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In nuclear fusion, two nuclei come together and ______.
A．form. a new nucleus
B．both split
C．give off free neutrons
D．reduce energy
答案
更多“In nuclear fusion, two nuclei come together and ______.A．form. a new nucleusB．both splitC．”相关的问题
第1题
Destructive weapons can be obtained from ______.
A．nuclear fusion
B．nuclear fission
C．both nuclear fusion and nuclear fission
D．nuclear splitting
第2题
Part A
Directions: Read the following four texts. Answer the questions below each text by choosing A, B, C or D. (40 points)
Nuclear fission is the splitting of the nucleus of an atom. Only a few elements are suitable for use in this way, the most important ones being Uranium-235, Uranium-233, and Plutonium-239. When a nucleus of one of these elements is struck by a free neutron it breaks down into two lighter nuclei which fly apart at high speed, colliding with surrounding atoms. Their kinetic energy is converted into heat energy. At the same time, two or three free neutrons are released and one of them enters the nucleus of a neighbouring atom, causing fission to occur again; and so on. The reaction spreads very quickly, with more and more heat energy released. This is called a "chain" reaction because the splitting of each nucleus is linked to another, and another and another.
If this reaction takes place in an atomic bomb, where nothing is done to slow it down, the result is a violent explosion that can destroy a town in a few seconds. Fission can also, however, take place within a construction called a nuclear reactor, or atomic pile. Here the highly fissile material (U-235, U-233, Pu-239) is surrounded by a substance that is non-fissile, for instance graphite. This material is called a moderator. The neutrons lose some of their energy and speed through colliding with the atoms of the moderator. Energy—heat energy—is still created on an enormous scale, but no expansion takes place. The moderator has another function: by slowing down the speed of the free neutrons, it makes it more likely that one of them will collide with the nucleus of a neighbouring atom to continue the chain reaction.
The chief advantage of nuclear energy is that it does not depend on any local factors. A nuclear reactor, unlike an oil-well or a coalmine, does not have to be sited on top of a fossil-fuel source; unlike the solar energy unit, it does not have to go out of production when the sun is not shining; unlike hydro-electric power, it does not depend on a large flow of water which may be reduced during some seasons of the year. With an atomic power station, the only limiting factor is that of safety.
In the opposite process, nuclear fusion, two nuclei come together, to form. a new nucleus of a different kind and this process also releases energy on an enormous scale. Fusion can only occur under conditions of very great heat—at least 50,000,000 degrees Celsius. (The temperature at the centre of the sun is estimated as 130,000,000 degrees Celsius.) A fusion reaction on earth has already been created—the hydrogen bomb. This is an uncontrolled reaction. It is not yet possible to produce a controlled fusion reaction that can be used for the production of useful energy.
Nuclear energy can be thought of as a kind of square, three of the quarters of the square are known and used, but the fourth cannot yet be used.
Which of the following headings is that of Paragraph Two？
A．Nuclear Fusion
B．The Nuclear Fission Chain Reaction
C．Uncontrolled and Moderated Nuclear Reactions
D．The Advantages of Nuclear Energy
第3题
It implies in the passage that ______.
A．the U.S. government has been helping Pakistan's economic development
B．the U.S. approved Pakistan's detonating nuclear bomb
C．the Pakistan government is corrupt
D．the Pakistan government didn't pay much attention to family planning
第4题
Asteroids are different forms of the meteoroids that race across the night sky. Most orbits the sun far from Earth and don't threaten us. But there are also thousands of asteroids whose orbits put them on a violent coming course together with Earth.
Buy $ 50 million worth of new telescopes right now. Then spend $10 mil]ion a year for the next 25 years to locate most of the space rocks. By the time we spot a fatal one, the scientists say, we'll have a way to change its course.
Some scientists favor pushing asteroids off course with nuclear weapons. But the cost wouldn't be cheap.
Is it worth it？ Two things experts consider when judging any risk are: 1) How likely the event is; and 2) How bad the consequences if the event occurs. Experts think asteroids big enough to destroy lots of life might strike Earth once every 500,000 years. Sounds pretty rare but if one did fall it would be the end of the world. "If we don't take care of these big asteroids, they'll take care of us. "Says one scientist. "Its that simple."
The cure, though, might be worse than the disease, Do we really want fleets of nuclear weapons silting around on Earth？ "The world has less to fear from doomsday rocks than from a great nuclear fleet set against them. "Said a New York Times article.
What does the passage say about asteroids and meteoroids？
A．They are heavenly bodies similar in nature.
B．There are more asteroids than meteoroids.
C．They are heavenly bodies different in composition.
D．Asteroids are more mysterious than meteoroids.
第5题
Skeptics may recall the burst of enthusiasm for conservation and renewable power when oil prices quadrupled in the 1970s. State-funded energy research and development surged, while tax incentives boosted solar, wind and other alternatives to petroleum and the atom. But when oil supplies loosened and prices dropped in the early 1990s, governments lost interest. In the state of California, subsidies evaporated, pushing wind companies into bankruptcy.
Clean energy has long way to go. Only 2.2% of the world's energy comes from "new" renewables such as small hydroelectric dams, wind, solar and geothermal. How to boost that share--and at what pace--is debated in industrialized nations--from Japan, which imports 99.7 % of its oil, to Germany, where the nearby Chernobyl accident turned the public against nuclear plants, to the U.S., where the Bush Administration has strong ties to the oil industry. But the momentum toward clean renewables is undeniable. How soon we reach an era of clean, inexhaustible energy depends on technology. Solar and wind energies are intermittent: When the sky is cloudy or the breeze dies down, fossil fuel or nuclear plants must kick into compensate. But scientists are working on better ways to store electricity from renewable sources.
While developed nations debate how to fuel their power plants, however, some 1.6 billion people--a quarter of the globe's population--have no access to electricity or gasoline. Many spend their days collecting firewood and cow dung, burning it in primitive stoves that belch smoke into their lungs. To emerge from poverty, they need modern energy. And renewables can help. From village-scale hydropower to household photovoltaic systems to bio-gas stoves that convert dung into fuel.
Ultimately, the earth can meet its energy needs without fouling the environment. "But it won't happen," asserts Thomas Johansson, an energy adviser to the United Nations Development Program, "without political will." To begin with, widespread government subsidies for fossil fuels and nuclear energy must be dismantled to level the playing field for renewables. Moreover, government should pressure utility to meet targets for renewable sources of energy.
The author's biggest worry about using nuclear energy is that ______.
A．it will do great harm to the inadequate reserves of coal
B．it is deadly if terrorists attack a nuclear plant
C．it will limit the development of many other alternatives
D．there will be a wider gap between developed and developing countries
第8题
A.Fusion ln sight HD
B.Fusion ln sight Farmer
C.Fusion ln sight Miner
D.Fnsion In sipht MPPDR
第9题
A、Fusion Compute
B、Fusion Storge
C、Fusion Manager
D、Fusion Access
E、Fusion Network
