Radioactive substances have an unstable atomic nucleus that decays spontaneously, emitting energy-rich, or ionising, radiation in the process. This radiation is not detectable by human senses: we can neither see, hear, smell nor taste it. This often causes discomfort or even anxiety.
Radiation can indeed be very dangerous. The risk of cancer increases with the radiation dose. Strict limits apply in Switzerland to minimise any risk. The hazards posed by radioactivity are the reason why we need to dispose of our radioactive waste safely. This is the only way we can protect humans and the environment.
Discovery and research
While radiation can be hazardous, it is also very well researched, which makes it safe to handle. The term “radioactivity” has been used since 1898 when Marie Curie and Pierre Curie (pictured) first coined the term. The married couple received one half of the Nobel Prize in Physics in 1903 honouring “their joint work on the radiation phenomena discovered by Professor Henri Becquerel”. In line with his acknowledgement in the above-mentioned diploma citation, the second half of the Nobel Prize went to Henri Becquerel, who discovered radioactivity in 1896.
Radiation soon became useful for medical purposes: the first X-ray image of a hand was published on 23rd January 1896. Only a short time later, the first cancer patient was treated. Thanks to the wide range of potential applications in medicine, but also in industry and research, radioactivity held a great appeal for researchers. For this reason, we know a lot about it today.
There are three main types of radiation:
- alpha and beta radiation; these are produced by the spontaneous alteration of an unstable nucleus into another nucleus
- gamma radiation; this is produced when an atomic nucleus emits excess energy
Explaining radioactivity in three minutes
Radioactivity decreases over time
Due to radioactive decay, radioactivity continuously decreases. This also applies to radiation from radioactive substances and thus also to the waste, which decreases over time until it reaches insignificant levels. To protect humans and the environment, this waste must be disposed of in a deep geological repository where safety barriers reliably enclose the waste.
Radioactive substances can be ingested through breathing or in food and then decay inside the body (internal radiation). We can only protect ourselves from internal radiation by avoiding the ingestion of radionuclides.
Radiation can damage cells in the body and eventually lead to cancer. Conversely, medical treatments rely on it for beneficial purposes. Beta radiation can be applied in a targeted manner to destroy cancer cells (radiotherapy).
Natural radioactivity
Small amounts of natural radioactivity can be found everywhere: in the soil, in building materials, in our food and in the air we breathe. Our bodies are thus continuously absorbing minuscule amounts of radioactive substances such as potassium-40 that is primarily incorporated into muscle tissue.
Exploding stars (supernovae) produced radioactive substances, some of which were naturally “incorporated” into our planet during its formation. Their decay makes a significant contribution to geothermal heat. To a small extent, natural radioactive substances continue to form through interaction with cosmic radiation in the atmosphere.
Cosmic and terrestrial radiation
The average radiation exposure for a resident of Switzerland is just below 6 millisieverts per year. Of this, the vast majority (4.3 millisieverts) is natural. This includes cosmic radiation from outer space, the intensity of which depends on the altitude at which we live.
Natural radioactivity in the Swiss Plateau, for instance, is around 0.1 microsieverts per hour. Humans are constantly exposed to this. After 10 hours, they will have received a radiation dose of 1 microsievert. About half of it is cosmic radiation. The other half, terrestrial radiation, comes from underground rock – for example, granite that contains uranium.
People living in Davos are exposed to higher levels of cosmic radiation than those living on the Swiss Plateau. This is because the protective layer of the atmosphere is thinner at high altitudes, which also explains why we absorb more radiation when flying than on the ground. People who live in Locarno in Ticino also absorb more natural radiation than people who live in Zürich. The reason for this is that Locarno is built on uranium-bearing gneiss.
Radon the most common radiation source
At 3.3 millisieverts, the highest dose from natural sources comes from gaseous radon in our homes (see Figure). Radon penetrates the house from the underground through natural cellars or cracks, or is released by materials used to build the house.
We are also exposed to artificial radiation. Higher doses are caused by medical applications and much lower doses due to industrial applications.
Effect on the human body
Alpha, beta and gamma rays are all forms of ionising radiation. They transfer so much energy to the atoms and molecules of the irradiated material that electrons are released from the atomic shell. This can cause chemical compounds to break up, resulting in damage to cells, tissue and organs.
The three types of radiation penetrate human tissue to different depths. Alpha rays have a short range and can only penetrate the top skin layer by fractions of a millimetre. Beta rays have a range of several millimetres and are therefore able to penetrate all skin layers. Energy-rich gamma rays fully penetrate the human body, spreading throughout the tissue and thereby slightly weakening the radiation.
How can we protect ourselves from radiation?
Radiation from natural and artificial sources differs only in origin but not in its properties and effects. We can protect ourselves from a radiation source outside the body by using suitable shielding, keeping a safe distance and by limiting exposure time.
Alpha and beta rays can be shielded with relatively little effort. In contrast, energy-rich gamma rays can be weakened with a shield of several centimetres of iron or a few metres of rock or concrete.
Medical applications
One protective device that many people are probably still familiar with is the lead apron. It can be used to shield those parts of the body that should not be exposed to radiation. When taking X-rays, medical staff usually protect themselves by leaving the room or moving behind a protective wall (distance and shielding). Incidentally, the lead apron is becoming obsolete. Thanks to advances in technology, radiation exposure during the X-ray procedure has fallen significantly. Today, X-rays can be taken in a very targeted manner, with hardly any scattering.
The body absorbs significantly more radiation when treating a tumour than with an X-ray. Cancer patients can be treated with radiotherapy. While chemotherapy impacts the entire body, radiotherapy targets a specific part of the body. Radiation is used to damage cancer cells. However, healthy body cells are also damaged.
Radioactivity is constantly monitored
The Swiss National Emergency Operations Centre (NEOC) operates its own network to measure radioactivity. Every ten minutes, 76 sensors distributed throughout Switzerland transmit current measurements. You can find the daily averages and progressions over time on the NEOC website.