Alpha, Beta, Gamma Decay — Definition

Definition

Imagine an atomic nucleus as a tiny, dense core at the center of an atom. This nucleus is made up of protons and neutrons. For many atoms, this nucleus is stable, meaning it stays the same indefinitely.

However, some nuclei are unstable, like a wobbly stack of blocks, and they naturally try to become more stable by releasing energy. This process of releasing energy and transforming is called radioactive decay.

It's a spontaneous event, meaning we can't predict exactly when a single nucleus will decay, but we can predict how a large group of them will behave over time.

There are three main ways an unstable nucleus can decay, each involving the emission of a different type of 'radiation':

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Alpha ($\alpha$) Decay — Think of a nucleus that's too big and has too many protons and neutrons, making it unstable. To shed some weight and become more stable, it ejects a 'chunk' consisting of two protons and two neutrons. This chunk is identical to the nucleus of a helium atom, so we call it an alpha particle. When a nucleus undergoes alpha decay, its atomic number (the number of protons) decreases by 2, and its mass number (total protons + neutrons) decreases by 4. This means the original atom transforms into a completely different, lighter element.

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Beta ($\beta$) Decay — This type of decay is a bit more subtle and involves a change within the nucleus itself, rather than ejecting a large chunk. There are two main types of beta decay:

* **Beta-minus ($\beta^-$) Decay**: This happens when a nucleus has too many neutrons relative to its protons. To achieve a better balance, one of its neutrons transforms into a proton. To conserve charge, an electron (which we call a beta particle when it comes from the nucleus) is emitted.

An antineutrino is also emitted, carrying away some energy. In beta-minus decay, the atomic number increases by 1 (because a neutron became a proton), but the mass number remains unchanged (since a neutron was replaced by a proton, keeping the total count the same).

The atom again transforms into a different element. * **Beta-plus ($\beta^+$) Decay**: This occurs when a nucleus has too many protons relative to its neutrons. Here, a proton transforms into a neutron.

To conserve charge, a positron (which is like an anti-electron, having the same mass but a positive charge) is emitted. A neutrino is also emitted. In beta-plus decay, the atomic number decreases by 1 (a proton became a neutron), but the mass number remains unchanged.

This also results in a different element.

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Gamma ($\gamma$) Decay — Sometimes, after an alpha or beta decay, the newly formed nucleus is still in an 'excited' state, meaning it has excess energy, much like a ball that has rolled down a hill but is still bouncing. To settle into its most stable, 'ground' state, this excited nucleus releases its excess energy in the form of high-energy electromagnetic radiation called gamma rays. Gamma rays are not particles with mass or charge; they are pure energy, like very powerful X-rays. Because no particles with mass or charge are emitted, gamma decay does not change the atomic number or mass number of the nucleus. It simply allows the nucleus to de-excite and become more stable.