Why have natural deposits of uranium not fully decayed? Wouldn’t the millions/billions of years since they were deposited have been enough time?
Why have natural deposits of uranium not fully decayed? Wouldn’t the millions/billions of years since they were deposited have been enough time?
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Half life of Uranium-238 is about 4.5 billion years.
Half life of Uranium-235 is about 703 million years.
Maybe one reason why there so little 235 isotope compared to 238 isotope.
The half life of uranium is almost 4.5 billion years. This is approximately the same age as the earth.
That means that at its creation, the earth had just about twize as much uranium as it does now.
The half life of Uranium-238 is 4.468 billion years, while the age of the Earth is estimated to be 4.543 billion years.
The deposits of uranium that formed and coalesced into those deposits have only existed long enough for half of the atoms to decay. The atoms may have been around longer before the Earth formed, but while scattered as particles from a supernova they wouldn’t have experienced geological forces grouping them together to form the deposits we find today yet.
Because radioactive decay of uranium is a very very slow process. The most common form of Uranium is Uranium 238. U-238 has a half-life of 4.5 billion years. That means it takes 4.5 billion years for half of all the atoms in of a sample of U-238 to decay into something else. In another 4.5 billion years, half of that half will have decayed, leaving you with 25% of that original amount.
If Uranium-238 were created with the Big Bang, there would still be ~36% of it left today.
Uranium has a really long half life. The estimated age of the earth is 4.543 billion years while the half life of uranium-238 is 4.468 billion years. This means that only just over half of the uranium 238 that formed up as part of the earth is gone now.
Uranium-235 has a half life of 703.8 million years which means that roughly 98.76% of the uranium-235 that was on earth when it formed is now gone via decay – assuming of course that there isn’t some sort of natural process to transform U-238 into U-235 that we haven’t discovered yet.
There is another naturally occurring isotope of uranium (uranium 234) that is formed as part of a decay chain for U-238 but that particular form has a half life of just 245,000 years which means that any U-234 that can be found in nature is likely significantly younger than the earth.
They’re currently decaying!
Just takes about 4.5 billion years to reduce about half the total material
They kind of have, haven’t they?
Billions of years ago, some deposits were so concentrated that they effectively became natural nuclear reactors. You won’t find anything like that today.