Radioactivity was discovered accidentally in 1896 by the French scientist Antoine Henry Becquerel. Studying a uranium mineral (pitchblende), Becquerel observed phosphorescence (a property of certain materials that allows them to absorb energy and then emit it in the form of radiation) without the mineral having been previously exposed to light. He found that the mineral … Read more

Radioactive Emissions

Between 1896 and 1903, scientists discovered that not all radioactive elements emit the same radiation. Some emit more powerful radiation than others, each of which transforms the nucleus in a different way. When radiation from a sample of a radioactive element, such as radium (Ra), is subjected to the action of a magnetic field, three … Read more

Discovery of X-rays

In 1895 Wilhelm Röentgen discovered X-rays. Studying the light emissions from an electric discharge tube, he observed that a screen covered with a fluorescent salt flashed every time he switched on the discharge tube. It was clear to Röentgen that the cathode rays were emissions that could not pass through the glass tube, yet for … Read more

What is an Isotope?

These are atoms of the same element that contain different numbers of neutrons in their nucleus and the same number of protons. Most elements are made up of two or more natural isotopes; for example, tin (Sn) is made up of a mixture of 10 different isotopes, while only 21 of the 90 elements found … Read more

What is Nuclear Fusion?

Fusion is the process by which two light nuclei join together to form a single daughter nucleus. Nuclear fusion, like fission, generates large amounts of energy, but has in its favor the fact that its products are not radioactive. A typical nuclear fusion reaction occurs in the Sun. Fusion reactions occur in the Sun. The … Read more

What is Nuclear Fission?

In the process of nuclear fission, a heavy nucleus (mass number > 200) is split to form smaller nuclei of intermediate mass and one or more neutrons. This process releases a large amount of energy because the heavy nucleus is less stable than its products. The first nuclear fission reaction studied was that of uranium-235 … Read more

What is the Atomic Nucleus?

The nucleus is the central portion of the atom that contains protons (positive particles, p+) and neutrons (neutral particles, n0). Around the nucleus revolve electrons (negative particles, e–). An atom can be characterized by its atomic and mass numbers. The atomic number (Z) corresponds to the number of protons contained in its nucleus and identifies … Read more