![]() įor weapon use, fission is necessary to start fusion, helps to sustain fusion, and captures and multiplies the energy carried by the fusion neutrons.Scientists at Lawrence Livermore National Laboratory’s National Ignition Facility have made history by successfully producing a nuclear fusion reaction resulting in a net energy gain, a breakthrough hailed by US officials as a “landmark achievement” and a “milestone for the future of clean energy.” If the 14 MeV neutron is captured by uranium (of either isotope 14 MeV is high enough to fission both 235U and 238U) or plutonium, the result is fission and the release of 180 MeV of fission energy, multiplying the energy output tenfold. The only practical way to capture most of the fusion energy is to trap the neutrons inside a massive bottle of heavy material such as lead, uranium, or plutonium. In this fusion reaction, 14 of the 17.6 MeV (80% of the energy released in the reaction) shows up as the kinetic energy of the neutron, which, having no electric charge and being almost as massive as the hydrogen nuclei that created it, can escape the scene without leaving its energy behind to help sustain the reaction – or to generate x-rays for blast and fire. The total energy output, 17.6 MeV, is one tenth of that with fission, but the ingredients are only one-fiftieth as massive, so the energy output per unit mass is approximately five times as great. The following equation shows one possible split, namely into strontium-95 ( 95Sr), xenon-139 ( 139Xe), and two neutrons (n), plus energy: 235 U + n ⟶ 95 S r + 139 X e + 2 n + 180 M e V The uranium-235 nucleus can split in many ways, provided the charge numbers add up to 92 and the mass numbers add up to 236 (uranium-235 plus the neutron that caused the split). Most of these have the speed (kinetic energy) required to cause new fissions in neighboring uranium nuclei. The fission chain reaction in a supercritical mass of fuel can be self-sustaining because it produces enough surplus neutrons to offset losses of neutrons escaping the supercritical assembly. When a free neutron hits the nucleus of a fissile atom like uranium-235 ( 235U), the uranium nucleus splits into two smaller nuclei called fission fragments, plus more neutrons (for 235U three about as often as two an average of just under 2.5 per fission). India Israel (undeclared) Pakistan North Korea Former ![]() United States Russia United Kingdom France China Others
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