[单项选择]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 call
A. Nuclear Fusion
B. The Nuclear Fission Chain Reaction
C. Uncontrolled and Moderated Nuclear Reactions
D. The Advantages of Nuclear Energy

[单项选择]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 call
A. to establish a controlled chain reaction in low concentrations of fissile material
B. to absorb neutrons travelling at a particular speed
C. to cause a rapid chain reaction in order to realease the greatest amount of energy
D. to last the chain reaction forever

[填空题]A nuclear fission is a process of a U-235 nucleus with a neutron trying to capture another neutron.

[填空题]The result of nuclear fission is to release energy in the form of ______.

[单项选择]The process of nuclear fission______requires the use of a reactor core, around which no lithium blanket of sufficient______has been developed to contain the hazardous byproducts of the process.
A. unfortunately… breadth
B. occasionally … unreliability
C. auspiciously … size
D. fortuitously… expense
E. technically … imagination

[简答题]nucleus ambiguus

[简答题]hypoglossal nucleus

[填空题]Splitting dinner checks can cause a splitting headache, even when the diners are mathematics majors. Three computer science (36) students at the US’s Carnegie Mellon University were (37) up with worrying about shared bills so they decided to act. Shashank, Amit and Ashwin created a free website, Buxfer.com, in September, to help people remember who (38) what and to whom.
Instead of trying to (39) out how every dinner bill should be split, the site allows users to form groups of friends or housemates to (40) shared expenses over longer periods of time. For example, if one housemate pays for dinner for everyone, he earns (41) in his Buxfer group and pays less on next month’s rent. Buxfer quickly became (42) among college students and young (43) who often pool expenses and borrow small amounts from each other.
News of the site has spread .largely by word of mouth and on blogs. (44)