What kind of radiation is most harmful?
We learned in school that there are different types of dangerous radiation. But why is radioactivity actually harmful to the body, and what kind of radiation is the most harmful to health?
Radiation passes right through us
Alpha radiation (red arrow). Consists of heavy helium cores. A single alpha particle can damage more than 100,000 molecules. However, it requires that the short-range particles find a way into the body, for example, through poisoning or inhalation.
Beta radiation (blue arrow). The electrons in the beta radiation have a significantly greater permeability and ten times the range of the alpha particles. In contrast, the small beta particles do not destroy the body's molecules as effectively.
Gamma radiation (green arrow). The short-wave and very energy-rich electromagnetic gamma rays arise from radioactive decay. In large doses, gamma radiation can be fatal, but we usually are not exposed to strong gamma sources.
Alpha particles can also destroy DNA, thereby causing unhealthy mutations.
Nuclear radiation is often divided into three types: alpha, beta and gamma radiation. Alpha radiation is the most dangerous, although it is considerably less energy-rich than the others.
The alpha radiation consists of the nuclei of helium atoms, which travel through the air at between 10,000 and 20,000 kilometres per second. Compared to beta particles, which are electrons, it is clear why they are dangerous. If we assume that beta particles are as large as a pea, the alpha particles would be heavy steel balls with a mass of eight kilos and a diameter of twelve centimetres.
The range is short
Fortunately, the range of the alpha particles is very short – in the air no more than a few centimetres. However, the alpha particles can be dangerous if they find their way into the body, for example, via inhalation of radioactive gases such as radon.
Radiation destroys water molecules
The body consists mostly of water, and the alpha particles first and foremost destroy water molecules. This creates so-called free radicals – unstable molecules that have to steal electrons from other substances to become stable. There, among other things, hydrogen peroxide is formed, which kills cells.
What is radioactivity?
Radioactive substances contain too many neutrons in the atomic nucleus in relation to the number of protons. It makes the atoms unstable, and to create stability, they emit radiation – or decay. The size of the atom determines what kind of radiation it emits.
There are three types of radiation:
1. Alpha radiation is helium nuclei: Large radioactive atoms decompose by emitting helium nuclei, i.e. nuclei consisting of two protons and two neutrons. The heaviest natural element, uranium-238, is radioactive and decomposes through a chain reaction with many steps. The skin easily slows the large alpha particles, but if the radiation reaches the body via food or inhalation, it is extremely harmful.
- It can stop alpha rays: human skin.
2. Beta radiation is electrons: Small radioactive atoms such as super-heavy hydrogen decomposes by emitting electrons, so-called beta radiation. A particle is emitted each time a neutron is converted to a proton. In direct radiation, the rays end up in the skin and can lead to cancer, but beta-radiation is most dangerous if we consume it.
- It can stop beta rays: an aluminium plate.
3. Gamma radiation is light: Many medium-sized radioactive atoms emit gamma radiation. The decay typically occurs in a two-step process, where a neutron is first converted to a proton by emitting an electron. The new atom then decays by emitting gamma radiation, which is short-wave light. The rays penetrate the body unhindered but are less dangerous than the other types of radiation.
- It can stop gamma rays: a thick lead plate.
Why is radioactive radiation dangerous?
Radioactive substances are dangerous because they emit radiation with such high energy that the radiation can tear electrons from atoms and molecules, making them electrically charged – so-called ions. If the whole body, organ or cells are exposed to radioactive radiation, damage can occur.
If the dose is large enough, the radiation will kill the affected cells. The dead cells can be replaced by new cells unless the cell death is so extensive that the entire organ is destroyed.
Smaller doses, which do not kill the cells, can instead destroy our DNA and cause genetic mutations. In some cases, enzymes can repair the damage, but not always and then the cell is converted into a cancer cell.
How is radioactivity measured?
The damage depends on both the radiation dose and the type of radiation. To assess the risk, experts use the term effective dose measured in sievert.
The sievert figure includes all types of radiation of different weight – alpha radiation is the highest. Six sievers kill almost all affected persons as a result of acute radiation sickness, while 1 sievert gives 5% higher risk of getting cancer.
The natural background radiation found everywhere on Earth is an average of 2.4 milliseconds.
What can radioactivity be used for?
As harmful as radioactive radiation can be, it is just as useful in modern medical science.
PET scanners use, e.g. a radioactive tracer to locate cancer tumours in the body. Before the scan, the patient eats a piece of grape sugar with the substance fluorine-18. The cancer cells absorb more sugar and there with more trace elements than the healthy cells. Four-18 disintegrates by releasing positrons detected by the scanner and revealing the cancerous tumour.
Cancer cells can also be killed by introducing radioactive substances into the body. One of the methods is so-called brachytherapy, where a container of radioactive material is placed in the tumour itself or right next to it. Compared to traditional radiation therapy, the advantage is that the radiation is concentrated in the cancer-affected area and kills fewer healthy cells.