Albert Teen

YOU ARE LEARNING:

Unstable atoms emit radiation to become stable, in the form of alpha and beta particles, neutrons and gamma rays.

This lesson looks at the concept of radioactive decay and the four different types of radiation.

What is an isotope?

Which of these options lists three different isotopes?

So these are all isotopes of carbon: $^{12}_6C,\:^{13}_6C,\: ^{14}_6C$. Actually, $^{14}_6C$ is a radioactive isotope. What do you think is the most reasonable explanation for why it's radioactive?

$^{14}_6C$ is a carbon isotope with too many neutrons. If a nucleus has an unbalanced number of neutrons and protons, or if it has too many of both, it can become unstable. An unstable nucleus really wants to go back to a stable state. To do that, the atom emits radiation. We call that radioactive decay.

Imagine you have a box full of pingpong balls, with only a small hole in the top. If you shake the box for long enough, one of the pingpong balls might escape through the hole. Radioactive decay is a bit like that. Would we call it a random or a non-random process?

It is important to remember that radioactive decay is a completely random process. This means that we cannot predict when an unstable nucleus will decay.

There are four different types of radiation which an unstable nucleus can emit. Which one depends on the size of this nucleus. Which of these options do you think are forms of radioactive decay?

Let's introduce each type of radioactive decay.

1

Alpha decay

An alpha $(\alpha)$ particle is simply a helium nucleus.

2

Helium has a proton number of 2, so what is the relative atomic mass of an *α-*particle?

3

Beta decay

This can either be beta plus $(\beta^+)$ or beta minus $(\beta^-)$ .

4

What do you think the plus and minus show in beta decay?

5

A beta particle is a fast-moving electron or positron.

*β-*decay occurs when a nucleus with an unbalanced number of neutrons and protons, emits a *β-*particle. $\beta^-$ is an electron with a charge of -1, and $\beta^+$ is a positron (an electron with a charge of +1).

6

Imagine an unstable nucleus that has too many neutrons. To be more stable, it wants to turn a neutron into a proton, but its charge still has to be zero. It can make sure that its charge remains zero by emitting a beta particle. What kind?

7

So *β-*decay occurs when an unstable nucleus has an unbalanced number of neutrons and protons.

If there are too many neutrons, one will turn into a proton and emit a $\beta^-$ particle. If there are too many protons, one will turn into a neutron and emit a $\beta^+$ particle.

8

We have looked at gamma $(\gamma)$ radiation in the topic of waves. What type of wave is a γ-ray?

9

Finally we have neutron emission.

This is simply when an unstable nucleus emits a neutron to become stable.

The four types of radioactive decay have different masses, ranging from quite large (a relative atomic mass of 4) to no mass at all. Which of the following options places the types of radiation in order of descending mass, so beginning with the one that has the most mass and ending with the one that has the least mass?

So α−particles have the most mass (or energy), then neutrons, then β−particles, and γ-rays have the least mass.

What form of radioactive decay do you think a very very large unstable nucleus undergoes?