Introduction

Introduction

Radiation vs. radioactivity

Nuclear physics is the branch of physics which deals with the nucleus of the atom. Within this field, some scientists focus their attention on looking at the particles inside the nucleus and understanding how they interact, while others classify and interpret the properties of nuclei. This detailed knowledge of the nucleus makes it possible for technological advances to be made. In this next chapter, we are going to touch on each of these different areas within the field of nuclear physics.

Nuclear structure and stability

You will remember from an earlier chapter that an atom is made up of different types of particles: protons (positive charge) neutrons (neutral) and electrons (negative charge). The nucleus is the part of the atom that contains the protons and the neutrons, while the electrons are found in energy orbitals around the nucleus. The protons and neutrons together are called nucleons . It is the nucleus that makes up most of an atom's atomic mass , because an electron has a very small mass when compared with a proton or a neutron.

Within the nucleus, there are different forces which act between the particles. The strong nuclear force is the force between two or more nucleons, and this force binds protons and neutrons together inside the nucleus. The electromagnetic force causes the repulsion between like-charged (positive) protons. In a way then, these forces are trying to produce opposite effects in the nucleus. The strong nuclear force acts to hold all the protons and neutrons close together, while the electromagnetic force acts to push protons further apart. In atoms where the nuclei are small, the strong nuclear force overpowers the electromagnetic force. However, as the nucleus gets bigger (in elements with a higher number of nucleons), the electromagnetic force becomes greater than the strong nuclear force. In these nuclei, it becomes possible for particles and energy to be ejected from the nucleus. These nuclei are called unstable . The particles and energy that a nucleus releases are referred to as radiation , and the atom is said to be radioactive . We are going to look at these concepts in more detail in the next few sections.

The discovery of radiation

Radioactivity was first discovered in 1896 by a French scientist called Henri Becquerel while he was working on phosphorescent materials. He wrapped a photgraphic plate in black paper and placed various phosphorescent substances on it. When he used uranium salts he noticed that the film blackened even if it was kept in a dark room. He eventually concluded that some rays must be coming out of the uranium crystals to produce this effect and that these rays were able to pass through the paper.

His observations were taken further by the Polish scientist Marie Curie and her husband Pierre, who increased our knowledge of radioactive elements. In 1903, Henri, Marie and Pierre were awarded the Nobel Prize in Physics for their work on radioactive elements. This award made Marie the first woman ever to receive a Nobel Prize. Marie Curie and her husband went on to discover two new elements, which they named polonium (Po) after Marie's home country, and radium (Ra) after its highly radioactive characteristics. For these dicoveries, Marie was awarded a Nobel Prize in Chemistry in 1911, making her one of very few people to receive two Nobel Prizes.