Word: nuclei
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...Springs. Compared with the difficulties of controlling fusion, producing energy from nuclear fission is relatively simple. In fission-which occurs in A-bomb explosions and powers today's nuclear plants-a speeding neutron is used to split the atomic nucleus of a heavy element like uranium into the nuclei of one or more lighter elements. In the process, more neutrons are given off. But the mass of the resulting nuclei and neutrons is somewhat less than the mass of the original nucleus; the missing matter-as predicted by the famed Einstein equation E=mc2-has been converted into energy...
...nuclear fusion-the process that feeds the fires of the sun and gives the H-bomb its awesome power-atomic nuclei of light elements like hydrogen collide and merge. The resulting nuclear particles contain less mass than the sum of the original nuclei; again, matter has been converted into energy. But while atomic nuclei easily split, they do not easily fuse; they have positive electric charges and thus repel each other, acting as if they had invisible springs between them. Getting them to join requires that they approach each other with enough energy to overcome their natural repulsion and smash...
...first steps on that ascent was the realization that the conditions of temperature and density necessary for the sustained fusion of ordinary hydrogen nuclei were far beyond the present capabilities of science. But experiments showed that it was easier to fuse two isotopes, or different forms, of hydrogen: deuterium and tritium. Reason: the nuclei of these isotopes have larger cross sections than those of ordinary hydrogen nuclei. Thus the probability of direct collisions between them is increased and that in turn means that less extreme conditions are required to make them fuse. The easiest fusion to attain, scientists determined...
Tiny Bombs. Still, to join enough deuterium and tritium nuclei to sustain a fusion reaction requires heroic efforts. Deuterium-tritium gas mixtures must be heated to as much as 100 million degrees Celsius and be maintained at that temperature for about one second at a density of about 1014 (100 trillion) particles per cubic centimeter. Scientists have taken two different routes in their efforts to achieve these critical conditions. One is to use a "magnetic bottle" -an enclosing magnetic field-to contain the hydrogen fuel. The other is to use lasers or electron beams to make miniature hydrogen "bombs...
...force holding the nucleus together was still an enigma. Theoretically, a nucleus should fly apart since it is composed of identically charge particles. The gravitational attraction of two protons is negligible when compared to their electric, or electromagnetic, repulsion. In fact, atomic nuclei are very tightly bound. Confronted with an otherwise successful theory and this apparent empirical contradiction, physicists simply invented another force, which protons and neutrons feel, but to which electrons are immune. Because it is so strong, they named it the "strong" force...