those of the lightest element, hydrogen. This is because all nuclei have a positive charge (due to their protons), and as like charges repel, nuclei strongly resist being put too close together. 5)___________, however, they can overcome this electromagnetic repulsion and get close enough for the strong nuclear force to be active, achieving fusion. The fusion of lighter nuclei, creating a heavier nucleus and a free neutron, will generally release more energy than it took to force them together-an exothermic process that can produce self-sustaining reactions.

The energy released in most nuclear reactions is much larger than that in chemical reactions, because the binding energy that holds a nucleus together is far greater than the energy that holds electrons to a nucleus. For example, the ionization energy gained by adding an electron to a hydrogen nucleus is 13.6 electron volts - less than one-millionth of the 17 MeV released in the D-T (deuterium-tritium) reaction shown to the top right. Fusion reactions have an energy density many times greater than nuclear fission-that is, per unit of mass the reactions produce far greater energies, even though individual fission reactions are generally much more energetic than individual fusion reactions – 6)________. Only the direct conversion of mass into energy, such as with collision of matter and antimatter, is more energetic per unit of mass than nuclear fusion.

2. Match the notions and their meanings:

1. nucleon a) a fundamental form of energy observable in positive and negative forms that occurs naturally (as in lightning) or is produced (as in a generator) and that is expressed in terms of the movement and interaction of electrons

2. nucleosynthesis b) a proton or neutron especially in the atomic nucleus

3. self-sustaining c) an uncharged elementary particle that has a mass nearly equal to that of the proton and is present in all known atomic nuclei except the hydrogen nucleus

4. electricity d) the production of a chemical element from simpler nuclei (as of hydrogen) especially in a star

5. neutron e) the distribution of a quantity (as mass, electricity, or energy) per unit usually of space (as length, area, or volume)

6. density f) matter composed of antiparticles

7. antimatter g) maintaining or able to maintain itself

3. Find words which mean the following in the text above:

Verbs

1. to happen/ take place

2. to free/ liberate

3. to take in/ concentrate inside

4. to operate/ check/ command

5. to accomplish/ get/ reach
to produce/ make

6. to compel/ to make sth/sb do smth.

7. to unite/ mix

4. Make a list of collocations with the words below and use them in sentences of your own:

		process nuclei   purposes bomb   design charge   repulsion neutron   density process

Date: 2015-05-18; view: 490; Нарушение авторских прав