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     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 pacemakers，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 radiation
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 Research
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 the battery could be thinner
than the thickness of human hair.

1 .Which of the following is true of Jae Kwon?________
    A. He teaches chemistry at MU.
    B .He developed a chemical battery.
    C .He is working on a nuclear energy source.
    D .He made a breakthrough in computer engineering.

2 .Jae Kwon gave examples in Paragraph 4________.
    A .to show chemical batteries are widely applied
    B .to indicate nuclear batteries can be safely used
    C .to describe a nuclearpowered system
    D .to introduce various energy sources

3 .Liquid semiconductor is used to________.
    A .get rid of the radioactive waste
    B .test the power of nuclear batteries
    C .decrease the size of nuclear batteries
    D .reduce the damage to lattice structure

4 .According to Jae Kwon，his nuclear battery________.
    A .uses a solid semiconductor
    B .will soon replace the present ones
    C .could be extremely thin
    D .has passed the final test