SafekipediaUranium-238
Adapted from Wikipedia · Adventurer experience
Uranium-238, written as 238U or U-238, is the most common form of isotope of uranium in nature. It makes up over 99% of all uranium. Unlike another form called uranium-235, U-238 cannot keep a chain reaction going in regular reactors with slow-moving neutrons. But it can be used in special ways when hit by fast-moving neutrons. It can then change into another useful material called plutonium-239.
This isotope takes a very long time to change — about 4.463 billion years. Because of this, it is still found in large amounts today. U-238 helps create about 40% of the heat inside Earth. As it changes over time, it gives off tiny particles. Scientists can detect these particles to learn more about our planet.
When uranium is changed and processed for use, like in depleted uranium or in fuel with a little more uranium-235, most of it is still U-238. This form is very important for scientists. They use it to study very old rocks and materials with a method called radiometric dating.
Nuclear energy applications
In a nuclear reactor, uranium-238 can help make plutonium-239 for energy and special tools. Most of the power in normal reactors comes from splitting plutonium-239, which forms when uranium-238 meets particles called neutrons.
Uranium-238 can also make energy when split by fast-moving neutrons. Special reactors called breeder reactors can change uranium-238 into plutonium-239, giving us more fuel. There is a lot of uranium-238 available for this.
Uranium-238 is also used to protect against harmful invisible rays. It blocks many types of radiation very well, making it useful in safety materials.
Nuclear weapons
Most modern nuclear weapons use 238U as a material called a "tamper." This material surrounds the core of the weapon and helps it work better. In some weapons, 238U can also surround other parts. When reactions happen, they create energetic neutrons that cause the 238U to split, adding more energy to the explosion. These are called fission-fusion-fission weapons.
A large part of the explosion in this design comes from the splitting stage fueled by 238U, which creates radioactive materials. The Soviet Union tested the Tsar Bomba in 1961. If they had used 238U, the explosion could have been much larger.
Decay
Uranium-238 changes over time into other elements. It starts by giving off a type of energy called an alpha particle, turning into thorium-234. Thorium-234 then changes by giving off beta particles, and this process continues through several steps. This series of changes is known as the radium series or uranium series, and it includes many different elements like astatine, bismuth, lead, polonium, protactinium, radium, radon, thallium, thorium, and uranium.
The process of changing from one element to another happens over very long periods. For example, uranium-238 takes about 4.5 billion years to change into thorium-234. Each step in this process has its own time it takes to happen, and eventually, the series ends with a stable form of lead. While uranium-238 itself is only slightly radioactive, the elements it changes into can be more active, giving off energy in different ways as they change as well.
| Nuclide | Decay mode | Half-life (a = years) | Energy released MeV | Decay product |
|---|---|---|---|---|
| 238U | α | 4.463×109 a | 4.270 | 234Th |
| 234Th | β− | 24.11 d | 0.195 | 234mPa |
| 234mPa | IT 0.16% β− 99.84% | 1.16 min | 0.079 2.273 | 234Pa 234U |
| 234Pa | β− | 6.70 h | 2.194 | 234U |
| 234U | α | 2.455×105 a | 4.858 | 230Th |
| 230Th | α | 7.54×104 a | 4.770 | 226Ra |
| 226Ra | α | 1600 a | 4.871 | 222Rn |
| 222Rn | α | 3.8215 d | 5.590 | 218Po |
| 218Po | α 99.98% β− 0.02% | 3.097 min | 6.115 0.257 | 214Pb 218At |
| 218At | α 100% β− | 1.28 s | 6.876 2.883 | 214Bi 218Rn |
| 218Rn | α | 33.75 ms | 7.262 | 214Po |
| 214Pb | β− | 27.06 min | 1.018 | 214Bi |
| 214Bi | β− 99.979% α 0.021% | 19.9 min | 3.269 5.621 | 214Po 210Tl |
| 214Po | α | 163.5 μs | 7.833 | 210Pb |
| 210Tl | β− β−n 0.009% | 1.30 min | 5.481 0.296 | 210Pb 209Pb (in neptunium series) |
| 210Pb | β− α 1.9×10−6% | 22.2 a | 0.0635 3.793 | 210Bi 206Hg |
| 210Bi | β− α 1.32×10−4% | 5.012 d | 1.161 5.035 | 210Po 206Tl |
| 210Po | α | 138.376 d | 5.407 | 206Pb |
| 206Hg | β− | 8.32 min | 1.307 | 206Tl |
| 206Tl | β− | 4.20 min | 1.532 | 206Pb |
| 206Pb | stable |
Radioactive dating
238U and its changes over time help scientists find the age of very old things. One way is called uranium-lead dating. It helps find the age of rocks older than a million years. This method showed that some of the oldest rocks on Earth are about 4.4 billion years old.
We can also learn the age of sediments and seawater by looking at the link between 238U and another type, 234U. This works for ages between 100,000 and 1,200,000 years. The end product of 238U, called 206Pb, is used in lead-lead dating. This helped find the age of the Earth. The Voyager spacecraft carry a tiny bit of pure 238U to help date things far in the future.
Health concerns
Uranium sends out a type of radiation called alpha radiation. If you are outside the uranium, it does not harm you much. But if tiny bits of uranium or its breakdown products, like thorium-230, radium-226, and radon-222, get inside your body, they can make you very sick.
Uranium can also harm your body because of its chemical properties. If you swallow uranium, it can damage your kidneys.
Related articles
This article is a child-friendly adaptation of the Wikipedia article on Uranium-238, available under CC BY-SA 4.0.
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