# How are isotopes of elements formed?

##### 1 Answer
Apr 1, 2014

Some isotopes occur naturally. Scientists make others in nuclear reactors.

The elements H, He, and minor amounts of Li formed in the original Big Bang.

Nuclear fusion reactions in stars have created all the heavier elements.

First H fuses to form He. When the H disappears, the star collapses. Then He is "ignited" to form Be and C.

There are many free neutrons in these reactors. Nuclei capture enough neutrons to stabilize themselves.

This process in stars has formed all the other elements up to uranium.

In the last stage, Fe forms by direct fusion of Si and other light elements. This reaction is rapid and results in an explosion. Our solar system condensed from the remnants of one of these supernova explosions.

Scientists make even heavier or “trans-uranium” elements in an accelerator. Two ions travel at high speeds in opposite directions. They fuse when they collide. For example,

""_92^238U + _7^14N → _99^248Es + 4 _0^1n

Other elements form by neutron bombardment in a nuclear reactor. For example,

""_94^239Pu + 2 _0^1n → _95^241Am + _-1^0e