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  3. Batteries can power anything from small sensors to large systems. While scientists are finding ways to make them smaller but eve

Batteries can power anything from small sensors to large systems. While scientists are finding ways to make them smaller but eve

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问题     Batteries can power anything from small sensors to large systems. While scientists are finding ways to make them smaller but even more powerful, problems can arise when these batteries are much larger and heavier than the devices themselves. University of Missouri (MU) researchers are developing a nuclear energy source that is smaller, lighter and more efficient.
    "To provide enough power, we need certain methods with high energy density(密度)" ,said Jae Kwon, assistant professor of electrical and computer engineering at MU. "The radioisotope (放射性同位素) battery can provide power density that is much higher than chemical batteries. "
    Kwon and his research team have been working on building a small nuclear battery, presently the size and thickness of a penny, intended to power various micro/nanoelectromechanical systems (M/NEMS). Although nuclear batteries can cause concerns, Kwon said they are safe.
    "People hear the word ’ nuclear’ and think of something very dangerous," he said, "However, nuclear power sources have already been safely powering a variety of devices, such as pace-makers, space satellites and underwater systems. "
    His new idea is not only in the battery’ s size, but also in its semiconductor(半导体). Kwon’ s battery uses a liquid semiconductor rather than a solid semiconductor.
    "The key part of using a radioactive battery is that when you harvest the energy, part of the ra- diation energy can damage the lattice structure (晶体结构) of the solid semiconductor," Kwon said, "By using a liquid semiconductor, we believe we can minimize that problem. "
Together with J. David Robertson, chemistry professor and associate director of the MU Re- search Reactor, Kwon is working to build and test the battery. In the future, they hope to increase the battery’ s power, shrink its size and try with various other materials. Kwon said that battery could be thinner than the thickness of human hair.
Jae Kwon gave examples in Paragraph 4______.
选项 A、to show chemical batteries are widely applied
B、to introduce nuclear batteries can be safely used
C、to describe a nuclear-powered system
D、to introduce various energy sources
答案B
解析 由第四段中的“However，nuclear power sources have already been safely powering a variety of devices”可知，下面所举的例子都是为了证明核能源可以安全使用。
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