People have had the conception of atoms for at least 2,500 years. The word comes from the Greek "atomos" which means indivisible.

Research reactor DR 3, which among other things was characterised by having slow neutrons, was primarily used for materials research. Here it was important to be able to capture many neutrons and slow them further down so that the atomic structure of the materials could be seen.

Hospitals use radioactive tracers to find, among other things, cancerous growth. Most often, the substance is bound to sugar and then injected into a vein, but it can also be eaten or inhaled. It typically disappears from the body within a day and provides a very low radiation dose.

In the upper 30 cm of an ordinary Danish detached house plot there is about 1 kg of uranium. If collected, it would not take up more space than one table tennis ball, as uranium has a very high density.

26 fuel rods were used at a time during operation of research reactor DR 3. A fuel rod could supply energy for about 9 months, after which it was replaced. The last fuel rods from DR 3 were returned to the United States in 2002.

Although alpha radiation is emitted with high energy and high speed, it reaches a maximum of 10 cm through air before it is completely stopped. It doesn’t get through a single sheet of paper either.

Each Dane receives an average of 3 millisieverts a year from natural background radiation. In addition, an average annual dose of 1 millisievert is obtained from medical radiation.

In the rest of Denmark, outside Risø, approximately 6-8 cubic metres of radioactive waste is produced per year. The waste mainly comes from hospitals, laboratories, schools and the industry.

Research reactor DR 3 was very popular among scientists, especially because of its high operational stability. As many of the researchers came from abroad, stable reactor operation was particularly important in terms of planning and conducting experiments.

Smoke alarms, especially older models, may contain a weak radioactive source (americium-241). Private individuals may throw out a small number of smoke alarms, but recycling stations must deliver larger quantities of smoke alarms to Danish Decommissioning.

A Troxler is a measuring device with two radioactive sources (caesium-137 and americium-241). When pressed against a road surface, a Troxler can measure the thickness of asphalt and gravel pavings.

Decommissioning is a technical term for the dismantling of especially chemical and nuclear installations.

While the research reactor DR 3 was in operation, it ran 23 days at a time, followed by a 5-day shutdown for maintenance and fuel replacement.

Blood to be used for transfusion is first sterilised by very powerful radioactive sources.

More than 1000 radioactive substances have been discovered. Many of them live only a few thousandths of a second, so it is usually the same 20-30 particularly useful substances that are utilised.

When operational, research reactor DR 3 was manned 24 hours a day by two engineers, two operators, a research assistant and a radiation protection officer.

Radiation is generally best inhibited by high density materials. Lead and iron are highly suitable as shielding material, while concrete is a more affordable alternative.