Search results
Results From The WOW.Com Content Network
The three long-lived nuclides are uranium-238 (half-life 4.5 billion years), uranium-235 (half-life 700 million years) and thorium-232 (half-life 14 billion years). The fourth chain has no such long-lasting bottleneck nuclide near the top, so almost all of the nuclides in that chain have long since decayed down to just before the end: bismuth-209.
Uranium-235 (235 U or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists in nature as a primordial nuclide. Uranium-235 has a half-life of 703.8 million years.
However, Bohr had argued that the uranium-235 isotope was far more likely to capture neutrons, so fissile even using neutrons of low energy. Frisch wondered what would happen if he were able to produce a sphere of pure uranium-235. When he used Peierls' formula to calculate this, he received a startling answer. [36] Peierls later observed that:
Meitner was certain that these had to be (n, γ) reactions, as slow neutrons lacked the energy to chip off protons or alpha particles. She considered the possibility that the reactions were from different isotopes of uranium; three were known: uranium-238, uranium-235 and uranium-234.
Uranium-235 makes up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a fission chain reaction. It is the only fissile isotope that is a primordial nuclide or found in significant quantity in nature. Uranium-235 has a half-life of 703.8 million years.
Created Date: 8/30/2012 4:52:52 PM
No pure uranium-235 was available, so experiments at Liverpool were conducted with natural uranium. The results were inconclusive, but tended to support Frisch and Peierls. [ 45 ] By March 1941, Alfred Nier had managed to produce a microscopic amount of pure uranium-235 in the United States, and a team under Merle Tuve at the Carnegie ...
Similarly, thorium gas mantles are very slightly radioactive when new, but become more radioactive after only a few months of storage as the daughters of 232 Th build up. Although it cannot be predicted whether any given atom of a radioactive substance will decay at any given time, the decay products of a radioactive substance are extremely ...