Wilhelm Röntgen (1845-1923) discovered active radiation at the end of the nineteenth century. His name lives on in medicine as the inventor of the radiograph or X-ray photo. Radio comes from radus and means ray. Active means that it does something. Radioactivity is to do with the ability of certain atomic nuclei to emit radiation.
Scientists talk about ionising radiation. In daily life, we usually talk about radioactivity. These terms are often used interchangeably. Ionising radiation is applied in many parts of society. For example, for producing electricity, for medical applications like diagnosing and treating diseases, and for checking welds for steel structures like windmills. Nuclear reactors are even used for the restoration of paintings. We also find ionising radiation in nature. Our planet and even our bodies contain radioactive substances, which emit radiation. Everyone is constantly exposed to natural sources of radiation. It's just that you don't notice it. Humans have no senses that can detect it. Compare it with radio waves, which you can only pick up through a device (radio).
You can therefore only see radiation using instruments. If you wore special measuring equipment (a dosimeter), you would see that when you fly or go skiing high in the mountains, you receive a considerably higher dose of radiation than during a cycling holiday around the IJsselmeer.
Types of radiation
There are three types of radiation: alpha, beta and gamma radiation.
- Alpha radiation consists of relatively big and heavy particles that are released from a disintegrating atom. These are easy to obstruct. Just using a sheet of paper is enough. Alpha radiation only negatively affects our health if we absorb it through food or inhale it. This can be prevented through checks and simple measures like breathing protection.
- Beta radiation consists of lighter particles. These penetrate more deeply into the material but cannot pass through an aluminium sheet or through three metres of air. It is also easy to protect ourselves from beta radiation.
- Gamma radiation consists of electromagnetic waves. These are like light waves or radio waves. However, gamma radiation penetrates deeper into the material. X-rays used in hospitals are an example. We can protect ourselves from undesired gamma radiation by shielding the source with lead or concrete. Many particles emit both beta and gamma radiation at the same time.
One feature of radioactivity is that the radiation decreases with time. This is controlled by nature. The longer the time that passes, the less radiation is emitted. This is due to radioactive decay. The instable atoms are looking for a new balance. Once they find that balance, the radioactive substance becomes stable and no longer emits radiation. The time this takes is called half-life, which is the time required for the substance to lose half its radioactivity. After two half-lives, the radioactivity is half of the half. So that is a quarter of the initial value. Each radioactive substance has its own fixed half-life. For one substance that may be seconds, for other substances it may be thousands of years. One radioactive substance is therefore harmless from the moment it is produced. Other radioactive material needs to be stored for thousands of years before it stops emitting radiation.