How does U 238 change to U 235 in natural in earth

[taregg]

how does U 238 change to U 235 in nature earth

or how does uranium enrichment in nature

 

[DrClaude]

U-238 doesn't change into U-235. Uranium ore contains about 0.72% U-235. To enrich uranium, you need to separate out U-235 from U-238.

 

[UltrafastPED]

The original stellar nucleosynthesis created U235 and U238 in about equal quantities.

Since they have different decay rates the U235 is much scarcer today.

For an interesting story read about the natural nuclear reactor at Oklo, Gabon:
http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor

 

[snorkack]

There is both a natural conversion of U-238 to U-235, and enrichment. Both are tiny effects.
U-238 may capture a neutron. Then it becomes U-239, which beta decays first to Np-239 then to Pu-239. Pu-239 then alpha decays to U-235.
Neutrons are rare on Earth outside reactors. They may come from cosmic rays, and in U deposits, they may come from spontaneous fission of U-238, or from nuclei that collide with alpha particles. How common are these effects? Spontaneous fission of U-238 happens roughly once per 2 million initial alpha decays of U-238... how frequent is neutron generation by alpha decay in nature, seeing that an U-238 emits 8 alphas in the chain to Pb-206?

And of course U is enriched or depleted in nature, just like H, C-12, N-14, O-16 or S-32 are enriched or depleted. U undergoes chemical reactions - it is sometimes oxidized and dissolved into UO2(2+) cation, sometimes reduced and precipitated as UO2. All these reactions have nonzero isotope effects.
What is the size of natural isotope effects of U isotope compositions?

 

[pmacias]

occur

Uranium-238 (U-238) is a naturally occurring isotope of uranium with a half-life of 4.5 billion years. It is the most abundant isotope of uranium found on Earth, making up about 99.3% of all naturally occurring uranium. U-238 can change to U-235 through a process called radioactive decay, where the nucleus of an atom spontaneously breaks down and releases particles and energy.

In this case, U-238 decays by emitting an alpha particle (two protons and two neutrons) and transforms into thorium-234. Thorium-234 then undergoes a series of decays, eventually producing U-235. This process is known as the uranium decay chain.

In nature, this process occurs very slowly, as U-238 has a long half-life. However, in certain conditions, such as in nuclear reactors or during nuclear explosions, the rate of decay can be accelerated. This is because these environments provide high levels of energy and particles that can trigger and speed up the decay process.

Uranium enrichment, on the other hand, is a man-made process that artificially increases the concentration of U-235 in uranium. This is typically done for the production of nuclear fuel for power plants or for the creation of nuclear weapons. The most common method of uranium enrichment is through a process called gaseous diffusion, where uranium gas is passed through a series of membranes to separate out the desired isotope.

In summary, U-238 changes to U-235 in nature through the process of radioactive decay, which occurs very slowly over time. However, in certain conditions, this process can be accelerated. Uranium enrichment is a man-made process that artificially increases the concentration of U-235 and is typically used for the production of nuclear fuel or weapons.