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The nominal spherical critical mass for an untampered 235 U nuclear weapon is 56 kilograms (123 lb), [6] which would form a sphere 17.32 centimetres (6.82 in) in diameter. The material must be 85% or more of 235 U and is known as weapons grade uranium, though for a crude and inefficient weapon 20% enrichment is sufficient (called weapon(s ...
The 4n+3 chain of uranium-235 is commonly called the "actinium series" or "actinium cascade". Beginning with the naturally-occurring isotope uranium-235, this decay series includes the following elements: actinium, astatine, bismuth, francium, lead, polonium, protactinium, radium, radon, thallium, and thorium. All are present, at least ...
Most neutrons released by a fissioning atom of uranium-235 must impact other uranium-235 atoms to sustain the nuclear chain reaction. The concentration and amount of uranium-235 needed to achieve this is called a 'critical mass'. To be considered 'enriched', the uranium-235 fraction should be between 3% and 5%. [123]
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.
This required uranium-235 (U 235), the fissionable isotope of uranium. However, the vast majority of uranium mined from the ground is uranium-238 , while only 0.7% is U 235 . Scientists developed several processes for separating the isotopes of uranium, including electromagnetic separation and gaseous diffusion.
They estimated a metallic sphere of uranium-235 with a radius of 2.1 centimetres (0.83 in) could suffice. This amount represented approximately 1 kilogram (2.2 lb) of uranium-235. [31] These results led to the Frisch–Peierls memorandum, which was the initial step in the development of the nuclear arms programme in Britain. This marked the ...
Special nuclear material (SNM) is a term used by the United States Nuclear Regulatory Commission to classify fissile materials.The NRC divides special nuclear material into three main categories, according to the risk and potential for its direct use in a clandestine nuclear weapon or for its use in the production of nuclear material for use in a nuclear weapon.
Nuclear material refers to the metals uranium, plutonium, and thorium, in any form, according to the IAEA. This is differentiated further into "source material", consisting of natural and depleted uranium, and "special fissionable material", consisting of enriched uranium ( U-235 ), uranium-233 , and plutonium-239 .