Alpha, Beta and Gamma (GCSE Physics)

Alpha, Beta and Gamma

Changing the Nucleus

Through emitting radiation, we can change the nucleus of an atom.

There are two ways in which the nucleus of an atom can be changed:

1. Charge. We can increase or decrease the charge of an atom through nuclear radiation.
2. Mass. We can decrease the mass of an atom through nuclear radiation.

Alpha and Beta Decay

Alpha Decay

Firstly, let us look at alpha decay with the following example:

• A helium nucleus has been emitted. Since a helium nucleus has been emitted, we know that this is alpha decay. The helium nucleus is made up of 2 protons and 2 neutrons, and it is the alpha particle.
• Mass and atomic numbers have changed. From the equation, we can see that both the mass number and the atomic numbers have changed. The mass number has decreased by 4, whilst the atomic number has decreased by 2.

Beta Decay

As we summarised before, in beta decay we essentially lose an electron. This happens when a nucleus has too many neutrons, so a neutron turns into a proton and emits a fast-moving electron.

We specifically call this electron a beta minus (β-) particle.

Now, let us look at beta decay with this example:

• An electron has been emitted. Since an electron has been emitted, we know that this is beta decay. The electron is the beta particle.
• Only the atomic number has changed. From the equation, we can see that only the atomic number has changed. The mass number does not change, since the electron has a negligible mass.

Writing Equations to Show Decay

Question: An isotope of barium is Ba-139. Ba-139 decays by beta decay to lanthanum-139 (La-139).
Complete the nuclear equation that represents the decay of Ba-139 to La-139.

1. We know that the Barium is undergoing beta decay, not alpha decay.
2. Now, we need to find the atomic number for barium. We can do this by looking at a periodic table.
   
3. From this, we can see that Barium has an atomic number of 56. Therefore, our first gap must be 56.
   
4. Next, we need to fill in the particle that is emitted in beta radiation. This is the beta particle:
   
5. Once we have filled this in, we just need to balance both sides of the equation.
   

Gamma Rays

Lastly, we have gamma rays. As previously mentioned, gamma rays are a form of electromagnetic radiation. Unlike beta and alpha decay, gamma rays do not cause a change in mass or charge.

This means that neither the atomic number or the mass number changes when gamma rays area emitted.

The only change is that the particles in the nucleus undergo re-arrangement, moving the nucleus to a lower energy state. It is this difference in energy which is emitted as a gamma ray.