What part of the atom is involved when an atom decays?

Answer 1

Really, it is the whole thing.

An atom decays because the nucleus is unstable. The nucleus contains protons and neutrons, and only certain combinations of the numbers of each are stable.

When a radioactive atom decays, it can do a number of different things. Best known by ordinary people, possibly, is nuclear fission, in which the whole atom breaks apart to become two atoms. In the process various pieces of the atom also are released.

Sometimes an atom decays by emitting an alpha particle, which means that two neutrons and two protons, combined in a single package, are emitted. This also implies that two electrons are somehow lost. In the process, the atom changes to a different element, with an atomic number reduced by two, and with an isotope number reduced by four.

Sometimes an atom undergoes a beta-negative emission. This means that the number of electrons and protons in the atom is increased by one, but the number of neutrons is reduced.

Sometimes an orbital electron is captured, to combine with a proton in the nucleus to make a neutron. When this happens, the atomic number is reduced by one, so the atom is of a different element, but the isotope remains the same.

There is a type of decay called an "isomeric transition," in which an atom emits a gamma ray (type of photon) but keeps both its atomic number and its isotope number. The notation of the isotope number before the has an "m" attached (indicating an excited meta state), which is gone after the transition has taken place. For example, zinc-69m decays to zinc-69.

These are just examples illustrating how the whole atom is affected. There are a number of others.

Answer 2

Matter is converted to energy, and is broken up.

This decay might either result in loss of protons and neutrons, or loss of electrons and energy, and the formation of new protons.

This occurs because of a metastable structure. For example, arrange six or seven small balls in a circle on a table - billiard balls and a table would be useful - cover them with a small towel and push in on them (keeping them all flat on the table. There is a gap in the middle, which would allow them to fit closer together, but they cannot, as one would have to move outwards or upwards first. However when this happens, they can do so.

The analogous result would be that when you push them and they collapse together, one of them is squished out of shape; there isn't quite enough room for it to fit completely, so part of it breaks off (i.e. it turns from a neutron to a proton, electron and energy) and leaves, while the larger part stays.

Similarly during decay, the large neutron breaks into smaller parts which fit better inside the forces and objects that apply to it. The extra bits which cannot fit are ejected from the nucleus. The result is that the remaining nucleons rearrange their structure to a lower-energy state. A specific change cannot be said for any atom or isotope, since we don't know exactly how the nucleons are arranged in the first place, just like we can't say how the balls will move together because we do not know how they are originally arranged.

Answer 3

The nucleus disintegrates spontaneously