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What is the most number of neutrons that can be in an element?

If the atom is not stable, and disintegrates quickly, you might find that it could have almost 200 neutrons in its nucleus. But this does not mean much, because it does not exist for very long. Now let us talk about STABLE elements. The most neutrons in any stable element turns out to be 126, found in lead-208 and bismuth-209. And if we want to stretch our rule about stability, we might include the common isotope of uranium, uranium-238. This has 146 neutrons, and is almost stable. Its half-life is 4 billion years!

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