Task: Question Answering
Input (English): Context: In nuclear fusion, two or more small nuclei combine to form a single, larger nucleus. You can see an example in the Figure 1.1. In this example, nuclei of two hydrogen isotopes (tritium and deuterium) fuse to form a helium nucleus. A neutron and a tremendous amount of energy are also released. Nuclear fusion of hydrogen to form helium occurs naturally in the sun and other stars. It takes place only at extremely high temperatures. Thats because a great deal of energy is needed to overcome the force of repulsion between the positively charged nuclei. The suns energy comes from fusion in its core, shown in the Figure 1.2. In the core, temperatures reach millions of degrees Kelvin. Click image to the left or use the URL below. URL: The Sun Q: Why doesnt nuclear fusion occur naturally on Earth? A: Nuclear fusion doesnt occur naturally on Earth because it requires temperatures far higher than Earth tempera- tures. Scientists are searching for ways to create controlled nuclear fusion reactions on Earth. Their goal is develop nuclear fusion power plants, where the energy from fusion of hydrogen nuclei can be converted to electricity. You can see how this might work in the Figure 1.3. In the thermonuclear reactor, radiation from fusion is used to heat water and produce steam. The steam can then be used to turn a turbine and generate electricity. The use of nuclear fusion for energy has several pros. Unlike nuclear fission, which involves dangerous radioactive elements, nuclear fusion involves just hydrogen and helium. These elements are harmless. Hydrogen is also very plentiful. There is a huge amount of hydrogen in ocean water. The hydrogen in just a gallon of water could produce as much energy by nuclear fusion as burning 1,140 liters (300 gallons) of gasoline! The hydrogen in the oceans would generate enough energy to supply all the worlds people for a very long time. Unfortunately, using energy from nuclear fusion is far from a reality. Scientists are a long way from developing the necessary technology. One problem is raising temperatures high enough for fusion to take place. Another problem is that matter this hot exists only in the plasma state. There are no known materials that can contain plasma, although a magnet might be able to do it. Thats because plasma consists of ions and responds to magnetism. Click image to the left or use the URL below. URL: 
 Question: nuclear fusion occurs inside
Output (English): stars.