 Lesson Video: Radioactivity | Nagwa Lesson Video: Radioactivity | Nagwa

In this video, we will learn how to describe the radiation produced by decaying atomic nuclei.

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### Video Transcript

In this video, we will learn how to describe the radiation produced by decaying atomic nuclei. Let’s start by looking at a single atom. Atoms are made of three kinds of particles: positively charged protons, negatively charged electrons, and neutrons which have no charge. In an atom, protons and neutrons all bunch together in the core, called the nucleus. As we’ll see, it’s the nucleus of an atom that causes it to be radioactive or not. Particles in the nucleus are held together by forces. There are attractive forces between the particles and also forces that push them apart. Both of these forces are needed for the nucleus to be balanced and stable. Let’s look now at a quick example.

Which of the following statements correctly describes the forces that act on the particles in the nucleus of an atom? (A) There are no forces on the particles. (B) There are only attractive forces on the particles. (C) There are only repulsive forces on the particles. (D) There are attractive and repulsive forces on the particles.

The nucleus of an atom is made up of protons and neutrons. These particles are bunched tightly together by forces. If there were new forces acting on these particles, over time, they would drift apart, moving away from one another. This is not what happens though. The nucleus does hold together. Considering our next answer option, if there were only attractive forces on the nucleus, the particles in it would be squished together. What’s more, they wouldn’t push back. Over time, the whole nucleus would collapse to a single point. We know, though, that this isn’t what happens.

A nucleus is made up of distinct protons and neutrons. They resist being compressed altogether. That means there must be some repulsive force on the particles. But what if there were only repulsive forces? Then there would be nothing to keep the nucleus together. The particles in it would fly off in all directions. Again, this isn’t what happens. So we know option (C) can’t be our answer. The last choice says there are attractive and repulsive forces acting on the particles with forces that both push and pull on the particles. The overall forces on the nucleus balance out. There are both attractive and repulsive forces on the particles of a nucleus.

Whenever we have more than one nucleus, we call them nuclei. Here, we have two nuclei. And notice that they’re different. The first nucleus has one, two, three protons and the same number of neutrons. The second nucleus has one, two, three, four protons as well as four neutrons. The number of protons in a nucleus gives an atom its identity. Different types of atoms are called elements. Since this nucleus has a different number of protons than this nucleus, we can say these nuclei belong to atoms of different elements.

Now, let’s consider a third nucleus. Counting the protons, we count one, two, three, four. This nucleus on the right must be part of an atom of the same element as the nucleus in the center. But then, look at this. If we count the number of neutrons in the nucleus on the right, we count one, two, three, four, five. This nucleus contains a different number of neutrons than this one. We’ve said that the number of protons in a nucleus determines what type of element the atom is. The number of neutrons tells us what is called the isotope of that element. Nuclei of atoms of the same element that have different numbers of neutrons are different isotopes of one another. Knowing this, let’s go back to thinking about just one atomic nucleus.

We’ve seen that the number of protons and neutrons in the nucleus tells us which element that atom is as well as the isotope of that element. When a nucleus is stable, when all the forces acting on it balance out, that means the number of protons and neutrons in the nucleus does not change. Examples of elements that are very stable include tin, iron, and oxygen. If the forces on the particles in a nucleus do not balance out, however, that nucleus is unstable. An unstable nucleus is one where the number of protons and neutrons can change. Unstable elements include uranium and plutonium. An unstable nucleus may at some point break apart. When this happens, the nucleus can release what is called radiation.

The process by which a nucleus gives off radiation is called radioactive decay. Any element that undergoes radioactive decay is called radioactive. Imagine we have an unstable nucleus. Through radioactive decay, the nucleus could release a particle. Here’s something interesting, though. There is no way to predict exactly when this will happen. Even if we have an unstable nucleus and we suspect that at some point it will decay, it’s impossible to predict when this decay will take place. Radioactive decay is what is called a spontaneous process. We don’t know when it will happen, but we do know that it does happen. Let’s look now at a couple of examples.

Which of the following does an atomic nucleus become if it loses only neutrons when it undergoes radioactive decay? (A) A different element from the one it was before the decay. (B) A different isotope of the element it was before the decay.

Here, we’re thinking about a nucleus that undergoes radioactive decay and loses only neutrons in the process. Atomic nuclei are made up of two types of particles, protons and neutrons. The number of protons in a nucleus tells us what element that nucleus is a part of. The number of neutrons tells us the isotope of the element that the nucleus is a part of. Therefore, radioactive decay where only neutrons are lost does not change the element that that nucleus is a part of. What it does change is the isotope of the element that that nucleus was a part of before the decay. We choose answer option (B).

Let’s look at another example.

Which of the following statements about the prediction of radioactive decay of unstable atomic nucleus is correct? (A) The time at which an unstable atomic nucleus will decay can be predicted. (B) The time at which an unstable atomic nucleus will decay cannot be predicted.

We see that the only difference between these answers is whether the timing of nuclear decay can or cannot be predicted. When the nucleus of an atom goes through radioactive decay, it emits or gives off particles or energy. This process is described as spontaneous. This is because we can’t say exactly when it will happen. In general, radioactive decay is a spontaneous process. The time at which an unstable nucleus decays can’t be predicted.

Let’s now look at some details of what takes place when a nucleus decays. When a nucleus is unstable, it may experience radioactive decay. When this happens, the nucleus gives off radiation. One type of radiation is called alpha radiation. This symbol here is the Greek letter 𝛼. A second type is called beta radiation. Here is the Greek letter 𝛽. Finally, there’s a third sort of radiation, gamma radiation. Alpha and beta radiation, both consist of particles. Gamma radiation is different. It consists of electromagnetic waves. Let’s look now at one last example.

Which of the following statements correctly describes the possible compositions of the radiation emitted by unstable atomic nuclei decaying? (A) The radiation emitted by unstable atomic nuclei decaying includes particles and electromagnetic waves. (B) The radiation emitted by unstable atomic nuclei decaying consists only of particles. (C) The radiation emitted by unstable atomic nuclei decaying consists only of electromagnetic waves.

We may wonder just what is it that makes a given nucleus stable or unstable? It comes down to the number of neutrons in the nucleus compared to the number of protons. For smaller nuclei, when the number of protons and neutrons is the same, the nucleus tends to be stable rather than unstable. However, the more the number of neutrons exceeds the number of protons in the nucleus of an isotope, the more likely it is that all nuclei of that isotope are unstable, likely to decay.

Let’s finish this lesson by reviewing a few key points. In this video, we learn that atomic nuclei are made of protons and neutrons held together by a force. The number of protons tells what element a nucleus is a part of. The number of neutrons tells the isotope of that element. Nuclei can be stable or unstable. Unstable nuclei break down spontaneously through a process called radioactive decay. Radioactive decay causes the emission of radiation. There are three types of radiation: alpha, beta, and gamma radiation. Finally, a nucleus is stable or unstable based on the number of protons it has compared to the number of neutrons it has. In general, the more the number of neutrons exceeds the number of protons, the more likely it is that that isotope is unstable. This is a summary of radioactivity.