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Nuclear Physics
Particle Physics

What changes the number of protons in a nucleus?


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May 15, 2010 10:27PM

The number of protons in an atomic nucleus can change by several different mechanisms. Let's look at each one and see what happens.

In an atom with "too many" protons in its nucleus, that unstable atom can undergo what is called beta decay. There are two types of beta decay, and the one that could happen here goes by the name beta plus decay. In beta plus decay, a proton in the nucleus of that unstable atom transforms into a neutron. A positron and an antineutrino will be ejected from the nucleus, and the number of protons will have gone down by one. If you guessed that nuclear transmutation has just occurred where one element has transformed into another one, you'd be correct.

In some other unstable atoms with "too many" protons in the nucleus, that nucleus could under an electron capture event. In electron capture, the nucleus "pulls in" a nearby electron from one of the inner shells of the atom, and that electron "combines" with a proton to become a neutron. Again, the number of protons in the nucleus goes down by one, and nuclear transmutation has occurred.

Lastly, it is possible to bombard atomic nuclei with particles and "knock" protons out of a nucleus that is "hit" by the bombarding particles. There are a few different activities that are carried out in nuclear physics labs to do this, but we'll leave it here for now. Just keep in mind that beta plus decay and electron capture are the two primary methods that unstable nuclei undergo when they change the number of protons they have. Links to related questions can be found below for more information.