The Foundation – Radioactivity was discovered in 1896 by the French physicist Henri Becquerel, who observed it in uranium. Radioactivity refers to the lack of stability in the isotopes that make up certain elements.
QUESTIONS: The Foundation – An isotope is an atom that has an equal number of protons and electrons, but a different number of neutrons. Elements can be made of different isotopes. Most isotopes are stable.
Isotopes – Each element has a unique atomic structure with a specific number of protons. The number of protons determines the element's atomic number. Atoms have the same number of electrons as they do protons.
QUESTIONS: Isotopes – Isotopes can be written in two ways. Both methods refer to the mass of the atom (the number of protons plus the number of neutrons).
Marie Curie – Around that time, Wilhelm Roentgen had discovered X-rays, and Henri Becquerel had discovered that the element uranium emitted rays. Marie was fascinated by this work, and began to do experiments of her own.
QUESTIONS: Marie Curie – Marie and Pierre investigated the pitchblende together, and eventually discovered two new elements within it. Marie named one of them polonium, after her native Poland.
Radium – Radium is a radioactive silvery metal. In the dark, it gives off light rays that make it glow. If exposed to air, it quickly becomes black in reaction to the nitrogen in the air. It reacts readily to other elements and substances.
QUESTIONS: Radium – Because radium is radioactive, it is very dangerous. In fact, it is a million times more radioactive than uranium, which is the element used to make nuclear bombs.
Uranium – Uranium is a normally a hard, dense, heavy silvery metal, though it is both malleable (able to be hammered or pressed out of shape) and ductile (able to be stretched).
QUESTIONS: Uranium – The German chemist Martin H. Klaproth discovered uranium in 1789 while working with the mineral pitchblende and named his discovery after the planet Uranus.
Radioactive Waste – Nuclear power plants generate power through a controlled fission chain reaction. They are capable of producing a very large amount of energy from relatively little uranium.
QUESTIONS: Radioactive Waste – Treatment of liquid and gas waste resulting from the production of nuclear power can include filtering, clean-up, storage, decay, and dilution depending on the level of radioactivity.
Half Life – The rate at which a radioactive isotope (radioisotope) decays is called its half-life. The half-life is the amount of time that it takes for half of the atoms in a given amount of isotopes to decay.
QUESTIONS: Half Life – Radioactivity is measured in unites called curies, in honor of Marie Curie who discovered the element radium.
Carbon Dating – Carbon dating is used by scientists to determine the approximate age of archeological and paleontological finds that are less than 50,000 years old.
QUESTIONS: Carbon Dating – Radiocarbon dating was developed after World War II by Willard F. Libby and associates. It can be used to determine the ages of many materials, including wood, charcoal, shell fragments, bone, antlers, peat, and organic-bearing sediments.
X-Rays – In 1895, the German physicist, W.C. Roentgen, was experimenting with a cathode ray tube. The tube looked a lot like the florescent light bulbs you find in modern office buildings. He created a vacuum inside the tube, filled it with a gas.
QUESTIONS: X-Rays – Further experiments confirmed that the ray could pass through many other substances, and that when it did so, it left imprints like shadows of solid objects on film.
Matter and Radiation – Everything is made up of matter, even air. X-rays and gamma rays can penetrate quite far through air, but eventually the air just absorbs them. These same rays can also penetrate the body of a human being, but not as deeply, since the human body has a greater density than air.
QUESTIONS: Matter and Radiation – Radiation is electromagnetic, and it is made of energy that moves at the speed of light. One of the basic laws of science is called the Law of Conservation of Energy. It says that energy cannot be created or destroyed, it can only be changed from one form into another or transferred from one object to another.