![]() About 85% of all absorption reactions result in fission. Therefore about 15% of all absorption reactions result in radiative capture of neutron. The cross-section for radiative capture for thermal neutrons is about 99 barns (for 0.0253 eV neutron). Most of absorption reactions result in fission reaction, but a minority results in radiative capture forming 236U. For fast neutrons its fission cross-section is on the order of barns. Uranium 235 is a fissile isotope and its fission cross-section for thermal neutrons is about 585 barns (for 0.0253 eV neutron). If mankind had been present at the beginning of the Earth, they would not have needed to enrich uranium, because the content of fissile 235U was significantly higher. The 0.72% observed today are only a residue caused by the difference in the half-lifes of 235U and 238U. At the time of the formation of the Earth, 235U was 85 times more abundant. In fact, 235U is the only existing fissile nucleus from naturally-occurring isotopes and therefore is a highly strategic material. 235U was the first isotope that was found to be fissile. 235U occasionally decays by spontaneous fission with very low probability of 0.0000000072%.Ģ35U is a fissile isotope, which means 235U is capable of undergoing fission reaction after absorbing thermal neutron. Moreover, 235U meets also alternative requirement that the amount ( ~2.43 per one fission by thermal neutron) of neutrons produced by fission of 235U is sufficient to sustain a nuclear fission chain reaction. 235U decays via alpha decay (by way of thorium-231) into 231Pa. For its very long half-life, it is still present in the Earth’s crust. 235U belongs to primordial nuclides, because its half-life is comparable to the age of the Earth (~4.5×10 9 years). This isotope has half-life of 7.04×10 8 years ( 6.5 times shorter than the isotope 238) and therefore its abundance is lower than 238U (99.28%). Uranium 235, which alone constitutes 0.72% of natural uranium is the second common isotope of uranium in the nature.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |